Dosimetric analysis of external irradiation with 10 MV photons using a miniature multileaf collimator and brachytherapy using phosphorus-32, yttrium-90, and rhenium-188 for the inhibition of arterial restenosis

Percutaneous transluminal coronary angioplasty (PTCA) is a non-operative treatment for coronary vascular stenosis. With (PTCA) restenosis rates as high as 43% have been observed. Many animal and clinical studies have shown the efficacy of prophylactic radiation treatment after PTCA in reducing the restenosis rate. The goals of this study were: (1) analyze dose distribution of intraluminal beta-sources (32P, 90Y, and 188Re) calculated using the integrated Tiger Series (ITS) Monte Carlo code, and (2) examine the feasibility of using external irradiation to prevent restenosis after PTCA for non-cancerous vascular lesions.;In the case of intraluminal brachytherapy using beta-sources dosimetric perturbation effects of calcified plaque and a stainless steel stent were investigated using the ITS code. The plaque and the stent have higher density than tissue and blood that are herein considered to be water equivalent. The original ITS code was modified for this study. The virtual sources studied were uniformly loaded radioactive 3.0mm x 0.3mm cylinders.;A prototype miniature multileaf collimator (MMLC) was constructed. Each jaw consisted of 20 leaves made of tungsten. The dimensions of each leaf were 0.25cm thick and 6cm high. The projected thickness of each leaf at isocenter was 0.5cm and the maximum field size was 5cm by 10cm. Two sets of leaves were constructed, one having the touching face of each leaf rounded (13cm radius) and another set being flat (no divergence compensation). The penumbra was scored as the geometrical distance between 80% and 20% of a beam profile at various leaf positions. Transmission factors and leakage were measured and compared with the transmission factor for conventional Cerrobend blocks. The outputs of slit beams and percent depth dose distributions were compared to those of equivalent square fields as listed in BJR (British Journal of Radiology), supplement 17.