Background: In the recent years PBI has emerged as an alternative to WBI. This results in less normal tissue irradiated, less morbidity and late complications, greater patient convenience. The comparative efficacy and toxicity profiles of PBI compared with WBI have shown similar ipsilateral breast tumor recurrence rates and reduced acute toxicities. With the advent of dedicated magnetic resonance-guided radiation therapy systems such as the MR-Linac there is potential for further improvement in the delivery of PBI and increased safety. We present our experience of MR-guided PBI in early-stage breast cancer (08/2017 -01/2021) and compare to patients treated with brachytherapy (1/2010 - 8/2015).
Objectives: 1) Assess the efficacy and toxicity of adjuvant PBI using MR-GRT in early-stage breast cancer. 2) Compare to outcomes of HDR brachytherapy patients 3) Determine situations where online adaptive RT may be beneficial.
Methods: Fifty patients treated with PBI (MR-GRT) and 29 treated with HDR brachytherapy (Contoura) were evaluated.
Criteria for PBI included: unifocal tumors.
Results: Acute reactions were minimal with skin reactions mild to none and limited to the lumpectomy site (RTOG score 0-1). Late effects were localized mild skin hyper-pigmentation. One patient had a rib fracture. There are no recurrences to date, with a median follow up of 12 months. None of the patients qualified for online adaptive planning, but end-inhale breath hold was utilized for left-sided tumors for cardiac sparing. In the brachytherapy group one had a local recurrence (at 3 y) and 12/29 had significant persistent seroma/thickening/retraction at the treated site.
Conclusions: PBI using MR-guided radiation therapy is a feasible, well tolerated regimen for early-stage breast cancer with a favorable acute and late toxicity profile and excellent cosmetic result. The follow-up is presently too short for recurrence evaluation, but so far no relapses were seen at a median follow up of 12 months. When compared with brachytherapy the acute and late morbidity are significantly lower and the cosmetic result superior
