Impact of the ASTRO 2024 Guideline on Partial Breast Irradiation Eligibility in Breast Cancer Patients (KROG 24-01).

Purpose: The American Society for Radiation Oncology (ASTRO) has recently published new guidelines for the eligibility for partial breast irradiation (PBI). This study aims to evaluate the eligibility rates of PBI according to the ASTRO 2017 and 2024 guidelines.

Methods and materials: Patients diagnosed with pTis-T2N0 breast cancer in 2019 from 3 tertiary medical centers were accrued. All patients received standard treatment consisting of breast-conserving surgery followed by radiation therapy. Subsequently, patients were classified according to the ASTRO 2017 and 2024 guidelines.

Results: For invasive breast cancer, 785 patients were included, among whom 192 received PBI. Classification according to the ASTRO guidelines showed a substantial increase in the proportion of patients eligible for PBI: 19.2% were classified as "suitable" under the ASTRO 2017 guidelines, while 42.4% were classified as "strongly recommended" under the ASTRO 2024 guidelines. Among 286 patients diagnosed with ductal carcinoma in situ (DCIS), 50 (17.5%) received PBI. The proportion of PBI-eligible patients nearly doubled, from 27.3% under the ASTRO 2017 guidelines to 51.7% under the ASTRO 2024 guidelines. The expanded age criterion from 50 to 40 years and the removal of the clear resection margin requirement were key factors contributing to this substantial increase in both invasive breast cancer and DCIS.

Conclusions: The eligibility for PBI has dramatically increased for both invasive breast cancer and DCIS under the ASTRO 2024 guidelines. These findings suggest a potential for increased use of PBI, offering individualized and optimized treatment options in early breast cancer.