Petrik David, Araujo Cynthia, Kim David, Halperin Ross, Crook Juanita M
Department of Radiation Oncology, British Columbia Cancer Agency, Center for the Southern Interior, Kelowna, BC, Canada.
Brachytherapy. 2012 Nov-Dec;11(6):435-40. doi: 10.1016/j.brachy.2012.05.001. Epub 2012 Jun 23.
Postplan quality assurance using CT shows considerable interobserver contour variability. We examined CT postplans of four experienced brachytherapists for comparison with MR-determined prostate volumes.
Seventy-five patients had CT and MR scans 1 month post-(125)I prostate brachytherapy. CT scans were contoured by the treating physician and dosimetry calculated. The prostate was contoured independently on MR by one observer with extensive MR experience, the scans were fused and dosimetric parameters compared.
The mean prostate volume on CT was 38.3 cc (17.5-78.6 cc), on MR 33.3 cc (16.3-66.1 cc). On average, the volume on CT was 16.1% larger than on MR (range, 8% smaller to 64% larger). Craniocaudal discordance of the CT vs. MR prostate contours ranged from 4 mm cranial to 10 mm caudal to MR base and from 6 mm cranial to 14 mm caudal to MR apex. The CT prostate volume not only included an average of 90% of the MR prostate (range, 75-99%) but also included normal tissue (mean, 8.3 cc; range, 2.9-17.1 cc). The average difference between the calculated D(90) from CT contours vs. MR contours was 10.0 Gy (standard deviation, 8.8; range, -37.6 to +41.6 Gy).
On average, only 90% of the MR-defined prostate is included in CT contours, while a volume of normal tissue is erroneously designated as prostate. Lack of awareness of this deficiency in planning and/or operative technique gives a false sense of appreciation of the true conformality, delays implementation of corrective measures, and risks unnecessary side effects.
使用CT进行计划后质量保证显示，观察者间的轮廓差异相当大。我们检查了四位经验丰富的近距离放射治疗师的CT计划后图像，以与磁共振成像（MR）确定的前列腺体积进行比较。
75例患者在接受（125）I前列腺近距离放射治疗1个月后进行了CT和MR扫描。由治疗医师对CT扫描进行轮廓勾画并计算剂量。由一位具有丰富MR经验的观察者在MR上独立勾画前列腺轮廓，将扫描图像融合并比较剂量学参数。
CT上前列腺的平均体积为38.3立方厘米（17.5 - 78.6立方厘米），MR上为33.3立方厘米（16.3 - 66.1立方厘米）。平均而言，CT上的体积比MR上大16.1%（范围为比MR小8%至大64%）。CT与MR前列腺轮廓的头脚不一致范围为：相对于MR基线，在头侧为4毫米至尾侧为10毫米；相对于MR尖部，在头侧为6毫米至尾侧为14毫米。CT前列腺体积不仅平均包含了MR前列腺的90%（范围为75% - 99%），还包含了正常组织（平均为8.3立方厘米；范围为2.9 - 17.1立方厘米）。根据CT轮廓与MR轮廓计算出的D（90）的平均差异为10.0戈瑞（标准差为8.8；范围为 - 37.6至 + 41.6戈瑞）。
平均而言，CT轮廓仅包含MR定义的前列腺的90%，同时有一定体积的正常组织被错误地认定为前列腺。在计划和/或手术技术中未意识到这种缺陷会导致对真正适形性的错误认识，延迟纠正措施的实施，并带来不必要的副作用风险。
