Irazola L, Lorenzoli M, Bedogni R, Pola A, Terrón J A, Sanchez-Nieto B, Expósito M R, Lagares J I, Sansaloni F, Sanchez-Doblado F
Departamento de Fisiología Médica y Biofísica, Universidad de Sevilla, Sevilla 41009, Spain and Servicio de Radiofísica, Hospital Universitario Virgen Macarena, Sevilla 41007, Spain.
Departimento di Ingegneria Nuclear, Politecnico di Milano, Milano 20133, Italy.
Med Phys. 2014 Nov;41(11):112105. doi: 10.1118/1.4898591.
Peripheral dose in radiotherapy treatments represents a potential source of secondary neoplasic processes. As in the last few years, there has been a fast-growing concern on neutron collateral effects, this work focuses on this component. A previous established methodology to estimate peripheral neutron equivalent doses relied on passive (TLD, CR39) neutron detectors exposed in-phantom, in parallel to an active [static random access memory (SRAMnd)] thermal neutron detector exposed ex-phantom. A newly miniaturized, quick, and reliable active thermal neutron detector (TNRD, Thermal Neutron Rate Detector) was validated for both procedures. This first miniaturized active system eliminates the long postprocessing, required for passive detectors, giving thermal neutron fluences in real time.
To validate TNRD for the established methodology, intrinsic characteristics, characterization of 4 facilities [to correlate monitor value (MU) with risk], and a cohort of 200 real patients (for second cancer risk estimates) were evaluated and compared with the well-established SRAMnd device. Finally, TNRD was compared to TLD pairs for 3 generic radiotherapy treatments through 16 strategic points inside an anthropomorphic phantom.
The performed tests indicate similar linear dependence with dose for both detectors, TNRD and SRAMnd, while a slightly better reproducibility has been obtained for TNRD (1.7% vs 2.2%). Risk estimates when delivering 1000 MU are in good agreement between both detectors (mean deviation of TNRD measurements with respect to the ones of SRAMnd is 0.07 cases per 1000, with differences always smaller than 0.08 cases per 1000). As far as the in-phantom measurements are concerned, a mean deviation smaller than 1.7% was obtained.
The results obtained indicate that direct evaluation of equivalent dose estimation in organs, both in phantom and patients, is perfectly feasible with this new detector. This will open the door to an easy implementation of specific peripheral neutron dose models for any type of treatment and facility.
放射治疗中的外周剂量是继发性肿瘤形成过程的一个潜在来源。在过去几年中，人们对中子附带效应的关注迅速增加，本研究聚焦于这一因素。先前建立的用于估计外周中子等效剂量的方法依赖于置于体模内的被动式（热释光剂量计、固体径迹探测器）中子探测器，同时在体模外放置一个主动式[静态随机存取存储器（SRAMnd）]热中子探测器。一种新的小型化、快速且可靠的主动式热中子探测器（热中子速率探测器，TNRD）针对这两种方法进行了验证。这种首个小型化主动系统消除了被动探测器所需的冗长后处理过程，可实时给出热中子注量。
为验证TNRD用于既定方法的有效性，评估了其固有特性、4个设施的特性[将监测值（MU）与风险相关联]以及一组200例真实患者（用于二次癌症风险估计），并与成熟的SRAMnd设备进行比较。最后，通过在拟人化体模内的16个战略点，针对3种通用放射治疗，将TNRD与热释光剂量计对进行比较。
所进行的测试表明，TNRD和SRAMnd这两种探测器与剂量的线性相关性相似，而TNRD的重现性略好（分别为1.7%和2.2%）。两种探测器在给予1000 MU时的风险估计结果高度一致（TNRD测量值相对于SRAMnd测量值的平均偏差为每1000例0.07例，差异始终小于每1000例0.08例）。就体模内测量而言，平均偏差小于1.7%。
所得结果表明，使用这种新探测器在体模和患者中直接评估器官等效剂量估计完全可行。这将为针对任何类型的治疗和设施轻松实施特定的外周中子剂量模型打开大门。
