CN108465163B

CN108465163B - Pencil beam dose algorithm based on density transformation

Info

Publication number: CN108465163B
Application number: CN201810260086.XA
Authority: CN
Inventors: 不公告发明人
Original assignee: Zhongke Chaojing Nanjing Technology Co Ltd
Current assignee: Zhongke Chaojing Nanjing Technology Co Ltd
Priority date: 2018-03-27
Filing date: 2018-03-27
Publication date: 2020-06-09
Anticipated expiration: 2038-03-27
Also published as: CN108465163A

Abstract

The invention discloses a pencil beam dose algorithm based on density transformation, which enlarges any source skin distance to a standard source skin distance according to the geometric dimension, scales the density inversely so as to convert the source skin distance into dose distribution irradiating other density die bodies under the standard source skin distance, and finally obtains the dose distribution of any ray source and any density die bodies from the standard water die dose distribution by utilizing a non-uniformity correction method. The invention utilizes O' Connor theorem to convert the dose distribution of pencil beams under different source skin distances into the dose distribution under the same source skin distances and different densities, and then utilizes density correction to obtain the relation between the dose distributions.

Description

Pencil beam dose algorithm based on density transformation

Technical Field

The invention relates to the field of dose calculation in tumor radiotherapy, in particular to a pencil beam dose algorithm based on density transformation.

Background

Dose calculation is a basic key in radiotherapy, and the dose distribution of a radiation beam in a human body can be accurately calculated when a radiotherapy plan is formulated, so that the radiotherapy plan is reasonably formulated. One of the main methods of clinical dose calculation is the pencil beam algorithm, which breaks the radiation beam into a number of very small pencil beams, calculates the dose distribution of each pencil beam separately, and then superimposes them to obtain the total dose distribution. It is therefore very critical in pencil beam dose algorithms to calculate the dose distribution of a single pencil beam incident perpendicularly in water, called the pen kernel. The form of the pen kernel includes an analytic form and a data table, and the latter can be obtained by Monte Care simulation or deconvolution and the like according to the measured data. However, regardless of the pen core type, the effect of different source-skin distances (i.e., the distance of the radiation source from the surface of the phantom upon which the pencil beam irradiates) is taken into account. The radiation dose distribution of the same pencil beam under different source skin distances is obviously different, but the dose distribution among different source skin distances is not simply related, and the dose distribution under any source skin distance is difficult to obtain from the dose distribution under one standard source skin distance. If the pen core dose distribution under each source skin distance is obtained respectively and made into a database, and the database is used for interpolation in dose calculation, the required data amount is too large and cumbersome, and the interpolation method cannot well fit actual distribution in a place with a large dose distribution gradient.

It is therefore desirable to provide a new pencil beam dose algorithm to solve the above problems.

Disclosure of Invention

The invention aims to provide a pencil beam dose algorithm based on density transformation, which can enable dose calculation to be free from preparing a plurality of pen cores and reduce interpolation errors.

In order to solve the technical problems, the invention adopts a technical scheme that: a pencil beam dose algorithm based on density transformation is provided, any source-skin distance is enlarged to a standard source-skin distance according to the geometric dimension, the density is inversely scaled, so that the source-skin distance is converted into dose distribution which irradiates other density mold bodies under the standard source-skin distance, and finally the non-uniformity correction method is utilized to obtain the dose distribution of any ray source and any density mold body from the standard water mold dose distribution.

In a preferred embodiment of the present invention, the pencil beam dose algorithm based on density transformation comprises the following steps:

a pencil beam of a given size is provided with its source at a standard distance SSD from the phantom, and the dose distribution F (d, x, y) of the pencil beam impinging on the phantom is known, where d represents the depth of the calculated spot and x, y represents the distance of the calculated spot from the central axis of the pencil beam as shown in fig. 1 (c). The dose distribution for the case of the same pencil beam, source-to-phantom distance h, is computed and is noted as G (d, x, y) as shown in fig. 1 (a).

