2460 - Efficacy of Preheating Bolus for Reducing Setup Errors in Patients with Breast Cancer Undergoing Postoperative Radiotherapy: A Randomized Controlled Study

L. Zhang¹, J. Zang², and F. Bai¹; ¹Department of Radiation Oncology, Xijing Hospital, Fourth Military Medical University, xian, Shaanxi, China, ²Department of Radiation Oncology, Xijing Hospital, Air Force Medical University, Xian, China

Purpose/Objective(s): Bolus is an essential tissue-equivalent material that allows 95-100% isodose transfer to the skin and subcutaneous tissue for patients with breast cancer receiving postoperative radiotherapy. However, the bolus with low-temperature (21-25?) may lead to involuntary body position movement and patient discomfort due to the temperature differences between bolus and body. Therefore, we designed a randomized controlled study to investigate whether preheating bolus with 37? could reduce setup errors and improve patients comfortable feeling during breast cancer radiotherapy. Materials/

Methods: Patients with breast cancer received radical resection and postoperative radiotherapy were randomly assigned into preheating group and non-preheating group in a 1:1 ratio from June 2023-February 2024. For preheating group, bolus was preheated in a thermostat for 30min with 37? before it was used for patients. For non-preheating group, bolus with room-temperature was used during radiotherapy. All patients received radiotherapy with bolus from first to 15th radiotherapy according to medical prescription. The cone beam computed tomography (CBCT) was used to evaluate setup errors once a week. The setup errors in translational directions ML, SI and AP were recorded based on CBCT image. The study also evaluated the variations in the anteroposterior diameter of the thorax and skin toxicity in the two groups. The comfort satisfaction score which was reported in a previous article was used to evaluate for each patient. The primary endpoint of this study was setup error between two groups. This registration number of this trial was ChiCTR2300072549.
Results: A total of 152 patients were enrolled in this study. Patient characteristics were well balanced in both arms. The AP and ML directional setup errors in the preheating group were less than non-preheating group (AP, 0.22±2.41 mm vs -0.54±2.46 mm, p <0.01;ML,-0.04±2.51 mm vs 0.62±2.48 mm, p< 0.01).Patients in preheating group had better comfort scores (33.25±2.62 vs 32.19±2.50, p< 0.01) and temperature satisfaction comfort scores (4.24±0.44 vs 3.71±0.54, p<0.01) than those in non-preheating group. Compared with non-preheating group, preheating bolus had a trend to reduce the AP directional setup error (0.17±0.15 vs. 0.23±0.19cm, p=0.054). There were no significant differences in incidence of grade 2 radiation-related dermatitis (47.6% vs. 44.3%, p=0.661) and grade 3 radiation-related dermatitis (2.7% vs. 2.9%, p=1.000).
Conclusion: Preheating bolus reduced setup errors in in the AP and ML directions without increasing skin toxicities in breast cancer patient receiving postoperative radiotherapy.