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Purpose We investigated the proportions of patients eligible for accelerated partial breast irradiation (APBI) among those with pT1- 2N0 breast cancer, based on the criteria set by the American Society for Radiation Oncology (ASTRO), the Groupe Européen de Curiethérapie and the European Society for Radiotherapy and Oncology (GEC-ESTRO), the American Brachytherapy Society (ABS), and the American Society of Breast Surgeons (ASBS). Additionally, we analyzed the rate of APBI utilization among eligible patients. Materials and Methods Patients diagnosed with pT1-2N0 breast cancer in 2019 were accrued in four tertiary medical centers in Korea. All patients had undergone breast conserving surgery followed by radiotherapy, either whole breast irradiation or APBI. To determine which guideline best predicts the use of APBI in Korea, the F1 score and Matthews correlation coefficient (MCC) were determined for each guideline. Results A total of 1,251 patients were analyzed, of whom 196 (15.7%) underwent APBI. The percentages of eligible patients identified by the ASTRO, GEC-ESTRO, ABS, and ASBS criteria were 13.7%, 21.0%, 50.5%, and 63.5%, respectively. APBI was used to treat 54.4%, 37.2%, 27.1%, and 23.7% of patients eligible by the ASTRO, GEC-ESTRO, ABS, and ASBS criteria, respectively. The ASTRO guideline exhibited the highest F1 score (0.76) and MCC (0.67), thus showing the best prediction of APBI utilization in Korea. Conclusion The proportion of Korean breast cancer patients who are candidates for APBI is substantial. The actual rate of APBI utilization among eligible patients may suggest there is a room for risk-stratified optimization in offering radiation therapy. [ABSTRACT FROM AUTHOR]

To analyze contemporary practice patterns in breast cancer radiotherapy (RT) and to assess longitudinal changes therein over 5 years in Korea. A nationwide survey was conducted among board-certified radiation oncologists in Korea by the Division for Breast Cancer of the Korean Radiation Oncology Group in March 2022. The survey consisted of 44 questions related to six domains: hypofractionated (HypoFx) whole breast RT, accelerated partial breast RT (APBI), regional nodal irradiation (RNI), RT for ductal carcinoma in situ (DCIS), postmastectomy RT (PMRT), and tumor bed boost. In total, 70 radiation oncologists from 61 of 101 (60%) institutions participated in the survey. HypoFx RT was used by 62 respondents (89%), which has significantly increased from 36% in 2017. The HypoFx RT was commonly administered at 40–42.5 Gy in 15–16 fractions. APBI was used by 12 respondents (17%), which has increased from 5% in 2017. The use of RNI did not change significantly: ≥ pN2 (6%), ≥ pN1 (33%), and ≥ pN1 with pathological risk factors (61%). However, the indications for use of internal mammary lymph node (IMN) irradiation have expanded. In particular, the rates of routine treatment of IMN (11% from 6% in 2017) and treatment in cases of ≥ pN2 (27% from 14% in 2017) have doubled; however, the rate of treatment for only IMN involvement, identified on imaging, has decreased to 31% from 47% in 2017. With regard to DCIS, the use of hypoFx RT increased to 75% from 25%, and the rate of omission on of RT after breast-conserving surgery decreased to 38% from 48% in 2017. The use of hypoFx RT for PMRT also increased to 36% from 8% in 2017. The adoption of HypoFx RT after breast-conserving surgery in invasive breast cancer and DCIS has increased significantly, whereas that for PMRT has increased moderately, compared to 2017. Further studies are required to determine the optimal use of RNI. [ABSTRACT FROM AUTHOR]

Purpose: Accelerated partial breast irradiation (A-PBI) in Korean women has been considered impracticable, owing to small breast volume and lack of high-precision radiotherapy experience. We present the first experience of stereotactic-PBI (S-PBI) with CyberKnife M6 to investigate feasibility of use and early toxicities in Korean women with early breast cancers. Materials and Methods: A total of 104 breasts receiving S-PBI at our institution between September 2017 and October 2018 were reviewed. Patients were selected based on the American Society for Radiation Oncology (ASTRO), American Brachytherapy Society, American Society of Breast Surgeons, and Groupe Européen de Curiethérapie-European Society for Therapeutic Radiology and Oncology guidelines. A dose of 30 Gy in 5 fractions (NCT01162200) was used. Gold fiducials were routinely inserted near the tumor bed for tracking. Constraints regarding organs-at-risk followed the NSABP-B39/RTOG 0413 protocol. Results: Median follow-up was for 13 months. Patients were categorized as "suitable" (71.2%) or "cautionary" (28.8%) according to 2017 the ASTRO guidelines. No tracking failure of inserted gold fiducials occurred. Median planning target volume (PTV) and PTV-to-whole breast volume ratio was 73.6 mL (interquartile range, 58.8–103.9 mL) and 17.0% (13.3–19.1%), respectively. Median PTV V95%, PTV Dmax, and ipsilateral breast V50% were 97.8% (96.2–98.8%), 105.3% (104.2–106.4%), and 35.5% (28.3–39.8%), respectively. No immediate post-S-PBI toxicity ≥ grade 2 was reported, except grade 2 induration in three breasts. All patients remain disease-free to date. Conclusion: The first use of S-PBI in Korean women was feasible and safe for selected early breast cancer. Based on these results, we have initiated a prospective study (NCT03568981) to test S-PBI in whole-breast irradiation for low-risk early breast cancer. [ABSTRACT FROM AUTHOR]