Study on relationship between the beginning plan and the anatomy and dosimetry change during intensity modulated radiotherapy for esophageal carcinoma / 中华放射肿瘤学杂志

ABSTRACT

Objective To study the dynamic changes of anatomy and the dosimeter distribution those changes influenced. Methods Initially simplified intensity modulated radiation therapy (sIMRT)were performed to twenty-nine patients with phase Ⅲ - Ⅳa esophageal carcinoma from January 2007 to March 2009. The target volumes and involving organs were contoured on the primary spiral CT pictures.After sIMRT planning being finished, secondary CT scan was acquired to rectify the treatment center. For eleven patients at every other week and eighteen patients at the fourth week, spiral CT images were acquired according to the same treatment center, and thereafter fused with the first CT images. Firstly, the law of change and the best time of replanning were searchedthe changed gross tumor volume (GTV), gross node volume (GTVnd), plan target volume (PTV) and normal organs (lung, spinal cord, heart and outline) on the fusion interface were modified by a single physician, the changes for each structure throughout treatment were measured by system software. Secondly, dose distributions were computed and evaluated for replanning CT using the same beams arrangement as the initial plan. Cumulative dose was estimated using weighted average and compared with the original plan. Results For eleven patients, The law of changethe volume of outlines and GTV gradually decreased, and the change come to peak in the fourth week. The conformal index for PTV gradually decreased, whereas the heterogeneous index gradually increased. For twenty-nine patients on the fourth week, the dose of GTV were more than 60 Gy. The dose of PTV-D95 and CTV-D99 decreased ( t = 1.49, P = 0. 147 and t = 2. 07, P = 0. 048 respectively). The dose of CTV-D99 in two patients deceased to 54 Gy or less. The cord-Dmax and lung V30 increased significantly ( t = - 2. 42, P = 0. 022 and t = -2. 26,P =0. 032). Conclusions During the course of sIMRT for esophageal cancer, the volume of GTV decreased and the change come to peak in the fourth week. It is the best time for evaluating the change of dose of target volume using CT-CT fusion. For some patients, revise of the treatment plan is needed to ensure adequate target volume dosage and safety of normal tissues.