Setup in a clinical workflow and impact on radiotherapy routine of an in vivo dosimetry procedure with an electronic portal imaging device

High conformal techniques such as intensity-modulated radiation therapy and volumetric-modulated arc therapy are widely used in overloaded radiotherapy departments. In vivo dosimetric screening is essential in this environment to avoid important dosimetric errors. This work examines the feasibility of introducing in vivo dosimetry (IVD) checks in a radiotherapy routine. The causes of dosimetric disagreements between delivered and planned treatments were identified and corrected during the course of treatment. The efficiency of the corrections performed and the added workload needed for the entire procedure were evaluated. The IVD procedure was based on an electronic portal imaging device. A total of 3682 IVD tests were performed for 147 patients who underwent head and neck, abdomen, pelvis, breast, and thorax radiotherapy treatments. Two types of indices were evaluated and used to determine if the IVD tests were within tolerance levels: the ratio R between the reconstructed and planned isocentre doses and a transit dosimetry based on the γ-analysis of the electronic portal images. The causes of test outside tolerance level was investigated and corrected and IVD test was repeated during subsequent fraction. The time needed for each step of the IVD procedure was registered. Pelvis, abdomen, and head and neck treatments had 10% of tests out of tolerance whereas breast and thorax treatments accounted for up to 25%. The patient setup was the main cause of 90% of the IVD tests out of tolerance and the remaining 10% was due to patient morphological changes. An average time of 42 min per day was sufficient to monitor a daily workload of 60 patients in treatment. This work shows that IVD performed with an electronic portal imaging device is feasible in an overloaded department and enables the timely realignment of the treatment quality indices in order to achieve a patient’s final treatment compliant with the one prescribed.

诸如调强放射治疗（Intensity-Modulated Radiation Therapy）与容积调强弧形治疗（Volumetric-Modulated Arc Therapy）等高适形技术，在负荷过载的放射治疗科室中应用广泛。在此类工作环境中，体内剂量筛查对于规避重大剂量误差至关重要。本研究探讨了在放射治疗日常流程中引入体内剂量测定（In Vivo Dosimetry, IVD）检查的可行性。研究期间，我们明确了实际递送治疗与计划治疗间的剂量学偏差成因，并予以纠正；同时评估了所实施纠正措施的有效性，以及整套流程所需的额外工作量。本次IVD流程基于电子端口成像设备（Electronic Portal Imaging Device, EPID）开展。本研究共为147例接受头颈部、腹部、盆腔、乳腺及胸部放射治疗的患者完成了3682次IVD检测。研究评估了两类用于判定IVD检测是否处于耐受阈值的指标：一是重建剂量与计划等中心剂量的比值R，二是基于电子端口图像γ分析（Gamma Analysis）的传输剂量学指标。对于超出耐受阈值的检测，我们对其成因展开调查并完成纠正，且在后续分次治疗中重新开展IVD检测。本研究记录了IVD流程各步骤所需的时长。盆腔、腹部及头颈部放射治疗的超出耐受阈值的检测占比达10%，而乳腺与胸部放射治疗的该占比最高可达25%。90%超出耐受阈值的IVD检测的主要成因是患者摆位误差，剩余10%则源于患者的形态学变化。每日平均耗时42分钟即可完成当日60例治疗患者的IVD监测工作。本研究表明，基于电子端口成像设备开展的IVD检测在负荷过载的放疗科室中具备可行性，且能够及时校正治疗质量指标，确保患者最终接受的治疗与处方方案一致。