Abstract P3-12-05: Technique and outcome of post-mastectomy adjuvant chest wall radiotherapy – The role of tissue equivalent bolus in reducing risk of local recurrence

Abstract

Abstract Introduction Adjuvant chest wall radiotherapy is used in post-mastectomy patients with high risk histological features, to reduce the risk of loco-regional recurrence. This treatment can be given with or without a tissue equivalent bolus to increase skin surface dose. The additional benefit of using a bolus remains unclear; however it is known to be associated with higher incidence of skin toxicity. This retrospective cohort study looks at patients treated between 2005-2010 at the Kent oncology centre (KOC), and compares rates of local chest wall recurrence in patients treated with chest wall radiotherapy with and without a bolus. Methods This was a retrospective cohort study of 319 consecutive patients who had received chest wall radiotherapy at the KOC between 2005-2010, identified from radiotherapy planning records. Data was collected on key histological, demographic and treatment parameters, as well as incidence and grade of acute skin reactions. Data was also collected on treatment outcomes, including chest wall recurrence, disease-free and overall survival. Results One hundred and one patients received treatment with a bolus compared to 213 patients without a bolus. At median follow-up time of 60 months, there was 1 chest wall recurrence in the bolus treatment group and 4 in the no bolus treatment group. Using Fisher's Exact test no statistically significant difference could be shown between the two groups. However a significantly higher incidence of acute skin toxicity was seen in the bolus treatment group (p<0.001). The radiotherapy plans of the 5 patients with chest wall recurrence were evaluated in further detail regarding dose distribution and skin surface dose coverage. Data was also collected on incidence of metastatic relapse and overall survival. Sixty-six patients (21%) had metastatic relapse, 24 (23.8%) in the bolus treatment group and 42 (19.7%) in the no bolus treatment group, (p=0.41). The median time to relapse 29.5 months. At last follow-up 70.4% of patients had no evidence of disease. A further 6.1% were alive with disease, 6.1% had died with no evidence of disease and 17.5% had died of disease. Overall survival in both bolus and no bolus treatment groups 76%. Conclusion No statistically significant difference can be demonstrated in the rate of chest wall recurrence between those treated with radiotherapy with and without a bolus to the chest wall. This is consistent with limited previous literature on the topic. This study invites further evaluation of the role of a bolus in post-mastectomy chest wall radiotherapy, considering the increased toxicity that use of a bolus generates. Citation Format: Turner JY, Zeniou A, Williams A, Jyothirmayi R. Technique and outcome of post-mastectomy adjuvant chest wall radiotherapy – The role of tissue equivalent bolus in reducing risk of local recurrence. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P3-12-05.