Muren Ludvig Paul, Ekerold Randi, Kvinnsland Yngve, Karlsdottir Asa, Dahl Olav
Department of Oncology and Medical Physics, Haukeland University Hospital, N-5021 Bergen, Norway.
Radiother Oncol. 2004 Jan;70(1):11-9. doi: 10.1016/j.radonc.2003.11.013.
To derive planning organ at risk volume (PRV) margins for the rectum and to analyse the impact of such margins on rectum dose volume histograms (DVHs).
Weekly repeat computer tomography (CT) scans of 19 bladder cancer patients acquired during a conformal radiotherapy course were registered with the corresponding planning CT scans. From these scans, the internal rectal motion was quantified, and the margins that had to be added to the rectum contour in the planning scan to encompass the observed span of rectum motion were determined. These margins were compared to the margins derived using a recent PRV margin recipe. To illustrate the impact of margins on rectum DVHs, the margins were applied in treatment plans of six prostate cancer patients.
Altogether 141 CT scans were analysed. On average 24% of the repeat scan rectum volume was displaced outside the planning scan contours, and wall movements of up to 30 mm were observed. Margins of 16 mm anterior and 11 mm posterior encompassed all rectal motion except for the two most displaced rectum walls in each of these directions, in 89% of the patients. Using a recently published statistics-based recipe, margins of 6 mm anterior and 5 mm posterior accounted for the systematic rectum variation, i.e. the average wall position, in 90% of the patients. Adding anterior margin only caused consistent increases (up to 20%) in the fraction of the volume inside the high-dose region (40-70 Gy) compared to the DVH of rectum only. When using both anterior and posterior margins only small shifts (<5%) in the volume fractions were observed.
Rectum PRV margins of 5-6 mm will encompass the systematic component of rectum motion, while margins up to 16 mm are required to also account for most of the random variation. Use of anterior margins only caused large shifts in the DVHs in the clinically significant dose range, while only minor shifts were seen when using both anterior and posterior margins.
推导直肠的计划危及器官体积（PRV）边界，并分析此类边界对直肠剂量体积直方图（DVH）的影响。
在适形放疗疗程中对19例膀胱癌患者进行的每周重复计算机断层扫描（CT）与相应的计划CT扫描进行配准。从这些扫描中，对直肠内部运动进行量化，并确定在计划扫描中必须添加到直肠轮廓上以涵盖观察到的直肠运动范围的边界。将这些边界与使用最近的PRV边界公式得出的边界进行比较。为说明边界对直肠DVH的影响，将这些边界应用于6例前列腺癌患者的治疗计划中。
共分析了141次CT扫描。平均而言，重复扫描的直肠体积的24%移位到计划扫描轮廓之外，并且观察到高达30 mm的壁运动。在89%的患者中，16 mm的前边界和11 mm的后边界涵盖了除每个方向上两个移位最大的直肠壁之外的所有直肠运动。使用最近发表的基于统计的公式，6 mm的前边界和5 mm的后边界在90%的患者中占直肠系统变化，即平均壁位置。仅添加前边界会导致高剂量区域（40 - 70 Gy）内的体积分数与仅直肠的DVH相比持续增加（高达20%）。当同时使用前边界和后边界时，仅观察到体积分数有小的变化（<5%）。
5 - 6 mm的直肠PRV边界将涵盖直肠运动的系统成分，而高达16 mm的边界对于考虑大部分随机变化也是必需的。仅使用前边界会导致在临床显著剂量范围内DVH有较大变化，而同时使用前边界和后边界时仅观察到较小变化。
