a Proton Therapy Center , National Cancer Center , Goyang , Korea.
b Department of Radiation Oncology , Korea Cancer Center Hospital , Seoul , Korea.
Acta Oncol. 2018 Oct;57(10):1359-1366. doi: 10.1080/0284186X.2018.1484155. Epub 2018 Jul 13.
The aim of the present study was to verify the dosimetric accuracy of two-dimensional (2D) in vivo rectal dosimetry using an endorectal balloon (ERB) with unfoldable EBT3 films for high-dose-rate (HDR) brachytherapy for cervical cancer. The clinical applicability of the technique was discussed.
ERB inflation makes the EBT3 films unrolled, whereas its deflation makes them rolled. Patient-specific quality assurance (pQA) tests were performed in 20 patient plans using an Ir-192 remote afterloading system and a water-filled cervical phantom with the ERB. The dose distributions measured in ERBs were compared with those of the treatment plans.
The absolute dose profiles measured by the ERBs were in good agreement with those of treatment plans. The global gamma passing rates were 96-100% and 91-100% over 20 pQAs under the criteria of 3%/3 mm and 3%/2 mm, respectively, with a 30% low-dose threshold. Dose-volume histograms of the rectal wall were obtained from the measured dose distributions and showed small volume differences less than 2% on average from the patients' plans over the entire dose interval. The positioning error of the applicator set was detectable with high sensitivity of 12% dose area variation per mm. Additionally, the clinical applicability of the ERB was evaluated in volunteers, and none of them felt any pain when the ERB was inserted or removed.
The 2D in vivo rectal dosimetry using the ERB with EBT3 films was effective and might be clinically applicable for HDR brachytherapy for cervical and prostate cancers to monitor treatment accuracy and consistency as well as to predict rectal toxicity.
本研究旨在验证使用可展开 EBT3 膜的内置直肠气囊（ERB）进行二维（2D）体内直肠剂量测定在宫颈癌高剂量率（HDR）近距离治疗中的剂量学准确性，并探讨该技术的临床适用性。
ERB 充气使 EBT3 膜展开，而其放气则使膜卷起。在带有 ERB 的 Ir-192 远程后装系统和充满水的宫颈模型中，对 20 例患者计划进行了患者特定的质量保证（pQA）测试。比较了在 ERB 中测量的剂量分布与治疗计划的剂量分布。
ERB 测量的绝对剂量曲线与治疗计划非常吻合。在 3%/3mm 和 3%/2mm 的标准下，20 例 pQA 中有 96-100%和 91-100%的全局伽马通过率，30%低剂量阈值。从测量的剂量分布中获得了直肠壁的剂量体积直方图，并显示出与患者计划相比，整个剂量间隔的平均体积差异小于 2%。施源器套的定位误差可以通过 12%剂量面积变化/毫米的高灵敏度检测到。此外，还在志愿者中评估了 ERB 的临床适用性，当 ERB 插入或取出时，没有志愿者感到任何疼痛。
使用带有 EBT3 膜的 ERB 进行 2D 体内直肠剂量测定是有效的，对于宫颈癌和前列腺癌的 HDR 近距离治疗，可能具有临床适用性，可用于监测治疗准确性和一致性，并预测直肠毒性。
