ESTRO 2025 - Abstract Book

S620

Clinical - Breast

ESTRO 2025

Purpose/Objective: Randomized controlled clinical trials and meta-analyses have demonstrated that adjuvant whole breast irradiation (WBI) significantly reduces the risk of in-breast tumor recurrence in patients with ductal carcinoma in situ (DCIS) treated with lumpectomy but does not improve overall survival. In addition, prospective studies have identified patients with favorable-risk DCIS that have low annual recurrence risk of 1-1.2%/year, indicating that adjuvant WBI may not be necessary in these patients. Based on these studies, the 2017 American Society of Radiation Oncology (ASTRO) consensus guidelines on accelerated partial breast irradiation (APBI) indicated that favorable-risk patients were suitable candidates for APBI. We hypothesize that while the utilization of APBI or favorable-risk DCIS may have increased since 2017, the rates of APBI use in these patients remains low. Material/Methods: Using the National Cancer Database (NCDB), we identified patients that had undergone margin-negative breast conserving surgery and adjuvant radiation therapy (RT) for DCIS with the following favorable-risk criteria: grade 1-2, size≤2.5 cm, and age≥50. Margin width was not available. We also restricted our analysis to patients with ER+ disease. We identified patients that received RT and no RT. In the RT patient group, we further classified them as having received WBI or APBI. We report trends in the use of RT and APBI vs. WBI (before 2017 and after 2017) using the chi-square test. Results: There were 86,803 that met all eligibility for favorable-risk DCIS and had radiation dose and fractionation data available to accurately characterize patients into RT omission, WBI, and APBI groups. In the entire cohort, 35,592 (41.0%) received no RT, 47,718 (55.0%) received WBI, and 3,493 (4.0%) received APBI. Omission of RT increased marginally in patients treated ≤2017 versus those treated after 2017: 40.4% vs. 41.9%, p = 0.01. When focusing only on the 51,211 patients that received radiation, 93.2% received Whole Breast Irradiation (WBI) and 6.8% received Accelerated Partial Breast Irradiation (APBI). The proportion of patients that received APBI increased significantly from 4.3% (≤2017) to 10.3% (after 2017), p < 0.0001. Conclusion: Overall, we found a small decrease in utilization of RT over time for patients with favorable-risk DCIS. Approximately 59.0% of patients received adjuvant RT for favorable-risk disease. When RT was used, the majority of patients received WBI. Utilization of APBI for favorable-risk DCIS remains quite low at only 10% of that receive adjuvant RT. Taken together, our study suggests that over-treatment of patients with favorable-risk DCIS persists in the NCDB patient population.

Keywords: dcis, apbi, low-risk

4330

Digital Poster Evaluation of Patterns of Recurrences in Carcinoma Breast Patients: Are we treating the right volumes or does the tumor biology play the role ?? Prabha Verma 1 , Rohini Khurana 2 , Dr Avinash Poojari 3 , Madhup Rastogi 2 , Rahat Hadi 2 , Shantanu Sapru 2 , Ajeet K Gandhi 2 , S P Mishra 2 , Anoop Srivastava 2 , Avinav Bharati 2 , Farhana K 2 1 Radiation Oncology, UP University of Medical Sciences, Saifai, Etawah, India. 2 Radiation Oncology, DR Ram Manohar Lohia Institute of Medical Sciences, Lucknow, India. 3 Radiation Oncology, JIPMER, Puducherry, India Purpose/Objective: To evaluate the patterns of loco-regional recurrences in women with breast cancer treated with curative intent surgery with post-operative highly conformal radiation therapy (RT). Secondary objective was to assess whether locoregional recurrences are mainly related to clinical target volume (CTV) coverage or to tumor biology.