Department of Radiooncology, Regional Oncological Hospital, Cagliari, Italy.
Strahlenther Onkol. 2011 Aug;187(8):473-8. doi: 10.1007/s00066-011-2241-7. Epub 2011 Jul 22.
To test megavolt cone-beam CT (MV-CBCT) in order to evaluate setup errors in prostate radiotherapy.
The setup of 9 patients was verified weekly by electronic portal imaging (EPI) and MV-CBCT, both per-formed in the same treatment session. EPI were compared with digitally reconstructed radiographies (DRRs). MV-CBCTs were matched to simulation CTs by manual registration based on bone markers (BMR), by manual registration based on soft tissues (STR) - rectum, bladder, and seminal vesicles - and by automatic registration (AR) performed by a mutual information algorithm. Shifts were evaluated along the three main axes: anteroposterior (AP), craniocaudal (CC), and laterolateral (LL). Finally, in 4 additional patients showing intraprostatic calcifications, the calcification mismatch error was used to evaluate the three MV-CBCT matching methods.
A total of 50 pairs of orthogonal EPIs and 50 MV-CBCTs were analyzed. Assuming an overall tolerance of 2 mm, no significant differences were observed comparing EPI vs BMR in any axis. A significant difference (p < 0.001) was observed along the AP axis comparing EPI vs AR and EPI vs STR. On the calcification data set (22 measures), the calcification mismatch along the AP direction was significantly lower (p < 0.05) after STR than after BMR or AR.
Bone markers were not an effective surrogate of the target position and significant differences were observed comparing EPI or BMR vs STR, supporting the assessment of soft tissue position by MVCBs to verify and correct patient setup in prostate radiotherapy.
利用兆伏锥形束 CT（MV-CBCT）进行检测，以评估前列腺放射治疗中的摆位误差。
每周对 9 例患者进行电子射野影像系统（EPIs）和 MV-CBCT 摆位验证，两者均在同一治疗时段内进行。EPIs 与数字重建射线照相术（DRRs）进行比较。MV-CBCT 基于骨标记（BMR）、基于直肠、膀胱和精囊的软组织（STR）手动配准以及互信息算法的自动配准（AR）与模拟 CT 进行匹配。沿三个主要轴（前后、头脚和左右）评估位移。最后，在另外 4 例显示前列腺内钙化的患者中，使用钙化不匹配误差来评估三种 MV-CBCT 匹配方法。
共分析了 50 对正交 EPIs 和 50 个 MV-CBCT。假设总体允许误差为 2mm，在任何轴上，EPI 与 BMR 比较均无显著差异。EPI 与 AR 和 EPI 与 STR 比较，沿前后轴存在显著差异（p < 0.001）。在钙化数据集（22 个测量值）中，与 BMR 或 AR 相比，STR 后沿前后方向的钙化不匹配明显更低（p < 0.05）。
骨标记不能有效替代靶位置，EPI 或 BMR 与 STR 比较存在显著差异，支持利用 MV-CBCT 评估软组织位置，以验证和纠正前列腺放射治疗中的患者摆位。
