Takahiro Kanehira1, Taeko Matsuura2, Seishin Takao3, Yuka Matsuzaki3, Yusuke Fujii3, Takaaki Fujii3, Yoichi M Ito4, Naoki Miyamoto5, Tetsuya Inoue1, Norio Katoh6, Shinichi Shimizu7, Kikuo Umegaki8, Hiroki Shirato9. 1. Department of Radiation Medicine, Graduate School of Medicine, Hokkaido University, Sapporo, Japan. 2. Proton Beam Therapy Center, Hokkaido University Hospital, Sapporo, Japan; Global Station for Quantum Medical Science and Engineering, Global Institution for Collaborative Research and Education, Hokkaido University, Sapporo, Japan; Division of Quantum Science and Engineering, Faculty of Engineering, Hokkaido University, Sapporo, Japan. Electronic address: matsuura@med.hokudai.ac.jp. 3. Proton Beam Therapy Center, Hokkaido University Hospital, Sapporo, Japan. 4. Department of Biostatistics, Hokkaido University Graduate School of Medicine, Sapporo, Japan. 5. Department of Medical Physics, Hokkaido University Hospital, Sapporo, Japan. 6. Department of Radiation Oncology, Hokkaido University Hospital, Sapporo, Japan. 7. Global Station for Quantum Medical Science and Engineering, Global Institution for Collaborative Research and Education, Hokkaido University, Sapporo, Japan; Department of Radiation Oncology, Graduate School of Medicine, 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, Hokkaido University, Sapporo, Japan.
Abstract
PURPOSE: To investigate the effectiveness of real-time-image gated proton beam therapy for lung tumors and to establish a suitable size for the gating window (GW). METHODS AND MATERIALS: A proton beam gated by a fiducial marker entering a preassigned GW (as monitored by 2 fluoroscopy units) was used with 7 lung cancer patients. Seven treatment plans were generated: real-time-image gated proton beam therapy with GW sizes of ±1, 2, 3, 4, 5, and 8 mm and free-breathing proton therapy. The prescribed dose was 70 Gy (relative biological effectiveness)/10 fractions to 99% of the target. Each of the 3-dimensional marker positions in the time series was associated with the appropriate 4-dimensional computed tomography phase. The 4-dimensional dose calculations were performed. The dose distribution in each respiratory phase was deformed into the end-exhale computed tomography image. The D99 and D5 to D95 of the clinical target volume scaled by the prescribed dose with criteria of D99 >95% and D5 to D95 <5%, V20 for the normal lung, and treatment times were evaluated. RESULTS: Gating windows ≤ ±2 mm fulfilled the CTV criteria for all patients (whereas the criteria were not always met for GWs ≥ ±3 mm) and gave an average reduction in V20 of more than 17.2% relative to free-breathing proton therapy (whereas GWs ≥ ±4 mm resulted in similar or increased V20). The average (maximum) irradiation times were 384 seconds (818 seconds) for the ±1-mm GW, but less than 226 seconds (292 seconds) for the ±2-mm GW. The maximum increased considerably at ±1-mm GW. CONCLUSION: Real-time-image gated proton beam therapy with a GW of ±2 mm was demonstrated to be suitable, providing good dose distribution without greatly extending treatment time.
PURPOSE: To investigate the effectiveness of real-time-image gated proton beam therapy for lung tumors and to establish a suitable size for the gating window (GW). METHODS AND MATERIALS: A proton beam gated by a fiducial marker entering a preassigned GW (as monitored by 2 fluoroscopy units) was used with 7 lung cancerpatients. Seven treatment plans were generated: real-time-image gated proton beam therapy with GW sizes of ±1, 2, 3, 4, 5, and 8 mm and free-breathing proton therapy. The prescribed dose was 70 Gy (relative biological effectiveness)/10 fractions to 99% of the target. Each of the 3-dimensional marker positions in the time series was associated with the appropriate 4-dimensional computed tomography phase. The 4-dimensional dose calculations were performed. The dose distribution in each respiratory phase was deformed into the end-exhale computed tomography image. The D99 and D5 to D95 of the clinical target volume scaled by the prescribed dose with criteria of D99 >95% and D5 to D95 <5%, V20 for the normal lung, and treatment times were evaluated. RESULTS: Gating windows ≤ ±2 mm fulfilled the CTV criteria for all patients (whereas the criteria were not always met for GWs ≥ ±3 mm) and gave an average reduction in V20 of more than 17.2% relative to free-breathing proton therapy (whereas GWs ≥ ±4 mm resulted in similar or increased V20). The average (maximum) irradiation times were 384 seconds (818 seconds) for the ±1-mm GW, but less than 226 seconds (292 seconds) for the ±2-mm GW. The maximum increased considerably at ±1-mm GW. CONCLUSION: Real-time-image gated proton beam therapy with a GW of ±2 mm was demonstrated to be suitable, providing good dose distribution without greatly extending treatment time.