(P018) Accelerated Partial Breast Radiotherapy Using VMAT-A Preliminary Dosimetric Comparison to Single-Entry Brachytherapy

Yucel Saglam, Yasemin Bolukbasi, Steve Kirsner,Vildan Alpan, Duygu Sezen, Ugur Selek; American Hospital, MD Anderson Radiation Treatment Center, Istanbul; Department of Radiation Oncology, UT MD Anderson Cancer Center; Department of Radiation Oncology, Koc University

PURPOSE: To compare the dosimetric aspects of accelerated partial breast irradiation (APBI) with a single-entry brachytherapy device, strut-adjusted volumetric (SAVI), and external APBI using volumetric arc therapy (VMAT), with the intent of investigating the feasibility of using VMAT for the delivery of APBI treatments.

MATERIALS AND METHODS: Five left breast cancer patients who were planned and treated with SAVI at MD Anderson Cancer Center in Istanbul at American Hospital were randomly and retrospectively chosen from a database for this preliminary study. All patients were staged with T1N0M0 invasive breast cancer after partial mastectomy and sentinel lymph node dissection. The age of the patients ranged from 50 to 82 years. None of the patients received chemotherapy. The average cavity size was 12.6 mm (range: 2.2–18 mm), and all patients had invasive ductal carcinoma.

The plans and their contours were sent from the Oncentra Treatment Planning System to the Philips Pinnacle treatment planning system for replanning. VMAT APBI treatment plans were run on these same patients using the same contours delineated in the Oncentra planning system. The target volumes and planning parameters were set according to the National Surgical Adjuvant Breast and Bowel Project (NSABP)-39 protocol for external beam APBI, with a prescription dose of 38.5 Gy in 10 fractions. Dosimetric criteria on the heart and ipsilateral lung were used to compare the two techniques. Paired two-tailed Student’s t-test was performed to assess the differences in lung mean dose, heart mean dose, V20, V10, and V5 (%).

RESULTS: Even VMAT resulted in a decreased low-dose volume of the lung (V5: 0.1% vs 12.2%; P = .03); mean dose (204.1 cGy vs 287.2 cGy; P = .08), and V10 (0.02% vs 2.83%; P = .132) and V20 (0.001% vs 4.540%; P = .063) percentages of the lung were found to be similar. The difference in heart mean dose (243.6 cGy vs 342.8 cGy; P = .022) was influenced by the significant difference of heart V5 (0.083% vs 21.4%; P = .004), but the V20 (0.0001% vs 0.126%; P = .374) and V10 (0.008% vs 3.448%; P = .104) values of the heart were found to be comparable between the two techniques.

CONCLUSION: VMAT planning for the delivery of APBI in this preliminary dosimetric evaluation has been shown to be a viable option for APBI. VMAT planning gives acceptable lung and heart doses and appears to deliver lower doses to the heart and ipsilateral lung than APBI delivered with the single-entry SAVI applicator.

Proceedings of the 97th Annual Meeting of the American Radium Society - americanradiumsociety.org