Accelerated partial breast irradiation in an Asian population: dosimetric findings and preliminary results of a multicatheter interstitial program.

Introduction: Accelerated partial breast irradiation (APBI) using the multicatheter method has excellent cosmesis and low rates of long-term toxicity. However, there are few studies looking at the feasibility of this procedure and the outcomes in an Asian population. This study aims to look at outcomes at our hospital. Methods: We identified 121 patients treated with APBI at our center between 2008 and 2014. The median follow-up for our patient group was 30 months (range 3.7-66.5). The prescribed dose per fraction was 3.4 Gy in 10 fractions. In this study population, 71% of the patients were Chinese while 15% (n=19) were of other Asian ethnicity. Results: In this study, the median breast volume was 850 cc (range 216-2,108) with 59.5% (n=72) patients with a breast volume of,1,000 cc. The average planning target volume was 134 cc (range 28-324). The number of catheters used ranged from 8 to 25 with an average of 18 catheters used per patient. We achieved an average dose homogeneity index of 0.76 in our patients. The average D90(%) was 105% and the average D90(Gy) was 3.6 Gy per fraction. The median volume receiving 100% of the prescribed dose (V100) was 161.7 cc (range 33.9-330.1), 150% of the prescribed dose (V150) and 200% of the prescribed dose (V200) was 39.4 cc (range 14.6-69.6) and 14.72 cc (range 6.48-22.25), respectively. Our dosimetric outcomes were excellent even in patients with breast volume under 1,000 cc. There were no cases of grade 3 skin toxicity or acute pneumonitis. Two patients had a postoperative infection and two patients had fat necrosis postprocedure. Conclusion: Multicatheter high dose rate APBI is a safe and feasible procedure that can be carried out with minimal toxicity in Asian patients with breast volumes under 1,000 cc.