CONFORMITY INDEX EVALUATION TOOL AND METHOD FOR RADIOTHERAPY TREATMENT PLANNING

Abstract

A dosimetric evaluation tool and method is used to determine how well the prescription isodose volume (PIV) conform to the size and shape both the tumor volume (TV) and the healthy tissue in radiotherapy treatment plans. The innovative, ideal, and universal dosimetric evaluation tools are Conformity Index (CI) and Unconformity Indexes (UCI.sub.underdose and UCI.sub.overdose). CI measures the conformity of the radiotherapy planning, and UCI.sub.underdose and UCI.sub.overdose measure the unconformity of the radiotherapy planning. In other words, UCI.sub.underdose and UCI.sub.overdose reflect the negative effect of dose distribution in planning, and CI reflects the positive effect of dose distribution.

Claims

1. A Conformity Index (CI) evaluation method, wherein the CI evaluation method utilizes a CI tool, an UCI.sub.underdose tool, and a UCI.sub.overdose tool in an iterative manner in order to evaluate a radiotherapy treatment plan for radiotherapy treatment planning, and the CI evaluation method comprises the following steps: 1) measuring a conformity of a dose distribution to a radiotherapy target, 2) determining if the dose distribution is successful with the CI tool; 3) determining a cause of an unconformity of the dose distribution; 4) measuring a magnitude of the unconformity of the dose distribution with the UCI.sub.underdose tool and UCI.sub.overdose tool.

2. The CI evaluation method according to claim 1, wherein to determine how well a prescription isodose volume (PIV) conforms to a size and a shape of both a tumor volume (TV) and a healthy tissue volume, step 1 comprises: measuring a proportion of a positive effect to V.sub.TV∪PIV in the dose distribution as a result the radiotherapy treatment plan; and calculating a proportion of TV.sub.PIV to V.sub.TV∪PIV; wherein the negative effect is when a part of the tumor volume is not irradiated, and a part of a healthy tissue is irradiated, and the positive effect is when the tumor volume is irradiated; V.sub.TV∪PIV is a total of the negative effect and the positive effect in the dose distribution as the result of the radiotherapy treatment plan; TV.sub.PIV is a tumor volume covered by the prescription isodose volume.

3. The CI evaluation method according to claim 2, wherein V.sub.TV∪PIV reflects a total effect of the radiotherapy treatment plan for each of the dose distribution, and V.sub.TV∪PIV is determined by the following formula:
V.sub.TV∪PIV=PIV+TV−TV.sub.PIV.

4. The CI evaluation method according to claim 1, wherein the UCI.sub.underdose tool is a measure of the unconformity of the dose distribution in the radiotherapy treatment plan, and the CI evaluation method comprises the step of calculating UCT.sub.underdose with the following formula to measure a negative effect of underdosing a tumor on the conformity of the dose distribution: $\text{?}$ $\text{?}\text{indicates text missing or illegible when filed}$ wherein the negative effect is when a part of the tumor volume is not irradiated, and a part of a healthy tissue is irradiated; PIV is a prescription isodose volume; TV is a tumor volume; TV.sub.PIV is a tumor volume covered by the prescription isodose volume.

5. The CI evaluation method according to claim 1, wherein the UCI.sub.overdose tool is a measure of the unconformity of the dose distribution in the radiotherapy treatment plan, and the CI evaluation method comprises the step of calculating UCI.sub.overdose with the following formula to measure a negative effect of overdosing a healthy tissue on the conformity of the dose distribution: $\text{?}$ $\text{?}\text{indicates text missing or illegible when filed}$ wherein the negative effect is when a part of the tumor volume is not irradiated, and a part of the healthy tissue is irradiated; PIV is a prescription isodose volume; TV is a tumor volume; TV.sub.PIV is a tumor volume covered by the prescription isodose volume.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] FIG. 1 shows the first dose distribution.

[0050] FIG. 2 shows the second dose distribution.

[0051] FIG. 3 shows the third dose distribution.

[0052] FIG. 4 shows the fourth dose distribution.

[0053] FIG. 5 shows the fifth dose distribution.

