Room: AAPM ePoster Library
Purpose: Convergent X-rays can deliver conformal and precise radiation therapy for treatment of shallow lesions using compact, highly movable, and relatively inexpensive system. It uses a Bragg diffraction lens to focus low energy X-rays to a fixed point in space defined by the geometry of the beam delivery system alone. The complexity of the resulting radiation field structure is one of the main challenges in bringing this promising treatment modality to the clinic. In this work we describe a development and verification of an accurate beam model for a prototype convergent X-ray machine.
Methods: We have used measurements of the X-ray spectrum and fluence to fit an analytical model of the energy fluence in a cross-sectional plane at the exit of the lens system. The energy spectrum measurements were performed using CdTe spectrometer (Amptek X-123) and fitted with three Gaussians. The directional fluence component consists of a five-Gaussian fit of the radial fluence and a second order polynomial fit of the direction cosines. The fit is based on the multiple flat panel measurements of the fluence along the beam path. The model was verified using film measurements in the water phantom.
Results: We have developed a relatively simple analytical model of the convergent X-ray beam. The model can be used for Monte Carlo and analytical computations of dose in water phantoms and CT based patient models.
Conclusion: The beam model that we have developed is an important step in the assessment of the advantages of convergent X-ray beam therapy in treatment of cancer. The methodology developed in this work can be applied to source modeling in other advanced treatment modalities that do not conform to the classical photon beam modeling approaches.