D'Souza Harold, Weatherburn Henry, Dwivedi Abhishek, Ganesh Tharmarnadar
Department of Radiation Oncology, Washington Adventist Hospital, Takoma Park, MD, USA.
Department of Radiotherapy, Cancer Center London, Wimbledon, London, UK.
J Med Phys. 2020 Jan-Mar;45(1):1-6. doi: 10.4103/jmp.JMP_86_19. Epub 2020 Mar 13.
This study aims to validate volumetric arc therapy (VMAT) plan correction method for a patient's lost weight during the course of radiotherapy.
VMAT plans of prostate and head and neck cancers were considered to evaluate dosimetric effects due to external surface changes caused by patient's weight loss during treatment. Accepted VMAT treatment plan was recalculated on the planning computed tomography (CT) with a newly created external contour from cone-beam CT and was compared with the original plan. Monitor unit (MU) correction was applied based on a simple formalism, and doses were recalculated. Dose statistics were compared with the original plan. Ten patients with significant weight loss were considered to validate proposed MU correction method by comparing the dose statistics before and after MU corrections.
We observed 3.7%-5.2% change in the plan maximum dose for one cm change in path length to isocenter with increased planning target volume dose, D95 by 4%. The organs at risk (OAR) doses increased as high as 6.8%. Using MU correction method, target volume and OARs dose changes were reduced to <1% when compared with the original plan. The correction method brought down the maximum plan dose and volume of 95% isodose (V95) cloud below an acceptable range of 1%-2% in 10 patients treatment plans.
Image-guided radiation therapy process detects the weight loss, which affects the treatment plan's dose distribution and should be corrected. Applying the correction method described here keeps the patient dosimetry within 1% of the original plan, which is clinically acceptable. The process of plan dosimetry correction to address weight loss can be completed within 30 min without repeating imaging and planning process.
本研究旨在验证容积弧形调强放疗（VMAT）计划校正方法，用于放疗过程中患者体重减轻的情况。
考虑前列腺癌和头颈癌的VMAT计划，以评估治疗期间患者体重减轻导致的体表变化所产生的剂量学影响。在计划计算机断层扫描（CT）上，利用锥形束CT新创建的外部轮廓重新计算已接受的VMAT治疗计划，并与原始计划进行比较。基于一种简单的形式主义应用监测单位（MU）校正，并重新计算剂量。将剂量统计结果与原始计划进行比较。通过比较MU校正前后的剂量统计结果，对10例体重显著减轻的患者进行研究，以验证所提出的MU校正方法。
我们观察到，等中心路径长度每变化1厘米，计划最大剂量变化3.7%-5.2%，计划靶体积剂量（D95）增加4%。危及器官（OAR）剂量增加高达6.8%。与原始计划相比，使用MU校正方法时，靶体积和OAR剂量变化降低至<1%。在10例患者的治疗计划中，校正方法使计划最大剂量和95%等剂量线（V95）体积降至1%-2%的可接受范围以下。
图像引导放射治疗过程可检测到体重减轻，这会影响治疗计划的剂量分布，应予以校正。应用此处所述的校正方法可使患者剂量测定保持在原始计划的1%以内，这在临床上是可接受的。解决体重减轻问题的计划剂量测定校正过程可在30分钟内完成，无需重复成像和计划过程。
