Duthoy Wim, De Gersem Werner, Vergote Koen, Coghe Marc, Boterberg Tom, De Deene Yves, De Wagter Carlos, Van Belle Simon, De Neve Wilfried
Division of Radiotherapy, Ghent University Hospital, Ghent, Belgium.
Int J Radiat Oncol Biol Phys. 2003 Nov 15;57(4):1019-32. doi: 10.1016/s0360-3016(03)00663-1.
Whole abdominopelvic radiation therapy (WAPRT) is a treatment option in the palliation of patients with relapsed ovarian cancer. With conventional techniques, kidneys and liver are the dose- and homogeneity-limiting organs. We developed a planning strategy for intensity-modulated arc therapy (IMAT) and report on the treatment plans of the first 5 treated patients.
Five consecutive patients with histologically proven relapsed ovarian cancer were sent to our department for WAPRT. The target volumes and organs at risk (OAR) were delineated on 0.5-cm-thick CT slices. The clinical target volume (CTV) was defined as the total peritoneal cavity. CTV and kidneys were expanded with 0.5 cm. In a preset range of 8 degrees interspaced gantry angles, machine states were generated with an anatomy-based segmentation tool. Machine states of the same class were stratified in arcs. The optimization of IMAT was done in several steps, using a biophysical objective function. These steps included weight optimization of machine states, leaf position optimization adapted to meet the maximal leaf speed constraint, and planner-interactive optimization of the start and stop angles. The final control points (machine states plus associated cumulative monitor unit counts) were calculated using a collapsed cone convolution/superposition algorithm. For comparison, two conventional plans (CONV) were made, one with two fields (CONV2), and one with four fields (CONV4). In these CONV plans, dose to the kidneys was limited by cerrobend blocks. The IMAT and the CONV plans were normalized to a median dose of 33 Gy to the planning target volume (PTV). Monomer/polymer gel dosimetry was used to assess the dosimetric accuracy of the IMAT planning and delivery method.
The median volume of the PTV was 8306 cc. The mean treatment delivery time over 4 patients was 13.8 min. A mean of 444 monitor units was needed for a fraction dose of 150 cGy. The fraction of the PTV volume receiving more than 90% of the prescribed dose (V(90)) was 9% higher for the IMAT plan than for the CONV4 plan (89.9% vs. 82.5%). Outside a build-up region of 0.8 cm and 1 cm away from both kidneys, the inhomogeneity in the PTV was 15.1% for the IMAT plans and 24.9% for the CONV4 plans (for CONV2 plans, this was 34.9%). The median dose to the kidneys in the IMAT plans was lower for all patients. The 95th percentile dose for the kidneys was significantly higher for the IMAT plans than for the CONV4 and CONV2 plans (28.2 Gy vs. 22.2 Gy and 22.6 Gy for left kidney, respectively). No relevant differences were found for liver. The gel-measured dose was within clinical planning constraints.
IMAT was shown to be deliverable in an acceptable time slot and to produce dose distributions that are more homogeneous than those obtained with a CONV plan, with at least equal sparing of the OARs.
全腹盆腔放射治疗（WAPRT）是复发性卵巢癌患者姑息治疗的一种选择。采用传统技术时，肾脏和肝脏是剂量及均匀性限制器官。我们制定了调强弧形放疗（IMAT）的计划策略，并报告了首批5例接受治疗患者的治疗计划。
连续5例经组织学证实为复发性卵巢癌的患者被送至我科接受WAPRT。在0.5厘米厚的CT图像上勾画靶区体积和危及器官（OAR）。临床靶区体积（CTV）定义为整个腹膜腔。CTV和肾脏外放0.5厘米。在预设的8度间隔的机架角度范围内，使用基于解剖结构的分割工具生成机器状态。同类机器状态分层为弧形。IMAT的优化分几步进行，使用生物物理目标函数。这些步骤包括机器状态的权重优化、适应最大叶片速度约束的叶片位置优化以及计划者交互式的起始和终止角度优化。使用坍缩圆锥卷积/叠加算法计算最终控制点（机器状态加上相关的累积监测单位计数）。为作比较，制定了两个传统计划（CONV），一个为两野计划（CONV2），另一个为四野计划（CONV4）。在这些CONV计划中，用铅块限制肾脏剂量。IMAT计划和CONV计划归一化为计划靶区体积（PTV）的中位剂量33 Gy。使用单体/聚合物凝胶剂量测定法评估IMAT计划和投照方法的剂量学准确性。
PTV的中位体积为8306立方厘米。4例患者的平均治疗投照时间为13.8分钟。给予150 cGy的分次剂量平均需要444个监测单位。IMAT计划中接受超过处方剂量90%（V(90)）的PTV体积分数比CONV4计划高9%（89.9%对82.5%）。在距离双肾0.8厘米和1厘米的剂量建成区之外，IMAT计划中PTV的不均匀性为15.1%，CONV4计划为24.9%（CONV2计划为34.9%）。所有患者IMAT计划中肾脏的中位剂量更低。IMAT计划中肾脏的第95百分位剂量显著高于CONV4计划和CONV2计划（左肾分别为28.2 Gy对22.2 Gy和22.6 Gy）。肝脏未发现相关差异。凝胶测量剂量在临床计划限制范围内。
IMAT可在可接受的时间内完成投照，且产生的剂量分布比CONV计划更均匀，对OARs的保护至少相当。
