Main Session
Sep 28
PQA 04 - Breast Cancer, Patient Reported Outcomes/QoL/Survivorship, Functional Radiation Medicine, Hematologic Malignancies, Palliative Care, and International/Global Oncology

2848 - Comparison of ASTRO APBI Guidelines (2009, 2017, 2024) for Risk Stratification of Ipsilateral Breast Tumor Recurrence in HDR Brachytherapy-Treated Patients

03:00pm - 04:00pm ET
Poster Hall - Exhibit Hall A
Screen: 5
POSTER

Presenter(s)

John Wilson V, BS - University of South Florida, Tampa, FL

J. Redding1, J. D. Wilson V2, M. N. Mills3, G. Luckey1, R. H. Nanda Jr4, K. A. Ahmed4, L. Stout5, P. Blumencranz5, and R. Diaz3; 1University of South Florida, Morsani College of Medicine, Tampa, FL, 2Morsani College of Medicine, University of South Florida, Tampa, FL, 3Department of Radiation Oncology, H. Lee Moffitt Cancer Center and Research Institute, Tampa, FL, 4H. Lee Moffitt Cancer Center and Research Institute, Department of Radiation Oncology, Tampa, FL, 5Morton Plant Hospital, Clearwater, FL

Purpose/Objective(s):

The ASTRO Accelerated Partial Breast Irradiation (APBI) guidelines have evolved over time (2009, 2017, and 2024). We sought to determine which guideline version best stratifies risk of ipsilateral breast tumor recurrence (IBTR) in a large cohort of patients with early-stage invasive breast cancer treated with APBI using high-dose-rate (HDR) multicatheter brachytherapy.

Materials/Methods:

Retrospective analysis of 772 consecutive patients with AJCC stage I-II invasive breast cancer treated from 2010–2022 at a single institution. All patients underwent lumpectomy with sentinel lymph node biopsy followed by HDR brachytherapy APBI (34 Gy in 10 twice-daily fractions). Patients were classified according to each ASTRO guideline version: Suitable/Cautionary/Unsuitable (2009 and 2017); Recommended/Conditionally Recommended/Not Recommended (2024). For each guideline version, low-risk patients (Suitable in 2009/2017; Recommended in 2024) were compared with all other categories combined. Primary endpoint was IBTR. Secondary endpoints included regional nodal recurrence (RNR), and distant metastasis (DM). Outcomes were analyzed using Kaplan-Meier estimates with log-rank testing.

Results:

Median follow-up was 8 years (range 2–14). Risk-group distributions shifted as follows: in 2009, 44% were Suitable, 54% Cautionary, and 1% Unsuitable; in 2017, 54% were Suitable, 46% Cautionary, and 1% Unsuitable; and in 2024, 69% were Recommended, 16% Conditionally Recommended, 14% Conditionally Not Recommended, and 1% Not Recommended. Overall crude IBTR rate was 7.8% (60 events). IBTR stratification by guideline is summarized below:

Regional nodal recurrence and distant metastases showed significant 10-year differences only in the 2024 Guidelines: Recommended 0.3% and 0.7% versus Not Recommended 3.2% and 3.1%, respectively, p=0.001 and p=0.017.

Conclusion:

None of the three ASTRO guidelines demonstrated statistically significant stratification of IBTR risk in this database (all log-rank p>0.76). Successive ASTRO guidelines progressively reclassified more patients into lower-risk categories (Suitable/Recommended increasing from 44% in 2009 to 69% in 2024) without worsening patient outcomes. Importantly, only the 2024 guideline achieved statistically significant separation for regional nodal recurrence and distant metastasis at 10 years.

These findings indicate that guideline evolution has successfully expanded the population considered appropriate for APBI and simplified physician decision making without loss of risk discrimination for ipsilateral breast tumor recurrence, while adding meaningful discrimination for clinically important regional and distant events.
Guideline
Suitable/Recommended % (5-, 10-yr IBTR)
Not Suitable/Recommended % (5-, 10-yr IBTR)
Log-rank p
2009

 44.4% (2.0%, 11.2%)

 55.6% (3.4%, 10.8%)

 0.812
2017

 53.8% (2.7%, 11.2%)

 46.2% (2.8%, 10.7%)

 0.864
2024

 68.9% (1.9%, 11.8%)

 31.1% (4.6%, 9.4%)

 0.76