Method of Constructing Model Function of Photon Source of Medical Linear Accelerator

Abstract

The invention relates to the field of radiation dose measurement technology, and proposes a method for constructing a photon source model function of a medical linear accelerator, which is used for dose calculation of rays in a radiotherapy plan. The source model of the therapeutic photon beam of the accelerator includes primary ray photons and scattering The source model for line photons has two parts. The physical parameters in the source model function of these two parts are the position coordinates of the emission point of the particle, the projection value of the unit momentum vector in the three-dimensional orthogonal direction, and the energy of the particle. The model function can be used to accurately calculate the photon fluence information, energy spectrum information, and photon unit momentum direction information on any phase space plane. The source model construction method and ideas involved in the present invention are suitable for use in radiotherapy The construction of photon beam source models with various nominal energies of the accelerator has the advantages of less modeling parameters, clear physical meaning of each parameter in the function, easy to use, and the ability to faithfully reproduce the photon distribution information of the radiation field with mathematical analysis methods.

Description

technical field [0001] The invention relates to the technical field of radiation dose measurement, in particular to a method for constructing a photon source model function of a medical linear accelerator. Background technique [0002] Radiation therapy is a method of treating tumors relying on high-energy ionizing rays, and it constitutes the three mainstream methods of tumor treatment together with surgical treatment and medical drug treatment. In radiation therapy, the killing probability of tumor cells and the degree of damage to normal tissues are related to the radiation dose. The dose of normal tissue, the maximum possible increase the dose of the tumor area, reduce the dose of normal tissues and organs, and reduce the normal tissue exposure volume as much as possible. Therefore, the accuracy of dose calculation is very important in the design stage of radiotherapy plan. [0003] Radiation therapy has a history of nearly a hundred years, and there are many dose calc...

AI Technical Summary

Problems solved by technology

However, due to the existence of the indispensable leveler inside the accelerator head, the fluence distribution of the bremsstrahlung photons on the target plane is different from that of the primary ray photons after being affected by the leveler;

[0019] (3) It can determine the emission direction of the photon or the position of the landing point on the calculation plane, but it cannot provide the fluence probability of the original ray photon in this direction, or the photon fluence probability along the photon momentum direction, so it cannot be used for Monte The source model in Carlo Dose Dose;

[0020] (4) The photon distribution function of the primary ray after being affected by the uniformizer is not a simple two-dimensional Gaussian function. In this model, the photon fluence distribution function on the source plane expresses that if the photon distribution is generated by the accelerator target, then the uniformity is missing. function of the homogenizer; if it is expressed in the form of the photon distribution of the primary ray after being affected by the homogenizer, this function is not a simple Gaussian function, because the particle fluence distribution of the bremsstrahlung photons generated by the target after passing through the homogenizer is no longer bell-shaped, It cannot faithfully reflect the fluence distribution information of photons, and is not suitable for calculating the dose of complex irradiation fields or detailed fields;

[0021] (5) The function of the model function to describe the scattered photon is very complicated, and it is cumbersome to obtain the position and momentum direction component information of the scattered photon through function calculation;

[0022] (6) The above model function lacks the particle distribution weight information on different annular zones

Images