The UK HeartSpare study

Recent evidence suggests that the risk of major coronary events after breast radiotherapy is linearly related to mean radiation dose received by the heart and that there is no threshold dose below which this risk is nullified. In addition, these effects are visible within the first four years after radiotherapy, much earlier than had previously been recognised. With numbers of breast cancer survivors increasing as a result of improvements in diagnosis and treatment, minimising the radiation dose received by the heart is one of the main priorities in current breast radiotherapy practice. However, breast radiotherapy is also one of the main users of UK radiotherapy time, accounting for approximately 30% of all radiotherapy treatments. As such, the challenge is to find effective solutions which will minimise the impact on radiotherapy resources, both financial and temporal. The 2012 Royal College of Radiologists audit into current UK breast radiotherapy practices demonstrated that the use of cardiac shielding in breast radiotherapy is not widespread. No cardiac shielding was used in over half the cases reported as having ‘heart in field’. In the majority of the remainder, multileaf collimation (MLC) was used. However, the use of MLC may also reduce target tissue coverage and uncertainties over the relative merits of target tissue vs organ at risk (OAR) compromise may explain the limited use of cardiac shielding in the UK. More complex radiotherapy techniques such as inverseplanned intensity modulated radiotherapy (IMRT) and arc therapy not only carry considerable resource implications, but may also increase undesirable low-dose irradiation of the heart (figure 1). Prone treatment, in which women are treated lying on their fronts, may reduce cardiac doses in larger breasted women, but questions remain over its reproducibility (figure 2). Breath-holding techniques, in which the heart is pushed down and away from the radiation field, may be the most eloquent solution to the problem of reducing cardiac dose while maintaining target tissue coverage (figure 3). There are currently two commercially available breath-hold techniques, the Active Breathing Coordinator (ABC) (Elekta, Crawley, UK) and the Real-time Position Management (RPM) System (Varian Medical Systems, Palo Alto, USA). However, the considerable cost of these systems is likely to hinder the implementation of heart-sparing breast radiotherapy in the UK. In view of this we have developed a lowcost, equipment-free technique (voluntary breath-hold) that can be implemented on any linear accelerator.