International Journal of Radiation Oncology*Biology*Physics, 2015
Results: Each beam arrangement resulted in a highly robust plan to standard setup and range calib... more Results: Each beam arrangement resulted in a highly robust plan to standard setup and range calibration errors for this patient. However, when evaluated for rectal variations through 5 treatments, we observe a drop in target coverages as shown in Table . Conclusion: For ano-rectal cancer treatments with proton scanning beam, conventional robustness evaluations based on planning CT alone would overestimate plan robustness. Interfractional anatomical changes should be taken into account in order to obtain complete plan robustness evaluations. Techniques to mitigate these effects should be considered.
Introduction. Spot scanning proton therapy (SSPT) treatments suffer from poor conformity, especia... more Introduction. Spot scanning proton therapy (SSPT) treatments suffer from poor conformity, especially at low energy, due to increased lateral spot size, which is further increased with the patient scattering. The University of Iowa Hospitals and Clinics recently proposed a dynamic collimation system (DCS) for SSPT, which is capable of providing spot-by-spot collimation. The purpose of this study is to quantify by simulations improvement in target conformity from the use of the DCS, in brain and head and neck tumor treatments. Methods. Two spot scanning proton therapy delivery systems (Universal Nozzle, UN, and Dedicated Nozzle, DN-IBA company) with median spot sizes of 5.2 mm and 3.2 mm over a range of energies from 100 to 230 MeV were considered. Uncollimated and collimated plans were calculated with both UN and DN beam models implemented within our in-house treatment planning system for five brain and ten head and neck datasets of patients previously treated with spot scanning proton therapy. The DCS was simulated as close as 5 cm from the patient surface. The average reduction of the mean dose to the 10-mm ring surrounding the target between the uncollimated and collimated plans was calculated for the UN and DN. Target conformity was analyzed using the mean dose to 1-mm thickness rings surrounding the target at increasing distances ranging from 1 mm to 10 mm. The dose reduction to some organsat-risk was also quantified. Results. The average reductions of the 10-mm ring mean dose for the UN and DN plans were 13.7% (95% CI: 11.6-15.7%; p < 0.0001) and 11.5% (95% CI: 9.5-13.5%; p < 0.0001) across all brain cases, and 7.1% (95% CI: 4.4-9.8%; p < 0.001) and 6.3% (95% CI: 3.7-9.0%; p < 0.001) respectively across all head and neck cases. The collimated UN plans were either more conformal (all brain cases and 60% of the head and neck cases) than or equivalent (40% of the head and neck cases) to the uncollimated DN plans. The collimated DN plans offered the highest conformity. Conclusions. According to these simulations, the DCS improved the target conformity for both the UN and the DN, and offered better dose reduction to OARs [1-3].
ABSTRACT Purpose: RapidArc is routinely used for stereotactic radiotherapy for lung cancer. While... more ABSTRACT Purpose: RapidArc is routinely used for stereotactic radiotherapy for lung cancer. While treatment dose is optimized and calculated on a static CT image, the motion of the target in conjunction with the motion of the MLC may Result in a delivered dose deviating from the planed dose. In this study, we investigate the dosimetric consequences of the inter-play effect by simulating dynamic dose delivery on a dynamic CT dataset of real patients. Methods: The target motion in 20 patients was analyzed and 5 patients with &gt;10 mm motion were chosen for this study. The RapidArc plan for eachpatient is optimized on a free-breathing CT using 2 arcs. Inherent in each plan is data on the associated parameters such as timestamp, MLC leave position, gantry angle and delivered beam MUs for each control point. Simulated dynamic delivery is performed by associating these parameters with each of the breathing phases of the 4D-CT. The starting breathing phase is selected randomly for each of the two arcs. Dose from the derived partial plans associated with each phase of the 4D-CT dose is recalculated in Eclipse. Accumulation of dose is performed using deformable image registration from each phase of the 4D-CT to the exhale phase of the 4D-CT. Results: The coverage of the GTV and PTV shows negligible variations from the interplay effect. But the Homogeneity Index is affected by the motion. The prescription isodose volume is smaller than what was from the treatment plan dose. There were both intra- and inter-fraction effects seen inthe OARs dose in some patients. Conclusions: We investigated the motioneffect in RapidArc Lung SBRT delivery in 5 patients. Negligible variations were shown for target coverage. However the motion effects were observed in high dose distribution and volume. Some OARs dose distributions were affected by the motion.
