Construction method of medical linear accelerator photon source model function

Abstract

The invention relates to the technical field of radiation dose measurement, provides a construction method of a medical linear accelerator photon source model function, and is used for calculating the dose of rays in a radiation treatment scheme. A source model of a treatment photon beam of the accelerator comprises two parts, namely a source model of original ray photons and a source model of scattered ray photons. Physical parameters in source model functions of the two parts are emission point position coordinates of particles, projection values of unit momentum vectors in the three-dimensional orthogonal direction and energy of the particles. The photon fluence information, the energy spectrum information and the photon unit momentum direction information on any phase space plane can be accurately calculated by utilizing the model function, the source model construction method and thought are suitable for construction of photon beam source models of various nominal energies of accelerators used in radiotherapy, and the method has the advantages of being few in modeling parameters, the physical significance of each parameter in the function is clear, the use is convenient, and the radiation field photon distribution information can be reproduced truthfully by using a mathematical analysis method.

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...

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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

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