Midwest Proton Radiotherapy Institute, Bloomington, Indiana 47408, USA.
Med Phys. 2010 Aug;37(8):4266-73. doi: 10.1118/1.3467753.
Entrance dose (or skin dose) is an important part of patient quality assurance in external beam radiation therapy. However, entrance dose verification in proton beam is not routinely performed. In this study, the OneDose single use MOSFET detector system for in vivo dosimetry measurement in proton therapy is investigated.
Using a solid water phantom, several fundamental dosimetric characteristics of the OneDose system are studied with a proton beam: The reproducibility (consistency) of the dosimeter, the linearity with dose and dose rate, energy dependence, directional dependence, LET dependence, and fading (delay readout with time) is studied.
OneDose detectors show dose and dose rate linearity but exhibit pronounced energy dependence at depth and a large variation in dose response with LET. On the other hand, the detector response remain relatively constant (within 3%) at surface over a wide range of energies. There is also a slight angular dependence (about 2%) up to 60 degrees angle of incidence. However, detector orientation such that incidence along the long axis of the detector should be avoided as the proton beam will have to traverse a large amount of the copper backing. Since most in vivo dosimetry involves entrance dose measurement, the OneDose at surface appears to be well suited for such application. OneDose exhibits small intrabatch variation (< or = 2% at one SD) indicating that it is only necessary to calibration a few detectors from each batch. The interbatch variation is generally within 3%.
The small detector size and its relatively flexible design of OneDose allow dose measurement to be performed on a curved surface or in small cavities that is otherwise difficult with the conventional diode detectors. The slight drawback in its angular dependence can be easily handled by angular dependence table. However, since OneDose is a single use detector, the intra-batch consistency must be verified before the remaining detectors from the same batch could be used for in vivo dosimetry. It is advisable that the detectors from the same batch be taken for the same application to reduce the dosimetric uncertainty. For detectors from different batches, inter-batch consistency should also be verified to obtain reliable results. OneDose provides an opportunity to measure in vivo dose with proton beam within acceptable clinical criterion of +/- (5.0%-6.5%).
入口剂量（或皮肤剂量）是外束放射治疗中患者质量保证的重要组成部分。然而，质子束的入口剂量验证并未常规进行。在这项研究中，研究了用于质子治疗中体内剂量测量的 OneDose 一次性 MOSFET 探测器系统。
使用固体水体模，使用质子束研究了 OneDose 系统的几个基本剂量学特性：剂量计的可重复性（一致性）、与剂量和剂量率的线性度、能量依赖性、方向依赖性、LET 依赖性和衰减（随时间延迟读取）。
OneDose 探测器显示出剂量和剂量率的线性度，但在深度处表现出明显的能量依赖性，并且随着 LET 的变化，剂量响应变化很大。另一方面，在宽能量范围内，探测器的响应在表面处相对恒定（在 3%以内）。在入射角度为 60 度时，也存在轻微的角度依赖性（约 2%）。然而，由于质子束必须穿过大量的铜背板，因此应避免探测器的入射方向与探测器的长轴平行。由于大多数体内剂量测量都涉及入口剂量测量，因此 OneDose 非常适合这种应用。OneDose 在表面处的表现表明，它在批次内的变化很小（在一个标准差内 <= 2%），这表明只需对每个批次中的几个探测器进行校准。批次间的变化通常在 3%以内。
OneDose 的小探测器尺寸及其相对灵活的设计允许在传统二极管探测器难以测量的曲面上或小腔体内进行剂量测量。其角度依赖性的微小缺点可以通过角度依赖性表轻松处理。然而，由于 OneDose 是一次性使用的探测器，因此在使用同一批次中的其余探测器进行体内剂量测量之前，必须验证批次内的一致性。建议使用同一批次的探测器进行相同的应用，以降低剂量不确定性。对于来自不同批次的探测器，也应验证批次间的一致性，以获得可靠的结果。OneDose 为使用质子束测量体内剂量提供了机会，符合可接受的临床标准（+/-（5.0%-6.5%））。
