Comparative dosimetric findings using accelerated partial breast irradiation across five catheter subtypes

Purpose: Accelerated partial breast irradiation (APBI) with balloon and strut adjusted volume implants (SAVI) show promising results with excellent tumor control and minimal toxicity. Knowing the factors that contribute to a high skin dose, rib dose, and D-95 coverage may reduce toxicity, improve tumor control, and help properly predict patient outcomes following APBI. Methods and materials: A retrospective analysis of 594 patients treated with brachytherapy based APBI at a single institution from May 2008 to September 2014 was grouped by applicator subtype. Patients were treated to a total of 34 Gy (3.4 Gy x 10 fractions over 5 days delivered BID) targeting a planning target volume (PTV) 1.0 cm beyond the lumpectomy cavity using a high dose rate source. Results: SAVI devices had the lowest statistically significant values of D(max)Skin (81.00 +/- 29.83), highest values of D-90 (101.50 +/- 3.66), and D-95 (96.09 +/- 4.55). SAVI-mini devices had the lowest statistically significant values of D(max)Rib (77.66 +/- 32.92) and smallest V-150 (18.01 +/- 3.39). Multi-lumen balloons were able to obtain the smallest V-200 (5.89 +/- 2.21). Strut-based applicators were more likely to achieve a D(max)Skin and a D(max)Rib less than or equal to 100 %. The effect of PTV on V-150 showed a strong positive relationship (p < .001). PTV and DmaxSkin showed a weak negative relationship in multi-lumen applicators (p = .016) and SAVI-mini devices (p < .001). PTV and DmaxRib showed a weak negative relationship in multi-lumen applicators (p = .009), SAVI devices (p < .001), and SAVI-mini devices (p < .001). Conclusion: PTV volume is strongly correlated with V-150 in all devices and V-200 in strut based devices. Larger PTV volumes result in greater V-150 and V-200, which could help predict potential risks for hotspots and resulting toxicities in these devices. PTV volume is also weakly negatively correlated with max skin dose and max rib dose, meaning that as the PTV volumes increase one can expect slightly smaller max skin and rib doses. Strut based applicators are significantly more effective in keeping skin and rib dose constraints under 125 and 100 % when compared to any balloon based applicator.