MRI-guided single fraction ablative radiotherapy for early-stage breast cancer: a brachytherapy versus volumetric modulated arc therapy dosimetry study

Background and purpose: A radiosurgical treatment approach for early-stage breast cancer has the potential to minimize the patient's treatment burden. The dosimetric feasibility for single fraction ablative radiotherapy was evaluated by comparing volumetric modulated arc therapy (VMAT) with an interstitial multicatheter brachytherapy (IMB) approach.

Methods and materials: The tumors of 20 patients with early-stage breast cancer were delineated on a preoperative contrast-enhanced planning CT-scan, co-registered with a contrast-enhanced magnetic resonance imaging (MRI), both in radiotherapy supine position. A dose of 15 Gy was prescribed to the planned target volume of the clinical target volume (PTVCTV), and 20 Gy integrated boost to the PTV of the gross tumor volume (PTVGTV). Treatment plans for IMB and VMAT were optimized for adequate target volume coverage and minimal organs at risk (OAR) dose.

Results: The median PTVGTV/CTV receiving at least 95% of the prescribed dose was ⩾99% with both techniques. The median PTVCTV unintentionally receiving 95% of the prescribed PTVGTV dose was 65.4% and 4.3% with IMB and VMAT, respectively. OAR doses were comparable with both techniques.

Conclusion: MRI-guided single fraction radiotherapy with an integrated ablative boost to the GTV is dosimetrically feasible with both techniques. We perceive IMB less suitable for clinical implementation due to PTVCTV overdosage. Future studies have to confirm the clinical feasibility of the single fraction ablative approach.