BackgroundThere remains wide variation in the use of chest wall boluses for postmastectomy radiotherapy (PMRT). Therefore, we aimed to prospectively evaluate the use of a 1-mm-thick daily tissue-equivalent bolus in patients who received PMRT using thermoluminescent dosimeters (TLDs) and skin toxicity assessment.Materials and MethodsWe collected data from patients with a 1-mm-thick daily bolus during PMRT at The Juntendo University Hospital. The surface dose was measured in vivo under the

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... ick bolus on the chest wall. We assessed the acute skin toxicity weekly during PMRT, and 1, 2, 4, and 12 weeks after the completion of PMRT.ResultsA total of 19 patients aged 32 − 79 years old received PMRT from July 2019 to January 2020. All patients completed the protocol treatment without interruptions, and the median follow-up was 32 weeks. In vivo dosimetry analysis revealed surface doses between 77% and 113% of the prescribed dose, with a mean of 92% of the prescribed radiation dose, and a standard deviation of 7% being delivered. Grade 2 dermatitis was found in 10 patients (53%), and Grade 3 dermatitis was found in one patient (5%). All cases of Grade 2 and 3 dermatitis were improved 4 weeks after PMRT. There were no cases of Grade 4 dermatitis and no chest wall recurrences during the treatment or follow-up period.ConclusionsThe 1-mm-thick daily bolus is a feasible regimen for PMRT, with appropriate dose buildup and acceptable skin toxicity without treatment interruptions.Trial registrationThe University Hospital Medical Information Network Clinical Trials Registry, UMIN000035773. Registered 1 July 2019, https://upload.umin.ac.jp/cgi-open-bin/ctr/ctr_view.cgi?recptno=R000040622