ESTRO 2024 - Abstract Book

S682

Clinical - Breast

ESTRO 2024

2835

Digital Poster

Estimating the risk of acute coronary event following radiotherapy for breast cancer: A hypothesis

Sapna Nangia

Apollo Proton Cancer Centre, Radiation Oncology, Chennai, India

Purpose/Objective:

Cardiac-sparing radiotherapy is the standard of care for left-sided breast cancer, in view of the correlation of the mean heart dose (MHD) with the risk of an acute coronary event (ACE) (1). Calculation of the absolute benefit of cardiac sparing techniques helps patients, oncologists and healthcare administrators make an informed decision and understand cost-versus-benefit for allocating resources. Notwithstanding a high prevalence of cardiovascular (CV) risk factors among Indians, risk estimation for CV disease for breast cancer patients in India/South Asia is constrained by the absence of a registry for ACE; risk estimation scores QRisk3 and QRisk Lifetime for 10-yr and lifetime ACE risk respectively, though designed for the UK, allow ethnicity-specific baseline ACE risk estimation (2).

Material/Methods:

Using the QRisk-Lifetime and QRisk3 risk calculator (2), to determine the baseline risk, the increase in the absolute lifetime cardiac risk @7.4% and 10yr cardiac risk @16% per Gy of MHD, respectively, was calculated for 4 hypothetical patients, fit, obese with no comorbidities, obese-diabetic and obese-diabetic-hypertensive. These estimations were made for Indian women aged 40-70 years, at 5yr intervals, for MHD 1-10Gy. The difference between the baseline risk of ACE, BR-ACE and the estimated absolute risk of ACE , EAR-ACE was termed Radiation related increase in absolute risk of Acute Coronary Event RIAR-ACE. This was calculated for expected lifespan RIAR ACE-Life and 10 yrs, RIAR-ACE-10.

The dose thresholds at which the RIAR-ACE increased 2% & 5% were calculated. The RIAR-ACE-Life and RIAR-ACE 10 at an MHD 4Gy were also calculated.

Results:

A total of 308 risk estimations were performed, 77 for each hypothetical situation, 44 for every age. The MHD for 2% and 5% RIAR-ACE Life was similar across ages for a given hypothetical clinical situation, 2.48Gy & 6.2Gy for a fit patient, 2.4Gy & 6Gy for an obese patient, 1.42Gy & 3.56Gy for an obese-diabetic patient and 1.21 Gy & 3.02Gy for an obese-diabetic-hypertensive patient.

The threshold dose for 2% and 5% RIAR-ACE_10, however, varied by age in addition to co-morbidity status. In an obese-hypertensive diabetic patient, the threshold dose for a 2% RIAR-ACE-10 was 2.3, 1.5, 0.9 and 0.52 Gy in a 40,