Modeling a superficial radiotherapy X-ray source for relative dose calculations
Christopher D Johnstone1, Richard LaFontaine, Yannick Poirier
1San Diego State University. ChrisDJohnstone@gmail.com.
Journal of Applied Clinical Medical Physics
|June 24, 2015
Summary
This study developed an accurate kilovoltage X-ray beam model for superficial therapy, improving relative dose calculations in water. The new model, kVDoseCalc, shows superior accuracy compared to existing British Journal of Radiology Supplement 25 data.
Area of Science:
- Medical Physics
- Radiotherapy Physics
- X-ray Beam Modeling
Background:
- Accurate dose calculation is crucial for effective radiotherapy.
- Existing percentage depth dose (PDD) data, such as British Journal of Radiology Supplement 25 (BJR 25), may have limitations for specific X-ray units.
- Empirical characterization of X-ray beam sources is essential for precise dosimetry.
Purpose of the Study:
- To empirically characterize and validate a kilovoltage (kV) X-ray beam source model for a superficial X-ray unit.
- To assess the accuracy of the BJR 25 PDD data for relative dose calculations in water.
- To develop and validate an in-house software tool (kVDoseCalc) for accurate dose computation.
Main Methods:
- Measured central axis PDDs and dose profiles using an Xstrahl 150 X-ray system in a scanning water phantom.
- Modeled the Xstrahl source as an effective point source with spatially varying fluence and spectra, derived from in-air ionization chamber and half-value layer (HVL) measurements.
- Input the characterized beam model into kVDoseCalc software to compute radiation doses and compared results with measurements and BJR 25 data.
Main Results:
- The kVDoseCalc software demonstrated good agreement with measurements, with percent differences in PDDs ranging from -4.8% to 4.8% (mean 1.5%, SD 0.7%).
- Dose profiles calculated by kVDoseCalc also showed good agreement with measurements (mean percent difference 1.4%, SD 1.4%).
- Measurements exhibited significantly better agreement with kVDoseCalc than with BJR 25 data, which showed larger percent differences for PDDs (-14.0% to 15.7%, mean 4.9%, SD 2.1%).
Conclusions:
- The empirically based X-ray source modeling approach accurately computes relative dose in water for superficial X-ray therapy.
- The developed kVDoseCalc software provides a reliable tool for dose calculations in this modality.
- The findings highlight limitations in the accuracy of BJR 25 PDD data for superficial X-ray units.
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