3011 - Cardiopulmonary Toxicity Risk Following Ultrahypofractionated Breast Radiotherapy Regimens

03:00pm - 04:00pm PT

Hall F

Screen: 13

POSTER

Presenter(s)

Matthew Case, MD - Emory University, Atlanta, GA

K. A. Ward, M. J. Case, M. Thomas, R. Bhatia, S. Hanasoge, H. G. Gatcombe, J. Y. Lin, M. Torres, and S. W. Dutta; Department of Radiation Oncology, Emory University, Atlanta, GA

Purpose/Objective(s):

Ultrahypofractionated external-beam regimens for adjuvant breast cancer radiotherapy have demonstrated favorable breast and chest wall toxicity profiles in multiple randomized trials. However, potential cardiopulmonary sequelae remain less clearly defined, particularly for five-fraction schedules. We aimed to assess heart and lung dose–volume parameters and correlate these with clinical cardiopulmonary toxicity.

Materials/Methods:

We retrospectively identified breast cancer patients treated at our institution (2020–2024) with five-fraction adjuvant radiation to the whole breast (WBRT, 3D: 26 Gy at 5.2 Gy per fraction daily or 28.5 Gy at 5.7 Gy per fraction weekly) or partial breast (APBI, IMRT: 30 Gy at 6 Gy per fraction every other day); breath hold and/or prone positioning was used at the discretion of the treating physician. Clinical characteristics, dosimetry, and acute/subacute cardiopulmonary toxicities (per CTCAE v5.0) were recorded. Primary dosimetric endpoints were adapted from UK FAST-FORWARD and APBI-IMRT-FLORENCE constraints for ipsilateral lung (V8Gy <15%, V10Gy <20%) and heart (V1.5Gy <30%, V3Gy <10%, V7Gy <5%). We used logistic regression and ROC curve analysis to evaluate ipsilateral lung V20Gy as a predictor of pneumonitis.

Results:

A total of 342 treatment plans were analyzed (265 WBRT, 77 APBI). While ipsilateral lung V8Gy and heart doses (V1.5Gy, V3Gy, V7Gy) were similar between groups (p>0.05, Table 1), APBI cases had significantly lower ipsilateral lung V10Gy and V20Gy values (p<0.001). Among 191 patients (133 WBRT, 58 APBI) with sufficient follow up (median 16 months), grade 2 pneumonitis occurred in 5% [7/133] of WBRT and 2% [1/58] of APBI patients (p>0.05), with no grade =3 events, corticosteroids prescribed, or cardiac toxicities observed. Logistic regression indicated that each 1% increase in ipsilateral lung V20Gy raised pneumonitis risk (OR=1.18, p=0.031). ROC analysis demonstrated an AUC of 0.733 (SE=0.073, 95% CI: 0.590–0.876, p=0.001) with a 7.5% cutoff yielding 75% sensitivity and 66% specificity, identifying patients at increased risk.

Conclusion:

Radiation pneumonitis risk from five-fraction whole- and partial-breast regimens is <5% for mild-moderate and <1% for severe symptoms. Our findings support targeting an ipsilateral lung V20Gy below 7.5% as a planning goal for both WBRT and APBI. When this additional goal is achieved, differences in cardiopulmonary toxicity between techniques are minimal, allowing patient counseling to focus primarily on breast tissue effects.

Abstract 3011 - Table 1

OAR Constraint	WBRT-3D (N = 265, mean ± SD)	APBI-IMRT (N = 77, mean ± SD)	p-value
Heart V1.5Gy (%)	0.7 ± 1.2	1.2 ± 2.4	>0.05
Heart V3Gy (%)	0.8 ± 1.7	1.2 ± 2.4	>0.05
Heart V7Gy (%)	0.8 ± 1.7	1.2 ± 2.3	>0.05
Ipsilateral Lung V8Gy (%)	11.5 ± 5.3	11.2 ± 7.5	>0.05
Ipsilateral Lung V10Gy (%)	10.4 ± 4.6	7.5 ± 5.6	<0.001
Ipsilateral Lung V20Gy (%)	6.7 ± 3.5	1.3 ± 1.6	<0.001