Abstract ES4-3: Techniques and technical considerations

Abstract Purpose: Partial breast irradiation (PBI) treats the lumpectomy cavity and a margin of adjacent breast tissue allowing for a reduction in treatment volume, duration and potentially toxicity. Body: Multiple PBI techniques are available. Interstitial brachytherapy (IB) represents the oldest PBI technique; mature data from randomized trials are available with 5-10 year follow-up and demonstrate comparable local control and toxicity profiles. Technically, multiple target volume definitions are currently utilized. Applicator based brachytherapy has evolved from single-lumen applicators, increasing the degrees of freedom for treatment planning. Prospective, non-randomized 5 year data are available with applicator based brachytherapy, demonstrating low rates of recurrence, comparable rates of toxicity, and high rates of excellent/good cosmetic outcomes. The treatment volume for applicator based brachytherapy is 1 cm surrounding the device, with adjustments for the skin and chest wall. External beam radiation therapy includes 3D-CRT, IMRT and proton based techniques. Data from 3D-CRT studies have suggested higher toxicities and inferior cosmetic outcomes. However, randomized studies evaluating IMRT PBI have not, demonstrating comparable or improved toxicity and cosmetic outcomes. Intraoperative radiation therapy (IORT) is unique as two randomized trials have evaluated IORT and found higher rates of local recurrence as compared to WBI. Low-energy IORT delivers 25-30% of prescription at 1 cm, different from other PBI techniques while electron IORT allows for modulation of energy/depth. Currently, ASTRO PBI guidelines do not recommend low-energy IORT off protocol and electron IORT only for suitable risk patients, while ABS guidelines do not recommend IORT off trial. Finally, newer PBI techniques include non-invasive image-guided breast brachytherapy and permanent seed implants. As with all PBI techniques, use of guidelines for the application of PBI is encouraged for patient selection and the application of well-established dosimetric criteria for target coverage and normal tissue tolerances. Partial Breast TechniquesTechniqueRandomized TrialsDose/Target VolumesDurationInterstitial BrachytherapyNational Institute of Oncology (Hungary);GEC-ESTRO;NSABP B-39/RTOG 041336.4 Gy/7 fx BID;32 Gy/8 fx BID, 30.3 Gy/7 fx BID, 50 Gy PDR; 34 Gy/10 fx BID15-20 mm expansion (limit skin, chest wall);20 mm minimum (sum of pathologic margin + radiation margin) CTV; Cavity + 15 mm (5 mm from skin, posterior breast)4-5 treatment days;4-5 treatment days; 5 treatment daysApplicator Based BrachytherapyNSABP B-39/RTOG 041334 Gy/10 fx BID10 mm from surface/device (5 mm from skin and posterior breast)5 treatment days3D-CRTNSABP B-39/RTOG 0413; RAPID38.5 Gy/10 fx BID; 38.5 Gy/10 fx BID15 mm CTV (5 mm from skin and posterior breast), 10 mm PTV, PTV-EVAL (5 mm from skin, posterior breast); 10 mm CTV inside breast, 10 mm PTV5 treatment days; 5 treatment daysIMRTUniversity of Florence; IMPORT LOW30 Gy/5 fx QOD; 40 Gy/15 fx10 mm CTV (3 mm from skin), 10 mm PTV ( 4 mm into lung, 3 mm from skin); 15 mm CTV (5 mm from skin, pec fascia)/10 mm PTV (5 mm from skin)5 treatment days over 2 weeks; 3 weeks (15 treatments) Conclusions: Partial breast irradiation represents a standard of care strategy for appropriately selected patients. Citation Format: Vicini F. Techniques and technical considerations [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr ES4-3.