Oozeer R, Chauvet B, Toy B J, Berger C, Garcia R, Felix-Faure C, Le Thanh H, Reboul F
Institut Sainte-Catherine, Avignon, France.
Cancer Radiother. 1999 Jul-Aug;3(4):333-40. doi: 10.1016/s1278-3218(99)80076-6.
Accuracy of conformal treatment planning for prostatic radiotherapy is based on the contours of target volumes (prostate +/- seminal vesicles) and normal tissues (rectum and bladder), drawn on CT (computed tomography) images by radiation oncologists. The interpretation of a given CT image can be different from one radiation oncologist to another, and may change in time with the state of filling of the bladder and of the rectum during the treatment. In order to quantify these variations, 12 patients treated with conformal radiotherapy for prostate carcinoma (pelvis 40 Gy/20 sessions + prostate 30 Gy/15 sessions) had two series of CT at one month intervals. Contouring of prostate, rectum and bladder were performed independently on each CT by two radiation oncologists. The first CT scan (planning CT) and the first series of contours (planning contours) were used for treatment planning. The contours of the second scan were compared to the planning contours after image fusion based on manual superimposition of bony anatomy of the two sets of CT images. Coherence ratio were defined to measure discrepancies in prostate volumes between radiation oncologists (RCE) and between scans (RCT). The mean RCE was 38 +/- 7% (1 standard deviation). Those discrepancies were primarily located at the prostate apex and at the interface between bladder and prostate and between rectum and prostate. The mean RCT was 42 +/- 8% (1 sigma). Those discrepancies were due to the prostate motion related to the state of filling of the rectum and bladder. For bladder and rectal walls, less important differences were observed between the two radiation oncologists for the same CT (4.5% for rectal volume receiving 65 Gy or more, 3% for bladder volume receiving 65 Gy or more). However, important differences in bladder and rectal volumes receiving 65 Gy or more (16% and 7% respectively) were noted for the same patient from a CT to another due to the variation in bladder or rectal filling. New techniques for planning CT acquisition are needed to decrease the discrepancies due to contouring. The treatment must, as far as possible, be delivered with an empty bladder and rectum in order to ensure a good reproduction of the initially planned treatment.
前列腺放疗适形治疗计划的准确性基于放射肿瘤学家在CT（计算机断层扫描）图像上勾勒出的靶区（前列腺±精囊）和正常组织（直肠和膀胱）轮廓。对于给定的CT图像，不同放射肿瘤学家的解读可能不同，并且在治疗过程中会随着膀胱和直肠的充盈状态而随时间变化。为了量化这些差异，12例接受前列腺癌适形放疗的患者（盆腔40 Gy/20次 + 前列腺30 Gy/15次）每隔一个月进行了两组CT扫描。两位放射肿瘤学家在每次CT扫描上独立勾勒前列腺、直肠和膀胱的轮廓。第一次CT扫描（计划CT）和第一组轮廓（计划轮廓）用于治疗计划。基于两组CT图像的骨骼解剖结构手动叠加进行图像融合后，将第二次扫描的轮廓与计划轮廓进行比较。定义一致性比率以测量放射肿瘤学家之间（RCE）以及扫描之间（RCT）前列腺体积的差异。平均RCE为38±7%（1个标准差）。这些差异主要位于前列腺尖部以及膀胱与前列腺之间、直肠与前列腺之间的界面处。平均RCT为42±8%（1个标准差）。这些差异是由于前列腺运动与直肠和膀胱的充盈状态有关。对于膀胱和直肠壁，在相同CT上两位放射肿瘤学家之间观察到的差异较小（接受65 Gy或更高剂量的直肠体积差异为4.5%，接受65 Gy或更高剂量的膀胱体积差异为3%）。然而，由于膀胱或直肠充盈的变化，同一患者在不同CT之间接受65 Gy或更高剂量的膀胱和直肠体积存在显著差异（分别为16%和7%）。需要新的计划CT采集技术来减少因轮廓勾勒导致的差异。治疗必须尽可能在膀胱和直肠排空的状态下进行，以确保最初计划的治疗能够良好重现。
