Radiation dose to the brain and subsequent risk of developing brain tumors in pediatric patients undergoing interventional neuroradiology procedures

Abstract

Radiation dose to the brain and subsequent lifetime risk of diagnosis of radiation-related brain tumors were estimated for pediatric patients undergoing intracranial embolization. Average dose to the whole brain was calculated using dosimetric data from the Radiation Doses in Interventional Radiology Study for 49 pediatric patients who underwent neuroradiological procedures, and lifetime risk of developing radiation-related brain tumors was estimated using published algorithms based on A-bomb survivor data. The distribution of absorbed dose within the brain can vary significantly depending on field size and movement during procedures. Depending on the exposure conditions and age of the patient, organ-averaged brain dose was estimated to vary from 6 to 1600 mGy. The lifetime risk of brain tumor diagnosis was estimated to be increased over the normal background rates (57 cases per 10,000) by 3 to 40% depending on the dose received, age at exposure, and gender. While significant uncertainties are associated with these estimates, we have quantified the range of possible dose and propagated the uncertainty to derive a credible range of estimated lifetime risk for each subject. Collimation and limiting fluoroscopy time and dose rate are the most effective means to minimize dose and risk of future induction of radiation-related tumors.

FIG. 1

Diagram of brain model based on MIRD phantom (35) showing division into layers and volume elements (voxels) for dose calculations. Reprinted with permission from the Society of Nuclear Medicine from: L. G. Bouchet, W. E. Bolch, D. A. Weber, H. L. Atkins, J. W. Poston, Sr., and in collaboration with the MIRD committee: W. E. Bolch (Task Group Leader), A. B. Brill, N. D. Charkes, D. R. Fisher, M. T. Hays, R. W. Howell, J. S. Robertson, J. A. Seigel, S. R. Thomas, E. E. Watson (Chair) and B. W. Wessels, MIRD Phamphlet No. 15: Radionuclide S Values in a Revised Dosimetric Model of the Adult Head and Brain.

FIG. 2

Simulation of a hypothetical composite non-uniform field. The x axis indicates the location of the collimated radiation field along a line from anterior to posterior (for a lateral field) or left to right (for a frontal field). The y axis indicates the beam-on time and by extension the relative radiation dose. If the radiation beam is directed at various locations along the x axis for the times indicated on the y axis, the histogram (in Gy) represents the relative dose distribution along the line.

FIG. 3

Simulation of irradiation with composite non-uniform radiation fields in three dimensions for a lesion located at the center of the brain. Histograms along each axis represent the relative amount of time the small field is focused on the lesion or, equivalently, the relative amount of dose received at that position.

FIG. 4

Calculated depth-dose curves (depth below cranium) for X-ray generation parameters (see Table 1) for six age groups and PA and LAT projections (also see Table 1 for depth-dose regression parameters).

FIG. 5

Spatial pattern of dose in the layers constituting the brain: irradiation by two large uniform fields.

FIG. 6

Spatial pattern of dose in brain of infant from irradiation by narrow non-uniform fields (black dot indicates location of lesion and center of examination field).

FIG. 7

Average absorbed doses (mGy) to the brain (panel A) and relative risk of brain tumor (panel B) for 49 cases when exposed to large uniform fields. The maximum dose is 1600 mGy and the maximum relative risk is 2.4

FIG. 8

Average absorbed doses (mGy) to the brain (panel A) and relative risk of brain tumor (panel B) for 49 cases when exposed to narrow nonuniform fields with pathologic focus in the center of the brain. The maximum dose is 200 mGy and the maximum relative risk is 1.25.

FIG. 9

Average absorbed doses (mGy) to the brain (panel A) and relative risk of brain tumor (panel B) for 49 cases when exposed to narrow nonuniform fields with pathologic focus at the inferior margin of the brain. The maximum dose is 150 mGy and the maximum relative risk is 1.15.

FIG. 10

Estimated relative risk (central estimate and 90% confidence interval) of radiation-related brain tumor for (panel A) females, n = 21, and (panel B) males, n = 28, when exposed to non-collimated uniform fields.