Browsing by Subject "Brachytherapy"
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Item 142pr glass seeds for the brachytherapy of prostate cancer(Texas A&M University, 2007-09-17) Jung, Jae WonA beta-emitting glass seed was proposed for the brachytherapy treatment of prostate cancer. Criteria for seed design were derived and several beta-emitting nuclides were examined for suitability. 142Pr was selected as the isotope of choice. Seeds 0.08 cm in diameter and 0.9 cm long were manufactured for testing. The seeds were activated in the Texas A&M University research reactor. The activity produced was as expected when considering the meta-stable state and epi-thermal neutron flux. The MCNP5 Monte Carlo code was used to calculate the quantitative dosimetric parameters suggested in the American Association of Physicists in Medicine (AAPM) TG-43/60. The Monte Carlo calculation results were compared with those from a dose point kernel code. The dose profiles agree well with each other. The gamma dose of 142Pr was evaluated. The gamma dose is 0.3 Gy at 1.0 cm with initial activity of 5.95 mCi and is insignificant to other organs. Measurements were performed to assess the 2-dimensional axial dose distributions using Gafchromic radiochromic film. The radiochromic film was calibrated using an X-ray machine calibrated against a National Institute of Standards and Technology (NIST) traceable ion chamber. A calibration curve was derived using a least squares fit of a second order polynomial. The measured dose distribution agrees well with results from the Monte Carlo simulation. The dose was 130.8 Gy at 6 mm from the seed center with initial activity of 5.95 mCi. AAPM TG-43/60 parameters were determined. The reference dose rate for 2 mm and 6 mm were 0.67 and 0.02 cGy/s/mCi, respectively. The geometry function, radial dose function and anisotropy function were generated.Item Feasibility of Using Stereotactic Body Radiation as an Alternative to HDR for Treatment of Cervical Cancers(2006-08-11) Hesami, Homeira; Forster, KennethPurpose: Brachytherapy is frequently used to boost volumes at risk in the treatment of cervical cancers. Not all centers have HDR, or LDR capabilities, however, all have at least a linear accelerator. The possibility of using external beam radiation therapy utilizing a Stereotactic Body Radiation Therapy (SBRT) or Intensity Modulated SBRT (IM-SBRT) approach was evaluated in this project. Method and Materials: Volumes covered by the HDR prescription were used to define a Clinical Target Volume (CTV), with a prescription of 3250 cGy to the CTV over 5 fractions. Planning started with 33 equally spaced non-coplanar beams. Beam weight optimization was used to choose the most effective beam orientations. An SBRT plan was generated using unmodulated beams and then, by allowing beam modulation, IM-SBRT plans were generated. Minimum doses to 0.5, 1, 2, and 5 cc of rectum and bladder in the highest dose region were compared among HDR, SBRT, and IM-SBRT plans. Total Dose Volume Histograms (DVHs) were also compared. Results: 98% of the CTV was covered by the prescription dose for SBRT and IM-SBRT plans. Comparing plans, the highest doses to small volumes, showed that the dose to the high dose region of the rectum was increased by 8% for both SBRT and IM-SBRT plans, and the dose to the bladder was 8% higher using SBRT and 3% lower using IM-SBRT planning. The rectal DVHs for two patients were very similar for all three plans while IM SBRT showed an advantage for three patients. The bladder DVHs were similar for all plans for all patients. In general the rectum and bladder received a higher dose using SBRT, while the femoral heads received less dose using HDR. As expected, a larger volume of normal tissue was exposed to radiation using external beam irradiation. Conclusion: SBRT and IM-SBRT methods provided similar tumor coverage to HDR though normal structures received less dose using IM-SBRT approach than SBRT approach. It is feasible to replace HDR with external beam. This substitution makes the standard of care available to females worldwide and has the potential to treat large and irregularly shaped tumors.Item Intercomparison of instrumentation systems for verification of ¹²⁵I brachytherapy source strength for use in radioactive seed localization procedures(2015-05) Metyko, John Patrick; Landsberger, Sheldon; Erwin, William D.Two different radiation detection instruments, both commonly found in nuclear medicine clinics, were investigated for potential use in ¹²⁵I brachytherapy seed source strength verification. The goal of this investigation was to determine if either or both of these instruments could replace the air-communicating well-type ionization chamber (standard source strength verification instrument) when the ¹²⁵I seed is used for radioactive seed localization procedures instead of brachytherapy. In radioactive seed localization, the ¹²⁵I seed merely localizes the tissue of interest and does not deliver a therapeutic dose to the patient. The ¹²⁵I seeds are inserted into nonpalpable lesions, which are then removed for biopsy within 5 days. Dose calculations and patient modeling are not performed. As a result of this, stringent source strength accuracy tolerances are not necessary. The accuracy, precision, and reproducibility of an activity calibrator and an ionization chamber survey meter were assessed and compared to regulatory requirements.