P260] Evaluation of cardiac dose after breast irradiation

Abstract

Purpose The importance of minimizing heart dose during breast irradiation has attracted increased interest in recent years stating that major coronary events are avoided if threshold of 3 Gy is kept for the mean heart dose and are increased linearly with the mean dose to heart by 7.4% per Gy and 4% increase in risk of heart disease. Current constraints for long term cardiac morbidity state that the volume of heart receiving more than 40 Gy needs to be kept lower than 5% ( V 40 5 % ) and the volume receiving more than 20 Gy be kept under 10% ( V 20 10 % ) . Treatment planning techniques used to reduce dose to heart during irradiation are discussed. Methods A sample of 100 patients from our centre (50% right breast and 50% left breast), were treated with 6MV 3D-conformal radiotherapy planning with two tangential fields. Angles were chosen to avoid OAR (lungs and heart) from receiving unnecessary dose and not compromising target coverage or increasing contra-lateral breast dose. After evaluating the OAR doses, a simple planning technique was used by blocking heart with the use of MLCs (MbT) on the medial tangential field. It was applied for patients with left sided breast cancer who had mean heart dose ranging from 4.2–8 Gy. Results For left sided breast patients the mean heart dose resulted in an average value of 3.54 Gy. 60% of the left sided breast patients in our sample had a mean heart dose greater than 3 Gy. 70% of the left breast patients were large sized. 32% of the left sided breast sample patients violated the V 40 constraint and 10% of them violated the V 20 . After applying the MbT, dose to the heart was reduced with a max reduce on MHD of 3 Gy and the criteria of V 20 and V 40 were achieved. Conclusion The necessity of minimising irradiated heart amount especially for young left sided-large breast patients and planning techniques to achieve this, were discussed in detail above. Although the ideal technique is the Active Breathing Coordinator, providing non-invasive, internal immobilization of anatomies affected by respiratory motion, considering the economic situation of our country, the alternative Mbt is suggested instead.