I= DEVELOPMENT OF STANDARD PROCEDURES FOR ABSORBED DOSE DETERMINATION BY IONIZATION CHAMBERS IN PHOTON AND ELECTRON BEAMS
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Title of Thesis
DEVELOPMENT OF STANDARD PROCEDURES FOR ABSORBED DOSE DETERMINATION BY IONIZATION CHAMBERS IN PHOTON AND ELECTRON BEAMS

Author(s)
SYED SALMAN AHMAD
Institute/University/Department Details
Department Of Physics/ Quaid-i-Azam University, Islamabad
Session
1992
Subject
Physics
Number of Pages
123
Keywords (Extracted from title, table of contents and abstract of thesis)
absorbed dose determination, ionization chambers, photon beams, electron beams, cavity chambers, aifb dosimetry, dosimetry protocol, absorbed dose, nacp dosimetry protocol, hpa dosimetry protocol, aapm dosimetry protocol, sefm dosimetry protocol, iaea dosimetry protocol

Abstract
The main objective of this thesis is to analyze the standard procedure for the accurate determination of absorbed dose to water at electron and photon clinical beams with energy up to 25 MeV. To this aim a number of cavity chambers of cylindrical and plane-parallel types were used. Emphasis is directed towards the analysis of the internal consistency of the Italian AIFB dosimetry protocol when applied to different types of ionization chambers. Some comparative measurement by a graphite calorimeter was also made to have an absolute and independent determination of the absorbed dose values. Measurements at photon and electron beams by cylindrical chambers give consistent results.

At electron beams plane-parallel chambers show some appreciable deviations in the absorbed dose values. In this case it is likely that the electron fluence perturbation factors, currently assumed equal to unity, differ from unity for the chambers and at the energies involved. Final results are discussed as far as chamber characteristics and protocol consistency are concerned.

A review of the various national and international dosimetry protocol for the determination of absorbed dose to water in high energy electron and photon beam is also presented in this thesis.

To develop standard procedures for the calibration of plane parallel chambers using Co-60 gamma-ray beam free in air, the influence of various build-up materials is studied and the composite correction factor kpp determined. The perturbation factors at the reference Co-60 gamma radiation for various plane parallel chambers were also determined in PMMA and graphite phantom using different calibration procedures. The results of these investigations are compared with the results presented in literature and a good agreement was found. These provisional results now provide the basis for the calibration of plane-parallel chambers, carried out at primary standard dosimetry laboratory of ENEA utilizing Co-60 gamma-ray beam.

Download Full Thesis
1658.61 KB
S. No. Chapter Title of the Chapters Page Size (KB)
1 0 Contents
91.79 KB
2 1 Introduction 1
45.72 KB
  1.1 Dosimetry Codes Of Practice (Protocols) 2
  1.2 Scope Of Work 3
3 2 Beam Quality Specification And Determination 6
122.66 KB
  2.1 High Energy Electron Beams 6
  2.2 High Energy Photon Beams 19
4 3 Calibration Of Ionization Chambers 21
67.09 KB
  3.1 Calibration Of Cylindrical Chambers 21
  3.2 Calibration Of Plane-Parallel Chambers 24
5 4 Determination Of Absorbed Dose To Water 26
240.66 KB
  4.1 Basic Expressions For Absorbed Dose Determination 27
  4.2 Dosimetry Phantoms 35
  4.3 Effective Point Of Measurement 36
  4.4 Reference Conditions For The Determination Of Absorbed Dose To Water 39
  4.5 Correction For Ion Recombination 41
  4.6 Reference Depth For Absorbed Dose 44
  4.7 Absorbed Dose Determination At Points Other Than The Reference Points 45
  4.8 Absorbed Dose Determination With Calorimeters 45
  4.9 Graphite Calorimeter 49
6 5 National And International Dosimetry Protocols 52
134.84 KB
  5.1 NACP Dosimetry Protocol 53
  5.2 HPA Dosimetry Protocol 55
  5.3 AAPM Dosimetry Protocol 58
  5.4 SEFM Dosimetry Protocol 60
  5.5 IAEA Dosimetry Protocol 62
  5.6 AIFB Dosimetry Protocol 64
  5.7 Comparison Of Various Dosimetry Protocols 66
7 6 Experimental Delerminations 68
480.64 KB
  6. 1 Radiation Beam Quality Measurements For Photons And Electrons 68
  6.2 Experimental Arrangements And Procedure For Calibration Of Cylindrical Chambers 68
  6.3 Experimental Arrangements And Procedure For The Calibration Of Plane-Parallel Chambers 70
  6.4 Irradiation On Clinic 71
  6.5 Measurements For Determination Of Absorbed Dose To Water 76
8 7 Results And Discussions 80
78.15 KB
  7.1 Absorbed Dose Measurement Results 81
9 8 Calibration Of Plane-Parallel Chambers Using Co-60 Gamma-Ray Beam 88
459.1 KB
  8.1 Objective 88
  8.2 Calibration Free-In -Air 89
  8.3 Calibration In PMMA Phantom At The Depth Of The Maximum Dose 91
  8.5 Results And Discussions 101
10 9 Conclusion 111
122.95 KB
  9.1 Appendix 1 113
  9.2 Reference 114