Does Prophylactic Breast Irradiation In Patients With Prostate Cancer Influence Cardiac Toxicity?

Main Category: Prostate / Prostate Cancer
Also Included In: Men's health;  Endocrinology;  Radiology / Nuclear Medicine
Article Date: 25 Jan 2008 - 0:00 PDT

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UroToday.com- Gynecomastia occurs in men receiving androgen deprivation therapy (ADT) for prostate cancer (CaP). Prophylactic mamillary radiation therapy (PMRT) prior to initiation of ADT may decrease the likelihood of gynecomastia. Breast radiotherapy without 3-dimensional CT-based treatment planning may lead to exposure of the heart to ionizing radiation. In the Journal of the National Cancer Institute, Dr. Nieder from Norway and colleagues from Germany report on a preliminary analysis of using CT-based PMRT to decrease radiation dose to the heart.

The study included 40 men ages 65 to 75 years who had left the mamilla (center of the PMRT) identified on the CT image and used to calculate the distance between skin and anterior border of the pectoral musculature for calculation of the electron beam energy needed for PMRT. They then evaluated the irradiation dose to the heart using the optimal CT-based electron beam energy and a clinically determined beam energy. They cite that the standard clinically determined beam is a 9-MeV electron beam, which covers a tissue depth of approximately 3cm from the surface of the skin. This is increased or decreased by 3-MeV for large or thin patients, respectively.

The median distance between skin and the outer heart contour decreased with age from 6.25 to 5.35 cm, but in both age groups patients with known serious cardiac morbidity had shorter distances than patients of the same age without cardiac morbidity. When applying the CT-based beam, 10% of younger patients and 15% of older patients would receive approximately 50% of the prescription dose to a part of the anterior myocardial wall of the left ventricle, including the small cardiac vessels in this area. When using the clinically determined beam, an additional 12.5% of the patients would be exposed to a dose comparable to that from the CT-based beam.

This suggests that CT-based PMRT might benefit approximately 20-28% of these patients as it can reduce the radiation dose to the heart compared with non-CT-based approaches. The endothelial lining of cardiac vasculature may be particularly vulnerable to radiation and result in damage. Radiobiologic data suggest that as little as 4-5Gy might result in cardiac toxicity.

Nieder C, Pawinski A, Andratschke NH, and Molls M

J Natl Cancer Inst. 99(21):1646-1647, November 2007
doi:10.1093/jnci/djm188

Reported by UroToday.com Contributing Editor Christopher P. Evans, M.D

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