Copenhagen, Denmark

ESTRO 2022

Session Item

Poster (digital)
Stereotactic APBI for Early-Stage Breast Cancer: Acute Toxicity Outcomes of a Prospective Trial
Jonathan Cantalino, USA


Stereotactic APBI for Early-Stage Breast Cancer: Acute Toxicity Outcomes of a Prospective Trial

Jonathan Cantalino1, Brian Collins1, Malika Danner1, Sonali Rudra1, Simeng Suy1, Sean Collins1, Monica Pernia Marin2, Michael Good3, Deborah Markiewicz3, Rachelle Lanciano3, Olusola Obayomi-Davies4

1Medstar Georgetown University Hospital, Department of Radiation Medicine, Washington, DC, USA; 2The George Washington University Hospital, Geriatric and Palliative Care Division, Washington, DC, USA; 3Philadelphia Cyberknife, Crozer Keystone Health Care Center, Department of Radiation Oncology, Havertown, PA, USA; 4Wellstar Medical Group, Department of Radiation Oncology, Marietta, GA, USA

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Purpose or Objective

Outcomes following adjuvant accelerated partial breast irradiation (APBI) in select women with early-stage breast cancer are comparable to whole breast irradiation. Robotic stereotactic accelerated partial breast irradiation (RSAPBI) with fiducial tracking is an attractive treatment option, but limited data are available regarding the acute radiation toxicity of this approach. We report our mature acute radiation toxicity outcomes for a prospective multi-institutional trial treating select women with RSAPBI.

Material and Methods

Post-menopausal women with DCIS and Stage IA breast cancer were treated over a five-year period extending from November 2015 to November 2020 and were followed for a minimum of one year. Treatments were delivered with a robotic radiosurgery system. Four gold fiducials were implanted around the lumpectomy cavity prior to the start of treatment for tumor bed delineation and target tracking. The CTV was defined as the lumpectomy cavity with a uniform 5-15 mm expansion confined to the breast tissue and the PTV was defined as the CTV with a 0-5 mm uniform expansion. The PTV was prescribed 30 Gy in 5 fractions. The maximum skin point dose allowed was < 36 Gy (skin = CT surface minus 2 mm).  Breast examination was completed at 1 month, 3 months, and 6 months. At each follow-up a toxicity case report form was completed.


Eighty-one patients (median age 68 years) with ER+/PR+ tumors were treated over a median 9 days (range, 5-15). Sixty-eight women had invasive ductal carcinoma (84%) and thirteen had DCIS (16%). The median treated PTV was 108 cm3 (IQR 66-156) and the median prescription isodose line was 81% (IQR 79-83). The median CTV expansion was 10 mm (range 5-10) and the median PTV expansion was 3 mm (range 0-5). Acute grade 1 radiation dermatitis was seen in 12 of 78 evaluable patients at 1 or 3 months (15.4%). On multivariable logistic regression, PTV (OR 1.01, 95% CI 1.001-1.02, p=0.024) and skin dose > 32 Gy (OR 7.4, 95% CI 1.40-40.3, p=0.021) were found to be significantly associated with acute radiation dermatitis. No other acute radiation toxicities were observed.


Early results suggest that RSAPBI with fiducial tracking is a well-tolerated technique for the adjuvant treatment of early-stage breast cancer patients. Acute radiation dermatitis may be mitigated by further decreasing lumpectomy cavity margins and by limiting the skin Dmax to < 32 Gy.