published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy

Stereotactic Body Radiation Therapy (SBRT) is a modern precision radiation therapy to deliver the dose in 1 to 5 fractions with high target dose conformity, and steep dose gradient towards healthy tissues. The dose delivered is influenced by the leaf width of the MLC, especially in case of SBRT. Treatment plans with high definition (HD) MLC having leaf-width 2.5 mm and normal MLC having leaf-width 5 mm, were compared to quantify dosimetric and radiobiological parameters. Dosimetric parameters conformity indices (CI), gradient indices (GI) and heterogeneity indices (HI) were compared. The radiobiological parameters were evaluated by normal tissue complication probability (NTCP) and tumor control probability (TCP) based on the equivalent uniform dose (EUD). The results show that there is dosimetric and radiobiological merit of the HD MLC over the normal MLC. However, the improvement is not consistent with all the plans and thus further research is required prior to conclusion. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2018. / FAU Electronic Theses and Dissertations Collection

by Chan Yiu Nam. / Chinese title: / Includes bibliographical references / Thesis (M.Phil.) -- Chinese University of Hong Kong, 1983

Digitized by Kansas Correctional Industries

Due to the difficulty of a complex commissioning technique for a multi energetic, multi-modality linear accelerator, I perform all the commissioning and acceptance testing for a TrueBeam linear accelerator with 4 megavoltage (MV) energies of which 2 are flattening filter-free (FFF) and 6 electron energies varying from 6 MeV to 20 MeV. A 2 dimensional (2D) water tank was used for scanning all the required field sizes for all the energies. The one dimensional (1D) water tank was used to collect all the output factors for all the photon fields sizes small to medium electron field sizes. For the large electron fields sizes, we had to use the 2D water tank. All the collected data was converted into a file type accepted by the planning system (Eclipse) and subsequently imported there. Treatment plans were generated using multiple forms of planning to verify the viability and quality of the beam data commissioned. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2019. / FAU Electronic Theses and Dissertations Collection

Graduation date: 2003

Graduation date: 1998

Current brachytherapy treatment planning systems are unable to accurately calculate dose distributions in the vicinity of brachytherapy sources having active lengths much greater than 5 mm. While low dose-rate ¹³⁷Cs sources are dosimetrically characterized using antiquated along-away tables with simple linear-linear interpolation errors in dose calculation exceeding 30% occur due to algorithm inadequacy. The method presented in this thesis permits dosimetric characterization of elongated brachytherapy sources with active lengths 0 < L < 10 cm for implementation on an FDA-approved clinical TPS. Low- and high-energy photon-emitting sources of Pd-103 and Ir-192, respectively, were examined.

Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, September 2003. / Thesis advisor(s): Todd R. Weatherford, Andrew A. Parker. Includes bibliographical references (p. 39). Also available online.

Energy modulated electron therapy (EMET) is a promising treatment modality that has the fundamental capabilities to enhance the treatment planning and delivery of superficially located targets. Although it offers advantages over x-ray intensity modulated radiation therapy (IMRT), EMET has not been widely implemented to the same level of accuracy, automation, and clinical routine as its x-ray counterpart. This lack of implementation is attributed to the absence of a remotely automated beam shaping system as well as the deficiency in dosimetric accuracy of clinical electron pencil beam algorithms in the presence of beam modifiers and tissue heterogeneities. In this study, we present a novel technique for treatment planning and delivery of EMET. The delivery is achieved using a prototype of an automated "few leaf electron collimator" (FLEC). It consists of four copper leaves driven by stepper motors which are synchronized with the x-ray jaws in order to form a series of collimated rectangular openings or "fieldlets". Based on Monte Carlo studies, the FLEC has been designed to serve as an accessory tool to the current accelerator equipment. The FLEC was constructed and its operation was fully automated and integrated with the accelerator through an in-house assembled control unit. The control unit is a portable computer system accompanied with customized software that delivers EMET plans after acquiring them from the optimization station. EMET plans are produced based on dose volume constraints that employ Monte Carlo pre-generated and patient-specific kernels which are utilized by an in-house developed optimization algorithm. The structure of the optimization software is demonstrated. Using Monte Carlo techniques to calculate dose allows for accurate modeling of the collimation system as well as the patient heterogeneous geometry and take into account their impact on optimization. The Monte Carlo calculations were validated by comparing them against output measurements with an ionization chamber. Comparisons with measurements using nearly energy-independent radiochromic films were performed to confirm the Monte Carlo calculation accuracy for 1-D and 2-D dose distributions. We investigated the clinical significance of EMET on cancer sites that are inherently difficult to plan with IMRT. Several parameters were used to analyze treatment plans where they show that EMET provides significant overall improvements over IMRT.