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Title: SU-F-T-189: Dosimetric Comparison of Spot-Scanning Proton Therapy Techniques for Liver Tumors Close to the Skin Surface

Abstract

Purpose: Spot-scanning technique has been utilized to achieve conformal dose distribution to large and complicated tumors. This technique generally does not require patient-specific devices such as aperture and compensator. The commercially available spot-scanning proton therapy (SSPT) systems, however, cannot deliver proton beams to the region shallower than 4 g/cm2. Therefore some range compensation device is required to treat superficial tumors with SSPT. This study shows dosimetric comparison of the following treatment techniques: (i) with a tabletop bolus, (ii) with a nozzle-mounted applicator, and (iii) without any devices and using intensity-modulated proton therapy (IMPT) technique. Methods: The applicator composed of a combination of a mini-ridge filter and a range shifter has been manufactured by Hitachi, Ltd., and the tabletop bolus was made by .decimal, Inc. Both devices have been clinically implemented in our facility. Three patients with liver tumors close to the skin surface were examined in this study. Each treatment plan was optimized so that the prescription dose of 76 Gy(RBE) or 66 Gy(RBE) would be delivered to 99% of the clinical target volume in 20 fractions. Three beams were used for tabletop bolus plan and IMPT plan, whereas two beams were used in the applicator plan because the gantrymore » angle available was limited due to potential collision to patient and couch. The normal liver, colon, and skin were considered as organs at risk (OARs). Results: The target heterogeneity index (HI = D{sub 5}/D{sub 95}) was 1.03 on average in each planning technique. The mean dose to the normal liver was considerably less than 20 Gy(RBE) in all cases. The dose to the skin could be reduced by 20 Gy(RBE) on average in the IMPT plan compared to the applicator plan. Conclusion: It has been confirmed that all treatment techniques met the dosimetric criteria for the OARs and could be implemented clinically.« less

Authors:
;  [1]; ;  [2];  [3]; ;  [4];  [5]; ;  [6];  [7]
  1. Proton Beam Therapy Center, Hokkaido University Hospital, Sapporo, Hokkaido (Japan)
  2. Faculty of Engineering, Hokkaido University, Sapporo, Hokkaido (Japan)
  3. (GI-CoRE), Hokkaido University, Sapporo, Hokkaido (Japan)
  4. Hokkaido University Graduate School of Medicine, Sapporo, Hokkaido (Japan)
  5. Department of Radiation Oncology, Hokkaido University Hospital, Sapporo, Hokkaido (Japan)
  6. Global Institution for Collaborative Research and Education (GI-CoRE), Hokkaido University, Sapporo, Hokkaido (Japan)
  7. (Japan)
Publication Date:
OSTI Identifier:
22648806
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 43; Journal Issue: 6; Other Information: (c) 2016 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; 61 RADIATION PROTECTION AND DOSIMETRY; EQUIPMENT; LARGE INTESTINE; LIVER; NEOPLASMS; PLANNING; PROTON BEAMS; RADIATION DOSE DISTRIBUTIONS; RADIOTHERAPY; RBE; SKIN