Purpose:Low‐energy treatments during spot scanning proton therapy (SSPT) suffer from poor conform... more Purpose:Low‐energy treatments during spot scanning proton therapy (SSPT) suffer from poor conformity due to increased spot size. Collimation devices can reduce the lateral penumbra of a proton therapy dose distribution and improve the overall plan quality. The purpose of this work was to study the advantages of individual energy‐layer collimation, which is unique to a recently proposed Dynamic Collimation System (DCS), in comparison to a standard, fixed aperture that allows only a single shape for all energy layers.Methods:Three brain patients previously planned and treated with SSPT were re‐planned using an in‐house treatment planning system capable of modeling collimated and un‐collimated proton beamlets. The un‐collimated plans, which served as a baseline for comparison, reproduced the target coverage of the clinically delivered plans. The collimator opening for the aperture based plans included a 0.6 cm expansion of the largest cross section of the target in the Beam's Eye View, while the DCS based plans were created by optimizing the collimator position for beam spots near the periphery of the target in each energy layer.Results:The reduction of mean dose to normal tissue adjacent to the target, as defined by a 10 mm ring, averaged 9.13% and 3.48% for the DCS and aperture plans, respectively. The conformity index, as defined by the ratio of the volume of the 50% isodose line to the target volume, yielded an average improvement of 16.42% and 8.16% for the DCS and aperture plans, respectively.Conclusion:Collimation reduces the dose to normal tissue adjacent to the target and increases dose conformity to the target region for low‐energy SSPT. The ability of the DCS to provide collimation to each energy layer yields better conformity in comparison to fixed aperture plans.This work was partially funded by IBA (Ion Beam Applications S.A.).
Purpose: A dynamic collimation system (DCS) based on two orthogonal pairs of mobile trimmer blade... more Purpose: A dynamic collimation system (DCS) based on two orthogonal pairs of mobile trimmer blades has recently been proposed to reduce the lateral penumbra in spot scanning proton therapy (SSPT). The purpose of this work is to quantify the therapeutic benefit of using the DCS for SSPT of brain cancer by comparing un-collimated and collimated treatment plans. Methods: Un-collimated and collimated brain treatment plans were created for five patients, previously treated with SSPT, using an in-house treatment planning system capable of modeling collimated and un-collimated beamlets. Un-collimated plans reproduced the clinically delivered plans in terms of target coverage and organ-at-risk (OAR) sparing, whereas collimated plans were re-optimized to improve the organ-at-risk sparing while maintaining target coverage. Physical and biological comparison metrics such as dose distribution conformity, mean and maximum doses, normal tissue complication probability (NTCP) and risk of secondary brain cancer were used to evaluate the plans. Results: The DCS systematically improved the dose distribution conformity while preserving the target coverage. The average reduction of the mean dose to the 10-mm ring surrounding the target and the healthy brain were 7.1% (95% CI: 4.2%–9.9%; p<0.01) and 14.3% (95% CI: 7.8%–20.8%; p<0.01), respectively. This yielded an average reduction of 12.0% (95% CI: 8.2%–15.7%; p<0.01) for the brain necrosis NTCP using the Flickinger model, and 14.2% (95% CI: 7.7%–20.8%; p<0.01) for the risk of secondary brain cancer. The average maximum dose reductions for the brainstem, chiasm, optic nerves, cochleae and pituitary gland when comparing un-collimated and collimated plans were 14.3%, 10.4%, 11.2%, 13.0%, 12.9% and 3.4%, respectively. Evaluating individual plans using the Lyman-Kutcher-Burman NTCP model also yielded improvements. Conclusion: The lateral penumbra reduction performed by the DCS increases the normal tissue sparing capabilities of SSPT for brain tumor treatment while preserving the target coverage. This research was financially supported by Ion Beam Applications S.A. (IBA, Louvain-La-Neuve, Belgium).
International Journal of Radiation Oncology Biology Physics, Nov 1, 2015
The purpose of this work was to quantify the benefits of using a dynamic collimation system (DCS)... more The purpose of this work was to quantify the benefits of using a dynamic collimation system (DCS) along with spot scanning proton therapy (SSPT) during the treatment of head and neck (HN) cancer. We hypothesize that the DCS will significantly increase the dose conformity to yield better sparing for organs-at-risk (OAR) while maintaining target coverage. Materials/Methods: Collimated and un-collimated HN treatment plans were created for five patients previously treated with SSPT and retrospectively enrolled in an Institutional Review Board approved study. All patients received postoperative adjuvant SSPT for advanced-stage disease, the majority of whom received bilateral, elective neck radiation in addition to treatment of the primary tumor site. Both collimated and un-collimated plans were generated using an in-house treatment planning system capable of accounting for the effects of collimation. The un-collimated plan was generated such that the target coverage was equivalent to the clinically delivered plan. The collimated plan maintained the same target coverage while improving the OAR sparing compared to the un-collimated plan. Physical and biological comparison metrics such as dose distribution conformity, mean and maximum doses and normal tissue complication probabilities based on the Lyman-Kutcher-Burman model were used to quantify the benefits of collimation. Results: The use of the DCS generally improves the dose distribution conformity. The average reduction of the mean dose to the 10-mm ring surrounding the target, the uninvolved parotid, the esophagus, the uninvolved mandible and the maximum dose to the cord were-5.9%,-9.5%,-16.7%,-19.6% and-24.5% respectively. The individual values for each plan are shown in Table 1. The dose reduction between the collimated and un-collimated plans quantified through the dose-volume histograms yields an average relative reduction of parotid xerostomia risk and cord myelitis/ necrosis risks of-33.6% and-16.8% respectively. Conclusion: The improvement in the dose conformity afforded by the DCS globally increases the normal tissue sparing capabilities of SSPT for HN treatment while preserving the target coverage. This improvement impacts the OARs with a magnitude dependent on the target location, size and shape.
