盆腔肿瘤三维适形放疗摆位重复性研究

Set-up errors in three-dimensional conformal radiation therapy of pelvic carcinoma

目的研究盆腔肿瘤三维适形放疗的摆位误差大小,为盆腔肿瘤适形放疗计划设计时CTV外放PTV提供参考数据。方法接受放疗的直肠癌病例3例和前列腺癌病例2例,均为男性,行俯卧位盆腔三维适形放疗。每例病例治疗时身下垫有孔泡沫板,连续5 d摆位照射,每次摆位时在患者体表固定点粘贴定位金点,热塑成型固定膜固定,加速器机头插入与治疗中心一致的定位“+”字刻度板,照射正侧位治疗验证片各1张,共计摆位25次,照射治疗验证片50张。以第1次摆位片为标准,计算前后、头尾、左右方向摆位误差。结果5例病例25次摆位误差,人与人间以及次与次间均存在一定差别。前后方向摆位误差最大,平均值为(0．98±0．68)cm,有9次摆位误差≥1 cm,占测算次数的45%,其中2次误差≥2 cm；头尾方向摆位误差为[(0．50～0．70)±0．45]cm,正位测定误差小于侧位,分别为(0．51±0．46)、(0．70±0．45)cm,正位和侧位分别有4次和7次摆位误差≥1 cm；左右方向误差最小,为(0．37±0．28)cm,仅1次误差≥1 cm。结论在三维适形技术放疗盆腔肿瘤时．左右方向摆位误差最小,头尾方向居中,前后方向最大；CTV外放PTV应考虑左右方向0．5 cm,头尾方向1．0 cm,前后方向1．5 cm。

Objective To study the spatial distribution of set-up errors for pelvic carcinoma patients treated with three-dimensional eonformal radiation therapy （3DCRT） and to provide referential safety margins out of clinical tumor volume （CTV） during treatment plan design. Methods Five patients with rectal or prostate cancers entered this study. All were treated with 3DCRT in the prone position. Belly board was used. Measurements were made on a daily basis setup under five consecutive treatments. During patients positioning, gold particles were placed on the skin with markers, one laterally, and the other on the back. Thermoplastic cast was used for immobilization. Portal fdms from two projections （ one anterior-posterior and one opposite lateral） were taken after the reticule localizer was inserted to the head of accelerator. Fifty portal films from 25 setups were analyzed. The spatial distribution of set-up errors from left-right, superior-inferior and anterior-posterior directions were evaluated as compared to the first set-up films （representing the standard treatment position）. Results The magnitude of set-up errors from 25 posifionings in 5 patients differed from patient to patient and day to day. Maximal set-up errors were inspected in the anterior-posterior direction, with a mean of （0.98 ±0.68） em. Nine of 20 measurements （45%） were ≥ 1 cm, and two in the 9 measurements were ≥2 cm; The set-up errors for superior-inferior were （[0.50-0.701 ± 0.45） cm, and the average magnitude measured from anterior-posterior fdms was smaller than those from opposite lateral films, （0.51 ± 0.46） cm and （0.70 ± 0.45） cm, respectively. The measurements of ≥ 1 cm were seen on 4 anterior-posterior films and 7 on lateral films; The smallest shift was observed in the left-right direction, with a mean error of （0.37 ±0.28） cm, only one measurement was ≥1 cm. Conclusions Set-up error always exists during the treatment course. It differs from patient to patient and day to day. The spatial distributions of set-up errors are smallest in the left-right direction, moderate in the superiorinferior direction and largest in the anterior-posterior direction. When pelvic carcinoma patient is treated with threedimensional confonnal radiation therapy, our suggestions for CTV margins are 0.5 cm in left-right direction, 1.0 cm in craniocandal direction and 1.5 cm in anterior-posterior direction.