SU-E-T-593: Outcomes and Toxicities From a Clinical Trial of APBI Using MERT+IMRT with the Same XMLC.

PURPOSE: We present the results from a clinical trial of accelerated partial breast irradiation (APBI), using mixed modulated photon and electron beams (MERT+IMRT) with the same photon multileaf collimator (xMLC).

METHODS: Seven patients were enrolled in the first year of the APBI clinical trial. Patients were selected following the conditions included in the NSABP B-39/RTOG 0413 protocol. The targets and clinically relevant normal structures were contoured on the CT images following this protocol for APBI-EBRT. All treatments were delivered using combined modulated electron and photon beams by means of the same xMLC installed in a SIEMENS Primus linac, with a reduced SSD equal to 60 cm for electron beams. The plans were performed with a treatment planning system based on full Monte Carlo simulations, called CARMEN, developed by our group. Simultaneously, an alternative IMRT plan was calculated with the commercial TPS PINNACLE v8.0m (Philips), and both plans were compared. An ad-hoc breast phantom with semi-spherical geometry called NAOMI was designed for a specific QA protocol. Patients received a total dose of 38.5 Gy, delivered in 10 fractions over 5 consecutive days, with a twice-a-day hypofractionated schema.Follow-up visits during 2.5 years on average were repeated at 1 month post-treatment, every 3 months for the first year, and every 6 months for the second year. Toxicity was scored according to National Cancer Institute Common Terminology Criteria for Adverse Events (CTCAE version 3.0).

RESULTS: This APBI technique achieved high loco-regional control rates and showed low acute toxicity (grade 1 of CTCAE) and no toxicities from first month onwards. Photographic assessment of cosmesis showed skin excellent results.

CONCLUSION: The clinical results achieved with MERT+IMRT by using the same xMLC are comparable or even better than those obtained with other APBI techniques, thanks to a software solution without any additional equipment or specific device.