This paper is intended as a preliminary study to demonstrate the quality assurance benefits from ... more This paper is intended as a preliminary study to demonstrate the quality assurance benefits from polymer gel detectors for proton pencil beam cranio-spinal treatments. A stable gel type was selected for protons to suppress the LET dependence at the end of the Bragg peak. The depth dose distributions in the gels were examined with regard of its dose dependences and compared to baseline measurements. The preliminary experimental results indicate polymer gel detectors may be able to verify dose in three dimensions along match line for proton therapy treatments.
PURPOSE The beam range uncertainty presents a special challenge for proton therapy. Novel technol... more PURPOSE The beam range uncertainty presents a special challenge for proton therapy. Novel technologies currently under development offer strategies to reduce the range uncertainty [1,2]. This work quantifies the potential advantages that could be realized by such a reduction for dosimetrically challenging chordomas at the base of skull. Therapeutic improvement was assessed by evaluating tumor control probabilities (TCP) and normal tissue complication probabilities (NTCP). METHODS Treatment plans were made for a modulated-scanned proton delivery technique using the Eclipse treatment planning system. The prescription dose was 7920 cGy to the CTV. Three different range uncertainty scenarios were considered: 5 mm (3.5% of the beam range + 1 mm, representing current clinical practice, "Curr"), 2 mm (1.3%), and 1 mm (0.7%). For each of 4 patients, 3 different PTVs were defined via uniform expansion of the CTV by the value of the range uncertainty. Tumor control probability (TCP) and normal tissue complication probabilities (NTCPs) for organs-at-risk (OARs) were calculated using the Lyman-Kutcher-Burman[3] formalism and published model parameters [ref Terahara[4], quantec S10, Burman Red Journal v21 pp 123]. Our plan optimization strategy was to achieve PTV close to prescription while maintaining OAR NTCP values at or better than the Curr plan. RESULTS The average TCP values for the 5, 2, and 1 mm range uncertainty scenarios are 51%, 55% and 65%. The improvement in TCP for patients was between 4 and 30%, depending primarily on the proximity of the GTV to OAR. The average NTCPs for the brainstem and cord were about 4% and 1%, respectively, for all target margins. CONCLUSION For base of skull chordomas, reduced target margins can substantially increase the TCP without increasing the NTCP. This work demonstrates the potential significance of a reduction in the range uncertainty for proton beams.
The CI for M2 equals 88%, but 90% CI can be achieved for M2 by extending slightly the lateral PTV... more The CI for M2 equals 88%, but 90% CI can be achieved for M2 by extending slightly the lateral PTV margin to encompass 92% of possible beam positions and 98% of possible ranges, leading to a 425% volume, thus still better than M3. Conclusion The best tradeoff between robustness and optimality was achieved through random sampling of all errors limited by the lateral conventional PTV margin and a large margin for the possible proton ranges.
International Journal of Radiation Oncology*Biology*Physics, 2016
High soft tissue contrast with MRI reduces GTV delineation uncertainty as compared to CT and PET ... more High soft tissue contrast with MRI reduces GTV delineation uncertainty as compared to CT and PET for cervical cancer. However, the GTVs defined by different imaging modalities are different. The average GTV volumes for T1, T2, ADC, and T1F+ were (in cm 3) 62.8
This paper is intended as a preliminary study to demonstrate the quality assurance benefits from ... more This paper is intended as a preliminary study to demonstrate the quality assurance benefits from polymer gel detectors for proton pencil beam cranio-spinal treatments. A stable gel type was selected for protons to suppress the LET dependence at the end of the Bragg peak. The depth dose distributions in the gels were examined with regard of its dose dependences and compared to baseline measurements. The preliminary experimental results indicate polymer gel detectors may be able to verify dose in three dimensions along match line for proton therapy treatments.
Purpose:Rotational proton radiotherapy would be an interesting treatment modality if it proves to... more Purpose:Rotational proton radiotherapy would be an interesting treatment modality if it proves to produce dose distributions that conform to the target as well or better than currently available treatment modalities, while reducing the dose to the surrounding organs at risk. A treatment planning study is presented, showing how this objective can be achieved using a single or small number of scanned mono‐energetic pencil beams delivered while the proton gantry rotates at the same time that they may deliver faster and more biologically effective treatments than current proton modalities.Methods Proton treatment using single‐ (SFO) and multi‐field optimized (MFO) PBS plans are compared with PMAT plans in phantoms of different shape and uniformity as well as on a brain case. The method followed in ECLIPSE to produce PMAT plans is presented and the feasibility is discussed. Results Table 1 shows that the conformity and uniformity of the PMAT plans is of similar order than those of the SF...
ABSTRACT Purpose: To propose the gradient optimization(GO) approach in planning for matching prot... more ABSTRACT Purpose: To propose the gradient optimization(GO) approach in planning for matching proton PBS fields and present two commonly used applications in our institution.
