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Purpose: To use Monte Carlo techniques to compute the scatter radiation dose distribution patterns around patients
undergoing Interventional Radiological (IR) examinations.
Method: MCNP was used to model the scatter radiation air kerma (AK) per unit kerma area product (KAP) distribution
around a 24 cm diameter water cylinder irradiated with monoenergetic x-rays. Normalized scatter fractions (SF) were
generated defined as the air kerma at a point of interest that has been normalized by the Kerma Area Product incident on
the phantom (i.e., AK/KAP). Three regions surrounding the water cylinder were investigated consisting of the area
below the water cylinder (i.e., backscatter), above the water cylinder (i.e., forward scatter) and to the sides of the water
cylinder (i.e., side scatter).
Results: Immediately above and below the water cylinder and in the side scatter region, values of normalized SF
decreased with the inverse square of the distance. For z-planes further away, the decrease was exponential. Values of
normalized SF around the phantom were generally less than 10-4. Changes in normalized SF with x-ray energy were less
than 20% and generally decreased with increasing x-ray energy. At a given distance from region where the x-ray beam
enters the phantom, the normalized SF was higher in the backscatter regions, and smaller in the forward scatter regions.
The ratio of forward to back scatter normalized SF was lowest at 60 keV and highest at 120 keV.
Conclusion: Computed SF values quantify the normalized fractional radiation intensities at the operator location relative
to the radiation intensities incident on the patient, where the normalization refers to the beam area that is incident on the
patient. SF values can be used to estimate the radiation dose received by personnel within the procedure room, and which
depend on the imaging geometry, patient size and location within the room. Monte Carlo techniques have the potential
for simulating normalized SF values for any arrangement of imaging geometry, patient size and personnel location and
are therefore an important tool for minimizing operator doses in IR.
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