First estimate of radiotherapy dose wasted in compensating for between-treatment tumor growth

For the first time, researchers have estimated the daily dose of radiotherapy that could be wasted in compensating for cancer cell growth that occurs overnight and during weekends in patients with early breast cancer.

In research to be presented to the 2013 European Cancer Congress (ECC2013) [1] today (Monday), Professor John Yarnold will say that, until now, there has been contradictory evidence as to whether gaps between radiotherapy treatments, for instance overnight or at weekends, makes any difference to the overall effectiveness of radiotherapy on breast cancer, and, if it does make a difference, why that could be.

Traditionally, breast cancer has not been regarded as a fast growing cancer, unlike some other cancer types, but our research now suggests that a significant part of the daily radiotherapy curative dose is 'used up' in compensating for tumour growth overnight and over weekends. We have estimated that the amount of radiotherapy dose that is used up in this way corresponds to approximately 0.60 Gray (Gy) [2] per day, says Prof Yarnold, who is Professor of Clinical Oncology at The Institute of Cancer Research, London, and Honorary Consultant at the Royal Marsden NHS Foundation Trust (London, UK).

This is the first numerical estimate to suggest that the duration of a course of radiotherapy has an effect on local cancer cure for patients with early breast cancer. The results of our analysis are hypothesis-generating; they offer an explanation as to why prolonged radiotherapy schedules may allow cancer cells to fight back, and suggest that breast cancer cell growth rates after surgery are higher than historically assumed. If confirmed, it means that current trends to deliver shorter radiotherapy schedules are likely to bear fruit in the future. However, I should emphasise that current schedules delivered over five weeks or more remain highly effective, and patients should follow recommendations from their specialists.

Radiotherapy is normally given as a series of treatments over a number of weeks in order to destroy any remaining cancer cells in the breast, chest wall or underarm area after surgery, and to reduce the risk of the cancer recurring in the same breast, while, at the same time, minimising harm to the healthy tissues.

Prof Yarnold and Ms Jo Haviland, a senior statistician at The Institute of Cancer Research (ICR) Clinical Trials and Statistics Unit (CTSU) based their research on the Standardisation of Breast Radiotherapy (START) trials (START Pilot, START A and START B), which have been evaluating the effects of giving shorter radiotherapy schedules after surgery for early breast cancer patients in the UK since 1986. [3]