Antolak J A, Rosen I I, Childress C H, Zagars G K, Pollack A
Department of Radiation Physics, The University of Texas M. D. Anderson Cancer Center, Houston 77030, USA.
Int J Radiat Oncol Biol Phys. 1998 Oct 1;42(3):661-72. doi: 10.1016/s0360-3016(98)00248-x.
The purpose of this study was to measure the mobility of the clinical target volume (CTV) in prostate radiotherapy with respect to the pelvic anatomy during a course of therapy. These data are needed to properly design the planning target volume (PTV).
Seventeen patients were studied. Each patient underwent computed tomography (CT) scanning for treatment planning purposes. Subsequently, three CT scans were obtained at approximately 2-week intervals during treatment. The prostate, seminal vesicles, bladder, and rectum were outlined on each CT study. The second through the fourth CT studies were aligned with the first study using a rigid body transformation based on the bony anatomy. The transformation was used to compute the center of mass position and bounding box of each organ in the subsequent studies relative to the first study. Differences in the bounding box limits and center of mass positions between the first and subsequent studies were tabulated and correlated with bladder and rectal volume and positional parameters.
The mobility of the CTV was characterized by standard deviations of 0.09 cm (left-right), 0.36 cm (cranial-caudal), and 0.41cm (anterior-posterior). Prostate mobility was not significantly correlated with bladder volume. However, the mobility of both the prostate and seminal vesicles was very significantly correlated with rectal volume. Bladder and rectal volumes decreased between the pretreatment CT scan and the first on-treatment CT scan, but were constant for all on-treatment CT scans.
Margins between the CTV and PTV based on the simple geometric requirement that a point on the edge of the CTV is enclosed by the PTV 95% of the time are 0.7 cm in the lateral and cranial-caudal directions, and 1.1 cm in the anterior-posterior direction. However, minimum dose to the CTV and avoidance of organs at risk are more important considerations when drawing beam apertures. More consistent methods for reproducing prostate position (e.g., empty rectum) and more sophisticated beam aperture optimization are needed to guarantee consistent coverage of the CTV while avoiding organs at risk.
本研究的目的是测量前列腺放疗过程中临床靶区（CTV）相对于盆腔解剖结构的移动性。这些数据对于合理设计计划靶区（PTV）是必要的。
对17例患者进行了研究。每位患者为进行治疗计划而接受了计算机断层扫描（CT）。随后，在治疗期间每隔约2周进行三次CT扫描。在每次CT检查中勾勒出前列腺、精囊、膀胱和直肠。使用基于骨骼解剖结构的刚体变换，将第二次至第四次CT检查与第一次检查对齐。该变换用于计算后续研究中每个器官相对于第一次研究的质心位置和边界框。将第一次与后续研究之间边界框极限和质心位置的差异制成表格，并与膀胱和直肠体积及位置参数相关联。
CTV的移动性表现为标准差在左右方向为0.09厘米、头脚方向为0.36厘米、前后方向为0.41厘米。前列腺的移动性与膀胱体积无显著相关性。然而，前列腺和精囊的移动性与直肠体积均非常显著相关。预处理CT扫描与第一次治疗时CT扫描之间膀胱和直肠体积减小，但所有治疗时CT扫描期间保持恒定。
基于CTV边缘上的一点在95%的时间内被PTV包围这一简单几何要求，CTV与PTV之间在横向和头脚方向的边界为0.7厘米，在前后方向为1.1厘米。然而，在绘制射野孔径时，CTV的最小剂量和对危及器官的避让是更重要的考虑因素。需要更一致的方法来重现前列腺位置（如直肠排空）以及更复杂的射野孔径优化，以确保在避让危及器官的同时一致地覆盖CTV。
