Author ORCID Identifier
Doctor of Philosophy
Dr. William Y. Song
Gynecologic brachytherapy (GYN-BT) is essential for treating cervical and endometrial cancers, the most prevalent female reproductive cancers. This technique enables high radiation doses to a target with rapid dose fall-off to protect adjacent healthy organs. This dissertation aims to address some of the limitations of intracavitary GYN-BT using an intensity modulated brachytherapy (IMBT) technique and Monte Carlo (MC) simulations.
First, a novel non-invasive shielded vaginal cylinder (VC) applicator was designed to provide optimized radiation coverage for the target volume at vaginal apex, site of most recurrences without BT, for endometrial cancer BT. Physical limitations of current applicators and their resulting treatment plans, such as the cold spots in the dose distribution due to BT radiation source design and presence of air gaps/suture materials can cause significant loss of coverage in this region. The new IMBT VC was designed using GEANT4 Monte Carlo (MC) simulation, by embedding a detachable high-density metal inside a standard VC applicator to directionally modulate the radiation beam and help the optimized coverage at the region.
Second, the effect of the VC heterogeneity on dose calculation for different commercial VCs was investigated. BrachyVision Acuros (BVA), a model-based dose calculation commercial treatment planning system capable of accounting for any inhomogeneity, was also benchmarked against MC simulations. Unlike BVA dose calculation, MC simulations showed the heterogeneity could reduce the target coverage and notably increase uncertainty when prescribing to the surface of the applicator.
Third, a novel IMBT tandem applicator was designed for BT of cervical cancer. This non-invasive approach can provide coverage for non-symmetric targets which present a big challenge in clinical applications. The novel applicator utilizes high-density iridium wires that can easily move inside a tandem base. Therefore, dynamic directional modulation of the radiation beam is achievable in any desired direction, through active insertion/removal of iridium wires in a multichannel base.
Finally, a benchmark study was implemented for another novel IMBT tandem applicator to help the ongoing clinical research. The applicator has been recently modeled in BVA TPS and has shown promising results for coverage of nonsymmetric targets in cervical cancer. Results indicated that the accuracy of the TPS in dose calculations depends notably on the phantom (and hence patient) size.
In summary, non-invasive solutions for coverage of big/nonuniform targets in cervical and endometrial cancers were successfully introduced and implemented, through applications of IMBT. Manufacturing of the applicator prototypes and development of required software/hardware would be the next steps for the advancement of the research. In addition, BVA was thoroughly benchmarked for GYN-BT dose calculations. The results may further be available for correlation with known clinical outcome.
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