Shorter radiotherapy schedules may compensate for between-dose tumor cell growth
For the first time, researchers estimated the daily dose of radiation therapy that is wasted in compensating for cancer cell growth that occurs overnight and during weekends in patients with early breast cancer. This may lead to a shorter radiation therapy schedule. The research was presented at the 2013 European Cancer Congress and published in The Lancet Oncology (2013;14(11):1086-1094).
Radiation therapy is normally given as a series of treatments over several weeks to destroy cancer cells remaining in the breast, chest wall, or axilla after surgery, and to reduce the risk of the cancer recurring in the same breast.
"Our research now suggests that a significant part of the daily radiotherapy curative dose is 'used up' in compensating for tumor growth overnight and over weekends,” said John Yarnold, MB ChB, Professor of Clinical Oncology at The Institute of Cancer Research, London, United Kingdom, and Honorary Consultant at the Royal Marsden NHS Foundation Trust, also in London. The amount of radiotherapy dose used up in this way is estimated to correspond to approximately 0.60 Gray (Gy) per day. Yarnold said the study results offer an explanation as to why prolonged radiation therapy schedules allow cancer cells to fight back.
Yarnold and colleagues used data from the Standardisation of Breast Radiotherapy (START, START Pilot, START A and START B), a series of randomized clinical trials that compared different schedules for delivering radiation therapy to early breast cancer patients in the United Kingdom. The START Pilot and START A trials compared the international standard schedule (50 Gy in 25 daily doses of 2.0 Gy over 5 weeks) with two other schedules of slightly higher daily doses (41.6 Gy or 39 Gy in 13 fractions over the same time period). The START B trial compared the international standard (50 Gy in 25 daily doses of 2.0 Gy over 5 weeks) with a shorter schedule (40 Gy in 15 daily doses of 2.67 Gy over 3 weeks).
The current 3-week schedule was adopted as standard practice in the United Kingdom in 2009, following publication of the 5-year results from the START A and START B trials. After 10 years of follow-up, the 3-week schedule was comparable to the 5-week schedule: it prevented cancer recurrence in the same breast, was gentler on the normal tissues, and had fewer late side effects.
"This suggests that a shorter 1-week radiotherapy schedule … may be more effective against breast cancer recurrence and reduce the chances of side effects on the surrounding normal tissues. In addition, shorter treatment schedules would be more convenient for patients, with benefits including fewer trips to the hospital, and also highly cost effective for health services," said Yarnold.
Professor Cornelis van de Velde, president of the European Cancer Organisation, said: "If further investigations confirm that a shorter radiotherapy schedule is as effective as the current standard of care, it will be another step towards making treatments easier and more bearable for patients, and possibly cheaper for health care services."