More risk than benefit for aggressive CT, PET/CT monitoring of eye cancer

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 - radiation dose, CT

Annual CT or PET/CT surveillance of patients with certain eye cancers increases estimated lifetime attributable risk of imaging associated cancer between 0.9 percent and 7.9 percent, depending on patient characteristics, according to a study published in the January issue of JAMA Ophthalmology.

“Aggressive surveillance protocols that entail CT scanning or PET/CT scanning for the monitoring of patients with primary choroidal or ciliary body melanoma for distant metastasis appear, on the basis of our study, to confer a significant substantial risk of secondary malignant tumors from exposure to ionizing radiation,” wrote Joanne C. Wen, MD, of the Jules Stein Eye Institute at the University of California, Los Angeles, and colleagues.

The authors explained that while local control of choroidal melanoma is often achieved, five- and 10-year cumulative metastasis rates have been shown to be 25 percent and 34 percent, respectively, with liver, lung and bone being among the most common sites. Annual surveillance using whole-body PET/CT or CT of the chest, abdomen and pelvis can be performed, but the added risk of cancer from these scans was not known.

To estimate the lifetime attributable risk of cancer associated with this surveillance strategy, Wen and colleagues first calculated effective radiation doses for CT and PET. For whole-body CT and CT of the chest, abdomen and pelvis, this was achieved with Monte Carlo simulations using anthropomorphic mathematical phantoms, and for PET, FDG activity was multiplied by organ-specific coefficients recommended by the International Commission on Radiological Protection. Lifetime attributable risk was then calculated using the method outlined in the Biological Effects of Ionizing Radiation VII report.

Results showed that for a 50-year-old patient, 10-year estimated lifetime attributable risk of cancer from CTs of the chest, abdomen and pelvis was 0.9 percent for men and 1.3 percent for women. Annual PET/CT for 10 years carried an estimated lifetime attributable risk of cancer of 1.6 percent for men and 1.9 percent for women.

Considering other patient populations, the authors reported that risks were highest for young, female patients, with the lifetime attributable risk of cancer estimated to be as high as 7.9 percent for a 20-year-old woman receiving PET/CT scans every six months for 10 years.

Wen and colleagues noted that these results are in line with previous studies, and suggested MRI, despite being limited in differentiating between benign and malignant lesions, could provide a radiation-free alternative to detect abnormal lesions which could then be characterized by PET/CT.

They also pointed to the fact that there is little evidence demonstrating a survival benefit from existing treatments of metastasis from choroidal melanoma. “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,” wrote the authors.