Retrospective dosimetric comparison of VMAT versus t-IMRT for patients with carbon dioxide tissue expanders undergoing left sided PMRT using the recent ESTRO-ACROP target volume delineation

Abstract

Introduction: The Aeroform tissue expander device (ATED) is a novel alternative system for patients who have had mastectomy for breast cancer (BC) and require adjuvant radiation therapy (RT), and investigations are required when used during RT. We aim to compare RT dosimetry outcomes using volumetric modulated arc therapy (VMAT) versus tangential intensity-modulated radiation therapy (t-IMRT) techniques when planning post-mastectomy RT (PMRT), using the recent European Society for Radiation Oncology – Advisory Committee on Radiation Oncology Practice (ESTRO-ACROP) target volume delineation consensus guideline.1 Methods: Five patients with left-sided BC undergoing PMRT with ATED in-situ were identified. Retrospectively, their CT-simulation scans were utilised to delineate the chest wall (CW) and nodal target volumes. A dose of 50.4Gy in 28 fractions was prescribed and four plans generated. Dosimetry for all target volumes and organs at risk were extracted, with paired means compared. Results: When comparing VMAT with t-IMRT techniques, there was no statistically significant difference in the PTV50.4 D95% or D2% coverage. Within t-IMRT plans, excluding internal mammary nodes (IMN) leads to higher D95% coverage. The heart mean dose and V25 were significantly lower with VMAT than t-IMRT. There was no significant difference to the heart dose whether IMN was included or not. The ipsilateral lung V20 was significantly lower with VMAT than t-IMRT, but not the V5. Within t-IMRT plans, excluding IMN leads to lower ipsilateral lung V20. The t-IMRT plans had lower contralateral lung V5, and even lower when IMN was not included. The contralateral breast mean dose was not significantly different between VMAT and t-IMRT. Within t-IMRT plans, the right breast mean dose was lower if IMN was excluded. Conclusion: We have not shown a clear advantage of VMAT over t-IMRT techniques when prescribing PMRT for left-sided BC patients with ATED in-situ.