NEW YORK (Reuters Health) – Aggressive CT or PET/CT surveillance protocols confer significant risk of radiation-induced cancer in patients being monitored for metastasis from primary choroidal melanoma, California-based researchers have shown.

“With limited treatment options for metastatic disease, a discussion of the risks and benefits of the various surveillance methods must take place with patients during the course of their management,” they stress in their report in the January issue of JAMA Ophthalmology.

Dr. Tara A. McCannel, at the University of California, Los Angeles, and colleagues note that while local control of choroidal melanoma is often achieved, metastasis occurs in about one-third of patients within 10 years. After detection of metastases, median survival is less than a year.

The high rate of metastasis has led to the use of aggressive surveillance protocols, including annual or biannual CT scans of the chest, abdomen and pelvis or whole-body PET/CT scans, the authors explain. However, concerns have increased regarding the risk of cancer related to radiation exposure.

The investigators looked into this issue using Monte Carlo simulation studies to calculate the lifetime attributable risk (LAR) of cancer due to radiation exposure from various CT or PET/CT surveillance protocols over a period of 5 or 10 years.

They found that the cancer risk varied by age and sex, and that “the LAR of cancer related to PET/CT protocols is higher than that related to CT of the chest, abdomen, and pelvis.”

For example, for a 50-year-old patient, with an annual CT scan performed for 10 years, the lifetime attributable risk of cancer is 0.9% for men and 1.3% for women. With an annual PET/CT scan for 10 years, corresponding risks are 1.6% for men and 1.9% for women. The risks are doubled if the scans are performed every 6 months instead of annually.

Young women are at the highest risk. The team calculated that a PET/CT scan performed every 6 months for 10 years confers a lifetime attributable risk of cancer of 7.9% (ie, 1 in 13) for a 20-year-old female.

Discussing the results, Dr. McCannel and colleagues point out that no surveillance protocol has been shown to improve survival in this setting, and there is not much evidence of a survival benefit with current treatments for metastatic choroidal melanoma. They therefore emphasize the importance of considering the pros and cons of intensive surveillance in relation to a patient’s age, sex and prognosis.

“For a young patient with an excellent probability of survival and at low risk for metastatic disease, the LAR of cancer from an aggressive PET/CT surveillance protocol may outweigh the benefits,” they suggest. “In this population, serial MRI studies may be a safer option, with PET/CT studies obtained only as needed to better characterize abnormal lesions.”

SOURCE: Radiation-Related Cancer Risk Associated With Surveillance Imaging for Metastasis From Choroidal Melanoma