Manuscript Title:

A STUDY ON THE EFFECTIVENESS OF TG-51 AT EXTENDED SSD IN IONISATION CHAMBER CALIBRATION BY CORRECTION FACTORS IN TOTAL BODY IRRADIATION DOSIMETRY

Author:

MAMOONA ASLAM, SAEED AHMAD BUZDAR, KHALID IQBAL, MEHRUN NISA, AYESHA IKHLAQ, SANA SALAHUDDIN, USMAN MUSTAFA

DOI Number:

DOI:10.17605/OSF.IO/3XEMF

Published : 2023-04-23

About the author(s)

1. MAMOONA ASLAM - Institute of Physics, The Islamia University of Bahawalpur, Pakistan.
2. SAEED AHMAD BUZDAR - Institute of Physics, The Islamia University of Bahawalpur, Pakistan.
3. KHALID IQBAL - Shaukat Khanum Memorial Cancer Hospital and Research Centre Lahore, Pakistan.
4. MEHRUN NISA - Department of Physics, Government Sadiq College Women University, Bahawalpur, Pakistan.
5. AYESHA IKHLAQ - Institute of Physics, The Islamia University of Bahawalpur, Pakistan.
6. SANA SALAHUDDIN - Institute of Physics, The Islamia University of Bahawalpur, Pakistan.
7. USMAN MUSTAFA - Institute of Physics, The Islamia University of Bahawalpur, Pakistan.

Full Text : PDF

Abstract

Purpose: The Aim of this study is to calculate and validate the ion collection efficiency of Farmerionization chamber and Markus ionization chamber by calculating ion correction factor Pion and polarity correction factor and applying these values in total raw ion chamber reading to calibrate the machines accurately at extended SSD and to check the effectiveness of these chambers in reference dosimetry of TBI. Also the application of TG-51 is being studied at extended SSD by verifying the values of ion correction factor (Pion), polarity correction factor (Ppol), percent depthdose (PDD) and dose rate. Materials and Methods: PDDs, Pion, Ppol were calculated for 6 MV and 18 MV photon beams under TBI standard conditions using solid water phantom and ion chambers (Markus 0.6 cc and Farmer 0.02cc).The standard deviations and correlation was also measured. Results: For 6 MV at SSD= 100 cm, the values of Pion and Ppol are 0.992 and 0.996 forFarmer chamber and for Markus chamber respectively, and at extended SSD the values are 0.98 and 0.84 and their relative error lies less than 1%. For 18 MV the deviations in Pion and Ppol values,at extended SSD were 15% and 13% respectively which are exceeding the permitted value of uncertainty, and at 100 cm SSD for Markus chamber the Pion and Ppol values are 0.986 and 0.856 respectively which shows good agreement with the prescribed tolerance limit. Conclusions: Farmer ionization chamber and Markus ionization chamber are consistent andefficient at 100 cm but due to cable effect, the Pion and Ppol values are not in good agreement at extended SSD hence these ionization chambers are not recommended at extended SSD for TBI dosimetry.


Keywords

Total Body Irradiation, Dosimetry, Pion, P pol, Mayneord’s Factor, Source to Surface Distance.