Booth Jeremy, Zavgorodni Sergei
Radiation Oncology, Royal Prince Alfred Hospital, Camperdown, NSW 2050, Australia.
Phys Med Biol. 2005 Nov 7;50(21):5055-74. doi: 10.1088/0031-9155/50/21/008. Epub 2005 Oct 12.
Prostate radiotherapy inevitably deposits radiation dose in the rectal wall, and the dose delivered to prostate is limited by the expected rectal complications. Accurate evaluation of the rectal dose is non-trivial due to a number of factors. One of these is variation of the shape and position of the rectal wall (with respect to the clinical target volume (CTV)), which may differ daily from that taken during planning CT acquisition. This study uses data currently available in the literature on rectal wall motion to provide estimates of mean population rectal wall dose. The rectal wall geometry is characterized by a population mean radius of the rectum as well as inter-patient and inter-fraction standard deviations in rectum radius. The model is used to evaluate the range of inter-fraction and inter-patient rectal dose variations. The simulation of individual patients with full and empty rectum in the planning CT scan showed that large variations in rectal dose (>15 Gy) are possible. Mean calculated dose accounting for treatment and planning uncertainties in the rectal wall surface was calculated as well as the map of planning dose over/underpredictions. It was found that accuracy of planning dose is dependent on the CTV-PTV margin size with larger margins producing more accurate estimates. Over a patient population, the variation in rectal dose is reduced by increasing the number of pre-treatment CT scans.
前列腺放疗不可避免地会在直肠壁沉积辐射剂量，而输送到前列腺的剂量受到预期直肠并发症的限制。由于多种因素，准确评估直肠剂量并非易事。其中一个因素是直肠壁的形状和位置（相对于临床靶区（CTV））存在变化，这可能与计划CT采集时的情况每日不同。本研究利用目前文献中关于直肠壁运动的数据来提供平均人群直肠壁剂量的估计值。直肠壁几何形状的特征在于直肠的人群平均半径以及患者间和分次间直肠半径的标准差。该模型用于评估分次间和患者间直肠剂量变化的范围。在计划CT扫描中对直肠充盈和排空的个体患者进行模拟显示，直肠剂量可能存在较大变化（>15 Gy）。计算了考虑直肠壁表面治疗和计划不确定性的平均计算剂量以及计划剂量高估/低估图。结果发现，计划剂量的准确性取决于CTV-PTV边界大小，边界越大，估计越准确。在患者群体中，通过增加治疗前CT扫描的数量可减少直肠剂量的变化。
