Journal of Medical Physics and Applied Sciences

Validating the Percentage Depth Doses Using Two Different Phantom Materials

Introduction: Percentage depth dose (PDD) is important for absolute dose measurements in external beam radiotherapy machines. Solid water has a density close to water. International Atomic Energy Agency (IAEA) TRS 398 protocol recommends water for absolute dosimetry measurements.

Aim: To conduct a quick PDD check using solid water without setting up a water tank for 6MV, 8 MV and 18 MV photon beam energies.

Materials and methods: RM457 solid water phantom, IBA Blue phantom2 water tank, PTW 30013 Farmer chamber (0.6 cc), IBA scanning chamber CC04, IBA Omnipro Accept 7.4b software, PTW UNIDOS E Electrometer, ELEKTA Synergy platform.

Set-up: 100 cm SSD, 10 × 10 cm² field size, 100 MU.

Results: Higher % difference observed for the build-up regions in ranges of; 6 MV: -4.3% to -1.1%; 8 MV: -5.6% to -1.6% and 18 MV: -8.1% to -1.3%. Zmax values shifted by ± 2 mm from the water phantom data.

Dose fall-off region-values were in agreement (within ± 1%) except for 6 MV at 20 cm, which was -1.2%.

Conclusion: The proposed method can be used as a practical recommendation for a quick dosimetric reference check for PDDs.

Author(s):

Keolathile Diteko, Thokozani Dudley Mkhize and Mohlapoli Stadium Mohlapholi

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