Assessing the radiation-induced second cancer risk in proton therapy for pediatric brain tumors: the impact of employing a patient-specific aperture in pencil beam scanning
Assessing the radiation-induced second cancer risk in proton therapy for pediatric brain tumors: the impact of employing a patient-specific aperture in pencil beam scanning
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DOI：
10.1088/0031-9155/61/1/12
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发表时间：
2016-01-07
影响因子：
3.5
通讯作者：
Paganetti, Harald
中科院分区：
文献类型：
--
作者：
Geng, Changran;Moteabbed, Maryam;Paganetti, Harald
本研究的目的是比较笔形束扫描 (PBS) 和被动散射质子治疗 (PPT) 的场内和场外器官和组织的辐射诱发的第二次癌症风险，并评估在儿童脑肿瘤患者的笔形束扫描中添加患者特定孔径以锐化半影的影响。使用 PPT 和 PBS 为三名儿科患者每人制定了五个质子治疗计划，具有两种光斑尺寸（等角点处的平均西格玛类似于 17 毫米和类似于 8 毫米）并选择患者特定的孔径。比较了五种输送技术中场内和场外组织和器官的终生第二恶性肿瘤风险。使用器官当量剂量计算现场组织的风险，该剂量由剂量体积直方图确定。对于场外器官，使用蒙特卡罗和拟人儿科模型计算二次中子的器官特异性剂量当量。我们发现，无论是小光斑尺寸 PBS 还是大光斑尺寸 PBS，患者特定孔径均可将现场癌症风险降低至低于 PPT 的值。大光斑尺寸的减少量（平均 43%）大于小光斑尺寸的减少量（平均 21%）。对于场外器官，通过采用患者特定孔径，风险仅略有变化（随着与肿瘤距离的增加，风险平均从 -2% 到 16%），但仍比 PPT 低一到两个数量级。总之，当笔形束斑尺寸较大时，增加孔径来锐化半影可降低场内辐射诱发的继发性癌症风险。由于中子从孔径中散射，场外癌症风险略有增加，但这种风险远远被使用具有大 PBS 光斑尺寸的孔径带来的场内风险益处所抵消。一般来说，即使使用孔径，PBS 的场外器官发生第二种恶性肿瘤的风险仍然比 PPT 低得多。
The purpose of this study was to compare the radiation-induced second cancer risks for in-field and out-of-field organs and tissues for pencil beam scanning (PBS) and passive scattering proton therapy (PPT) and assess the impact of adding patient-specific apertures to sharpen the penumbra in pencil beam scanning for pediatric brain tumor patients. Five proton therapy plans were created for each of three pediatric patients using PPT as well as PBS with two spot sizes (average sigma of similar to 17 mm and similar to 8 mm at isocenter) and choice of patient-specific apertures. The lifetime attributable second malignancy risks for both in-field and out-of-field tissues and organs were compared among five delivery techniques. The risk for in-field tissues was calculated using the organ equivalent dose, which is determined by the dose volume histogram. For out-of-field organs, the organ-specific dose equivalent from secondary neutrons was calculated using Monte Carlo and anthropomorphic pediatric phantoms. We find that either for small spot size PBS or for large spot size PBS, a patient-specific aperture reduces the in-field cancer risk to values lower than that for PPT. The reduction for large spot sizes (on average 43%) is larger than for small spot sizes (on average 21%). For out-of-field organs, the risk varies only marginally by employing a patient-specific aperture (on average from -2% to 16% with increasing distance from the tumor), but is still one to two orders of magnitude lower than that for PPT. In conclusion, when pencil beam spot sizes are large, the addition of apertures to sharpen the penumbra decreases the in-field radiation-induced secondary cancer risk. There is a slight increase in out-of-field cancer risk as a result of neutron scatter from the aperture, but this risk is by far outweighed by the in-field risk benefit from using an aperture with a large PBS spot size. In general, the risk for developing a second malignancy in out-of-field organs for PBS remains much lower compared to PPT even if apertures are being applied.