Over-Response Correction of SNC 350p ROOS and PTW Markus Chambers in the Surface Dose and Build-Up Region Dosimetry of 6MV Photon Beam

Document Type : Original Paper

Authors

1 Department of Medical Physics,State Cancer Institute, Indira Gandhi Institute of Medical Sciences,Patna, Bihar.

2 Indira Gandhi Institute Of Medical Sciences ,Sheikhpura ,Patna

3 BALCO Medical Center, Vedanta Research Foundation, New Raipur, atal Nagar, Chhattisgarh 493661

4 Department of Radiation Oncology, Kiran Multi Super Speciality Hospital, Surat-395004, Gujarat.

5 Department of Radiation Oncology, STARLIT Cancer Center, Ahmadabad-382350, Gujarat.

Abstract

Introduction: The design characteristics of ionization chambers are critical for the accurate measurement of Percentage Surface Dose (PSD) and Percentage Depth Dose (PDD) in the build-up region. This study assesses the over-response correction in PSD and PDD for different field sizes, using Markus and ROOS fixed separation parallel-plate ionization chambers.
Material and Methods: The Sun Nuclear Corporation SNC 350P ROOS and PTW Markus parallel plate ionization chambers were used to measure 6 MV photon beam PDD along the central axis in the build-up region.The experiment was performed on a Solid Water® HE phantom with a density of 1.032 g/cm3.The Measurements were taken at a Source Surface distance (SSD) of 100 cm with Field sizes of 10x10cm2,20x20 cm2, and 30x30cm2 and at variable depths.
Results: For field sizes of 10x10 cm2, 20x20 cm2, and 30x30 cm2 at a source-to-axis distance (SAD) of 100 cm, the PSD values obtained with the Markus chamber, before and after applying Rawlinson's equation for over-response correction, were as follows: 35.11%, 42.92%, 50.72% (before correction) and 28.37%, 36.19%, 44.05% (after correction). Similarly, the PSD values measured using the ROOS chamber, before and after applying over-response correction, were as follows: 41.61%, 50.50%, 58.04% (before correction), and 33.96%, 42.87%, 50.38% (after correction).
Conclusion: The application of over-response correction using Rawlinson's equation improved the accuracy of measurements for both chambers, emphasizing the significance of employing appropriate correction techniques to ensure precise dose measurements in the build-up region using ionization chambers.

Keywords

Main Subjects

References

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Iranian Journal of Medical Physics
Volume 21, Issue 4 - Serial Number 4
July and August 2024
Pages 272-279

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History

  • Receive Date: 31 March 2023
  • Revise Date: 01 August 2023
  • Accept Date: 11 August 2023

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