Various buildup-bolus regimens in post-mastectomy intensity modulated radiotherapy : dosimetric and radiobiological evaluation

Explicit standards for buildup-bolus applications in post-mastectomy radiotherapy remain unclear. This study aimed to perform a dosimetric evaluation of target volumes and organs at risk associated with various buildup-bolus thicknesses and application frequencies to identify the optimal buildup-bolus regimen. Thirty-eight post-mastectomy patients were randomly selected between 2017 and 2024. Four sets of simulated treatment plans were created using virtual buildup-boluses with different protocols: daily 3-mm-thick, daily 5-mm-thick, half-time 5-mm-thick, and half-time 10-mm-thick. Cumulative dose-volume histograms were generated for each buildup-bolus regimen to assess dosimetric differences in target volumes and organs at risk. Equivalent uniform dose and normal tissue complication probability were evaluated for the skin. In terms of target volumes, the daily 5-mm-thick buildup-bolus regimen could reduce hot-spot doses while ensuring adequate target dose coverage, and improved dose homogeneity and conformity; For organs at risk, it could deliver necessary chest wall dose while minimizing high-dose exposure to the skin. Radiobiological evaluation of the skin indicated that the daily 5-mm-thick buildup-bolus regimen could reduce recurrence risk. Additionally, this regimen required the fewest monitor units, thereby reducing treatment time and alleviating machine wear and tear. It is concluded that the daily 5-mm-thick buildup-bolus regimen represented the optimal balance for target coverage and chest-wall skin sparing. These findings provide clinical guidance for treatment planning in post-mastectomy radiotherapy.