Department of Radiation Oncology, Dongtan Sacred Heart Hospital, Hwaseong, Korea.
Department of Radiation Oncology, Chuncheon Sacred Heart Hospital, Hallym University College of Medicine, Gangwon-do, Korea.
J Appl Clin Med Phys. 2023 Jul;24(7):e14052. doi: 10.1002/acm2.14052. Epub 2023 May 31.
Dry eye syndrome has been recently reported in patients who underwent whole brain radiotherapy (WBRT). WBRT based on a couch with three-degrees of freedom (3D) can occasionally be performed in which the rotational head motion is not corrected. This study assessed the dependency of the rotational errors on the mask and the dose variation of the lens and lacrimal gland in WBRT patients.
Translational and rotational setup errors were obtained at the first treatment with cone-beam CT (CBCT) for patients under WBRT and frameless stereotactic radiosurgery (SRS) (n = 20 each) immobilized using a conventional WB mask and an SRS mask with a bite block, respectively. For the CT sets of SRS cases, WBRT plans were generated for the study. To simulate the rotational error, rotated CT images were created with each rotational error, on which initial WBRT plans were copied and doses were recalculated. The lens and lacrimal gland doses with and without rotation errors were compared.
Despite similar translational setup errors for the two masks, the SRS mask showed a dramatic reduction in rotational errors compared to those of the WB mask. The errors varied within -2.9° to 2.9° and -1.2° to 0.7° for the WB and SRS masks, respectively. Accordingly, the SRS mask confined the change in the maximum lens dose, mean dose of the lacrimal gland, and lacrimal volume receiving 15 Gy to one-third of those using the WB mask.
When the six-degrees of freedom (6D) couch is not available, the frameless SRS mask is beneficial to WBRT for the faithful treatment as it was planned.
全脑放疗（WBRT）后患者最近出现干眼症综合征。基于具有三维自由度（3D）的治疗床偶尔可以进行 WBRT，在此过程中不纠正旋转头部运动。本研究评估了旋转误差对眼罩的依赖性以及 WBRT 患者晶状体和泪腺的剂量变化。
通过锥形束 CT（CBCT）在 WBRT 患者首次治疗时获得平移和旋转设置误差，并分别使用常规 WBR 面罩和带咬块的无框架立体定向放射外科（SRS）面罩固定。对于 SRS 病例的 CT 集，生成了 WBRT 计划。为了模拟旋转误差，使用每个旋转误差创建了旋转 CT 图像，并在其上复制了初始 WBRT 计划并重新计算了剂量。比较了有和没有旋转误差的晶状体和泪腺剂量。
尽管两种面罩的平移设置误差相似，但 SRS 面罩的旋转误差明显小于 WBR 面罩。误差范围分别为-2.9°至 2.9°和-1.2°至 0.7°。因此，SRS 面罩将最大晶状体剂量、泪腺平均剂量和接受 15 Gy 的泪腺体积的变化限制在使用 WBR 面罩的三分之一以内。
当无法使用六自由度（6D）治疗床时，无框架 SRS 面罩有利于 WBRT 进行忠实治疗，因为它是按计划进行的。
