(a) Diagram of the SBDX system to scale. An electron beam is magnetically deflected to raster across a transmission, thin film anode. The collimator has 100 × 100 holes. The distances shown are source-detector-distance (SDD), tumor-detector-distance (TDD), tumor depth in patient (12.5 cm), patient thickness (25 cm), and tumor thickness (5 mm). (b) To achieve a greater maximum tomographic angle on the system a new collimator can be designed for a smaller SDD.
SBDX images of a lung tumor phantom. Both acquired with 150 cm SDD. The left image has the tumor 100 cm from the source (thus having a maximum tomographic angle of 11.35°); the right image has the tumor at 50 cm from the source (with a maximum tomographic angle of 5.69°).
(a) SBDX system source and detector, and the ENB system transmitter are indicated. (b) The ENB calibration fixture, seen in Fig. 3(a) on the ENB transmitter. It is used to find the measurement error of the ENB system.
RMS error and TME were measured on the ENB system when integrated with the SBDX system with the original 150 cm SDD. The distance from the source was measured to the center of the calibration fixture. The dotted lines indicate the reference value, when the accuracy test was performed far away from the SBDX system.
Tomographic angle as a function of distance from the detector for various SDDs as measured between the midline of the detector and the midline of the source collimator.
Dose as a function of source-to-tumor distance. Each beamlet was run for 0.03 mAs (there are 10 000 beamlets) and the fluoroscopy unit was run for 300 mAs. These simulations used an SDD of 110 cm. (a) This shows three organs which had the highest doses and an increase in dose as the patient was moved farther from the source. (b) The dose to the esophagus and active bone marrow decrease as the patient is moved farther from the source. (c) The average dose in the total body (in gray, not sieverts) and the skin are shown. (d) These are the effective doses in sieverts. One can see that the effective doses are dominated by the lungs because of the “geometry” of the organs themselves and the trajectory of the beamlets.
The effective dose to the patient in mSv to achieve a tumor SNR of 5. Calculations shown here were made using the ICRP 103 protocol. Air KERMA at the skin entrance is also shown for fluoroscopy and SBDX. These simulations used a SDD of 110 cm.
Air KERMA and number of beamlets with changing patient location while maintaining tumor SNR on the SBDX. (a) The air KERMA at the detector (if the patient were absent) necessary for maintaining SNR at multiple patient locations while collimating down the beams to various distances around the tumor. The beam collimation measurements represent a square (with a length of our measurement) in the plane of the tumor outside of which beamlets are removed. (b) the number of beamlets which contribute to tumor signal and the number of beamlets used when different collimator sizes are used. The dashed lines represent the number of beamlets necessary for the trend to continue if our collimator had more than 10 000 beamlets. These simulations used a SDD of 110 cm.
The air KERMA needed at the detector to achieve a tumor SNR of 5 as a function of the ratio of source-to-tumor distance over the SDD for multiple SDDs on the SBDX system.
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