Radiation dose monitoring important for long-term health of pediatric cancer survivors

Diagnostic imaging is an essential component of follow-up care for pediatric cancer survivors. However, it carries the risk of causing radiation-induced secondary cancers later in life, especially as cumulative radiation doses increase. Pediatric radiologists from Korea strongly advocate the use of automated dose monitoring systems to track individual and cumulative radiation dose exposure of children receiving treatment for cancer.

The risk of developing and dying from a radiation-induced cancer is higher for children than adults. An infant has approximately more than 10 times the risk of developing a cancer from exposure to a specific radiation dose than an adult; a 10-year old has approximately four times the risk than a middle aged adult. As a steadily increasing number of children survive their cancer into adulthood, the cumulative radiation doses of advanced imaging exams ordered for follow-up monitoring of recurrence or metastases is critically important. This is especially true for patients whose treatment has included radiation therapy.

The increasing use of PET/CT has particularly concerned radiologists at the Severance Children’s Hospital of Yongsei University College of Medicine in Seoul. Lead author Yeun Yoon Kim and colleagues in the Department of Radiology and Research Institute of Radiological Science conducted a study to evaluate the utility of an automated dose monitoring system to calculate and monitor the effective radiation dose of pediatric patients with neuroblastoma. They felt that data from the retrospective analysis, published in Diagnostic and Interventional Radiology, can provide insight into future ordering patterns and beneficial changes to reduce the radiation dose risk to these vulnerable patients.

The authors identified 63 patients treated for neuroblastoma at the hospital from January 2008 through September 2014. The children ranged in age from infancy to 7 years, with a mean age of 3.2 years. Twenty-eight patients, or 44%, received radiation therapy of a mean dose of 31.9 Gy. The highest radiation therapy dose delivered to a patient was 97.2 Gy. Radiation therapy treatment increased the risk of subsequent cancer by more than four fold in these patients, according to the radiologists.

Electronic medical records (EMR) of all patients were reviewed during this time frame, and RIS/PACS records were reviewed from 2003 through 2007 to identify additional exposure to ionizing radiation. Data of the patients’ age at time of diagnosis, gender, organ of tumor origin, weight at the time of first CT or PET/CT, and radiation therapy treatment details (if applicable) were recorded.

The researchers used a dose monitoring program (DoseTrack™, GE Healthcare) to calculate the effective dose from radiographs, conventional CT, and the CT of PET/CT performed from October 2012 onward for each patient. Effective dose was calculated as the sum of the organ doses using tissue weighting factors. Radiation dose for PET was calculated by multiplying the flurodeoxyglucose activity (5 MGq per body weight in kg) by the dose coefficient. Effective dose, the whole body equivalent of partial body irradiations, was estimated by applying the mean dose per exam calculated by the data from the DoseTrack group for all exams performed before October 2012.

Findings

The authors determined that the average cumulative dose per patient from CT or PET/CT was 18.35 mSv. The proportion of the effective dose from CT of PET/CT accounted for approximately 46%. PET and PET/CT contributed to more than 70% of the total diagnostic radiation doses. They also discovered that the mean number of x-ray exams taken per patient was 85.1, representing a relative radiation dose of 8.5%. (Conventional CT exams generated a relative radiation dose of 19.1% and for PET alone, 26.7%.)

Recommendations

The authors advocate that dose monitoring be performed for every patient with cancer, preferably using automated dose monitoring software. They also recommend that follow-up imaging be individualized to help reduce radiation dose exposure. They note that when PET/MRI is substituted for a PET/CT exam, it produces the equivalent of only one-fifth of the effective dose. Radiation dose from radiographs, albeit very low, also needs to be monitored, in view of the high number of x-ray exams these patients had in the course of seven years or less.

In addition to potentially helping reduce the risk of developing a radiation-induced secondary cancer, the authors also note that a dose monitoring program can be used to optimize and lower dose protocols for studies of the same modality as long as diagnostic quality can be obtained. It also may be used to establish dose reference levels or to develop guidelines for use of imaging studies from diagnosis to follow-up in a scenario of a specific disease.

REFERENCE

1. Kim YY, Shin JH, Kim M-J, et al. Comparison of effective radiation doses from X-ray, CT, and PET/CT in pediatric patients with neuroblastoma using a dose monitoring program. Diagn Interv Radiol. 2016 22: 390-394.