Stereotactic APBI for Early-Stage Breast Cancer: Acute Toxicity Outcomes of a Prospective Trial
PO-1226
Abstract
Stereotactic APBI for Early-Stage Breast Cancer: Acute Toxicity Outcomes of a Prospective Trial
Authors: 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.
Results
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.
Conclusion
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.