Purpose: To examine proton edge scattering effects from a tungstenMLC, specifically in comparison... more Purpose: To examine proton edge scattering effects from a tungstenMLC, specifically in comparison with proton edge effects using a non‐divergent brass aperture. Methods and Materials: The standard for proton therapy beam shaping is a custom‐cut, non‐divergent aperture with thickness ∼65mm. To make comparisons with tungstenMLC simulations, a Monte Carlo simulation model created with GEANT4 was run for non‐divergent apertures made of tungsten and brass at thicknesses of 65, 75, and 85 mm. Simulations with each type of aperture were run for IBA's proton double‐scattering options B1, B4, and B7 at 100 and 550 mm elevations with square field sizes of 15×15, 10×10, and 5×5 cm2 and aperture‐to‐phantom air gaps of 1 and 4 cm. MLC simulations were verified with beam profile measurements using the same treatment parameters. Results: Dose profiles of proton beams have horns similar to dose profiles with X‐ray beams, but they originate from protons scattering back into the field at the field edge. Using non‐divergent tungsten and brass apertures, the size of the horns on dose profiles at the entrance of the simulated water phantom were found to follow the same trends as the leaf edge fields of the MLC. The profiles from the tungstenMLC fields were compared with the best case thickness (65 mm) for brass and tungsten apertures. MLC profiles have horns only along the axis of leaf travel due to MLC design, while the non‐divergent apertures have equally large horns along both axes, as expected given the symmetry. Along the axis of leaf travel the horns resulting from edge scatter off of the MLC were approximately equal to or smaller than horns from edge scatter off of the non‐divergent apertures. Conclusions:Proton dose profiles using a tungstenMLC have no worse edge‐scattering effects than a non‐divergent brass aperture.
International Journal of Radiation Oncology*Biology*Physics, 2017
nipple-areolar region with a field-in-field technique. All patients underwent respiratory-gated c... more nipple-areolar region with a field-in-field technique. All patients underwent respiratory-gated computed tomography immediately after irradiation at inhale breathing status weekly, and the central positions of tumor and markers, and the entire figure of breast cup were determined. The treatment time per day since patients entered a treatment room until they left was measured to assess the feasibility of the HyBIS. We examined the correlation between the central positions of tumor and markers to verify the accuracy of HyBIS, and also evaluated the reproducibility of the HyBIS by analyzing the displacements for tumor of a three-dimensional space specified by skeletal structures, markers, and the entire figure of breast cup. Results: The average treatment time in each patient were 44, 39, 42, and 52 minutes, respectively, and shortening treatment time by accumulation of knowledge and experience was not observed. The mean values of the displacement of markers for tumor in each patient were 3.9AE1.3, 2.0AE0.7, 2.8AE0.8, and 3.4AE1.2 mm, respectively. The average values of the displacement for tumor of a three-dimensional space specified by skeletal structures, markers, and the entire figure of breast cup were 5.6AE3.2, 4.6AE2.7, and 3.8AE2.3 mm, respectively. These results indicated that position displacement correction with breast cup in the treatment of early breast cancer with the HyBIS was more precise and reliable rather than those with skeletal structures or fiducial markers. Conclusion: We verified the feasibility, the accuracy, and the reproducibility of the HyBIS in the phase I clinical trial, and demonstrated that the HyBIS could help to reliably and precisely perform proton beam therapy for early breast cancer.
Purpose: We dosimetrically compared pencil beam scanning (PBS) proton therapy and intensity-modul... more Purpose: We dosimetrically compared pencil beam scanning (PBS) proton therapy and intensity-modulated radiation therapy (IMRT) for pelvic and para-aortic lymph node disease in endometrial carcinoma and present acute toxicities associated with extendedfield PBS. Patients and Methods: Twenty-five patients with locally advanced endometrial malignancies were enrolled in an image-guided registry study. Seven of these patients were treated with PBS, and 18 patients were treated with IMRT. Organs at risk included pelvic bone marrow (PBM), small bowel (SB), large bowel (LB), rectum, bladder, and kidneys. The IMRT and PBS dosimetric parameters were compared using Wilcoxon rank-sum tests. Results: Compared with IMRT PBM dose-volume histograms, PBS resulted in significantly lower dose volumes from 0 to 26.0 Gy (P , .05) and higher dose volumes from 33.9 to 42.9 Gy (P , .05). Overall, PBS resulted in 22% lower median PBM volume irradiated to 10 Gy (RBE) (PBS 71.3% versus IMRT 93.4%, P , .001) and 14% lower median volume irradiated to 20 Gy (RBE) (PBS 65.1% versus IMRT 79.4%, P , .001). Compared with IMRT, PBS also significantly reduced SB dose volumes from 0 to 27.5 Gy, LB dose volumes from 0 to 31.6 Gy, bladder dose volumes from 0 to 27.3 Gy, and rectal dose volumes from 0 to 7.6 Gy (all P , .05). However, PBS resulted in higher rectal dose volumes compared with IMRT from 26.0 to 48.4 Gy. Grade 3þ hematologic toxicities were present in 2 (11%) IMRT-treated patients and no PBS-treated patients. No grade 3þ gastrointestinal or genitourinary toxicities were present in either treatment group. Conclusion: In endometrial carcinoma, extended-field PBS is clinically feasible, resulting in statistically significant dose reduction to PBM as well as SB, LB, and bladder in the lower dose regions.
