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In-House Computer Controlled Automatic 2D RFA and Dosimeteric Comparison with BJR-25 Report

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S Senthilkumar

S Senthilkumar1*, P Vinothkumar2, (1) Madurai Medical College & Govt. Rajaji Hospital, Madurai, TAMILNADU,India (2) Bharathidasan University, Trichy, TAMILNADU

SU-E-T-34 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

The main purpose of this work was to fabricate an indigenous computer controlled two dimensional Radiation Field Analyzer ₍2D RFA₎ for external beam radiotherapy machines to measure the output, PDD, TMR, TPR and isodose profile automatically. The 2D RFA is fast, accurate, simple and easy to setup.

This 2D RFA consist of water phantom, DC stepper motor, electronic circuit, acrylic chamber holding assembly, Buzzer and LED. An automatic ionization chamber movement tool was fabricated for radiation dose measurement in X direction using a DC stepper motor. There was an arrangement helping to move the ionization chamber in the Y direction. A cylindrical rod was made of acrylic and the other setup also made up of the same low atomic number material to avoid the scatter contribution from the water phantom. An easy mechanism was provided to fix the movable chamber holder setup in the water phantom.

The beam output, PDD, isodose profile for different field sizes and, off-axis ratio were measured for external beam radiotherapy machines using the 2D RFA device with a 0.6cc farmer type ionization chamber. The device was used to measure the dose profiles for various field sizes at various depths. The values were normalized at 0.5cm depth. The measured values and values obtained by BJR25 were compared. The measured values agreed well with those published in the BJR25 report. The average difference was found the maximum variation of 2 percentage.

Dosimetry is important for external beam teletherapy machines. The routine machine output calibrations can be performed with this device. From this, it can be concluded that it is very suitable for routine radiotherapy dosimetery produces. Salient features of the 2D RFA is its speed, accuracy, simplicity, and low cost.

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