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CHAPTER 5: Radiation Environment Survey
Scatter Measurements:
All data was acquired using two Technical Associates Mark V integrating ion chamber meters.
Data was acquired in concentric circles of radii listed in the tables. Foot phantoms (one or two
as indicated) were placed in the beam to act as the scattering agent. The position of highest
dose was determined to be approximately 1 foot off the floor. Shielding and dose calculations at
this location will be slightly conservative as dose received to the lower extremities is not
considered whole body dose. Measurements were made at 0, 45, 90, 180, 225, 270 and 315
degrees. Where the patient steps into the system is 0 degrees. The two calibrated integrating
ion chambers were used to measure dose resulting from scatter at each location. These meters
were verified to have excellent agreement. The integration time for each mode was the entire
scan time.
Scatter intensity drops off approximately in accordance with the inverse square law. Scatter
measurements were similar to other units of this type given slight variations in kVp, mA, and
rotation time. The levels as measured should pose no unusual problems in shielding. The
angle with the highest scatter measurements for all scans was 315 degrees.
Dose Profile:
Dose Profile was determined with a ~1 mm thick solid state detector. The profile for the small
field size was determined 1 cm increments in the PMMA phantom. The dose profile for the large
field size was determined in air as the phantom material was not long enough to reliably
encompass the entire profile.
CTDI:
CTDI measurements were made in the 16 cm diameter PMMA phantom. Measurements were
made at the center and the periphery of the phantom. CTDIw (CTDIvol) was determined by
routine means.
Содержание pedCAT
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