ESTRO 2025 - Abstract Book

S440

Clinical - Breast

ESTRO 2025

designed to be applicable to new treatment techniques, such as VMAT, to prevent increased radiation exposure to contralateral organs and reduce the risk of long-term radiation-induced side effects. It is noted that OAR constraints are not safety limits, and systematic prospective follow up to detect normal tissue toxicities is recommended. Keywords: Organs at Risk Dose Limits, Guidelines

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Digital Poster Adaptive Repeat Quad shot RT for Uncontrolled Symptomatic Fungating or Skin Infiltrating Breast Tumors in patients with Metastatic Breast Cancer Whoon Jong Kil 1,2 , Eugene Muchnik 3 , Ryan Collins 4 , David Cousins 1 1 Radiation Oncology, UPMC Hillman Cancer Center, Williamsport, USA. 2 Radiation Oncology, University of Pittsburgh School of Medicine, Pittsburgh, USA. 3 Medical Oncology, UPMC Hillman Cancer Center, Williamsport, USA. 4 Pathology, UPMC Williamsport, Williamsport, USA Purpose/Objective: To report clinical response from adaptive repeat quad shot radiotherapy (QS) for uncontrolled symptomatic fungating or skin infiltrating breast/chest wall (CW) tumor and regional lymph nodes (R-LN) without interrupting systemic therapy (ST) in patients with metastatic breast cancer (mBC). Material/Methods: We reviewed 17 cases of QS to breast/CW ± R-LN in patients with mBC (11 de novo, 6 metachronous; 2 with bone only, 15 with visceral metastasis; 5 with ≤ 5, 12 with > 5 metastasis) in our institute. Patients median age was 67 years (range, 38-98). Histology of breast/metastatic lesion was an invasive ductal carcinoma with hormone receptor positive/human epidermal growth factor recepter-2 negative (HR+/HER2-, n=12), HR+/HER2+ (n=4), or triple negative (n=1). Before QS, 1 st , 2 nd , and ≥ 3 rd line of ST was given in 4, 5, and 8 cases, respectively. Presenting symptoms (multiple) from fungating/skin infiltrating tumor include pain (n=16), bleeding (n=9), ulceration (n=7), infection (n=7), malodorous discharge (n=6), and arm/neck edema (n=5). Planning target volume includes gross tumor (GTV) and area at risk for microscopic disease + 0.5-1.0 cm margin. Re-evaluation and new CT-simulation for creating adaptive repeat QS were performed at 3 weeks after 1 st QS (QS1). All patients received total QS3. Results: QS1 was delivered to breast/CW (n=7), R-LN (n=1), or breast/CW + R-LN (n=9). All patients reported noticeably less pain, bleeding, and discharge within 1 week after QS1. Other symptoms (ulceration, infection, malodor, and edema) were at least partly resolved within 2 weeks after QS1. Adaptive repeat QS was scheduled 3-5 weeks apart from previous QS, and between ST cycles to avoid delay or interrupting ST. Adaptive repeat QS resulted in 82% complete symptoms resolution (n=14) and 18% near complete symptoms resolution (n=3). Compared to QS1, GTVs were decreased by 30% and 80% at QS2 and QS3 (average 657-, 460, and 129 cc, respectively, p<0.05). At median follow up of 9 months (range, 3-19) after QS1, in-field tumor control was 88% (6 partial- and 9 complete response). Two patients (12%) developed in-field recurrence at 3- and 7-months after QS1, respectively. Two grade 1 and no grade 2 or higher dermatitis was reported. Conclusion: Without delay or interrupting ST, adaptive repeat QS successfully delivered high-dose radiation to uncontrolled symptomatic breast/CW ± R-LN resulting in rapid symptoms relief (100%) and high in-field tumor control (88%). Our findings suggest adaptive repeat QS to Breast/CW ± R-LN during ST may improve local-regional tumor control in select patient with mBC.

Keywords: Fungating breast tumor, Adaptive Repeat Quad shot