National Institute of Radiological Sciences, Chiba, Japan.
Med Phys. 2010 Aug;37(8):4046-55. doi: 10.1118/1.3458721.
Successful results in carbon-ion and proton radiotherapies can extend patients' lives and thus present a treatment option for younger patients; however, the undesired exposure to normal tissues outside the treatment volume is a concern. Organ-specific information on the absorbed dose and the biological effectiveness in the patient is essential for assessing the risk, but experimental dose assessment has seldom been done. In this study, absorbed doses, quality factors, and dose equivalents in water phantom outside of the irradiation field were determined based on lineal energy distributions measured with a commercial tissue equivalent proportional counter (TEPC) at passive carbon-ion and proton radiotherapy facilities.
Measurements at eight positions in the water phantom were carried out at the Heavy-Ion Medical Accelerator in Chiba of the National Institute of Radiological Sciences for 400 and 290 MeV/u carbon beams and at the National Cancer Center Hospital East for a 235 MeV proton beam.
The dose equivalent per treatment absorbed dose at the center of the range-modulated region H/Dt, decreased as the position became farther from the beam axis and farther from the phantom surface. The values of H/Dt ranged from 6.7 to 0.16 mSv/Gy for the 400 MeV/u carbon beam, from 1.3 to 0.055 mSv/Gy for the 290 MeV/u carbon beam, and from 4.7 to 0.24 mSv/GV for the 235 MeV proton beam. The values of the dose-averaged quality factor QD ranged from 2.4 to 4.6 for the 400 MeV/u beam, from 2.8 to 5.3 for the 290 MeV/u beam, and from 5.1 to 8.2 for the proton beam. The authors also observed differences in the distributions of H/Dt and QD between the carbon and proton beams.
The authors experimentally obtained absorbed doses, dose-averaged quality factors, and dose equivalents in water phantom outside of the irradiation field in passive carbon-ion and proton radiotherapies with TEPC. These data are very useful for estimating the risk of secondary cancer after receiving passive radiotherapies and for verifying Monte Carlo calculations.
碳离子和质子放射疗法的成功结果可以延长患者的生命，因此为年轻患者提供了一种治疗选择；然而，治疗体积外的正常组织受到不必要的照射是一个关注点。患者体内吸收剂量和生物效应的器官特异性信息对于评估风险至关重要，但很少进行实验剂量评估。在这项研究中，基于在国立放射研究所重离子医疗加速器和国家癌症中心东医院用商业组织等效正比计数器（TEPC）测量的线性能量分布，在被动碳离子和质子放射治疗设施外的水模体中确定了吸收剂量、品质因数和水当量。
在国立放射研究所重离子医疗加速器对 400 MeV/u 和 290 MeV/u 碳束，以及在国家癌症中心东医院对 235 MeV 质子束，在水模体的八个位置进行了测量。
调强区域中心的剂量当量 H/Dt 随位置离束轴越远和离模体表面越远而减小。400 MeV/u 碳束的 H/Dt 值范围为 6.7 至 0.16 mSv/Gy，290 MeV/u 碳束的 H/Dt 值范围为 1.3 至 0.055 mSv/Gy，235 MeV 质子束的 H/Dt 值范围为 4.7 至 0.24 mSv/GV。400 MeV/u 束的剂量平均品质因数 QD 值范围为 2.4 至 4.6，290 MeV/u 束的 QD 值范围为 2.8 至 5.3，质子束的 QD 值范围为 5.1 至 8.2。作者还观察到碳束和质子束之间 H/Dt 和 QD 分布的差异。
作者用 TEPC 实验获得了被动碳离子和质子放射治疗外照射场中水模体的吸收剂量、剂量平均品质因数和水当量。这些数据对于估计接受被动放射治疗后发生二次癌症的风险以及验证蒙特卡罗计算非常有用。
