ESTRO 2024 - Abstract Book

S507

Clinical - Breast

ESTRO 2024

Sanjoy Chatterjee 1 , Santam Chakraborty 1 , Nikhil Bathija 1 , Anurupa Mahata 2 , Samar Mandal 2 , Selvamani B 3 , Rajesh Balakrishnan 3 , Patricia Solomon 3 , Punita Lal 4 , Shagun Misra 4 , HYPORT Adjuvant Trialists Group 1 1 Tata Medical Center, Radiation Oncology, Kolkata, India. 2 Tata Medical Center, Medical physics, Kolkata, India. 3 Christian Medical College, Radiation Oncology, Vellore, India. 4 SGPGI, Radiation Oncology, Lucknow, India

Purpose/Objective:

HYPORT Adjuvant is a phase III randomized trial comparing 1 versus 3 weeks of adjuvant breast RT [1]. In this study we report the adherence to the protocol specified radiation dose constraints for the heart and lung. Furthermore we use the individual dose volume data to model the excess lifetime risk of mortality from ischemic heart disease (IHD) and compare it between the arms.

Material/Methods:

Patients recruited between March 2018 and August 2022 received adjuvant radiotherapy (Control (CONTROL) 40 Gy/15 fractions / 3 weeks versus Experimental (EXP) 26 Gy/5 fractions/ 1 week) [1]. Plans had to meet set mandatory constraints for lung and heart doses [2]. Individual dose volume histograms (DVH) were extracted and analyzed to determine compliance to mandatory and optimal constraints [2]. Use of cardiac sparing radiotherapy techniques like deep inspiration breath hold (DIBH) was recommended [3]. Equivalent Dose at 2 Gy (EQD2) assuming an alpha beta ratio of 3 were calculated for each volume bin from the absolute doses. Risk of death due to IHD in Indian females was obtained from the Global Burden of Disease study. [4]. From this we calculated the cumulative mortality for each five year age interval from 20 - 80 years. This was reversed to obtain the lifetime risk of mortality per age group due to IHD. The excess lifetime risk of ischemic heart disease was obtained by multiplying the baseline risk with the excess absolute risk per Gy mean heart dose (8.4% per Gy MHD EQD2) [5]. As the two dose schedules were different we used the EQD2 of MHD instead of the physical doses. Excess absolute lifetime mortality was calculated for each patient, summarized across age groups and compared between the two arms. For each patient we also calculated the upper estimate of increased mortality by multiplying the upper 95% confidence intervals of the lifetime risk with the upper 95% confidence interval of the estimate of excess risk of major cardiac events per Gy of MHD (15.9% per Gy MHD EQD2) [5].

Results:

Out of 1075 patients, 546 had left sided breast cancer. Three patients received bilateral breast radiotherapy. Median age was 52 (IQR 45-60) years. Table 1 shows the percentages of structures where the mandatory and optimal dose constraints were met. Lung doses were within constraints for all patients. A total of 13 patients (2.3%) failed to meet one or more mandatory dose constraints. Grand mean heart dose (MHD) for left sided patients was 78 cGy (SD 27) versus 119 cGy (SD 44 cGy) for the EXP and CTR arms respectively. Grand mean EQD2 MHD were 0.52 cGy (SD 0.28) versus 0.76 cGy (SD 0.32) respectively. Among patients receiving IMN RT (n=15, Left sided n=8), mean heart dose was 532 cGy (585 cGy versus 500 cGy respectively). Grand mean dose to LAD for left sided cancers was 384 cGy (308 versus 461 in Arm A versus B respectively. Mean dose to LAD for left sided patients with IMN RT was 876 Versus 1035 cGy.