Kruszyna-Mochalska Marta
Electroradiology Department, University of Medical Sciences, Poznan, Poland.
Greater Poland Cancer Centre, Medical Physics Department, Poznan, Poland.
Rep Pract Oncol Radiother. 2018 Sep-Oct;23(5):309-314. doi: 10.1016/j.rpor.2018.05.003. Epub 2018 Aug 8.
The aim of the work was to catch potential errors with daily EPID measurements of repeatability of the dose distribution during irradiation of IMRT patients.
In the first stage, measurements were made using an anthropomorphic phantom in which the method of collecting data with an EPID device and the possibility of detecting errors in positioning were developed. Next, for 23 patients, the pelvis (P) and head and neck (H&N) regions, images were collected with an EPID device for each IMRT subfield daily and compared to reference images using the gamma method (DTA 3 mm, DD 3%). Finally, the dependencies between treatment plan parameters, pre-verification results and repeatability of collected images were evaluated.
The anthropomorphic phantom study has shown what kind of effects we can expect with EPID measured at potential shifts during radiotherapy. For the clinical case, score results were obtained for individual tumor regions as below: (P) 0.786 ± 1.046, (H&N) 0.720 ± 1.552. For most evaluated cases, score values were below 1%: (P) 75.5% and (H&N) 83.9% of analyzed fields. 95% of all evaluated data was with the score below: (P) 2.86% and (H&N) 3.40%. The relationship between the results of the analysis of daily collected images and the results of pre-verification, field size and irradiation time was shown.
The EPID-based daily verification can provide extra information about day-to-day repeatability of treatment, without additional dose.
本研究旨在捕捉在调强放疗（IMRT）患者照射期间，利用电子射野影像装置（EPID）每日测量剂量分布重复性时的潜在误差。
在第一阶段，使用人体模型进行测量，在此过程中开发了利用EPID设备收集数据的方法以及检测定位误差的可能性。接下来，对23例患者的骨盆（P）和头颈部（H&N）区域，每天使用EPID设备为每个IMRT子野采集图像，并使用γ方法（剂量阈值3毫米，剂量差异3%）与参考图像进行比较。最后，评估治疗计划参数、预验证结果与采集图像重复性之间的相关性。
人体模型研究表明了在放疗期间EPID测量潜在位移时我们可能预期到的影响类型。对于临床病例，各肿瘤区域的评分结果如下：（P）0.786±1.046，（H&N）0.720±1.552。对于大多数评估病例，评分值低于1%：（P）为分析野的75.5%，（H&N）为83.9%。所有评估数据的95%评分低于：（P）2.86%，（H&N）3.40%。显示了每日采集图像的分析结果与预验证结果、射野大小和照射时间之间的关系。
基于EPID的每日验证可在不增加额外剂量的情况下，提供有关治疗每日重复性的额外信息。
