Akin Mustafa, Öksüz Didem Colpan, Iktueren Basak, Ambarcioglu Pinar, Karacam Songul, Koca Sedat, Dincbas Fazilet Öner
Tumori. 2014 Sep-Oct;100(5):529-35. doi: 10.1700/1660.18172.
To assess the variations in actual doses delivered to the rectum and bladder in the course of postprostatectomy radiotherapy using kilovoltage-cone-beam computed tomography datasets acquired during image-guided radiotherapy.
Twenty consecutive patients treated with intensity-modulated or intensity-modulated arc therapy to the prostate bed were retrospectively evaluated. Both the planning tomography and kilovoltage-cone-beam computed tomography were acquired with an empty rectum and a half-full bladder. Target localization was performed on the basis of soft tissue matching using cone-beam computed tomography scans before each treatment fraction. A total of 16 cone-beam computed tomography scans per patient (acquired at the first 5 fractions and twice weekly thereafter) were used for the assessments. The bladder and rectum were re-contoured offline on each cone-beam computed tomography scan by a single physician, and the delivered doses were recalculated. The variations in certain dose-volume parameters for the rectum and bladder (BD2cc, RD 2cc, V40%, V50%, V60%, V65%) were analyzed using the paired t test.
Most of the dose volume variations for rectum and bladder were significantly higher than predicted (P <0.05) for the 320 kilovoltage-cone-beam computed tomography sets, except for the doses received by 2 cc of the bladder and V50 and V60 of the rectum. The dose-volume parameters of the bladder did not meet our criteria of V65 ≤25% and V40 ≤50% in 10% and 20% of the patients, respectively. None of the dose-volume histograms showed rectal V65 ≥17%; however, the rectal V40 ≤35% dose constraint was not met in 11 patients. For all patients, the ANOVA test revealed no significant difference between the variations.
Actual doses delivered during treatment were found to be higher than predicted, but the majority of calculated bladder and rectal doses remained in the limits of our plan acceptance criteria. Interfraction variability of the rectum and bladder is a major concern in the postprostatectomy radiotherapy setting, even when patients are instructed about rectal and bladder preparation before the radiotherapy course. Image guidance with cone-beam computed tomography at each treatment fraction may offer a viable tool to account for interfraction variations of the rectum and bladder throughout the treatment course.
利用图像引导放疗期间获取的千伏级锥形束计算机断层扫描数据集，评估前列腺切除术后放疗过程中直肠和膀胱实际接受剂量的变化情况。
对连续20例接受调强放疗或调强弧形放疗至前列腺床的患者进行回顾性评估。计划断层扫描和千伏级锥形束计算机断层扫描均在直肠空虚且膀胱半充盈的状态下进行。在每个治疗分次前，基于锥形束计算机断层扫描图像的软组织匹配进行靶区定位。每位患者共16次锥形束计算机断层扫描（在前5个分次时获取，之后每周两次）用于评估。由一名医生在每次锥形束计算机断层扫描图像上离线重新勾画膀胱和直肠轮廓，并重新计算所给予的剂量。使用配对t检验分析直肠和膀胱某些剂量体积参数（BD2cc、RD 2cc、V40%、V50%、V60%、V65%）的变化情况。
除膀胱2cc体积所接受的剂量以及直肠的V50和V60外，320组千伏级锥形束计算机断层扫描图像中，直肠和膀胱的大多数剂量体积变化均显著高于预期（P<0.05）。分别有10%和20%的患者，膀胱的剂量体积参数未达到我们设定的V65≤25%和V40≤50%的标准。剂量体积直方图均未显示直肠V65≥17%；然而，11例患者未满足直肠V40≤35%的剂量限制。对于所有患者，方差分析显示各变化之间无显著差异。
发现治疗期间实际给予的剂量高于预期，但大多数计算得出的膀胱和直肠剂量仍在我们计划接受标准的范围内。即使在放疗疗程前指导患者做好直肠和膀胱准备，直肠和膀胱的分次间变异性仍是前列腺切除术后放疗中的一个主要问题。在每个治疗分次时使用锥形束计算机断层扫描进行图像引导，可能为解决整个治疗过程中直肠和膀胱的分次间变化提供一个可行的工具。
