In High Dose Rate (HDR) brachytherapy, treatment dose to patients is highly dependent on the accuracy of positioning and duration of the source. Source misplacement or wrong duration of treatment could potentially result in adverse clinical side effects to patients. In order to maintain successful treatment for patients, an independent Quality Assurance (QA) verification is crucial to measure the High Dose Rate (HDR) source positioning and dwell time periodically to ensure the prescribed dose is correct and safe for brachytherapy treatment. The current QA practice used to validate the accuracy of dwell time of the source is by using a stopwatch and measure the dwell position on the source position check ruler. Nevertheless, reaction time of human poses a major concern regarding the accuracy in these manual operating procedures. In this thesis, a new QA tool is proposed to acquire accurate information about time structure and source positioning in HDR brachytherapy. The tool consists of a consumer-grade webcam, a source position check ruler, a laptop computer and a custom-made combined camera-ruler mounting tool. The camera is used to capture the motion of the moving source in real time. Each frame contains positional and temporal information that are important to determine the difference between the measured and the actual HDR source position and time structure. Finally, a Graphical User Interface (GUI) application program is developed to receive the input from the camera for image processing. The measured results (time structure and positional information) are displayed on the computer screen as the output of the designed application. The tool was found to be able to reduce the time required significantly for the QA and minimize the impact of human errors. At the time of writing, the sensitivity of the system to luminous changes in the environment warrants further efforts to render the tool even more useful. Based on the experimental results, the accuracy of dwell time measured by the proposed system was ± 40 ms. The minimum detectable dwell time of the proposed system was 200 ms. The range of effective dwell position that could be measured by the system ranged from 1300 mm to 1500 mm (excluding 1300 mm and 1500 mm). The accuracy of dwell position measured by the proposed system was ± 1mm. / published_or_final_version / Diagnostic Radiology / Master / Master of Medical Sciences

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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.

Multi-helix rotating shield brachytherapy (RSBT) applicator and multi-source RSBT apparatus are two novel intensity-modulated brachytherapy techniques for the treatment of cervical and prostate cancer, respectively. The use of imaging techniques such as magnetic resonance imaging guided brachytherapy has enabled the precise identification and contouring of tumor volumes for treatment planning, as well as demonstrated the challenges associated with using conventional high dose rate brachytherapy (HDR-BT) approaches to conform the radiation dose to the target and avoid surrounding sensitive healthy tissues. The target conformity of conventional HDR-BT dose distributions is restricted based on the geometrical constraints imposed by the position and shape of the tube-shaped applicators, as well as the radially-symmetric radiation dose distributions produced by the radiation sources. Dose distribution conformity for cervical and prostate cancer can be significantly improved relative to conventional HDR-BT through the use of multi-helix and multi-source RSBT techniques, respectively. In this study, two novel RSBT concepts for treating cervical and prostate cancer were introduced and the dosimetric impact was evaluated. A Henschke-type cervical cancer applicator, designed for an electronic brachytherapy (eBx) source (Xoft AxxentTM) and a 0.5 mm thick tungsten partial shield with 180° or 45° azimuthal emission angles, is proposed. The interior wall of the applicator contains six evenly-spaced helical keyways that rigidly define the emission direction of the partial radiation shield as a function of depth in the applicator. The shield contains three uniformly-distributed protruding keys on its exterior wall and is attached to the source such that it rotates freely, thus longitudinal translational motion of the source is transferred to rotational motion of the shield. RSBT treatment plans were generated for five cervical cancer patients with a diverse range of high-risk target volume (HR-CTV) shapes and applicator positions. Treatment delivery time and tumor coverage (D90 of HR-CTV) were the two metrics used as the basis for evaluation and comparison. With multi-source RSBT apparatus, precise angular and linear positioning of partially-shielded 153Gd brachytherapy sources in interstitial needles for the treatment of locally-advanced prostate cancer is carried out. Following needle implantation through the patient template, an angular drive mechanism is docked to the patient template. Each needle is coupled to a multisource afterloader catheter by a connector passing through a shaft. The shafts are rotated about their axes by translating a moving template between two stationary templates. Shafts’ surfaces and moving template holes are helically threaded with the same pattern such that translation of the moving template causes simultaneous rotation of the shafts. The catheter angles are simultaneously incremented throughout treatment. For each rotation angle, source depth in each needle is controlled by a multisource afterloader, which is proposed as an array of belt-driven linear actuators, each of which drives a wire that controls catheter depth in a needle. In conclusion, the helical RSBT approach for treating cervical cancer and the multi-catheter RSBT approach for treating prostate cancer, powered with novel radiation sources amenable to shielding, are clinically- and mechanically-feasible techniques that dosimetrically outperform conventional brachytherapy methods while minimizing damage to healthy tissues inside and/or adjacent to the target.

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Thesis (M. D.)--University of Hong Kong, 2007. / Also available in print.

No description available.

[Truncated abstract] Purpose: Permanent prostate brachytherapy (PPB) as a treatment option for prostate cancer requires implantation of 80-150 radioactive iodine-125 (I-125)

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2006. / Härtill 4 uppsatser.

No description available.