Monte Carlo techniques for radiation dosimetry and the experimental verifications of the Monte Carlo simulations have been developed for the treatment geometry of intravascular brachytherapy, a form of radionuclide therapy for occluded coronary disease (restenosis). Utilizing the recent version of the Monte Carlo code, MCNP4C, on both Sun workstations and Intel PC's, the radiation dose that is generated from the encapsulated array of P-emitting seeds (90Sr/Y-source train) has been calculated in both linear and curved coronary vessels. At the total activity of 42 mCi (1.55 x lo9 Bq), dose delivery varies from 32.05 to 0.63 Gy/min as the radial distance (r) from the source central axis increases from 0.5 to 5.0 mm in the linear vessel model. The dose rates at r = 2 mm in the lesion, which corresponds to the reference distance recommended by AAPM TG 60, are related to: 5.92 Gy/min in the central seed region of the 90Sr/Y beta-source train, and 3.32 Gy/min in the last seed region at the edge of the source train.The present investigation attempted for the first time the effect of the seed curvatures on the actual dose delivery to the target area in coronary vessels. While the dose difference for the 5-degree curved vessel at the prescription point of r = 2.0 mm is 7.41%, within the 10 % guideline set by the AAPM, however, the difference increased dramatically to 16.85 % for the 10-degree case. This suggests the formation of the hot and cold areas of dose delivery in the curved coronary arteries. As the radial distance increases beyond r = 3 mm, the degree of increase in dose in the region of inward curvature is further enhanced, while in the region of outward-curvature the change in dose remains less significant. Solid water phantoms have been fabricated to measure the dose on the radiochromic films that were exposed to the beta source train under linear and curvedvessel geometries ranging from 5 to 10 degrees. The radiochromic films were preexposed to the Gammacell irradiator for the constant exposure with 10 Gy. The experimental dose measurements are in good agreement with the simulation results for the r-8 iso-dose contours and the radial dose rates.Keywords: Monte Carlo, intravascular brachytherapy, radiation dose, beta-emitters, GafChromic film...
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ACKNOWLEDGEMENTSThe principal investigator would like to express his sincere appreciation to Dr. Prasanna Kumar, Chief of Medical Physics at the Deaconess Hospital in Evansville, Indiana, for his generosity and collaboration for our performing beta-dosimetry measurements for this current project. Support and encouragement from the NEER program manager, Ms.Nancy Elizondo at the DOE Idaho office, for the current project and the graduate students are gratehlly acknowledged.... AAPM TG-43.3 However, these protocols do not properly account for the complicated source geometries (e.g., guide wire, stent, and coronary vessel curvatures) and tissue inhomogeneity. The irradiated target site is generally located in a very complicated geometry that consists of both ...