First, the dose distribution in any radiation scene is invariant if its geometry and density are scaled inversely and the ray intensity is also scaled inversely with the square of the geometry. The dose distribution at the source-to-phantom distance h is equivalent to a pencil beam irradiation density of

The distribution of the dose under the phantom is shown in FIG. 1(b), and the distribution of the dose is recorded as S (d, x, y), then

S (d, x, y) is obtained from F (d, x, y) by a non-uniformity processing method, and since the two cases in FIG. 1(b) and (c) have different densities, the dose distribution of the pencil beam in the water mold can be obtained by a non-uniformity correction method such as an equivalent path or a Batho method

The dose distribution under the density die body can be obtained by adopting an equivalent path method and utilizing the inverse distance theorem and the density relation of the two conditions

And obtaining the dose distribution G (d, x, y) at the distance h between any ray source and the model body by utilizing the relationship between G (d, x, y) and S (d, x, y).

The invention has the beneficial effects that: the invention utilizes O' Connor theorem to convert the dose distribution of pencil beams under different source skin distances into the dose distribution under the same source skin distances and different densities, and then utilizes density correction to obtain the relation between the dose distributions.

Drawings

FIG. 1 is a process diagram of a preferred embodiment of the pencil beam dose algorithm based on density transformation according to the present invention.

Detailed Description

The following detailed description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings, will make the advantages and features of the invention easier to understand by those skilled in the art, and thus will clearly and clearly define the scope of the invention.

Referring to FIG. 1, a rectangular pencil beam, Batho non-uniformity correction method is used as an example to illustrate how to calculate the non-standard distance pencil beam dose distribution from the existing standard distance pencil beam dose distribution.

The dose distribution of the pencil beam when irradiated at the water phantom at standard source-skin distance is known and is denoted as F (d, x, y), d denoting the depth of the calculated point and x, y denoting the distance of the calculated point from the central axis of the pencil beam. The Maximum Tissue air Ratio (TMR) at the field size of the pencil beam is known and is denoted as TMR (A, d), where A denotes the field size.

In the case of a phantom illuminated by a pencil beam of the same size at a distance h, the dose distribution is denoted as G (d, x, y),

first the dose distribution in the case of source-to-phantom distance h is equivalent to a pencil beam irradiation density at the standard distance SSD of

The distribution of the dose under the phantom, noting that the distribution of the dose is S (d, x, y), then

S (d, x, y) can be obtained from F (d, x, y) by the heterogeneity processing method using the Batho correction method,

from the above relationship can be obtained

The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes performed by the present specification and drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.

Claims

1. A pencil beam dose algorithm based on density transformation is characterized in that any source skin distance is enlarged to a standard source skin distance according to the geometric dimension, the density is inversely scaled, so that the source skin distance is converted into dose distribution which irradiates other density die bodies under the standard source skin distance, and finally the non-uniformity correction method is utilized to obtain the dose distribution of any ray source and any density die body from the standard water die dose distribution; the method comprises the following steps:

providing a pencil beam with a known field size A, wherein the distance between a radiation source and a mold body is a standard distance SSD, and the dose distribution F (d, x, y) of the pencil beam irradiated on the water mold body is known, wherein d represents the depth of a calculation point, and x and y represent the distance between the calculation point and the central axis of the pencil beam; and the maximum Tissue air ratio (TMR) under the size of the field of the pencil beam is known and is recorded as TMR (A, d);

for the same pencil beam, the dose distribution at a source-phantom distance h is denoted as G (d, x, y); the dose distribution at source-to-phantom distance h is equivalent to a pencil beam irradiation density at standard distance of

S (d, x, y) is obtained from F (d, x, y) by using an equivalent path non-uniformity correction method, and the relation between the distance inverse ratio theorem and two density situations of the same standard source-skin distance can be obtained

Or

2. The density transform based pencil beam dose algorithm of claim 1 wherein the dose distribution in any radiation scene is invariant if its geometry and density are inversely scaled and the ray intensity is scaled with the inverse of the geometry squared.