Jong Wei Loong, Ung Ngie Min, Vannyat Ath, Jamalludin Zulaikha, Rosenfeld Anatoly, Wong Jeannie Hsiu Ding
Clinical Oncology Unit, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia.
Clinical Oncology Unit, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia.
Phys Med. 2017 Jan;33:127-135. doi: 10.1016/j.ejmp.2016.12.020. Epub 2017 Jan 6.
Dosimetry in small radiation field is challenging and complicated because of dose volume averaging and beam perturbations in a detector. We evaluated the suitability of the "Edge-on" MOSkin (MOSFET) detector in small radiation field measurement. We also tested the feasibility for dosimetric verification in stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT). "Edge-on" MOSkin detector was calibrated and the reproducibility and linearity were determined. Lateral dose profiles and output factors were measured using the "Edge-on" MOSkin detector, ionization chamber, SRS diode and EBT2 film. Dosimetric verification was carried out on two SRS and five SRT plans. In dose profile measurements, the "Edge-on" MOSkin measurements concurred with EBT2 film measurements. It showed full width at half maximum of the dose profile with average difference of 0.11mm and penumbral width with difference of ±0.2mm for all SRS cones as compared to EBT2 film measurement. For output factor measurements, a 1.1% difference was observed between the "Edge-on" MOSkin detector and EBT2 film for 4mm SRS cone. The "Edge-on" MOSkin detector provided reproducible measurements for dose verification in real-time. The measured doses concurred with the calculated dose for SRS (within 1%) and SRT (within 3%). A set of output correction factors for the "Edge-on" MOSkin detector for small radiation fields were derived from EBT2 film measurement and presented. This study showed that the "Edge-on" MOSkin detector is a suitable tool for dose verification in small radiation field.
由于探测器中的剂量体积平均效应和射束扰动，小辐射野中的剂量测定具有挑战性且复杂。我们评估了“边缘入射式”MOSkin（MOSFET）探测器在小辐射野测量中的适用性。我们还测试了其在立体定向放射外科（SRS）和立体定向放射治疗（SRT）中进行剂量验证的可行性。对“边缘入射式”MOSkin探测器进行了校准，并确定了其重现性和线性度。使用“边缘入射式”MOSkin探测器、电离室、SRS二极管和EBT2胶片测量了侧向剂量分布和输出因子。对两个SRS计划和五个SRT计划进行了剂量验证。在剂量分布测量中，“边缘入射式”MOSkin探测器的测量结果与EBT2胶片的测量结果一致。与EBT2胶片测量相比，所有SRS射束的剂量分布半高宽平均差值为0.11mm，半值宽度差值为±0.2mm。在输出因子测量中，对于4mm的SRS射束，“边缘入射式”MOSkin探测器与EBT2胶片之间观察到1.1%的差异。“边缘入射式”MOSkin探测器为实时剂量验证提供了可重现的测量结果。测量剂量与SRS（误差在1%以内）和SRT（误差在3%以内）的计算剂量一致。根据EBT2胶片测量结果得出并给出了一组适用于小辐射野的“边缘入射式”MOSkin探测器的输出校正因子。本研究表明，“边缘入射式”MOSkin探测器是小辐射野剂量验证的合适工具。
