Borowicz Dorota Maria, Malicki Julian, Mytsin Gennady, Shipulin Konstantin
Department of Medical Physics, Greater Poland Cancer Centre, Poznan, Poland.
Laboratory of Nuclear Problems, Joint Institute for Nuclear Research, 141980, Dubna, Moscow region, Russia.
Med Phys. 2017 Apr;44(4):1538-1544. doi: 10.1002/mp.12159. Epub 2017 Mar 22.
To evaluate the impact of radiochromic film positioning relative to the central beam axis (CAX) in proton beam therapy. Secondarily, to compare the dosimetric measurements obtained by RTQA and EBT film and to compare these to the doses calculated by the treatment planning system (TPS).
The EBT and RTQA dosimetric radiochromic films were immersed in a water phantom and irradiated with a proton beam. The films were placed parallel to the CAX and at a 5° angle on the horizontal plane to assess the effect of film inclination on Bragg peak profiles. Calibration was performed by irradiating small pieces of film at doses ranging from 0.0 Gy to 3.5 Gy in increments of 0.5 Gy. The TPS was used to create treatment plans for two different geometrical targets (cylindrical and cuboidal). After irradiation, all film pieces were scanned on a flatbed scanner and red channel data were extracted from the 48-bit RGB images using ImageJ, Photoshop, Origin8, and Excel software. The dose distributions from the irradiated films were compared to the dose obtained from the TPS. Bragg peak profiles were abstracted from the irradiated films and compared.
The dosimetric measurements obtained by both EBT and RTQA positioned at a 5° to the CAX closely matched the dose calculated by the TPS for the cylindrical target. In contrast, dose distributions measured in the cuboidal targets were less precise. Gamma index (GI) values (3%/3 mm acceptance criteria for isodose >90% of dose) were 99.8% and 93% for EBT film placed at a 5° angle versus 47.1% and 80.8% for EBT film parallel to the beam. The dosimetric measurements in RTQA film positioned parallel to the CAX showed GI values with <27% agreement with the TPS-calculated dose.
Our finding show that RTQA film can be used to accurately measure doses in the proton beam at the region of Bragg peak; however, to obtain the most accurate readings, the film should be positioned at a small angle to the CAX.
评估质子束治疗中放射变色胶片相对于中心束轴（CAX）的位置影响。其次，比较通过放疗质量保证（RTQA）和EBT胶片获得的剂量测量结果，并将这些结果与治疗计划系统（TPS）计算的剂量进行比较。
将EBT和RTQA剂量学放射变色胶片浸入水模中，并用质子束照射。胶片与CAX平行放置，并在水平面上以5°角放置，以评估胶片倾斜对布拉格峰轮廓的影响。通过以0.5 Gy的增量在0.0 Gy至3.5 Gy的剂量范围内照射小块胶片进行校准。TPS用于为两个不同的几何靶区（圆柱形和长方体形）创建治疗计划。照射后，所有胶片在平板扫描仪上进行扫描，并使用ImageJ、Photoshop、Origin8和Excel软件从48位RGB图像中提取红色通道数据。将照射后胶片的剂量分布与TPS获得的剂量进行比较。从照射后的胶片中提取布拉格峰轮廓并进行比较。
对于圆柱形靶区，与CAX成5°角放置的EBT和RTQA所获得的剂量测量结果与TPS计算的剂量紧密匹配。相比之下，长方体形靶区的剂量分布不太精确。对于与束平行的EBT胶片，伽马指数（GI）值（等剂量>90%剂量时的3%/3 mm验收标准）为47.1%和80.8%，而与束成5°角放置的EBT胶片的GI值为99.8%和93%。与CAX平行放置的RTQA胶片中的剂量测量显示，与TPS计算剂量的一致性<27%。
我们的研究结果表明，RTQA胶片可用于准确测量质子束布拉格峰区域的剂量；然而，为了获得最准确的读数，胶片应与CAX成小角度放置。
