Impact of Real-Time Image Gating on Spot Scanning Proton Therapy for Lung Tumors: A Simulation Study

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• 作者：Takahiro Kanehira ; MSc^&lowast ; ; Taeko Matsuura ; PhD^&dagger ; ; ^&Dagger ; ; ^§ ; ; ^{matsuura@med.hokudai.ac.jp} ; Seishin Takao ; PhD^&dagger ; ; Yuka Matsuzaki ; PhD^&dagger ; ; Yusuke Fujii ; MSc^&dagger ; ; Takaaki Fujii ; PhD^&dagger ; ; Yoichi M. Ito ; PhD^‖ ; Naoki Miyamoto ; PhD^¶ ; ; Tetsuya Inoue ; MD ; PhD^&lowast ; ; Norio Katoh ; MD ; PhD^# ; Shinichi Shimizu ; MD ; PhD^&Dagger ; ; ^&lowast ; &lowast ; ; Kikuo Umegaki ; PhD^&dagger ; ; ^§ ; ; Hiroki Shirato ; MD ; PhD^&lowast ; ; ^&Dagger ;
• 刊名：International Journal of Radiation Oncology*Biology*Physics
• 出版年：2017
• 出版时间：1 January 2017
• 年：2017
• 卷：97
• 期：1
• 页码：173-181
• 全文大小：1715 K
• 卷排序：97

文摘

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 MaterialsA 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.ResultsGating 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.ConclusionReal-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.