Dose and Position Measurements using a Novel Four-Dimensional In Vivo Dosimetry System

This work presents a comprehensive characterization of the dosimetric and position measurement characteristics as well as clinical implementation of a novel four-dimensional in vivo dosimetry system, RADPOS. Preliminary dose and position measurements were first conducted to evaluate any deviation from known characteristics of metal-oxide semiconductor field-effect transistors, MOSFETs, and electromagnetic positioning systems when they are used alone. The system was then combined with a deformable tissue equivalent lung phantom to simulate respiratory-induced tumour motion and lung deformation and to evaluate the potential use of the system as an effective quality assurance tool for 4D conformal radiotherapy. The final phase of testing involved using the RADPOS 4D in vivo dosimetry system in two different clinical trials. The first involved characterizing the breathing patterns of lung cancer patients throughout the course of treatment and measuring inter-fraction variations in skin dose. Within this framework, the feasibility of general use of the RADPOS system on patients during daily treatment fractions was also assessed. The second trial involved a modified RADPOS detector that contained a MOSFET array, allowing for dose measurements at five different points. This detector was used to measure dose and position in the prostatic urethra throughout seed implantation for transperineal interstitial permanent prostate brachytherapy.;transmitter and when interfering metal objects are kept at least 200 mm away. Combining the RADPOS system with a deformable lung equivalent phantom allowed for efficient quality assurance of 4D radiation therapy, as agreement between dose measurements and treatment plan calculations was within 5% for both free breathing and adaptive treatment deliveries and position measurements were accurate and consistent between the CT and treatment delivery rooms. The two clinical trials demonstrated that the RADPOS system can be used during daily treatments without any disruption to the treatment schedule or discomfort to patients. The lung patient study found significant deviations in external surface motion which emphasize a need for continued position monitoring. Average measured dose values were in agreement with treatment plan dose calculations for the majority of points. The second clinical trial highlighted deviations from calculated treatment plan values as well as changes in position due to needle placement, swelling, and other internal motion as well as changes due to the TRUS probe. These changes were found to be significant in several cases and should therefore be quantified to evaluate influence on dose distributions.;It has been found that the dosimetric response is similar to that of a microMOSFET, when used alone, aside from a slightly higher variation in angular response. Position measurements can be obtained with an uncertainty of +/- 2 mm when the detector remains within a specific optimal volume with respect to the magnetic field...