Evaluation of three APBI techniques under NSABP B-39 guidelines

This work compares two accelerated partial breast irradiation modalities, MammoSite brachytherapy and three dimensional conformal radiotherapy (3D-CRT), to a new method, SAVI brachytherapy, following NSABP B-39 guidelines. A total of 21 patients treated at UC San Diego with the SAVI device were evaluated in this comparison. 9 of the 21 patients were eligible for all three modalities and were dosimetrically compared evaluating V90, V150, V200, total target volume, maximum skin, lung, and chestwall/rib dose. The target volumes (PTV_EVAL) differed with SAVI having the least total volume at 59.9 cc vs. 71.5 cc and 351.6 cc for MammoSite and 3D-CRT, respectively. The median V90, V150 and V200 for the three modalities were 97.7%, 25.0 cc, 10.4 cc (SAVI) vs. 97.6%, 23.9 cc, 5.0 cc (MammoSite) vs. 100% (V90 3D-CRT). The maximum dose for SAVI, MammoSite, and 3D-CRT, respectively, relative to the prescribed dose, for the: lung was 80.0%, 150.0%, and 104.9%; for rib 108.8%, 225.0%, and 114.7%: for skin 75.0%, 135.0%, and 108.6%. Comparing modalities, PTV coverage varied between 97.6% - 100.0% with more breast tissue covered by 3D-CRT, as expected, given the differences between external beam and brachytherapy. The maximum lung, skin and rib doses were lowest for the SAVI, highlighting its ability to conform to exclude normal tissues. In offering partial breast radiation, the availability of a variety of techniques allows for maximal patient eligibility, and comparison of individual method pros and cons may guide the most appropriate choice for each patient.