Fontenot Jonas D, Taddei Phillip, Zheng Yuanshui, Mirkovic Dragan, Newhauser Wayne D
The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Boulevard Unit 94, Houston, Texas 77030.
Nucl Technol. 2009 Oct 1;168(1):173-177. doi: 10.13182/nt09-a9121.
The purpose of this study was to evaluate the suitability of the quantity ambient dose equivalent H*(10) as a conservative estimate of effective dose E for estimating stray radiation exposures to patients receiving passively scattered proton radiotherapy for cancer of the prostate. H*(10), which is determined from fluence free-in-air, is potentially useful because it is simpler to measure or calculate because it avoids the complexities associated with phantoms or patient anatomy. However, the suitability of H*(10) as a surrogate for E has not been demonstrated for exposures to high-energy neutrons emanating from radiation treatments with proton beams. The suitability was tested by calculating H*(10) and E for a proton treatment using a Monte Carlo model of a double-scattering treatment machine and a computerized anthropomorphic phantom. The calculated E for the simulated treatment was 5.5 mSv/Gy, while the calculated H*(10) at the isocenter was 10 mSv/Gy. A sensitivity analysis revealed that H*(10) conservatively estimated E for the interval of treatment parameters common in proton therapy for prostate cancer. However, sensitivity analysis of a broader interval of parameters suggested that H*(10) may underestimate E for treatments of other sites, particularly those that require large field sizes. Simulations revealed that while E was predominated by neutrons generated in the nozzle, neutrons produced in the patient contributed up to 40% to dose equivalent in near-field organs.
本研究的目的是评估周围剂量当量H*(10)作为有效剂量E的保守估计值，用于估算接受被动散射质子放射治疗前列腺癌患者的杂散辐射暴露的适用性。H*(10)由空气中的注量确定，因其测量或计算更简单，避免了与体模或患者解剖结构相关的复杂性，所以可能很有用。然而，对于质子束放射治疗产生的高能中子暴露，H*(10)作为E的替代指标的适用性尚未得到证实。通过使用双散射治疗机的蒙特卡罗模型和计算机化人体模型计算质子治疗的H*(10)和E来测试其适用性。模拟治疗的计算有效剂量E为5.5 mSv/Gy，而异中心处计算的H*(10)为10 mSv/Gy。敏感性分析表明，对于前列腺癌质子治疗中常见的治疗参数区间，H*(10)保守地估计了E。然而，对更广泛参数区间的敏感性分析表明，对于其他部位的治疗尤其是那些需要大野尺寸的治疗，H*(10)可能会低估E。模拟显示，虽然有效剂量E主要由喷嘴中产生的中子主导，但患者体内产生的中子对近场器官的剂量当量贡献高达40%。