Citation Formats

Takao, S, Matsuzaki, Y, Matsuura, T, Umegaki, K, Global Institution for Collaborative Research and Education, Fujii, Y, Fujii, T, Katoh, N, Shimizu, S, Shirato, H, and Hokkaido University Graduate School of Medicine, Sapporo, Hokkaido. SU-F-T-189: Dosimetric Comparison of Spot-Scanning Proton Therapy Techniques for Liver Tumors Close to the Skin Surface. United States: N. p., 2016. Web. doi:10.1118/1.4956326.
Takao, S, Matsuzaki, Y, Matsuura, T, Umegaki, K, Global Institution for Collaborative Research and Education, Fujii, Y, Fujii, T, Katoh, N, Shimizu, S, Shirato, H, & Hokkaido University Graduate School of Medicine, Sapporo, Hokkaido. SU-F-T-189: Dosimetric Comparison of Spot-Scanning Proton Therapy Techniques for Liver Tumors Close to the Skin Surface. United States. doi:10.1118/1.4956326.
Takao, S, Matsuzaki, Y, Matsuura, T, Umegaki, K, Global Institution for Collaborative Research and Education, Fujii, Y, Fujii, T, Katoh, N, Shimizu, S, Shirato, H, and Hokkaido University Graduate School of Medicine, Sapporo, Hokkaido. 2016. "SU-F-T-189: Dosimetric Comparison of Spot-Scanning Proton Therapy Techniques for Liver Tumors Close to the Skin Surface". United States. doi:10.1118/1.4956326.
@article{osti_22648806,
title = {SU-F-T-189: Dosimetric Comparison of Spot-Scanning Proton Therapy Techniques for Liver Tumors Close to the Skin Surface},
author = {Takao, S and Matsuzaki, Y and Matsuura, T and Umegaki, K and Global Institution for Collaborative Research and Education and Fujii, Y and Fujii, T and Katoh, N and Shimizu, S and Shirato, H and Hokkaido University Graduate School of Medicine, Sapporo, Hokkaido},
abstractNote = {Purpose: Spot-scanning technique has been utilized to achieve conformal dose distribution to large and complicated tumors. This technique generally does not require patient-specific devices such as aperture and compensator. The commercially available spot-scanning proton therapy (SSPT) systems, however, cannot deliver proton beams to the region shallower than 4 g/cm2. Therefore some range compensation device is required to treat superficial tumors with SSPT. This study shows dosimetric comparison of the following treatment techniques: (i) with a tabletop bolus, (ii) with a nozzle-mounted applicator, and (iii) without any devices and using intensity-modulated proton therapy (IMPT) technique. Methods: The applicator composed of a combination of a mini-ridge filter and a range shifter has been manufactured by Hitachi, Ltd., and the tabletop bolus was made by .decimal, Inc. Both devices have been clinically implemented in our facility. Three patients with liver tumors close to the skin surface were examined in this study. Each treatment plan was optimized so that the prescription dose of 76 Gy(RBE) or 66 Gy(RBE) would be delivered to 99% of the clinical target volume in 20 fractions. Three beams were used for tabletop bolus plan and IMPT plan, whereas two beams were used in the applicator plan because the gantry angle available was limited due to potential collision to patient and couch. The normal liver, colon, and skin were considered as organs at risk (OARs). Results: The target heterogeneity index (HI = D{sub 5}/D{sub 95}) was 1.03 on average in each planning technique. The mean dose to the normal liver was considerably less than 20 Gy(RBE) in all cases. The dose to the skin could be reduced by 20 Gy(RBE) on average in the IMPT plan compared to the applicator plan. Conclusion: It has been confirmed that all treatment techniques met the dosimetric criteria for the OARs and could be implemented clinically.},
doi = {10.1118/1.4956326},
journal = {Medical Physics},
number = 6,
volume = 43,
place = {United States},
year = 2016,
month = 6
}
  • Purpose: To develop and validate a novel delivery strategy for reducing the respiratory motion–induced dose uncertainty of spot-scanning proton therapy. Methods and Materials: The spot delivery sequence was optimized to reduce dose uncertainty. The effectiveness of the delivery sequence optimization was evaluated using measurements and patient simulation. One hundred ninety-one 2-dimensional measurements using different delivery sequences of a single-layer uniform pattern were obtained with a detector array on a 1-dimensional moving platform. Intensity modulated proton therapy plans were generated for 10 lung cancer patients, and dose uncertainties for different delivery sequences were evaluated by simulation. Results: Without delivery sequence optimization,more » the maximum absolute dose error can be up to 97.2% in a single measurement, whereas the optimized delivery sequence results in a maximum absolute dose error of ≤11.8%. In patient simulation, the optimized delivery sequence reduces the mean of fractional maximum absolute dose error compared with the regular delivery sequence by 3.3% to 10.6% (32.5-68.0% relative reduction) for different patients. Conclusions: Optimizing the delivery sequence can reduce dose uncertainty due to respiratory motion in spot-scanning proton therapy, assuming the 4-dimensional CT is a true representation of the patients' breathing patterns.« less
  • Purpose: To quantitatively evaluate dosimetric consequence of spot size variations and validate beam-matching criteria for commissioning a pencil beam model for multiple treatment rooms. Methods: A planning study was first conducted by simulating spot size variations to systematically evaluate dosimetric impact of spot size variations in selected cases, which was used to establish the in-air spot size tolerance for beam matching specifications. A beam model in treatment planning system was created using in-air spot profiles acquired in one treatment room. These spot profiles were also acquired from another treatment room for assessing the actual spot size variations between the twomore » treatment rooms. We created twenty five test plans with targets of different sizes at different depths, and performed dose measurement along the entrance, proximal and distal target regions. The absolute doses at those locations were measured using ionization chambers at both treatment rooms, and were compared against the calculated doses by the beam model. Fifteen additional patient plans were also measured and included in our validation. Results: The beam model is relatively insensitive to spot size variations. With an average of less than 15% measured in-air spot size variations between two treatment rooms, the average dose difference was −0.15% with a standard deviation of 0.40% for 55 measurement points within target region; but the differences increased to 1.4%±1.1% in the entrance regions, which are more affected by in-air spot size variations. Overall, our single-room based beam model in the treatment planning system agreed with measurements in both rooms < 0.5% within the target region. For fifteen patient cases, the agreement was within 1%. Conclusion: We have demonstrated that dosimetrically equivalent machines can be established when in-air spot size variations are within 15% between the two treatment rooms.« less
