Volume 30, Issue 8, August 2003
Index of content:
- PH. D. THESES ABSTRACTS
30(2003); http://dx.doi.org/10.1118/1.1590451View Description Hide Description
Due to the possible side-effects of radical cystectomy for muscle-invading urinary bladder cancer (UBC), radiotherapy remains an attractive organ-sparing treatment option, either alone or combined with increasingly effective chemotherapy.Radiationdose escalation may further improve the results obtained with radiotherapy. This Ph.D. program aimed at developing improved conformal radiotherapy techniques required for dose escalation in bladder irradiation. Initially, computer-controlled movement of the collimators during beam delivery was applied to shape partially wedged beams (PWBs), designed to conform the dose distribution to bladder targets. The dosimetric verification and treatment planning implementation of PWBs were addressed. Particular attention was given to dynamic beam isodose verification with the BMS-96 diode array. The theoretical clinical impact of PWBs in bladder irradiation was evaluated in a planning study. Using PWBs the dose homogeneity inside bladder targets improved and normal tissue (small intestine and rectum) doses were reduced. Judged from normal tissue complication probability (NTCP) modeling, PWBs would allow radiationdose escalation with 2–6 Gy in up to 60% of the patients without increasing the estimated combined NTCP relative to the standard setup. This work also demonstrated the uncertainty in intestine and rectum tolerance data and the differences between the various NTCP models. Finally, the internal bladder motion and patient setup variation were quantified from weekly repeat CT scans and electronic portal images, and new bladder treatment margins were derived. Currently, a bladder dose escalation trial using the PWB principle is performed, testing if the whole bladder target dose can be increased from 64 to 68 Gy while maintaining a low level of treatment-induced complications.
30(2003); http://dx.doi.org/10.1118/1.1593781View Description Hide Description
This thesis deals with the advancements made in the field of Electron Paramagnetic Resonance(EPR) for biophysical dosimetry with tooth enamel for accident, emergency, and retrospective radiationdose reconstruction. A methodology has been developed to measure retrospective radiation exposures in human tooth enamel. This entails novel sample preparation procedures with minimum mechanical treatment to reduce the preparation induced uncertainties, establish optimum measurement conditions inside the EPRcavity, post-process the measured spectrum with functional simulation of dosimetric and other interfering signals, and reconstruct dose. By using this technique, retrospective gamma exposures as low as have been successfully deciphered. The notion of dose modifier was introduced in EPR biodosimetry for low dose measurements. It has been demonstrated that by using the modified zero added dose (MZAD) technique for low radiation exposures, doses in 100 mGy ranges can be easily reconstructed in teeth that were previously thought useless for EPRdosimetry. Also, the use of a dose modifier makes robust dose reconstruction possible for higher radiation exposures. The EPRdosimetry technique was also developed for tooth samples extracted from rodents, which represent small tooth sizing. EPRdoses in the molars, extracted from the mice irradiated with whole body exposures, were reassessed and shown to be correct within the experimental uncertainty. The sensitivity of human tooth enamel for neutron irradiation, obtained from the 3 MV McMaster K.N. Van de Graaff accelerator, was also studied. For the first time this work has shown that the neutron sensitivity of the tooth enamel is approximately 1/10th of the equivalent gamma sensitivity. Parametric studies for neutrondose rate and neutron energy within the available range of the accelerator, showed no impact on the sensitivity of the tooth enamel. Therefore, tooth enamel can be used as a dosimeter for both neutrons as well as gamma radiation. We will continue experiments to develop this end point as a sensitive accident or emergency tool for our response capabilities.