BERKELEY, CA (UroToday.com) - The risk of secondary malignancy from radiotherapy (RT) for prostate cancer is a controversial topic and has been investigated by at least 15 institutional or population-based studies to date.
The results have been conflicting, and the interpretation of the data is further confounded by the diverse methodologies used among the studies. For those who are less familiar with RT, two important facts may be overlooked. First, radiotherapy for prostate cancer has dramatically changed over the last two decades. Second, not all RT techniques have the same radiobiological effect on adjacent normal tissues.
To clarify such risk in the modern era, this study generated a unique dataset by matching prostate cancer patients treated with RT to those treated with surgery according to age and follow-up time. This method reduced the impact of selection bias and accounted for the two major confounding factors for the development of second malignancies. The resulting matched-pair data were then stratified into four subsets according to radiotherapy techniques. For the subset with older conventional external beam RT (2DRT), the second malignancy risks were increased for multiple organ-sites as compared to the surgical patients. However, replacing part of the 2DRT treatment with a brachytherapy boost reduced the second malignancy risk to a level comparable to its surgical control. Brachytherapy, by delivering radiation from radioactive sources within the prostate and taking advantage of the inverse square law of physics, would have significantly reduced the dose being delivered to the normal tissues outside of prostate. Furthermore, the more conformal modern external beam RT (3DCRT and/or IMRT) also reduced the risk to a level comparable to the surgical control. These more conformal techniques would have allowed a reduction of RT field as compared to 2DRT, which would translate to a significant reduction of normal tissue being irradiated directly as well as possible scattering radiation to more distant tissues. Therefore, this study provided clinical evidence to support theoretical hypothesis based on dosimetric modeling.
In conclusion, the most important implication of our findings may be that the risk of radiation-related second malignancy should not be simply answered with yes or no. Instead, it can be modified by reducing the amount of normal tissues irradiated as well as the total dose delivered to the normal tissues. Further technology advances may continue to reduce such risk, however small or controversial it is. Over-interpretation or extrapolation of results from older RT techniques should be cautioned as they may provide prostate cancer patients with misleading information regarding their treatment choices in the present.
Jiayi Huang, MD, and Frank A. Vicini, MD as part of Beyond the Abstract on UroToday.com. This initiative offers a method of publishing for the professional urology community. Authors are given an opportunity to expand on the circumstances, limitations etc... of their research by referencing the published abstract.