A theoretical evaluation of transmission dosimetry in 3D conformal radiotherapy.
Date
2008
Authors
Reich, Paul D.
Editors
Advisors
Bezak, Eva
Van Doorn, Timothy
Van Doorn, Timothy
Journal Title
Journal ISSN
Volume Title
Type:
Thesis
Citation
Statement of Responsibility
Conference Name
Abstract
Two-dimensional transmission dosimetry in radiotherapy has been discussed in the literature
for some time as being a potential method for in vivo dosimetry. However, it still
remains to become a wide spread practice in radiotherapy clinics. This is most likely due
to the variety in radiotherapy treatment sites and the challenges they would present in
terms of detection and interpretation at the transmitted dose level. Thus, the full potential
and limitations of applying transmission dosimetry in the presence of dosimetry
errors still need to be demonstrated.
This thesis is a theoretical evaluation of transmission dosimetry using the Pinnacle3 treatment planning system. The accuracy of predicting reliable and accurate absolute transmitted dose maps using the planning system dose algorithm for comparison with measured
transmitted dose maps was initially investigated. The resolution in the dose calculations
at the transmitted level was then evaluated for rectilinear and curved homogeneous phantoms
and rectilinear inhomogeneous phantoms, followed by studies combining both surface
curvature and heterogeneities using anthropomorphic phantoms. In order to perform
transmitted dose calculations at clinically relevant beam focus-to-transmitted dose plane
distances using clinical patient CT data it was first necessary to extend the CT volume.
Finally, the thesis explored the efficacy of applying transmission dosimetry in the clinic by
simulating realistic dosimetry errors in the planning system using patient treatment plans
for a prostate, head and neck, and breast CRT (Conformal Radiotherapy) treatment. Any
differences at the transmitted dose level were interpreted and quantified using the gamma
formalism. To determine whether the transmitted dose alone was a sufficient indicator of the dosimetry errors, the magnitude in transmission dose differences were compared
with those predicted at the midplane of the patient. Dose-Volume Histograms (DVHs)
were also used to evaluate the clinical significance of the dose delivery errors on the target volume and surrounding healthy tissue structures.
School/Discipline
School of Chemistry and Physics : Physics and Mathematical Physics
Dissertation Note
Thesis (Ph.D.) - University of Adelaide, School of Chemistry and Physics, 2008
Provenance
Copyright material removed from digital thesis. See print copy in University of Adelaide Library for full text.