ABSTRACT

The aim of the study is to determine the dosimetric effects of the anatomical change during the course of IMRT. Two anatomical head and neck (H&N) phantoms were designed using Perspex material: phantom A, representing the patient before starting the treatment, and phantom B, representing the same patient after weight loss. Four treatment plans from treatment Planning System (TPS) were applied to both phantoms, and the delivered doses at organ at risks (OARs) and PTV were measured. An adjustment on original plan was made to adapt the change in tumor size and weight loss after repeating CT scan, which was then delivered to phantom B. Measured doses at various regions at both phantoms were compared with the constraint doses. The maximum dose (Dmax) to OARs increased in all patients’ plans without adjustments. At the optic nerve, the Dmax increased by 9.4 Gy (25.5 %), brainstem by 29.8 Gy (46.8 %), and the parotid glands increased by 12.4 Gy (40.3 %). When the adjustment is not considered, the average dose difference between the delivered doses and planned doses by TPS increased from 1.6 to 3.5 Gy to the range of 4.1 to 29.8 Gy due to tumor shrinking and weight loss.

摘要

该研究的目的是确定IMRT过程中解剖变化的剂量学影响。使用有机玻璃材料设计了两个解剖学的头部和颈部（H＆N）体模：体模A代表开始治疗前的患者，体模B代表减肥后的同一位患者。将治疗计划系统（TPS）的四个治疗计划应用于两个体模，并测量了处于危险器官（OARs）和PTV的给药剂量。对原始计划进行了调整，以适应重复进行CT扫描后肿瘤大小和体重减轻的变化，然后将其递送至体模B。将两种体模在各个区域的测量剂量与限制剂量进行比较。未经调整，所有患者计划中OAR的最大剂量（Dmax）都会增加。在视神经处 Dmax增加9.4 Gy（25.5％），脑干增加29.8 Gy（46.8％），腮腺增加12.4 Gy（40.3％）。如果不考虑调整，由于肿瘤缩小和体重减轻，TPS的给药剂量和计划剂量之间的平均剂量差异将从1.6 Gy Gy增加到3.5 Gy Gy到29.8 Gy Gy。