Post-mastectomy radiotherapy: Impact of bolus thickness and irradiation technique on skin dose

Frédéric A Miéville; Nicolas Pitteloud; Vérane Achard; Giorgio Lamanna; Olivier Pisaturo; Pierre-Alain Tercier; Abdelkarim S Allal

doi:10.1016/j.zemedi.2023.03.004

Post-mastectomy radiotherapy: Impact of bolus thickness and irradiation technique on skin dose

Z Med Phys. 2023 May 5:S0939-3889(23)00041-7. doi: 10.1016/j.zemedi.2023.03.004. Online ahead of print.

Authors

Frédéric A Miéville¹, Nicolas Pitteloud², Vérane Achard², Giorgio Lamanna², Olivier Pisaturo², Pierre-Alain Tercier², Abdelkarim S Allal²

Affiliations

¹ Department of Radiation Oncology, Hôpital Fribourgeois, 2-6 Chemin des Pensionnats, 1752 Villars-sur-Glâne, Fribourg, Switzerland. Electronic address: frederic.mieville@h-fr.ch.
² Department of Radiation Oncology, Hôpital Fribourgeois, 2-6 Chemin des Pensionnats, 1752 Villars-sur-Glâne, Fribourg, Switzerland.

PMID: 37150728
DOI: 10.1016/j.zemedi.2023.03.004

Abstract

Purpose: To determine 10 MV IMRT and VMAT based protocols with a daily bolus targeting a skin dose of 45 Gy in order to replace the 6 MV tangential fields with a 5 mm thick bolus on alternate days method for post-mastectomy radiotherapy.

Method: We measured the mean surface dose along the chest wall PTV as a function of different bolus thicknesses for sliding window IMRT and VMAT plans. We analyzed surface dose profiles and dose homogeneities and compared them to our standard 6 MV strategy. All measurements were performed on a thorax phantom with Gafchromic films while dosimetric plans were computed using the Acuros XB algorithm (Varian).

Results: We obtained the best compromise between measured surface dose (mean dose and homogeneity) and skin toxicity threshold obtained from the literature using a daily 3 mm thick bolus. Mean surface doses were 91.4 ± 2.8% [85.7% - 95.4%] and 92.2 ± 2.3% [85.6% - 95.2%] of the prescribed dose with IMRT and VMAT techniques, respectively. Our standard 6 MV alternate days 5 mm thick bolus leads to 89.0 ± 3.7% [83.6% - 95.5%]. Mean dose differences between measured and TPS results were < 3.2% for depths as low as 2 mm depth.

Conclusion: 10 MV IMRT-based protocols with a daily 3 mm thick bolus produce a surface dose comparable to the standard 6 MV 5 mm thick bolus on alternate days method but with an improved surface dose homogeneity. This allows for a better control of skin toxicity and target volume coverage.

Keywords: Bolus; EBT3 film; IMRT/VMAT; Post-mastectomy radiation therapy; Surface skin dose; Thorax phantom.