Radiation Oncology Update - Dr Andrew See

Traditionally, radiotherapy has been administered over 6 to 6 ½ weeks comprising between 30 and 33 daily treatments. This is delivered in two phases. The first phase, which spans 5 weeks, is termed ‘whole breast radiotherapy’. During this phase, the whole breast is treated through a technique called opposed tangents. The second phase of treatment, also called the ‘boost’, is delivered in the final 1 to 1.5 weeks. During this component of therapy, just the immediate breast tissue surrounding the original primary tumour is irradiated. Not all women require a ‘boost’ dose however in those who do, it is considered to further improve local tumour control.

Over the last two decades, a number of clinical trials have explored the merits as to whether it is possible to shorten the duration of whole breast radiotherapy from the traditional 6 ½ weeks to anywhere between three and 3.5 weeks. These studies were conducted in countries where radiotherapy machines were scarce and as a result the waiting times for treatment unacceptably long. Three trials, accruing over 5000 women have now been published and peer reviewed. They appear to show that a select group of women can be safely treated with a shortened 3.5 week course of therapy yet still enjoy equivalent long term cure rates and acceptable cosmetic outcome.

In the modern era, radiotherapy is considered safe and equitable although there still are some potential long-term side effects that can manifest years after the treatment has been administered. In the case of women who require left-sided breast radiotherapy one of the long-term side effects involves the potential for radiotherapy to damage the heart. This occurs because the radiotherapy beams do come close to the front of the left ventricle (main chamber of the heart that pumps blood around the body) and also the left anterior descending coronary artery (main artery that feeds the left chamber of heart). Although the overall risk is considered to be low, a small increase in ischemic heart disease is observed when treating left sided breast cancer that is not apparent when managing right sided disease. This risk is magnified even further in women requiring left sided breast radiotherapy who also have other cardiac risk factors such as diabetes, active smokers, hypertension or a familial history or predisposition for heart disease.

A recent refinement in the management of left-sided breast cancer is a technique called ‘deep respiratory breath hold’ or DIBH.