International Journal of Radiation Oncology*Biology*Physics, 2015
Results: Each beam arrangement resulted in a highly robust plan to standard setup and range calib... more Results: Each beam arrangement resulted in a highly robust plan to standard setup and range calibration errors for this patient. However, when evaluated for rectal variations through 5 treatments, we observe a drop in target coverages as shown in Table . Conclusion: For ano-rectal cancer treatments with proton scanning beam, conventional robustness evaluations based on planning CT alone would overestimate plan robustness. Interfractional anatomical changes should be taken into account in order to obtain complete plan robustness evaluations. Techniques to mitigate these effects should be considered.
Introduction. Spot scanning proton therapy (SSPT) treatments suffer from poor conformity, especia... more Introduction. Spot scanning proton therapy (SSPT) treatments suffer from poor conformity, especially at low energy, due to increased lateral spot size, which is further increased with the patient scattering. The University of Iowa Hospitals and Clinics recently proposed a dynamic collimation system (DCS) for SSPT, which is capable of providing spot-by-spot collimation. The purpose of this study is to quantify by simulations improvement in target conformity from the use of the DCS, in brain and head and neck tumor treatments. Methods. Two spot scanning proton therapy delivery systems (Universal Nozzle, UN, and Dedicated Nozzle, DN-IBA company) with median spot sizes of 5.2 mm and 3.2 mm over a range of energies from 100 to 230 MeV were considered. Uncollimated and collimated plans were calculated with both UN and DN beam models implemented within our in-house treatment planning system for five brain and ten head and neck datasets of patients previously treated with spot scanning proton therapy. The DCS was simulated as close as 5 cm from the patient surface. The average reduction of the mean dose to the 10-mm ring surrounding the target between the uncollimated and collimated plans was calculated for the UN and DN. Target conformity was analyzed using the mean dose to 1-mm thickness rings surrounding the target at increasing distances ranging from 1 mm to 10 mm. The dose reduction to some organsat-risk was also quantified. Results. The average reductions of the 10-mm ring mean dose for the UN and DN plans were 13.7% (95% CI: 11.6-15.7%; p < 0.0001) and 11.5% (95% CI: 9.5-13.5%; p < 0.0001) across all brain cases, and 7.1% (95% CI: 4.4-9.8%; p < 0.001) and 6.3% (95% CI: 3.7-9.0%; p < 0.001) respectively across all head and neck cases. The collimated UN plans were either more conformal (all brain cases and 60% of the head and neck cases) than or equivalent (40% of the head and neck cases) to the uncollimated DN plans. The collimated DN plans offered the highest conformity. Conclusions. According to these simulations, the DCS improved the target conformity for both the UN and the DN, and offered better dose reduction to OARs [1-3].
ABSTRACT Purpose: RapidArc is routinely used for stereotactic radiotherapy for lung cancer. While... more ABSTRACT Purpose: RapidArc is routinely used for stereotactic radiotherapy for lung cancer. While treatment dose is optimized and calculated on a static CT image, the motion of the target in conjunction with the motion of the MLC may Result in a delivered dose deviating from the planed dose. In this study, we investigate the dosimetric consequences of the inter-play effect by simulating dynamic dose delivery on a dynamic CT dataset of real patients. Methods: The target motion in 20 patients was analyzed and 5 patients with &gt;10 mm motion were chosen for this study. The RapidArc plan for eachpatient is optimized on a free-breathing CT using 2 arcs. Inherent in each plan is data on the associated parameters such as timestamp, MLC leave position, gantry angle and delivered beam MUs for each control point. Simulated dynamic delivery is performed by associating these parameters with each of the breathing phases of the 4D-CT. The starting breathing phase is selected randomly for each of the two arcs. Dose from the derived partial plans associated with each phase of the 4D-CT dose is recalculated in Eclipse. Accumulation of dose is performed using deformable image registration from each phase of the 4D-CT to the exhale phase of the 4D-CT. Results: The coverage of the GTV and PTV shows negligible variations from the interplay effect. But the Homogeneity Index is affected by the motion. The prescription isodose volume is smaller than what was from the treatment plan dose. There were both intra- and inter-fraction effects seen inthe OARs dose in some patients. Conclusions: We investigated the motioneffect in RapidArc Lung SBRT delivery in 5 patients. Negligible variations were shown for target coverage. However the motion effects were observed in high dose distribution and volume. Some OARs dose distributions were affected by the motion.