  • Purpose: This study seeks to evaluate the dosimetric effects of intra-fraction motion during spot scanning proton beam therapy as a function of beam-scan orientation and target motion amplitude. Method: Multiple 4DCT scans were collected of a dynamic anthropomorphic phantom mimicking respiration amplitudes of 0 (static), 0.5, 1.0, and 1.5 cm. A spot-scanning treatment plan was developed on the maximum intensity projection image set, using an inverse-planning approach. Dynamic phantom motion was continuous throughout treatment plan delivery.The target nodule was designed to accommodate film and thermoluminescent dosimeters (TLD). Film and TLDs were uniquely labeled by location within the target. The phantommore » was localized on the treatment table using the clinically available orthogonal kV on-board imaging device. Film inserts provided data for dose uniformity; TLDs provided a 3% precision estimate of absolute dose. An inhouse script was developed to modify the delivery order of the beam spots, to orient the scanning direction parallel or perpendicular to target motion.TLD detector characterization and analysis was performed by the Imaging and Radiation Oncology Core group (IROC)-Houston. Film inserts, exhibiting a spatial resolution of 1mm, were analyzed to determine dose homogeneity within the radiation target. Results: Parallel scanning and target motions exhibited reduced target dose heterogeneity, relative to perpendicular scanning orientation. The average percent deviation in absolute dose for the motion deliveries relative to the static delivery was 4.9±1.1% for parallel scanning, and 11.7±3.5% (p<<0.05) for perpendicularly oriented scanning. Individual delivery dose deviations were not necessarily correlated to amplitude of motion for either scan orientation. Conclusions: Results demonstrate a quantifiable difference in dose heterogeneity as a function of scan orientation, more so than target amplitude. Comparison to the analyzed planar dose of a single field hint that multiple-field delivery alters intra-fraction beam-target motion synchronization and may mitigate heterogeneity, though further study is warranted.« less
  • Purpose: Radiotherapy plays a major role in the treatment strategy of childhood sarcomas. Consequences of treatment are likely to affect the survivor's quality of life significantly. We investigated the feasibility of spot-scanning proton therapy (PT) for soft tissue tumors in childhood. Methods and Materials: Sixteen children with soft tissue sarcomas were included. Median age at PT was 3.3 years. In 10 children the tumor histology was embryonal rhabdomyosarcoma. All tumors were located in the head or neck, parameningeal, or paraspinal, or pelvic region. In the majority of children, the tumor was initially unresectable (Intergroup Rhabdomyosarcoma Study [IRS] Group III inmore » 75%). In 50% of children the tumors exceeded 5 cm. Fourteen children had chemotherapy before and during PT. Median total dose of radiotherapy was 50 cobalt Gray equivalent (CGE). All 16 children were treated with spot-scanning proton therapy at the Paul Scherrer Institute, and in 3 children the PT was intensity-modulated (IMPT). Results: After median follow-up of 1.5 years, local control was achieved in 12 children. Four children failed locally, 1 at the border of the radiation field and 3 within the field. All 4 children died of tumor recurrence. All 4 showed unfavorable characteristic either of site or histopathology of the tumor. Acute toxicity was low, with Grade 3 or 4 side effects according to Radiation Therapy Oncology Group/European Organization for Research and Treatment of Cancer (RTOG/EORTC) criteria occurring in the bone marrow only. Conclusions: Proton therapy was feasible and well tolerated. Early local control rates are comparable to those being achieved after conventional radiotherapy. For investigations on late effect, longer follow-up is needed.« less
  • Purpose: To develop a method for treating shallow and moving tumors (e.g., lung tumors) with respiratory-gated spot-scanning proton therapy using real-time image guidance (RTPT). Methods: An applicator was developed which can be installed by hand on the treatment nozzle. The mechanical design was considered such that the Bragg peaks are placed at the patient surface while a sufficient field of view (FOV) of fluoroscopic X-rays was maintained during the proton beam delivery. To reduce the treatment time maintaining the robustness of the dose distribution with respect to motion, a mini-ridge filter (MRF) was sandwiched between two energy absorbers. The measurementsmore » were performed to obtain a data for beam modeling and to verify the spot position-invariance of a pencil beam dose distribution. For three lung cancer patients, treatment plans were made with and without the MRF and the effects of the MRF were evaluated. Next, the effect of respiratory motion on the dose distribution was investigated. Results: To scan the proton beam over a 14 x 14 cm area while maintaining the φ16 cm of fluoroscopic FOV, the lower face of the applicator was set 22 cm upstream of the isocenter. With an additional range variance of 2.2 mm and peak-to-peak distance of 4 mm of the MRF, the pencil beam dose distribution was unchanged with the displacement of the spot position. The quality of the treatment plans was not worsened by the MRF. With the MRF, the number of energy layers was reduced to less than half and the treatment time by 26–37%. The simulation study showed that the interplay effect was successfully suppressed by respiratory-gating both with and without MRF. Conclusions: The spot-scanning proton beam was successfully delivered to shallow and moving tumors within a sufficiently short time by installing the developed applicator at the RTPT nozzle.« less