October 28, 2013

expert reaction to breast cancer radiotherapy and heart disease

Among patients with early stages of breast cancer, those whose hearts were more directly irradiated with radiation treatments on the left side in a facing-up position had higher risk of heart disease, according to research in JAMA Internal Medicine.

Dr Stephen Tozer-Loft, Head of Radiotherapy Physics, Sheffield Teaching Hospitals NHS Foundation Trust, said:

“The major finding of this paper is that radiotherapy techniques have improved in recent years.  This new paper is a response to a previous study that looked at the risk of heart disease in women following radiotherapy for breast cancer (Darby et al 2013; reference 2 in this paper), and shows that patients treated since 2005 have one third of the mean cardiac doses of patients treated prior to 2001.  Even since 2005, techniques have continued to improve – radiation can be directed even more accurately with modern technology to avoid sensitive structures such as the heart.  Therefore, for current and future patients, cardiac doses will be even lower.”

Professor Malcolm Sperrin, Director of Medical Physics and Clinical Engineering, Royal Berkshire Hospital, said:

“This study seems to be eminently sensible and arises from studies at a medical facility of high quality.  The link between breast radiotherapy and cardiac disease is well known but this study adds to the science by the inclusion of further risk factors and quantification.

“Radiotherapy is designed to impart damage to tissue and that is its method of operation, but the extent of the damage is carefully controlled by the clinician and physics planning teams to ensure that as a far as possible the damage is restricted to the target tumour and the surrounding tissue is spared.  However, the surrounding tissue inevitably is irradiated, although to a degree that is as low as possible especially where the tissue is radio sensitive such as the heart and nerves. 

“Being an external beam of radiation, some radiation will propagate and irradiate tissue before and after the tumour meaning that the heart may receive a radiation dose although how much radiation will depend on factors such as tumour size, precise location, direction of beam etc.  The dose to the target tumour is built up from adding external beams from a variety of directions leading to a high tumour dose but much lower doses to the surrounding tissues.

“Because the heart lies to the left of the chest, radiotherapy for breast tumours in the left breast will lead to a higher cardiac dose than those on the right.  Careful consideration is given not just to an effective dose to the tumour but also to the risks to the surrounding tissues and this forms part of the clinical assessment of treatment options.

“This paper does provide valuable insight into this complex specialty and the additional factors can only help the clinicians, physics planners and patient.”

Dr Heidi Probst, Reader in Radiotherapy, Sheffield Hallam University, said:

“This data adds a useful dimension to the current knowledge of cardiac risk following radiotherapy to the breast in women diagnosed with a breast cancer. The comparison of techniques between patients lying supine (on their back) compared with prone (lying face down) is interesting but the data needs further clarification before this information can be used to inform practice. For example, it is not clear if the sample studied included women with smaller breasts as well as those with larger breasts (i.e. with a cup size ≥C). Previous research has shown that the prone technique maybe detrimental for women treated for a left-sided breast cancer with smaller breasts (e.g. Kirby et al, Journal of the European Society for Therapeutic Radiology and Oncology, 2010), as the dose to the heart may be increased in these cases. Furthermore, previous research also shows that the prone technique may not be as accurate (i.e. positioning may vary more day to day) as positioning in the supine position.”

Professor Wade Allison, Emeritus Professor of Physics, University of Oxford, said:

“This paper appears to demonstrate that radiotherapy breast cancer patients have different risk factors for subsequent heart disease depending on their lifestyle and whether they receive radiotherapy to left or right breast, in supine or prone position.

“It may be true that they do, but this article is unrelated to any evidence for this.

“The study refers to 48 women, a number which would be quite insufficient to answer such questions. [The following paper asked the question about left/right radiotherapy based on data for 20,871 women: Roychoudhuri, R. et al (2007) ‘Increased cardiovascular mortality more than fifteen years after radiotherapy for breast cancer: a population-based study’. BioMed Central Cancer, 7: 9. http://www.ncbi.nlm.nih.gov/pubmed/17224064].

“What does this present paper say? It is simply the result of a calculation for 48 patients of the radiation dose to their hearts received during radiotherapy treatment. End of story.

“No adequate justification is given for anything deduced from that.

“The suggestion that this article might be of interest to the mainstream press may be motivated by the need to encourage people to improve their lifestyle but such a principal intention is not made clear.”

‘Risk and risk reduction of major coronary events associated with contemporary breast radiotherapy’ by David J. Brenner et al. published in JAMA Internal Medicine on Monday 28 October 2013.