Fukumitsu Nobuyoshi, Hayakawa Tomokatsu, Yamashita Tomohiro, Mima Masayuki, Demizu Yusuke, Suzuki Takeshi, Soejima Toshinori
Department of Radiation Oncology, Kobe Proton Center, Kobe, Hyogo 650-0047, Japan.
Division of Radiation Therapy, Radiation and Proton Therapy Center, Shizuoka Cancer Center, Shizuoka, Shizuoka 411-8777, Japan.
Mol Clin Oncol. 2022 Jan;16(1):25. doi: 10.3892/mco.2021.2458. Epub 2021 Dec 1.
The aim of the present study was to investigate the effects on the dose distribution and beam delivery time in spot scanning proton beam therapy (PBT) incorporating the spot deletion technique. A spot scanning plan was created for 30 patients with prostate cancer. The plan was then modified via two processes: Spots with lower weighting depositions were deleted (process A) and spots that were distant from the clinical target volume (CTV) were deleted (process B). The dose distribution to the organs at risk (OAR), the expanded CTV (exCTV), which was defined by a uniform expansion of the CTV by a radius of 5 mm, and the beam delivery time were compared among initial and modified plans. The V to the rectum and bladder, and V to the urethral bulb, inhomogeneity index (INH) of the exCTV showed a difference (P=1.1x10, P=6.4x10, P=2.7x10, P=3.2x10), although only changes by process B were significant. Modified plan by process B showed the V to the rectum and bladder decreased by -2.4±1.6 and -2.3±1.4%, and the V to the urethral bulb decreased by -15.9±19.4%. The INH of the exCTV increased by 0.05±0.03%. On the other hand, modification of the initial plan by process A did not affect the dose of the OAR, exCTV or beam delivery time. In spot scanning PBT, modification of the initial radiotherapy plan by systemic deletion of spots distant from the CTV could result in a dose reduction to the OAR.
本研究的目的是探讨在采用光斑删除技术的点扫描质子束治疗（PBT）中对剂量分布和束流输送时间的影响。为30例前列腺癌患者制定了点扫描计划。然后通过两个过程对该计划进行修改：删除权重沉积较低的光斑（过程A）和删除远离临床靶区（CTV）的光斑（过程B）。比较初始计划和修改后计划中危及器官（OAR）、通过将CTV均匀扩展5mm半径定义的扩展CTV（exCTV）的剂量分布以及束流输送时间。直肠和膀胱的V 、尿道球部的V 、exCTV的不均匀性指数（INH）显示存在差异（P = 1.1×10，P = 6.4×10，P = 2.7×10，P = 3.2×10），尽管只有过程B引起的变化具有显著性。过程B的修改计划显示直肠和膀胱的V 分别降低了-2.4±1.6%和-2.3±1.4%，尿道球部的V 降低了-15.9±19.4%。exCTV的INH增加了0.05±0.03%。另一方面，过程A对初始计划的修改未影响OAR、exCTV的剂量或束流输送时间。在点扫描PBT中，通过系统性删除远离CTV的光斑对初始放射治疗计划进行修改可导致OAR剂量降低。