Purpose:Low‐energy treatments during spot scanning proton therapy (SSPT) suffer from poor conform... more Purpose:Low‐energy treatments during spot scanning proton therapy (SSPT) suffer from poor conformity due to increased spot size. Collimation devices can reduce the lateral penumbra of a proton therapy dose distribution and improve the overall plan quality. The purpose of this work was to study the advantages of individual energy‐layer collimation, which is unique to a recently proposed Dynamic Collimation System (DCS), in comparison to a standard, fixed aperture that allows only a single shape for all energy layers.Methods:Three brain patients previously planned and treated with SSPT were re‐planned using an in‐house treatment planning system capable of modeling collimated and un‐collimated proton beamlets. The un‐collimated plans, which served as a baseline for comparison, reproduced the target coverage of the clinically delivered plans. The collimator opening for the aperture based plans included a 0.6 cm expansion of the largest cross section of the target in the Beam's Eye View, while the DCS based plans were created by optimizing the collimator position for beam spots near the periphery of the target in each energy layer.Results:The reduction of mean dose to normal tissue adjacent to the target, as defined by a 10 mm ring, averaged 9.13% and 3.48% for the DCS and aperture plans, respectively. The conformity index, as defined by the ratio of the volume of the 50% isodose line to the target volume, yielded an average improvement of 16.42% and 8.16% for the DCS and aperture plans, respectively.Conclusion:Collimation reduces the dose to normal tissue adjacent to the target and increases dose conformity to the target region for low‐energy SSPT. The ability of the DCS to provide collimation to each energy layer yields better conformity in comparison to fixed aperture plans.This work was partially funded by IBA (Ion Beam Applications S.A.).
Purpose: A dynamic collimation system (DCS) based on two orthogonal pairs of mobile trimmer blade... more Purpose: A dynamic collimation system (DCS) based on two orthogonal pairs of mobile trimmer blades has recently been proposed to reduce the lateral penumbra in spot scanning proton therapy (SSPT). The purpose of this work is to quantify the therapeutic benefit of using the DCS for SSPT of brain cancer by comparing un-collimated and collimated treatment plans. Methods: Un-collimated and collimated brain treatment plans were created for five patients, previously treated with SSPT, using an in-house treatment planning system capable of modeling collimated and un-collimated beamlets. Un-collimated plans reproduced the clinically delivered plans in terms of target coverage and organ-at-risk (OAR) sparing, whereas collimated plans were re-optimized to improve the organ-at-risk sparing while maintaining target coverage. Physical and biological comparison metrics such as dose distribution conformity, mean and maximum doses, normal tissue complication probability (NTCP) and risk of secondary brain cancer were used to evaluate the plans. Results: The DCS systematically improved the dose distribution conformity while preserving the target coverage. The average reduction of the mean dose to the 10-mm ring surrounding the target and the healthy brain were 7.1% (95% CI: 4.2%–9.9%; p<0.01) and 14.3% (95% CI: 7.8%–20.8%; p<0.01), respectively. This yielded an average reduction of 12.0% (95% CI: 8.2%–15.7%; p<0.01) for the brain necrosis NTCP using the Flickinger model, and 14.2% (95% CI: 7.7%–20.8%; p<0.01) for the risk of secondary brain cancer. The average maximum dose reductions for the brainstem, chiasm, optic nerves, cochleae and pituitary gland when comparing un-collimated and collimated plans were 14.3%, 10.4%, 11.2%, 13.0%, 12.9% and 3.4%, respectively. Evaluating individual plans using the Lyman-Kutcher-Burman NTCP model also yielded improvements. Conclusion: The lateral penumbra reduction performed by the DCS increases the normal tissue sparing capabilities of SSPT for brain tumor treatment while preserving the target coverage. This research was financially supported by Ion Beam Applications S.A. (IBA, Louvain-La-Neuve, Belgium).
International Journal of Radiation Oncology Biology Physics, Nov 1, 2015
The purpose of this work was to quantify the benefits of using a dynamic collimation system (DCS)... more The purpose of this work was to quantify the benefits of using a dynamic collimation system (DCS) along with spot scanning proton therapy (SSPT) during the treatment of head and neck (HN) cancer. We hypothesize that the DCS will significantly increase the dose conformity to yield better sparing for organs-at-risk (OAR) while maintaining target coverage. Materials/Methods: Collimated and un-collimated HN treatment plans were created for five patients previously treated with SSPT and retrospectively enrolled in an Institutional Review Board approved study. All patients received postoperative adjuvant SSPT for advanced-stage disease, the majority of whom received bilateral, elective neck radiation in addition to treatment of the primary tumor site. Both collimated and un-collimated plans were generated using an in-house treatment planning system capable of accounting for the effects of collimation. The un-collimated plan was generated such that the target coverage was equivalent to the clinically delivered plan. The collimated plan maintained the same target coverage while improving the OAR sparing compared to the un-collimated plan. Physical and biological comparison metrics such as dose distribution conformity, mean and maximum doses and normal tissue complication probabilities based on the Lyman-Kutcher-Burman model were used to quantify the benefits of collimation. Results: The use of the DCS generally improves the dose distribution conformity. The average reduction of the mean dose to the 10-mm ring surrounding the target, the uninvolved parotid, the esophagus, the uninvolved mandible and the maximum dose to the cord were-5.9%,-9.5%,-16.7%,-19.6% and-24.5% respectively. The individual values for each plan are shown in Table 1. The dose reduction between the collimated and un-collimated plans quantified through the dose-volume histograms yields an average relative reduction of parotid xerostomia risk and cord myelitis/ necrosis risks of-33.6% and-16.8% respectively. Conclusion: The improvement in the dose conformity afforded by the DCS globally increases the normal tissue sparing capabilities of SSPT for HN treatment while preserving the target coverage. This improvement impacts the OARs with a magnitude dependent on the target location, size and shape.
