Steenbakkers Roel J H M, Deurloo Kirsten E I, Nowak Peter J C M, Lebesque Joos V, van Herk Marcel, Rasch Coen R N
The Netherlands Cancer Institute, Antoni van Leeuwenhoek Hospital, Amsterdam, The Netherlands.
Int J Radiat Oncol Biol Phys. 2003 Dec 1;57(5):1269-79. doi: 10.1016/s0360-3016(03)01446-9.
The prostate volume delineated on MRI is smaller than on CT. The purpose of this study was to determine the influence of MRI- vs. CT-based prostate delineation using multiple observers on the dose to the target and organs at risk during external beam radiotherapy.
CT and MRI scans of the pelvic region were made of 18 patients and matched three-dimensionally on the bony anatomy. Three observers delineated the prostate using both modalities. A fourth observer delineated the rectal wall and the bulb of the penis. The planning treatment volume (PTV) was generated from the delineated prostates with a margin of 10 mm in three-dimensions. A three-field treatment plan with a prescribed dose of 78 Gy to the International Commission on Radiation Units and Measurements point was automatically generated from each PTV. Dose-volume histograms were calculated of all PTVs, rectal walls, and penile bulbs. The equivalent uniform dose was calculated for the rectal wall using a volume exponent (n = 0.12).
The equivalent uniform dose of the CT rectal wall in plans based on the CT-delineated prostate was, on average, 5.1 Gy (SEM 0.5) greater than in the plans based on the MRI-delineated prostate. For the MRI rectal wall, this difference was 3.6 Gy (SEM 0.4). Allowing for the same equivalent uniform dose to the CT rectal wall, the prescribed dose to the PTV could be raised from 78 to 85 Gy when using the MRI-delineated prostate for treatment planning. The mean dose to the bulb of the penis was 11.6 Gy (SEM 1.8) lower for plans based on the MRI-delineated prostate. The mean coverage (volume of the PTV receiving > or =95% of the prescribed dose) was 99.9% for both modalities. The interobserver coverage (coverage of the PTV by a treatment plan designed for the PTV delineated by another observer in the same modality) was 97% for both modalities. The MRI rectum was significantly more ventrally localized than the CT rectum, probably because of the rounded tabletop and no knee support on the MRI scanner.
The dose delivered to the rectal wall and bulb of the penis is significantly reduced with treatment plans based on the MRI-delineated prostate compared with the CT-delineated prostate, allowing a dose escalation of 2.0-7.0 Gy for the same rectal wall dose. The interobserver coverage was the same for CT and MRI delineation of the prostate. A statistically significant difference in position between the CT- and MRI-delineated rectum was observed, probably owing to a different tabletop and use of knee support.
MRI上勾勒出的前列腺体积小于CT上的。本研究的目的是确定在多观察者使用基于MRI与CT的前列腺勾勒方法时，对外照射放疗中靶区和危及器官剂量的影响。
对18例患者进行盆腔区域的CT和MRI扫描，并在骨骼解剖结构上进行三维匹配。三名观察者使用两种模式勾勒前列腺。第四名观察者勾勒直肠壁和阴茎球部。从勾勒出的前列腺三维向外扩10mm生成计划靶体积（PTV）。从每个PTV自动生成一个三野治疗计划，向国际辐射单位与测量委员会点规定剂量为78Gy。计算所有PTV、直肠壁和阴茎球部的剂量体积直方图。使用体积指数（n = 0.12）计算直肠壁的等效均匀剂量。
基于CT勾勒前列腺的计划中，CT直肠壁的等效均匀剂量平均比基于MRI勾勒前列腺的计划高5.1Gy（标准误0.5）。对于MRI直肠壁，这一差异为3.6Gy（标准误0.4）。若使CT直肠壁的等效均匀剂量相同，在使用基于MRI勾勒前列腺进行治疗计划时，PTV的规定剂量可从78Gy提高到85Gy。基于MRI勾勒前列腺的计划中，阴茎球部的平均剂量低11.6Gy（标准误1.8）。两种模式下PTV的平均覆盖率（接受≥95%规定剂量的PTV体积）均为99.9%。观察者间覆盖率（同一模式下为另一名观察者勾勒的PTV设计的治疗计划对PTV的覆盖率）在两种模式下均为97%。MRI直肠比CT直肠在腹侧定位更明显，可能是因为MRI扫描仪的圆形检查床且没有膝部支撑。
与基于CT勾勒前列腺的治疗计划相比，基于MRI勾勒前列腺的治疗计划可显著降低直肠壁和阴茎球部的剂量，在直肠壁剂量相同时可使剂量增加2.0 - 7.0Gy。前列腺的CT和MRI勾勒的观察者间覆盖率相同。观察到CT和MRI勾勒的直肠在位置上存在统计学显著差异，可能是由于检查床不同以及是否使用膝部支撑。
