YY 0831.1-2011Stereotactic radiotherapy system with gamma beam - Part 1: Multi-source stereotactic radiotherapy system with gamma beam for head lesion (English PDF)

4.6 Deviation of positioning reference point

Deviation of the positioning reference point of the system shall meet the following requirements.

a) For the minimum focused field, the deviation between the positioning reference point and the focus shall be less than or equal to 0.5 mm;

b) The deviations of positioning reference point for each focused field shall be included in accompanying documents.

4.7 Integrated error of dose calculation

For each focused field, the error between the absorbent dose value calculated by the therapeutic planning software AND the actual measured value shall not exceed ±5%.

4.8 Position error of therapeutic plan reference point

Reconstruction position error of therapeutic planning software shall not exceed 1.5 mm.

4.9 Safety requirements

The system shall meet the requirements of GB 9706.1-2007, GB 9706.15-2008, GB 9706.17-2009 and YY 0637-2012.

5.1 Coordinate system

Check the accompanying documents. It shall comply with the requirements of 4.1.

5.2 Accompanying documents

Check the accompanying documents. It shall comply with the requirements of 4.2.

5.3 Nominal absorbed dose rate of the focus

5.3.1 The ionization chamber and the dosimeter used for measurement shall meet the requirements of the measurement conditions. Install the special spherical die body (hereinafter referred to as "Special Die body", see Appendix A) of which the diameter is 160 mm on the positioning bracket. The die body's center is located at the positioning reference point. Insert it into ionization chamber, so as to make its effective measurement point to coincide with the die body's center. Transfer the special die body along with the therapeutic bed into a predetermined irradiation position. Use the maximum focused field. minimum focused field;

Dmax - Dosimeter readings at the focus in special spherical die body when using the maximum focused field.

5.4 Focused field size

5.4.1 Grayscale-dose calibration

Radiate a series of films in the allowed test area of grayscale-dose response curve of the film. Use a suitable mathematical model according to the radiating dose values and the corresponding film's grayscale value, Draw the grayscale-dose response curve for the radiation films used.

5.4.2 Focused field film radiation

According to following steps to respectively measure the maximum deviations of the focused field size and the nominal value.

a) Select a set of collimator for therapy. Measure at least on 2 focal planes;

b) Put the film of which the size fits the measurement of focused field onto the central position of special die body. Let the film to be located on some focal plane;

c) Transfer the special die body, together with the therapeutic bed, into focus position.

Start to radiate. Radiation dose shall be within the appropriate response area of the grayscale-dose response curve of the film used.

d) Repeat b). Let the film to be located on another focal plane. Repeat the radiation operation of c);

e) Replace the collimator. Repeat tests b)-e). Complete the radiation of each group of focused field;

f) Perform the therapy to the film.

5.4.3 Calculation of focused field size

According to following steps to calculate the focused field size.

a) Use a scanner to scan the film. The resolution shall not be less than 300 DPI. Respectively scan the focused field films of 5.4.2;

b) Use the grayscale-dose response curve of 5.4.1 to convert the film grayscale TO corresponding dose values. Draw a dose distribution curve on directions of 3 axes.

c) Separately find out the dose of each film at positioning reference point. Define the dose value as the 100% dose value of the film; planning software AND the actual measured absorbed dose value shall comply with the requirements of 4.7.

Calculate the absorbed doses at 3 reference points. Calculate the relative deviation according to Formula (6); Where.

deltaP - Relative deviation between focus planned dose and measured dose, %;

P0 - Planned dose at die body center (i.e., focused plan dose), in unit of Gy;

P1 - Actual measured absorbed dose at die body center, in unit of Gy.

5.8 Position deviation of therapeutic planning reference point

According to the image parameter's requirements that are given by accompanying documents and are required to achieve the reconstruction precision of three-dimensional image of therapeutic planning software, fix the imaged head die body that is installed with 3 known target volumes INTO the stereotaxic positioning apparatus. Mount together on an imaging system to scan, so as to obtain satisfactory image. Input the image data into therapeutic planning system. Calculate the coordinates of the 3 target volumes.

Respectively calculate the position coordinates of the center of the 3 target volumes in the 3 directions of X, Y, Z. Calculate the reconstruction position deviation of the three-dimensional image of therapeutic planning software according to Formula (7). Where.

delta2 - The distance between the center of the target volume and reconstruction target volume of therapeutic planning software, in unit of mm (mm);

deltaX2 - In X-axis direction, the distance between the center of the target volume and reconstruction target volume of therapeutic planning software, in unit of millimeter (mm); […]