By Richard Pearlman, M.D., radiation oncologist at Alliance Cancer Care
Historically, two primary OARs, or organs at risk, have been identified in the treatment of breast cancer, which are the lung and the heart. Of these two organs, the heart is given higher priority for sparing. In 2013, Darby et al. published a landmark study in The New England Journal of Medicine on women who underwent radiation therapy for breast cancer between 1958 and 2001. The primary conclusion from this paper was that the mean, or average, heart dose and risk of cardiovascular events were correlated. As a result of this publication, our field has developed techniques to minimize the heart dose as aggressively as possible.
To reduce dose to the heart, two primary methods have been utilized. These two techniques are deep inspiration breath hold (DIBH) and prone treatment. Each has specific advantages and disadvantages.
The primary advantage of DIBH is that it increases the physical distance between the heart and the breast by maximally inflating the lung. For this technique, the respiratory motion of the patient is tracked and treatments are only delivered during maximum inspiration, which is held by the patient for as long as is comfortable. Treatment is not delivered during the period of free breathing in between breath holds. This process is entirely automated by the usage of special software and infrared monitoring systems in the treatment room. Inflation of the lung pushes the chest wall away from the heart, improving cardiac sparing. As a result, there is a small increase in the amount of lung treated. On MA.20, in a trial comparing breast-only radiation to regional nodal irradiation, the rate of grade 2 or greater pneumonitis, or lung inflammation, in the whole breast-only arm was 0.2% (1 in 500 patients). Thus, treating more lung, likely does not significantly increase the risk of side effects to the lung. Secondary advantages of this technique include increased reproducibility and patient comfort. This technique can also be used to increase heart sparing in patients undergoing regional nodal irradiation.
Another technique that is sometimes implemented to help spare the heart is prone treatment. The prone method uses a specialized treatment board in which the patient lies in the prone position with the treated breast hanging freely through a hole in the treatment board. The opposite breast is compressed and positioned laterally to avoid the incoming lateral radiation beams.
Since the breast falls away from the chest wall, the heart is more likely to be spared. While this technique may reduce heart dose compared to a free-breathing supine treatment, the heart may also be affected by gravity and fall towards the treatment field with this positioning. Arguably, the best usage of prone positioning may be in the treatment of right-sided breast cancer to spare more lung compared to free breathing supine. This technique is generally reserved for younger, more fit patients as achieving the desired positioning requires greater strength and coordination.
Studies have shown that DIBH has a superior ability to spare the heart compared to prone positioning. The UK HeartSpare study, which was a randomized, crossover study, compared the mean (average) heart and the left anterior descending artery doses using a supine, DIBH technique versus a prone technique. The study showed a significantly decreased mean heart dose for the DIBH method. The study was stopped early due to the significant benefit of DIBH. Patients also reported that they were more comfortable in the supine position. Overall treatment times were found to be longer and reproducibility of positioning was more difficult in the prone position.
Taking into account the differences between DIBH and prone treatment, we have elected to treat our left-sided breast cancer patients using DIBH due to its increased heart-sparing effect, greater reproducibility, increased patient comfort, and decreased treatment time.
If you have questions about treatment planning for your breast cancer, your physician will be more than happy to answer them. If you have been diagnosed with breast cancer and would like a consultation, please call contact our center today at 256-319-5400.