White Peter, Yee Chui Ka, Shan Lee Chi, Chung Lee Wai, Man Ng Ho, Cheung Yik Shing
The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong.
Radiat Oncol. 2014 Jan 22;9:29. doi: 10.1186/1748-717X-9-29.
Reproducibility of different immobilization systems, which may affect set-up errors, remains uncertain. Immobilization systems and their corresponding set-up errors influence the clinical target volume to planning target volume (CTV-PTV) margins and thus may result in undesirable treatment outcomes. This study compared the reproducibility of patient positioning with Hipfix system and whole body alpha cradle with respect to localized prostate cancer and investigated the existing CTV-PTV margins in the clinical oncology departments of two hospitals.
Forty sets of data of patients with localized T1-T3 prostate cancer were randomly selected from two regional hospitals, with 20 patients immobilized by a whole-body alpha cradle system and 20 by a thermoplastic Hipfix system. Seven sets of the anterior-posterior (AP), cranial-caudal (CC) and medial-lateral (ML) deviations were collected from each patient. The reproducibility of patient positioning within the two hospitals was compared using a total vector error (TVE) parameter. In addition, CTV-PTV margins were computed using van Herk's formula. The resulting values were compared to the current CTV-PTV margins in both hospitals.
The TVE values were 5.1 and 2.8 mm for the Hipfix and the whole-body alpha cradle systems respectively. TVE associated with the whole-body alpha cradle system was found to be significantly less than the Hipfix system (p < 0.05). The CC axis in the Hipfix system attained the highest frequency of large (23.6%) and serious (7.9%) set-up errors. The calculated CTV to PTV margin was 8.3, 1.9 and 2.3 mm for the Hipfix system, and 2.1, 3.4 and 1.8 mm for the whole body alpha cradle in CC, ML and AP axes respectively. All but one (CC axis using Hipfix) margin calculated did not exceed the corresponding hospital protocol. The whole body alpha cradle system was found to be significantly better than the Hipfix system in terms of reproducibility (p < 0.05), especially in the CC axis.
The whole body alpha cradle system was more reproducible than the Hipfix system. In particular, the difference in CC axis contributed most to the results and the current CC margin for the Hipfix system might be considered as inadequate.
不同固定系统的可重复性尚不确定，而这可能会影响摆位误差。固定系统及其相应的摆位误差会影响临床靶区体积到计划靶区体积（CTV-PTV）的边界，进而可能导致不理想的治疗结果。本研究比较了使用Hipfix系统和全身阿尔法托架进行患者定位时针对局限性前列腺癌的可重复性，并调查了两家医院临床肿瘤科现有的CTV-PTV边界。
从两家地区医院随机选取40组局限性T1-T3前列腺癌患者的数据，其中20例患者使用全身阿尔法托架系统固定，20例使用热塑性Hipfix系统固定。从每位患者收集七组前后（AP）、头脚（CC）和内外（ML）方向的偏差数据。使用总矢量误差（TVE）参数比较两家医院内患者定位的可重复性。此外，使用范·赫克公式计算CTV-PTV边界。将所得值与两家医院当前的CTV-PTV边界进行比较。
Hipfix系统和全身阿尔法托架系统的TVE值分别为5.1毫米和2.8毫米。发现与全身阿尔法托架系统相关的TVE明显小于Hipfix系统（p < 0.05）。Hipfix系统中CC轴出现大（23.6%）和严重（7.9%）摆位误差的频率最高。对于Hipfix系统，计算得出的CC、ML和AP轴上CTV到PTV的边界分别为8.3毫米、1.9毫米和2.3毫米，全身阿尔法托架在相应轴上分别为2.1毫米、3.4毫米和1.8毫米。除了一项（使用Hipfix系统的CC轴）计算得出的边界外，其他均未超过相应医院的方案。发现全身阿尔法托架系统在可重复性方面明显优于Hipfix系统（p < 0.05），尤其是在CC轴上。
全身阿尔法托架系统比Hipfix系统具有更高的可重复性。特别是，CC轴上的差异对结果影响最大，Hipfix系统当前的CC边界可能被认为是不够的。