This paper is intended as a preliminary study to demonstrate the quality assurance benefits from ... more This paper is intended as a preliminary study to demonstrate the quality assurance benefits from polymer gel detectors for proton pencil beam cranio-spinal treatments. A stable gel type was selected for protons to suppress the LET dependence at the end of the Bragg peak. The depth dose distributions in the gels were examined with regard of its dose dependences and compared to baseline measurements. The preliminary experimental results indicate polymer gel detectors may be able to verify dose in three dimensions along match line for proton therapy treatments.
PURPOSE The beam range uncertainty presents a special challenge for proton therapy. Novel technol... more PURPOSE The beam range uncertainty presents a special challenge for proton therapy. Novel technologies currently under development offer strategies to reduce the range uncertainty [1,2]. This work quantifies the potential advantages that could be realized by such a reduction for dosimetrically challenging chordomas at the base of skull. Therapeutic improvement was assessed by evaluating tumor control probabilities (TCP) and normal tissue complication probabilities (NTCP). METHODS Treatment plans were made for a modulated-scanned proton delivery technique using the Eclipse treatment planning system. The prescription dose was 7920 cGy to the CTV. Three different range uncertainty scenarios were considered: 5 mm (3.5% of the beam range + 1 mm, representing current clinical practice, "Curr"), 2 mm (1.3%), and 1 mm (0.7%). For each of 4 patients, 3 different PTVs were defined via uniform expansion of the CTV by the value of the range uncertainty. Tumor control probability (TCP) and normal tissue complication probabilities (NTCPs) for organs-at-risk (OARs) were calculated using the Lyman-Kutcher-Burman[3] formalism and published model parameters [ref Terahara[4], quantec S10, Burman Red Journal v21 pp 123]. Our plan optimization strategy was to achieve PTV close to prescription while maintaining OAR NTCP values at or better than the Curr plan. RESULTS The average TCP values for the 5, 2, and 1 mm range uncertainty scenarios are 51%, 55% and 65%. The improvement in TCP for patients was between 4 and 30%, depending primarily on the proximity of the GTV to OAR. The average NTCPs for the brainstem and cord were about 4% and 1%, respectively, for all target margins. CONCLUSION For base of skull chordomas, reduced target margins can substantially increase the TCP without increasing the NTCP. This work demonstrates the potential significance of a reduction in the range uncertainty for proton beams.
The CI for M2 equals 88%, but 90% CI can be achieved for M2 by extending slightly the lateral PTV... more The CI for M2 equals 88%, but 90% CI can be achieved for M2 by extending slightly the lateral PTV margin to encompass 92% of possible beam positions and 98% of possible ranges, leading to a 425% volume, thus still better than M3. Conclusion The best tradeoff between robustness and optimality was achieved through random sampling of all errors limited by the lateral conventional PTV margin and a large margin for the possible proton ranges.
International Journal of Radiation Oncology*Biology*Physics, 2016
High soft tissue contrast with MRI reduces GTV delineation uncertainty as compared to CT and PET ... more High soft tissue contrast with MRI reduces GTV delineation uncertainty as compared to CT and PET for cervical cancer. However, the GTVs defined by different imaging modalities are different. The average GTV volumes for T1, T2, ADC, and T1F+ were (in cm 3) 62.8
This paper is intended as a preliminary study to demonstrate the quality assurance benefits from ... more This paper is intended as a preliminary study to demonstrate the quality assurance benefits from polymer gel detectors for proton pencil beam cranio-spinal treatments. A stable gel type was selected for protons to suppress the LET dependence at the end of the Bragg peak. The depth dose distributions in the gels were examined with regard of its dose dependences and compared to baseline measurements. The preliminary experimental results indicate polymer gel detectors may be able to verify dose in three dimensions along match line for proton therapy treatments.
Purpose:Rotational proton radiotherapy would be an interesting treatment modality if it proves to... more Purpose:Rotational proton radiotherapy would be an interesting treatment modality if it proves to produce dose distributions that conform to the target as well or better than currently available treatment modalities, while reducing the dose to the surrounding organs at risk. A treatment planning study is presented, showing how this objective can be achieved using a single or small number of scanned mono‐energetic pencil beams delivered while the proton gantry rotates at the same time that they may deliver faster and more biologically effective treatments than current proton modalities.Methods Proton treatment using single‐ (SFO) and multi‐field optimized (MFO) PBS plans are compared with PMAT plans in phantoms of different shape and uniformity as well as on a brain case. The method followed in ECLIPSE to produce PMAT plans is presented and the feasibility is discussed. Results Table 1 shows that the conformity and uniformity of the PMAT plans is of similar order than those of the SF...
ABSTRACT Purpose: To propose the gradient optimization(GO) approach in planning for matching prot... more ABSTRACT Purpose: To propose the gradient optimization(GO) approach in planning for matching proton PBS fields and present two commonly used applications in our institution.
