Ultrasound elevation beamwidth is the out of plane thickness causing image artefacts normally appearing around anechoic areas in the medium. These artefacts could also cause uncertainties in localizing objects (such as a surgical needle) in the ultrasound image slices. This thesis studies the clinical significance of elevation beamwidth artefacts in needle insertion procedures. A new measurement device was constructed to measure the transrectal ultrasound elevation beamwidth. The beam profiles of various lateral and axial distances to the transducer were generated. It is shown that the ultrasound elevation beamwidth converges to a point within its focal zone close to the transducer. This means that the transrectal ultrasound images have the best resolution within the focal zone of the ultrasound close to the transducer. It is also shown that the ultrasound device settings have a considerable impact on the amount of beamwidth artefacts. Needle tip localization error was examined for a curvilinear transrectal ultrasound transducer. Beveled prostate brachytherapy needles were inserted through all holes of a grid template orthogonal to the axial beam axis. The effects of device imaging parameters were also investigated on the amount of localization error. Based on the developed results, it was found that the imaging parameters of an ultrasound device have direct impact on the amount of object localization error from 0.5 mm to 4 mm. The smallest localization error occurs laterally close to the center of the grid template, and axially within the beam’s focal zone. Similarly, the largest localization error occurs laterally around both sides of the grid template, and axially within the beam’s far field. Using the ultrasound device with appropriate imaging settings could minimize the effects of these artefacts. We suggest to reduce the gain setting of the ultrasound device. This will reduce the energies assigned to the off-axis beams and as a result, the elevation beamwidth artefacts are minimized. / Thesis (Master, Computing) -- Queen's University, 2011-09-01 15:27:43.098

Prostate cancer continues to be the most commonly diagnosed cancer among men. Brachytherapy has emerged as one of the definitive treatment options for early stage prostate cancer which entails permanent implantation of radioactive seeds into the prostate to eradicate the cancer with ionizing radiation. Successful brachytherapy requires the ability to perform dosimetry -which requires seed localization- during the procedure but such function is not available today. If dosimetry could be performed intraoperatively, physicians could implant additional seeds into the under-dosed portions of the prostate while the patient is still on the operating table. This thesis addresses the brachytherapy seed localization problem with introducing intensity based registration between transrectal ultrasound (TRUS) that shows only the prostate and a 3D seed model drawn from fluoroscopy that shows only the implanted seeds. The TRUS images are first filtered and compounded, and then registered to the seed model by using mutual information. A training phantom was implanted with 48 seeds and imaged. Various ultrasound filtering techniques were analyzed. The effect of false positives and false negatives in ultrasound was investigated by randomly masking seeds from the fluoroscopy volume or adding seeds to that in random locations. Furthermore, the effect of sparse and dense ultrasound data was analyzed by running the registration for ultrasound data with different spacing. The registration error remained consistently below clinical threshold and capture range was significantly larger than the initial guess guaranteed by the clinical workflow. This fully automated method provided excellent registration accuracy and robustness in phantom studies and promises to demonstrate clinically adequate performance on human data. / Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2008-09-27 12:35:16.691

Interstitial brachytherapy using permanent seeds is a common modality for the treatment of early stage prostate cancer. It consists of inserting hundreds of radioactive seeds (size of a grain of rice) in the prostate by means of transperineal needles. In this procedure, dose delivery to healthy surrounding organs at risk (OAR) and dose homogeneity within the prostate are of prime concern. Placement errors should therefore be minimized to avoid unacceptable area underdosage or overdosage. At present, brachytherapy seeds can be loaded with three different radionuclides: iodine-125 (¹²⁵I: 28.37 keV; 59.40 days), palladium-103 (¹⁰³Pd: 20.74 keV; 16.991 days), and cesium-131 (¹³¹Cs: 30.45 keV; 9.689 days). Long or short term morbidity is the main drawback of ¹²⁵I and ¹³¹Cs due to their deeper penetration in the normal tissues. However, both provide a good homogeneity of the dose distribution within the prostate. By contrast, ¹⁰³Pd offers a short penetration depth that reduces the dose to OAR. Nevertheless, it could result in cold spot (underdosage) where a recurrence of the cancer could appear. A compromise had to be found between good implant uniformity and low dose to OAR. We propose therefore to study if the combination of two radionuclides inside the same seed could be a solution. Two mixtures were considered: ¹⁰³Pd_0.75-¹²⁵I_0.25 and ¹⁰³Pd_0.25-¹³¹Cs_0.75. The subscripts denote the fractions of internal activity of each radionuclide. The work is subdivided into three steps. First we adapt the AAPM TG-43U1 dosimetry formalism used by the physician to make multiple-radionuclides sources compatible with Treatment Planning Systems (TPS). Then the dose distributions around the bi-radionuclide seeds are determined. Second, the prescription doses for both sources are derived using the linear quadratic model for tumor cell surviving fraction. They were computed using mono-radionuclide implants as benchmarks. Finally, treatment plans and Dose-Volume Histograms parameters have been computed on real patients virtually implanted with bi-radionuclide seeds and the results were compared with the mono-radionuclide one. These parameters can then be used to evaluate the Normal Tissue Complication Probability (NTCP) of urethra, the most exposed organ at risk in prostate brachytherapy. First, dosimetry results show that, from a pure physical point of view (i.e. without tissue reponse), the dose distributions of both mixtures lies in between that for ¹⁰³Pd and ¹²⁵I/¹³¹Cs. The compromise between homogeneity and reduced dose at large distance can be reached. Second, the averaged prescription doses for the Pd-I mixture are 142⁺¹⁵_-16Gy and 142⁺⁶_-8Gy using ¹⁰³Pd and ¹²⁵I as benchmarks, respectively. The values for the Pd Cs mixture are 128⁺¹³_-13Gy and 115⁺⁶_-7Gy, using ¹⁰³Pd and ¹³¹Cs, respectively, as benchmarks. Finally, urethral NTCP results fall in the 19 to 23% range. However, they are affected by large uncertainties, making the comparison difficult. At present, no conclusion could be drawn about the efficiency of bi-radionuclide brachytherapy in comparison with mono-radionuclide using the available models. Permanent seed prostate brachytherapy suffers a lot from the lack of precision on radiobiological modelling parameters. A better knowledge of their values could significantly improve the predicting models and therefore lead to better treatment outcome.