SAN DIEGO, CA USA (UroToday.com) - With the increased use of active surveillance in the management of cT1a renal cell carcinoma (RCC), the risk of radiation-induced secondary malignancies presents a legitimate risk to patients. In a well-attended session at the Society of Urologic Oncolgy meeting in San Diego, Dr. Erick Remer presented an update on the risk of radiation-induced malignancy.
Of all imaging modalities, CT scan exposes patients to the highest dose of radiation, and accounts for 50% of radiation exposure in the U.S., with the other half coming from background radiation. Background radiation exposure in the U.S. is approximately 3mSv/year (mSv is the SI unit of effective radiation dose). On average, a CT of the abdomen and pelvis exposes patients to 8-10 mSv. To analyze the effect of radiation exposure on cancer risk, the BEIR VII report studied the effects of ionizing radiation exposure in nuclear attack survivors. The damaging effects of radiation increase linearly with dose. At cumulative doses < 100mSv, cancer risk assessment is difficult to estimate. The lifetime risk of cancer development from exposure to 100mSv of ionizing radiation is approximately 1%, whereas 42% of patients will develop cancer from other causes. On average, a CT of the abdomen and pelvis in a middle-aged male increases the risk of cancer development from 42.1% to 43%.
For surveillance of RCC following surgical treatment, the NCCN guidelines call for CT scans every 6 months for the first year, and then CT scans yearly for at least 5 years, leading to an estimated cumulative dose of 48mSv. The impact of radiation damage incurred during surveillance is impacted by RCC clinical stage. At 20 years of follow-up, the estimated overall risk of cancer development increases by 0.48%. By stage, the increased risk of cancer development is as follows: pT1a, 42 to 43% and pT1b, 42 to 46.5%. For patients with stage 3 and 4 disease, the increased risk is not relevant. Methods to decrease radiation exposure and dose include elimination of the pelvic portion of the scan (optional per NCCN guidelines), use of thicker slices, modulation of tube current, and performance of a uni-phasic scan. Urologists should remember that the risk of radiation-induced cancer is delayed approximately 10-20 years following treatment.
Presented by Erick Remer, MD at the Society of Urologic Oncology (SUO) meeting preceding the American Urological Association (AUA) Annual Meeting - May 4 - 8, 2013 - San Diego Convention Center - San Diego, California USA
Cleveland Clinic, Cleveland, OH USA
Reported for UroToday.com by Jeffrey Tomaszewski, MD