Preliminary Results Of A Prospective Feasibility Study Testing Preoperative Accelerated Partial Breast Radiotherapy (Apbi) Using 3 Dimensional Conformal Radiotherapy (3d Crt)

We have previously reported the dosimetric benefits/advantages of preoperative APBI using 3 D CRT. Preoperative therapy significantly decreases the volume irradiated, which decreases the dose to all surrounding critical structures, and increases the number of patients eligible for APBI (1). This is the preliminary results of the first 10 patients on a prospective trial of pre-operative APBI. This is an IRB approved prospective trial testing the feasibility of preoperative APBI for patients with early stage breast cancer. Patients eligible for this trial had unifocal invasive carcinomas of the breast that were < 3 cm. Axillary nodes were assessed clinically and by ultrasound, and they were required to be clinical N0. If a node was suspicious by ultrasound, a negative FNA was required to be eligible. Invasive lobular and in situ cancers were excluded. Treatment was very similar to those described in RTOG 03-19 (i.e. CTV and PTV expansions). The only difference was the tumor as seen on the CT simulation replaced the post-operative as described in RTOG 03-19. The dose delivered was 3.85 Gy per fraction administered 2 times a day with at least 6 hours between treatments to a total dose of 38.5 Gy. Four weeks later, a lumpectomy and sentinel lymph node biopsy were performed. Between April 2010 and March 2011, 10 patients have consent for treatment on this study. The median age was 60.5 (range 53 to 83), the median tumor size was 0.9cm (range 0.45 cm to 1.3 cm), all with ER/PR positive disease. Nine of the 10 patient's treatment plans met dosimetric qualifications. One patient was deemed ineligible, due to the ratio of the PTV to the reference breast volume exceeding 25% and was not treated with radiation therapy prior to surgery. One patient with a tubular carcinoma had a complete pathologic response to treatment. One patient was found to have a positive sentinel lymph node after a negative pre-operative ultrasound and then underwent a completion axillary dissection with no further positive lymph nodes. One patient with diabetes had a persistent sinus following lumpectomy which has taken 6 months to heal. There were no grade 3, 4, or 5 complications secondary to radiation. Preoperative APBI using 3 D CRT appears feasible with no unexpected side effects. We plan to continue accrual for an additional 30 patients. Further refinements in immobilization and image guidance will allow further increases in eligibility by decreasing PTV margins.