Takaaki Yoshimura1, Rumiko Kinoshita2, Shunsuke Onodera3, Chie Toramatsu4, Ryusuke Suzuki5, Yoichi M Ito6, Seishin Takao4, Taeko Matsuura7, Yuka Matsuzaki4, Kikuo Umegaki8, Hiroki Shirato9, Shinichi Shimizu10. 1. Proton Beam Therapy Center, Hokkaido University Hospital, Sapporo, Japan; Department of Radiation Medicine, Graduate School of Medicine, Hokkaido University, Sapporo, Japan. 2. Department of Radiation Oncology, Hokkaido University Hospital, Sapporo, Japan. Electronic address: rumiko0220@pop.med.hokudai.ac.jp. 3. Department of Radiation Medicine, Graduate School of Medicine, Hokkaido University, Sapporo, Japan. 4. Proton Beam Therapy Center, Hokkaido University Hospital, Sapporo, Japan. 5. Department of Medical Physics, Hokkaido University Hospital, Sapporo, Japan. 6. Department of Biostatistics, Hokkaido University Graduate School of Medicine, Sapporo, Japan. 7. Proton Beam Therapy Center, Hokkaido University Hospital, Sapporo, Japan; Global Station for Quantum Medical Science and Engineering, Global Institution for Collaborative Research and Education (GI-CoRE), Hokkaido University, Sapporo, Japan; Division of Quantum Science and Engineering, Faculty of Engineering, Hokkaido University, Sapporo, Japan. 8. Proton Beam Therapy Center, Hokkaido University Hospital, Sapporo, Japan; Division of Quantum Science and Engineering, Faculty of Engineering, Hokkaido University, Sapporo, Japan. 9. Department of Radiation Medicine, Graduate School of Medicine, Hokkaido University, Sapporo, Japan; Global Station for Quantum Medical Science and Engineering, Global Institution for Collaborative Research and Education (GI-CoRE), Hokkaido University, Sapporo, Japan. 10. Global Station for Quantum Medical Science and Engineering, Global Institution for Collaborative Research and Education (GI-CoRE), Hokkaido University, Sapporo, Japan; Department of Radiation Oncology, Graduate School of Medicine, Hokkaido University, Sapporo, Japan.
Abstract
PURPOSE: This treatment planning study was conducted to determine whether spot scanning proton beam therapy (SSPT) reduces the risk of grade ⩾3 hematologic toxicity (HT3+) compared with intensity modulated radiation therapy (IMRT) for postoperative whole pelvic radiation therapy (WPRT). METHODS AND MATERIALS: The normal tissue complication probability (NTCP) of the risk of HT3+ was used as an in silico surrogate marker in this analysis. IMRT and SSPT plans were created for 13 gynecologic malignancy patients who had received hysterectomies. The IMRT plans were generated using the 7-fields step and shoot technique. The SSPT plans were generated using anterior-posterior field with single field optimization. Using the relative biological effectives (RBE) value of 1.0 for IMRT and 1.1 for SSPT, the prescribed dose was 45Gy(RBE) in 1.8Gy(RBE) per fractions for 95% of the planning target volume (PTV). The homogeneity index (HI) and the conformity index (CI) of the PTV were also compared. RESULTS: The bone marrow (BM) and femoral head doses using SSPT were significantly lower than with IMRT. The NTCP modeling analysis showed that the risk of HT3+ using SSPT was significantly lower than with IMRT (NTCP=0.04±0.01 and 0.19±0.03, p=0.0002, respectively). There were no significant differences in the CI and HI of the PTV between IMRT and SSPT (CI=0.97±0.01 and 0.96±0.02, p=0.3177, and HI=1.24±0.11 and 1.27±0.05, p=0.8473, respectively). CONCLUSION: The SSPT achieves significant reductions in the dose to BM without compromising target coverage, compared with IMRT. The NTCP value for HT3+ in SSPT was significantly lower than in IMRT.
PURPOSE: This treatment planning study was conducted to determine whether spot scanning proton beam therapy (SSPT) reduces the risk of grade ⩾3 hematologic toxicity (HT3+) compared with intensity modulated radiation therapy (IMRT) for postoperative whole pelvic radiation therapy (WPRT). METHODS AND MATERIALS: The normal tissue complication probability (NTCP) of the risk of HT3+ was used as an in silico surrogate marker in this analysis. IMRT and SSPT plans were created for 13 gynecologic malignancypatients who had received hysterectomies. The IMRT plans were generated using the 7-fields step and shoot technique. The SSPT plans were generated using anterior-posterior field with single field optimization. Using the relative biological effectives (RBE) value of 1.0 for IMRT and 1.1 for SSPT, the prescribed dose was 45Gy(RBE) in 1.8Gy(RBE) per fractions for 95% of the planning target volume (PTV). The homogeneity index (HI) and the conformity index (CI) of the PTV were also compared. RESULTS: The bone marrow (BM) and femoral head doses using SSPT were significantly lower than with IMRT. The NTCP modeling analysis showed that the risk of HT3+ using SSPT was significantly lower than with IMRT (NTCP=0.04±0.01 and 0.19±0.03, p=0.0002, respectively). There were no significant differences in the CI and HI of the PTV between IMRT and SSPT (CI=0.97±0.01 and 0.96±0.02, p=0.3177, and HI=1.24±0.11 and 1.27±0.05, p=0.8473, respectively). CONCLUSION: The SSPT achieves significant reductions in the dose to BM without compromising target coverage, compared with IMRT. The NTCP value for HT3+ in SSPT was significantly lower than in IMRT.