Dosimetric comparison of organs at risk exposure in multicatheter high-dose-rate interstitial brachytherapy vs. VMAT-based APBI for real patient treatment plans
Department of Medical Physics, Bialystok Oncology Center, Bialystok, Poland
Department of Medical Physics, Radiotherapy Center, Dr Alfred Sokolowski Specialist Hospital, Walbrzych, Poland
Department of Radiotherapy, Bialystok Oncology Center, Bialystok, Poland
J Contemp Brachytherapy 2026
Purpose
To dosimetrically compare multicatheter interstitial high-dose-rate brachytherapy (MIBT) with two volumetric modulated arc therapy (VMAT) techniques, i.e., continuous (cVMAT) and tangential (tVMAT), for accelerated partial breast irradiation (APBI), specifically focusing on organs at risk (OARs) exposure.
Material and methods
Treatment plans of 50 early-stage breast cancer patients treated with interstitial multicatheter HDR brachytherapy (MIBT) were analyzed. Using identical CT datasets with catheters in situ and standardized contours, MIBT, cVMAT, and tVMAT plans were generated for each patient. For VMAT plans, planning target volume (PTV) was created by adding a 5 mm margin to clinical target volume (CTV). A uniform prescription dose of 32 Gy in
8 fractions was applied across all techniques. Dosimetric parameters were evaluated for target volumes, heart (including tumor quadrant sub-group analysis for left-sided cases), ipsilateral lung, skin, ribs, and non-target breast.
Results
VMAT safety margins increased target volume by 129% vs. MIBT. MIBT achieved superior sparing of non-target breast (median V50%: 15.84% vs. 27.66% tVMAT and 23.91% cVMAT, p < 0.0001), skin, and ribs (D1cc,
p < 0.0001). For left-sided tumors, overall, tVMAT reduced mean heart dose vs. MIBT (0.38 Gy vs. 1.54 Gy, p < 0.0001). However, sub-group analysis revealed that this cardiac advantage was restricted to upper and outer quadrant tumors, with no significant differences for lower quadrant lesions. cVMAT delivered a high low-dose lung bath (V5%, 52.60%), which was significantly limited by tVMAT (19.26%) and MIBT (15.48%) (p < 0.0001).
Conclusions
APBI technique selection should be individualized based on anatomy and intramammary tumor bed location. MIBT optimizes sparing of healthy breast tissue, skin, and chest wall across all locations. Conversely, tVMAT provides a cardiac advantage mainly for left-sided upper/ outer quadrant tumors, and effectively minimizes low-dose lung exposure compared with continuous arc arrangements.
Keywords
early-stage breast cancer, accelerated partial breast irradiation (APBI), multicatheter interstitial brachytherapy (MIBT), high-dose-rate (HDR) brachytherapy, volumetric modulated arc therapy (VMAT), external beam radiation therapy (EBRT)
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