Electronic brachytherapy as adjuvant therapy for early stage breast cancer: a retrospective analysis

William C Dooley¹, James C Wurzer², Mohamed Megahy³, Gary Schreiber⁴, Tapan Roy⁵, Gary Proulx⁶, Susan Laduzinsky⁷, Steven Lane⁸, James Dalzell⁹, Kambiz Dowlatshahi¹⁰, Dwelvin Simmons¹¹, John P Thropay¹², Harish Ahuja¹³, Peter Beitsch¹⁴, Randall W Holt¹⁵, Charles A Lee^16
1Oklahoma University Health Sciences Center, Oklahoma City, OK, USA; ²Atlanticare, Egg Harbor Township, NJ, USA; ³Maryville Oncology, Maryville, IL, USA; ⁴Swedish Covenant Hospital, Chicago, IL, USA; ⁵Cape Girardeau Cancer Center, Cape Girardeau, MO, USA; ⁶Exeter Hospital, Exeter, NH, USA; ⁷St. Elizabeth's Medical Center, Swansea, IL, USA; ⁸Brockton Hospital, Brockton, MA, USA; ⁹Nazha Cancer Center, Northfield, NJ, USA; ¹⁰Rush University Medical Center, Chicago, IL, USA; ¹¹Florida Radiation Oncology Group, Jacksonville, FL, USA; ¹²Beverly Oncology and Imaging Center, Montebello, CA, USA; ¹³Aspirus Cancer Center, Wausau, WI, USA; ¹⁴Dallas Surgical Group, Dallas, TX, USA; ¹⁵Pacific Crest Medical Physics, Chico, CA, USA; ¹⁶Gulf Coast Cancer Treatment Center, Panama City, FL, USA

Purpose: This multicenter, retrospective study evaluated treatment and clinical outcomes of patients with early stage breast cancer who received adjuvant high-dose rate (HDR) electronic brachytherapy (EBT) treatment post-lumpectomy using the Axxent^® EBT system. Dosimetric data from the EBT treatment plans were compared with those based on iridium-192 HDR brachytherapy.
Material and methods: Medical records of 63 patients with early stage breast cancer (Tis, T1a, T1b, T1c, and T2) who were treated post-lumpectomy with EBT alone or in combination with external beam radiation therapy were reviewed. The prescribed EBT dose was 34 Gy (10 fractions over 5 days, 3.4 Gy each) to 1 cm from the balloon surface. Dosimetry data from 12 patients were compared with these of treatment plans using an iridium-192 source prepared for the same 12 patients.
Results: The majority of patients (90.5%) were older than 50 years and had one or more risk factors for breast cancer (80.6%). Tumor sizes were 0.1 cm to 3.5 cm (mean 1.3 cm). Median follow-up was 7 months (1 to 18 months) post-EBT. Balloon applicators were implanted 0 to 85 days (mean 13.4 days) post-lumpectomy/re-excision. The most common adverse events were erythema, rash dermatitis, and pain or breast tenderness. No recurrences were reported. Dosimetric analyses demonstrated comparable target coverage, increased high-dose regions, and a significantly reduced dose to the ipsilateral breast and lungs as well as the heart with EBT as compared with the iridium-192 treatment plans.
Conclusion: This retrospective, multicenter study showed that postsurgical adjuvant radiation therapy for early stage breast cancer can be administered using the EBT system with similar toxicity outcomes to those reported with iridium-192 brachytherapy. EBT offers a convenient, portable, nonisotope alternative to HDR brachytherapy using iridium-192.

Keywords: electronic brachytherapy, breast cancer, radiation therapy