Department of Radiation Medicine, Roswell Park Cancer Institute, Buffalo, USA.
Radiol Oncol. 2011 Jun;45(2):132-42. doi: 10.2478/v10019-011-0012-9. Epub 2011 Apr 23.
The GammaPlan(™) treatment planning system (TPS) does not fully account for shutter dose when multiple shots are required to deliver a patient's treatment. The unaccounted exposures to the target site and its periphery are measured in this study. The collected data are compared to a similar effect from the Gamma Knife(®) model 4C. MATERIALS AND METHODS.: A stereotactic head frame was attached to a Leksell(®) 16 cm diameter spherical phantom; using a fiducial-box, CT images of the phantom were acquired and registered in the TPS. Measurements give the relationship of measured dose to the number of repositions with the patient positioning system (PPS) and to the collimator size. An absorbed dose of 10 Gy to the 50% isodose line was prescribed to the target site and all measurements were acquired with an ionization chamber.
Measured dose increases with frequency of repositioning and with collimator size. As the radiation sectors transition between the beam on and beam off states, the target receives more shutter dose than the periphery. Shutter doses of 3.53±0.04 and 1.59±0.04 cGy/reposition to the target site are observed for the 16 and 8 mm collimators, respectively. The target periphery receives additional dose that varies depending on its position relative to the target.
The radiation sector motions for the Gamma Knife(®) Perfexion(™) result in an additional dose due to the shutter effect. The magnitude of this exposure is comparable to that measured for the model 4C.
当需要多次射击来完成患者的治疗时，GammaPlan（™）治疗计划系统（TPS）并没有完全考虑快门剂量。本研究测量了目标部位及其周围未被计算在内的暴露量。收集的数据与 Gamma Knife（®）型号 4C 的类似影响进行了比较。
立体定向头架固定在 Leksell（®）直径为 16 厘米的球形模体上；使用基准盒，对模体进行 CT 图像采集并在 TPS 中进行注册。测量结果给出了患者定位系统（PPS）和准直器尺寸与测量剂量之间的关系。将 10 Gy 的吸收剂量规定给目标部位的 50%等剂量线，所有测量均使用电离室进行。
测量剂量随重新定位的频率和准直器尺寸的增加而增加。当辐射扇区在束开和束关状态之间转换时，目标接收的快门剂量比周围组织多。对于 16 和 8 毫米准直器，分别观察到目标部位的快门剂量为 3.53±0.04 和 1.59±0.04 cGy/重定位。目标周围组织接收到的额外剂量取决于其相对于目标的位置。
Gamma Knife（®）Perfexion（™）的辐射扇区运动导致快门效应产生额外剂量。这种暴露的幅度与测量的模型 4C 相当。
