In Vivo Dosimetry using Plastic Scintillation Detectors for External Beam Radiation Therapy

part of an Institutional Review Board approved protocol. PSDs were attached to 
endorectal balloons used routinely during prostate radiotherapy, positioning the detectors 
in close proximity with the rectal wall. Two PSDs were used for two treatment fractions 
each week for the duration of each patient’s treatment. The difference between the 
measured dose and expected dose was used to evaluate the accuracy and precision of the 
system. The mean difference between the measured and expected dose for the five patient 
population was -0.4%, with a standard deviation of 2.8%. The mean differences for 
individual patients fell between -3.3% and 3.3%. 
Finally, a thorough characterization of the response of PSDs used for absolute 
entrance dosimetry in proton beams was performed. Entrance dose measurements for a 
passively scattered proton beam performed with a PSD were compared to measurements 
made with an ion chamber and radiochromic film. Ionization quenching, an under-
response due to densely ionizing radiation, was found to be responsible for a 7% loss of 
signal at the highest energy studied (250 MeV) and a 10% loss at the lowest (140 MeV). 
The under-response was found to be insensitive to other beam parameters, such as the 
width of the spread out Bragg peak.
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TABLE OF CONTENTS 
Title Page ...................................................................................................................ii 
Dedication ..................................................................................................................iii 
Acknowledgements ....................................................................................................iv 
Abstract ......................................................................................................................v 
Table of Contents .......................................................................................................vii 
List of Illustrations .....................................................................................................xi 
List of Tables .............................................................................................................xiii 
Abbreviations .............................................................................................................xiv 
1. Introduction ............................................................................................................1 
1.1 Purpose Statement ....................................................................................2 
1.2 Rationale and Significance ......................................................................2 
1.3 Specific Aims ...........................................................................................4 
1.4 Organization .............................................................................................5 
2. Background ............................................................................................................6 
2.1 Physical Mechanism of Scintillation .......................................................7 
2.2 Design of Plastic Scintillation Detector Systems .....................................12 
2.3 Dosimetric Properties of Plastic Scintillation Detectors ..........................16 
2.4 In Vivo Dosimetry ....................................................................................18 
2.5 Challenges of In Vivo Dosimetry .............................................................21 
2.6 Plastic Scintillation Detectors for In Vivo Dosimetry ..............................23 
3. Temperature Dependence of Plastic Scintillation Detectors .................................26 
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3.1 Introduction ............................................................................................27 
3.2 Methods and Materials ...........................................................................29