Purpose: To examine proton edge scattering effects from a tungstenMLC, specifically in comparison... more Purpose: To examine proton edge scattering effects from a tungstenMLC, specifically in comparison with proton edge effects using a non‐divergent brass aperture. Methods and Materials: The standard for proton therapy beam shaping is a custom‐cut, non‐divergent aperture with thickness ∼65mm. To make comparisons with tungstenMLC simulations, a Monte Carlo simulation model created with GEANT4 was run for non‐divergent apertures made of tungsten and brass at thicknesses of 65, 75, and 85 mm. Simulations with each type of aperture were run for IBA's proton double‐scattering options B1, B4, and B7 at 100 and 550 mm elevations with square field sizes of 15×15, 10×10, and 5×5 cm2 and aperture‐to‐phantom air gaps of 1 and 4 cm. MLC simulations were verified with beam profile measurements using the same treatment parameters. Results: Dose profiles of proton beams have horns similar to dose profiles with X‐ray beams, but they originate from protons scattering back into the field at the field edge. Using non‐divergent tungsten and brass apertures, the size of the horns on dose profiles at the entrance of the simulated water phantom were found to follow the same trends as the leaf edge fields of the MLC. The profiles from the tungstenMLC fields were compared with the best case thickness (65 mm) for brass and tungsten apertures. MLC profiles have horns only along the axis of leaf travel due to MLC design, while the non‐divergent apertures have equally large horns along both axes, as expected given the symmetry. Along the axis of leaf travel the horns resulting from edge scatter off of the MLC were approximately equal to or smaller than horns from edge scatter off of the non‐divergent apertures. Conclusions:Proton dose profiles using a tungstenMLC have no worse edge‐scattering effects than a non‐divergent brass aperture.
International Journal of Radiation Oncology*Biology*Physics, 2017
nipple-areolar region with a field-in-field technique. All patients underwent respiratory-gated c... more nipple-areolar region with a field-in-field technique. All patients underwent respiratory-gated computed tomography immediately after irradiation at inhale breathing status weekly, and the central positions of tumor and markers, and the entire figure of breast cup were determined. The treatment time per day since patients entered a treatment room until they left was measured to assess the feasibility of the HyBIS. We examined the correlation between the central positions of tumor and markers to verify the accuracy of HyBIS, and also evaluated the reproducibility of the HyBIS by analyzing the displacements for tumor of a three-dimensional space specified by skeletal structures, markers, and the entire figure of breast cup. Results: The average treatment time in each patient were 44, 39, 42, and 52 minutes, respectively, and shortening treatment time by accumulation of knowledge and experience was not observed. The mean values of the displacement of markers for tumor in each patient were 3.9AE1.3, 2.0AE0.7, 2.8AE0.8, and 3.4AE1.2 mm, respectively. The average values of the displacement for tumor of a three-dimensional space specified by skeletal structures, markers, and the entire figure of breast cup were 5.6AE3.2, 4.6AE2.7, and 3.8AE2.3 mm, respectively. These results indicated that position displacement correction with breast cup in the treatment of early breast cancer with the HyBIS was more precise and reliable rather than those with skeletal structures or fiducial markers. Conclusion: We verified the feasibility, the accuracy, and the reproducibility of the HyBIS in the phase I clinical trial, and demonstrated that the HyBIS could help to reliably and precisely perform proton beam therapy for early breast cancer.
Purpose: We dosimetrically compared pencil beam scanning (PBS) proton therapy and intensity-modul... more Purpose: We dosimetrically compared pencil beam scanning (PBS) proton therapy and intensity-modulated radiation therapy (IMRT) for pelvic and para-aortic lymph node disease in endometrial carcinoma and present acute toxicities associated with extendedfield PBS. Patients and Methods: Twenty-five patients with locally advanced endometrial malignancies were enrolled in an image-guided registry study. Seven of these patients were treated with PBS, and 18 patients were treated with IMRT. Organs at risk included pelvic bone marrow (PBM), small bowel (SB), large bowel (LB), rectum, bladder, and kidneys. The IMRT and PBS dosimetric parameters were compared using Wilcoxon rank-sum tests. Results: Compared with IMRT PBM dose-volume histograms, PBS resulted in significantly lower dose volumes from 0 to 26.0 Gy (P , .05) and higher dose volumes from 33.9 to 42.9 Gy (P , .05). Overall, PBS resulted in 22% lower median PBM volume irradiated to 10 Gy (RBE) (PBS 71.3% versus IMRT 93.4%, P , .001) and 14% lower median volume irradiated to 20 Gy (RBE) (PBS 65.1% versus IMRT 79.4%, P , .001). Compared with IMRT, PBS also significantly reduced SB dose volumes from 0 to 27.5 Gy, LB dose volumes from 0 to 31.6 Gy, bladder dose volumes from 0 to 27.3 Gy, and rectal dose volumes from 0 to 7.6 Gy (all P , .05). However, PBS resulted in higher rectal dose volumes compared with IMRT from 26.0 to 48.4 Gy. Grade 3þ hematologic toxicities were present in 2 (11%) IMRT-treated patients and no PBS-treated patients. No grade 3þ gastrointestinal or genitourinary toxicities were present in either treatment group. Conclusion: In endometrial carcinoma, extended-field PBS is clinically feasible, resulting in statistically significant dose reduction to PBM as well as SB, LB, and bladder in the lower dose regions.
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Papers by Maura Kirk