Nicolle Dunkerley, Frederick R Bartlett, Anna M Kirby, Philip M Evans, Ellen M Donovan

The purpose of the work was to estimate the dose received by the heart throughout a course of breath holding breast radiotherapy. 113 cone beam CT (CBCT) scans were acquired for 20 patients treated within the HeartSpare 1A study in which both an Active Breathing Control (ABC) device and a voluntary breath hold method (VBH) were used. Predicted mean heart doses were obtained from treatment plans. CBCT scans were imported into a treatment planning system, heart outlines defined, images registered to the CT planning scan and mean heart dose recorded. Two observers outlined two cases three times each to assess inter- and intra-observer variation. There were no statistically significant differences between ABC and VBH heart dose data from CT planning scans, or in the CBCT based estimates of heart dose , and no effect from the order of the breath hold method.Variation in mean heart dose per fraction over the 3 imaged fractions was < 6 cGy without set up correction, decreasing to 3.3 cGy with set-up correction. If scaled to 15 fractions, all difference between predicted and estimated mean heart doses were <0.5Gy and in 80% of cases were <0.25Gy. Variation in mean heart dose was at an acceptable level over the duration of breath-holding radiotherapy and was well predicted by the planning system. Mean heart dose was not adversely affected by fraction to fraction variations throughout a course of heart sparing radiotherapy using two well-established breath-holding methods.