1083 - Multi-Institutional Phase II Trial Using Dose Escalated Five Fraction Stereotactic Partial Breast Irradiation (S-PBI) with a Cobalt Stereotactic Unit for Early-stage Breast Cancer
Presenter(s)
A. S. Rahimi1, D. W. N. Kim2, D. D. M. Parsons1, M. Leitch3, E. M. Nichols4, T. D. Chiu5, X. Gu6, W. Lu7, S. J. Becker4, P. G. Alluri1, C. R. Nwachukwu8, C. Ahn9, Y. Zhang8, M. Stein1, V. Puliyadi1, D. Farr3, R. Wooldridge3, S. Bahrami1, S. Stojadinovic1, and R. D. Timmerman1; 1Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX, 2Vanderbilt University Medical Center, Nashville, TN, 3Department of Surgery, University of Texas Southwestern Medical Center, Dallas, TX, 4University of Maryland School of Medicine, Baltimore, MD, 5University of Texas Southwestern Medical Center, Dallas, TX, 6Stanford University Department of Radiation Oncology, Palo Alto, CA, 7Medical Artificial Intelligence and Automation (MAIA) Lab, Department of Radiation Oncology, UT Southwestern Medical Center, Dallas, TX, 8University of Texas Southwestern Department of Radiation Oncology, Dallas, TX, 9Kidney Cancer Program, Simmons Comprehensive Cancer Center, University of Texas Southwestern Medical Center, Dallas, TX
Purpose/Objective(s):
We hypothesize that using dose escalated S-PBI (40Gy/5 fractions) and smaller PTV margins (3mm), than 3D-CRT or IMRT techniques, we will have high 3 year (yr) patient global cosmesis satisfaction and low adverse cosmesis using a cobalt stereotactic unit. We report on a multi-institutional phase II study of dose escalated 5 fraction (S-PBI) for early-stage breast cancer after partial mastectomy using a cobalt stereotactic radiation system.Materials/Methods:
Patient eligibility included DCIS or invasive epithelial histologies, AJCC clinical stage 0, I, or II, tumor size < 3 cm and negative margins. Prior safety of Phase I dose escalation has been reported. 40 Gy dose delivered in 5 fractions to the CTV, and minimum 30 Gy dose in 5 fractions to the PTV. CTV margin was 1 cm and PTV margin 3 mm. For PTV cavities > 100 cc, dose reduced to 35 Gy in 5 fractions to the CTV and 30 Gy in 5 fractions to the PTV. Primary endpoint is to determine 3 yr patient global cosmesis score (4 point scale excellent, good, fair or poor) and adverse cosmesis using dose escalated approach with smaller PTV margins than conventional methods. Patients and physicians completed baseline and follow-up (f/u) cosmesis outcome questionnaires. Treatment related toxicity graded with NCI CTCAE v5.0 and RTOG/EORTC late radiation scale.Results:
From 3/2019-10/2021, 74 patients were treated; 38 received 40 Gy and 36 received 35 Gy. Median f/u was 46 months (mo), range 12-60 mo. Median age was 63 yrs (r 43-77). Histology included 28 DCIS and 46 invasive carcinomas. 45/46 invasive tumors were ER+. 60/74 (81.0%) patients received endocrine therapy and 7/74 (9.5%) patients received chemotherapy. There were 224 acute Grade (gr) 1 toxicities and 15 gr 2 toxicities, with no gr 3 or higher acute toxicities (< 90 days). Common gr 2 toxicities were radiation dermatitis (6), breast pain (4),blister (2), skin infection (1), nipple discharge (1) and fatigue (1). In the late period there were 80 gr 1 late toxicities, 2 gr 2 late toxicities and no gr 3 or higher late toxicities. Gr 2 toxicities included pain (2). 3 patients developed gr 1 asymptomatic nonpalpable fat necrosis. The most common gr 1 late toxicities were breast pain (23), hyperpigmentation (11) and fatigue (5). Physicians scored cosmesis excellent or good 73/76 (96.0%), 59/61 (96.7%), 61/62 (98.3%), 52/54 (96.3%), 29/30 (96.7%) respectively at baseline, 12 mo, 24 mo, 36 mo, and 48 mo post S-PBI while patients scored the same periods 66/75 (88.0%), 54/60 (90.0%), 57/64 (89.0%), 55/61 (90.1%), 30/33(90.1%). There have been no local or regional recurrences but 1 distant recurrence.Conclusion:
Our study demonstrates that with judicious reduction of PTV margin afforded with this technology, excellent to good long term cosmetic outcomes and tumor control can prevail in the setting of dose escalated therapy. ClinicalTrials.gov identifier: NCT03581136.