Author: Anthony R Bardwell, Dong Won Kim, Faith S Kim, Isaac Y Kim, Juying Zhang 👨🔬
Affiliation: Kaiser Permanente 🌍
Purpose: When a patient develops a significant skin reaction at some point during postmastectomy radiotherapy, a clinical decision is often made to discontinue the planned daily use of bolus. The aim of this study is to evaluate the dosimetric changes to the target PTV (chest wall minus 3 mm) and other organs-at-risk (OAR) depending on the number of days the bolus is discontinued.
Methods: Using 3D-conformal planning, multiple plans with decreasing number of fractions using bolus (0.5 cm) were ran on planning CTs of multiple left-sided breast cancer patients for both 25 fraction (5000 cGy) and 15 fraction (4005 cGy) regimens. The average percentage change of dose to the target and OARs was calculated for decreasing fractions with bolus use.
Results:: Minimal changes (1-2%) occur to the mean target dose, max target dose, mean lung dose, mean implant/expander dose, and max skin (first 3 mm) dose regardless of how many days the bolus was discontinued. However, the mean skin dose (MSD) decreases by 1% (0.8 – 1.3%) per day the bolus is discontinued with a total loss of about 20% if no bolus is used. The mean heart dose (MHD) also decreases by 0.4% (0.3-0.4%) per day the bolus is discontinued with a total decrease of about 5-10%.
Conclusion: If significant skin reactions occur during postmastectomy radiotherapy, the bolus can be discontinued any time during treatment with limited concerns for changes in the doses to the main target volume and most OARs, except for the MSD and MHD. If the MSD is clinically important (for example, in skin involvement by tumor), a general estimate of a 1% decrease in dose per day the bolus is discontinued can be used to make a clinical decision on if or when bolus could be discontinued.