[0054] FIG. 6 shows the simulation of the AUB (the union of the A and B) and the A\B (A difference B) used in mathematics for PIV and TV.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0055] To eliminate these first and second problems mentioned in the technical problems section where the invention aims to solve, the CI must measure the proportion of the positive effect to the total of the negative and positive effects in the dose distribution as a result the treatment plan. [0056] The negative effect is that part of the TV is not irradiated, and healthy tissues are irradiated. [0057] The positive effect is that part of the TV is irradiated.

[0058] The TV covered by the PIV (TV.sub.PIV) reflected positive effect of a treatment plan has already been defined in the literature. However, a new volume formed by the union of the TV and PIV (overall treatment plans) is needed. This volume must reflect the total effect of the treatment plan for each dose distribution. That is, the CI must measure the proportion of TV.sub.PIV to this new volume to give the conformity of a plan with 100% agreement.

[0059] This new volume called V.sub.TV∪PIV can be written with the union formula used in mathematics (FIG. 6).

V.sub.TV∪PIV=PIV+TV−TV.sub.PIV  (1)

[0060] Where V.sub.TV∪PIV=volume formed by union of TV and PIV.

[0061] Thus, conformity of a plan can be expressed as:

[00005]$\begin{array}{cc}\mathrm{CI}=\frac{T{V}_{\mathrm{PIV}}}{V_{\mathrm{TV}.Math.\mathrm{PIV}}}=\frac{T{V}_{\mathrm{PIV}}}{TV+PIV-T{V}_{\mathrm{PIV}}}& \left(2\right)\end{array}$

[0062] Also, to eliminate the last problem mentioned in the technical problems section where the invention aims to solve, new expressions supporting the ideal CI expression should be derived. In this invention, UCI.sub.underdose (Unconformity Index created by cold spots remaining in tumor volume) and UCI.sub.overdose (Unconformity Index formed by dose of healthy tissues) will be dosimetric evaluation tools.

[0063] To interpret the result of the conformity index, we also need to measure the effect on the CI of underdosing the tumor and the overdosing healthy tissues. These UCI.sub.underdose and the UCI.sub.overdose equalities can be described with the difference formula used in mathematics: (FIG. 6)

[00006]$\begin{array}{cc}{\mathrm{UCI}}_{\mathrm{underdose}}=\frac{TV-T{V}_{\mathrm{PIV}}}{TV+PIV-T{V}_{\mathrm{PIV}}}& \left(3\right)\end{array}$$\begin{array}{cc}{\mathrm{UCI}}_{\mathrm{overdose}}=\frac{PIV-T{V}_{\mathrm{PIV}}}{TV+PIV-{\mathrm{TV}}_{\mathrm{PIV}}}& \left(4\right)\end{array}$

[0064] CI measures the conformity of planning, and UCI.sub.overdose and UCI.sub.underdose measure the unconformity of planning. In other words, UCI.sub.overdose and UCI.sub.underdose reflect the negative effect of dose distribution in planning, and CI reflects the positive effect of dose distribution. This is correct, because the sum of CI, UCI.sub.overdose and UCI.sub.underdose are equal to 1, as shown below:

[00007]$\mathrm{CI}+{\mathrm{UCI}}_{\mathrm{underdose}}+{\mathrm{UCI}}_{\mathrm{overdose}}=1\frac{{\mathrm{TV}}_{\mathrm{PIV}}}{TV+PIV-{\mathrm{TV}}_{\mathrm{PIV}}}+\frac{\mathrm{TV}-{\mathrm{TV}}_{\mathrm{PIV}}}{TV+PIV-{\mathrm{TV}}_{\mathrm{PIV}}}+\frac{PIV-{\mathrm{TV}}_{\mathrm{PIV}}}{TV+PIV-{\mathrm{TV}}_{\mathrm{PIV}}}=\frac{TV+PIV-{\mathrm{TV}}_{\mathrm{PIV}}}{TV+PIV-{\mathrm{TV}}_{\mathrm{PIV}}}=1$

[0065] After the patient's treatment plan was established, CI and UCI.sub.overdose and UCI.sub.underdose evaluation tools are calculated. If the CI result complies with clinical protocols, the patient is taken into treatment through the relevant treatment planning. If the results do not comply with clinical protocols results, UCI.sub.overdose and UCI.sub.underdose are evaluated. According to these results, the cause of unconformity is determined. Finally, new treatment plans are created that eliminate this cause. CI should re-evaluate for this new treatment plan and if the result complies with clinical protocols, the patient is treated with the relevant plan.