Enhancement of MD-55-2 radiochromic film sensitivity using a multilayer film technique for applications in the low dose range

MD-55-2 is one of the Radiochromic film models with the sensitivity suitable for dose measurements ranging from 5 to 100 Gy. However, this lower limit makes the film impractical for its applications in many areas such as brachytherapy source dosimetry. n this project, the useful range of the film has been extended by using a multilayer film technique. In this technique, single-, double-, and triple- layers of films were exposed to the doses ranging from 0.5 to 10 Gy using a Co-60 photon beam. Calibration curves for corresponding layers of films were obtained with a spectrophotometer using a 680nm wavelength. The results indicated that the sensitivities of double and triple layers were approximately 200% and 300%, respectively, higher than a single-layer film. The impact of multilayer film arrangement on the energy dependence of the MD-55-2 Radiochromic film has also been examined using 100KVp, 80 KVp, and 6 MV X-ray beams. The results indicated an insignificant [within 5%] change in film responses with the beam energy. Therefore, the multilayer technique enhances the Radiochromic film sensitivity and expands its application to the low dose range in field of brachytherapy source dosimetry

Dosimetry of [188]Re and [186]Re sources based on Monte Carlo calculations for endovascular brachytherapy after balloon angioplasty

Background: Recent pre-clinical and clinical studies indicate that irradiation in the dose range of 15 to 30 Gy can reduce rate of restenosis in patients who have undergone an angioplasty. The use of filled balloon with radioactive solution was proposed as one of the possible intravascular irradiation techniques

Materials and Methods: The Monte Carlo N-particle Transport Code [MCNP4b] was used to calculate the dose rate distribution in the tissue equivalent material around the [188]Re and [186]Re liquid sources. Schematic of Medical Internal Radiation Dose [MIRD] for homogeneous distribution of radio-nuclide in a lesion was used for mean organ absorbed dose calculation due to the internal distribution

Results: Results indicate that [188]Re liquid with 100 mCi/ml and [186]Re liquid with 250 mCi/ml can deliver desired dose in the vessel wall to reduce restenosis. The dose ratio in depth of 0.5 mm to surface of vessel wall for [188]Re and [186]Re were 40% and 18%, respectively. Therefore in case of [186]Re, there is a little non-uniformity with respect to the [188]Re case. The delivery of form [186]Re dose to normal tissue around target tissue is less than [188]Re

Conclusion: Use of the Monte Carlo simulation with [188]Re-DTPA and [186]Re-DTPA for intra-vascular brachytherapy is a feasible method of delivering a desired dose to the vessel walls. Although [188]Re-DTPA delivers the desired dose to the target tissue with lower radioactive concentration [mCi/ml], but with the use of [186]Re-DTPA, the delivery dose to normal tissue around the target tissue is less

3D MRI gel dosimetry bases on image intensity: a new approach

Since 1984 MRI gel dosimetry has been introduced as a potential technique for 3D dosimetry. Most of the studies have measured R1 [1/T1] or R2 [1/T2] properties of the gel depending on the gel type. We have studied image intensity change in the Fricke gel by different MRI protocols. Materials and Gel Dosimeters contain 0.4 mM ferrous sulphate, 1 mM NaCl, 50 mM H2SO4 and 1% by weight agarose in distilled water. Prepared gels were poured in Plastic tube phantom and irradiated to a beam of Co-60 gamma rays. Imaging was performed by a 0.5T MRI system in the head coil with SE and GRE techniques. Our results showed that linear response exists between the variations of image intensity with absorbed dose [1-15 Gy]. Optimal imaging parameters should be defined locally according to the type of MRI scanner and exact composition of the gel. Gradient echo [GRE] imaging technique also have been studied in comparison with classic spin echo [SE] imaging technique which will be discussed in detail. Conclusions: Linearity of absorbed dose with intensity exists up to 15 Gy and can be used for MRI gel dosimetry. Reduction of imaging time is achievable in image intensity technique so that it's possible to image the gel in less than 20 minutes, which is critical to over-come the adverse ion-diffusion properties of the Fricke gel