Rheumatoid arthritis is one of the most common epidemic diseases in the world. For some patients, the treatment with steroids or nonsteroidal antiinflammatory drugs is not effective, thus necessitating physical removal of the inflamed synovium. Alternative approaches other than surgery will provide appropriate disease control and improve the patient's quality of life. In this research, we evaluated the feasibility of conducting boron neutron capture synovectomy (BNCS) with the Tsing Hua open-pool reactor (THOR) as a neutron source. Monte Carlo simulations were performed with arthritic joint models and uncertainties were within 5%. The collimator, reflector and boron concentration were optimized to reduce the treatment time and normal tissue doses. For the knee joint, polyethylene with 40%-enriched Li 2 CO 3 was used as the collimator material, and a rear reflector of 15 cm thick graphite and side reflector of 10 cm thick graphite were chosen. The optimized treatment time was 5.4 min for the parallel-opposed irradiation. For the finger joint, polymethyl methacrylate was used as the reflector material. The treatment time can be reduced to 3.1 min, while skin and bone doses can be effectively reduced by approximately 9% compared with treatment using the graphite reflector. We conclude that using THOR as a treatment modality for BNCS could be a feasible alternative in clinical practice.

Purposes: To verify the output factors (OFs) of Gamma Knife Model B2 by various conventional dosimeters and to determine an effective correction factor for compensating the dosimeter sizes. Method and Materials: The TLDs, radiochromic films, PTW 31002 ion chamber and the diamond detector were used to obtain the OFs, normalized to the 18 mm helmet, for four helmets. The factors were measured in the centre of an 80 mm polystyrene spherical phantom that was positioned at the mechanical center of the machine. The dosimeters were placed in the center of the sphere using different cassettes and oriented their effective center in the center of helmet coordinate system. Based on the volumetric averaging theory we used the specificity of dose profile of the 4 mm helmet to correct the measurement by the integrated Gaussian curve method. Results: The relative OFs measured with TLDs/ion chamber, before applying correction factors, were 0.977/0.967, 0.905/0.845 and 0.755/0.313 for the 14, 8 and 4 mm helmets, respectively. After applying correction factors, the results show a reasonable agreement with the data used in the current RTP system for Gamma Knife procedure. The results also showed great spatial accuracy. The symmetry of spatial distribution was 1.84%, 0.59%, 1.25%, and 1.16% for the 4, 8, 14 and 18 mm helmets, respectively. And the distance between mechanical center and dosimetric center was less than 0.25mm for all four helmets. Conclusion: The accuracy of the measurements was affected by a number of factors, especially the dosimeter size. This work provides the potential for using conventional dosimeters, with appropriate correction factor, to determine and to evaluate the clinical dosimetric parameters for Gamma Knife Unit for routine QA procedure. With the verification of spatial accuracy, Gamma Knife unit could be used to treat functional disorder case accurately.

Purpose: To evaluate the feasibility of Boron Neutron Capture Synovectomy by Tsing Hua Opening‐pool Reactor (THOR) in Taiwan and to determine the optimal treatment parameters with epithermal neutron beam. Method and Materials: MCNP5 was used to model the THOR epithermal neutron beam interactions with knee and finger phantom. The phantom was established according to the structure of human joints with different boron concentration. The treatment parameters were used to model the optimum treatment assembly, such as different thickness of reflectors and beam orientations. The Figure of merits (FOMs) such as total treatment time, total maximum skin dose and synovium to bone treatment ratio were used to evaluate the effect of the treatment parameters. Results: Monte Carlo calculations predict a total therapy time of BNCS between 5 and 15 min for the human knee by optimum THOR beam assembly. The treatment parameters of BNCS vary with joint sizes. The optimum treatment condition for different joint size can be achieved by using the opposed parallel beam, placing the inflamed joint near the source, and adding 10cm side and rear graphite reflectors. To compare with BNCS using the neutron beam produced by accelerator, the THOR epithermal beam will reduce the total skin dose from 205 RBEcGy to 130.24 RBEcGy and increase the TRbone from 72 to 74.28. Conclusion: This study predicts the optimum THOR beam assembly for BNCS. The result shows the quality and overall clinical efficacy of THOR epithermal neutron beam for BNCS is more suitable than the beam produced by accelerator. It provides the potential application of BNCS by epithermal neutron beam.

Purpose: To evaluate the feasibility of constancy check of PTW 2D‐Array seven29 ion chambers by Ir‐192 HDR Remote after loading system and to provide a method of checking 2D‐Array performance that ensures the results of IMRT routine QA is reliable. Method and Materials: We used Nucletron microSelectron HDR brachytherapy system which has an Ir192 source and well control of source position. By matching the markers on the surface of PTW 2D‐Array seven29 and the Nucletron source position checking tube, we collected each ion chamber's reading row by row. We adjusted the influence of Ir192 decay by mathematically calculation. By comparing the measurement data with calibration file from PTW Company and analyze data by EXCEL Macro Enterprise, we can evaluate the performance of each ion chamber. Results: The average of total measurement time was 162.97 mins, including setup and measurement time. And in 2 hours spans, the influence of Ir192 decay is 0.078%. The 729 ion chambers performance grouped into five types :< 1%, 1–2%, 2–2.5%, 2.5–3%, >3%. There have 8 ion chambers under1%, 692 ion chambers in 1–2%, 22 ion chambers in 2–2.5%, 4 ion chambers in 2.5–3% and 3 ion chambers over 3%. Conclusion: This study provides a method to check the constancy of PTW 2D‐Array seven29. By this method, we can check this IMRT QA tool's performance in hospital. Moreover, we can save time and money in order to send this whole package to Germany Calibration Center.

Purpose: To study the inhomogeneity effect from skull and air cavity on Gamma Knife Stereotactic Radiosurgery. Method and Materials: Patient CT data from Gamma Knife procedure was used in a Monte Carlo simulation. In the Monte Carlo simulation, the 201 Cobalt‐60 sources were considered to have the same activity. Each Cobalt‐60 source was contained in a cylindric stainless steel capsule. The beam data was stored in four beam phase‐space files which were generated in the inner side for each of 4 treatment helmets, after the Cobalt beam passed through primary collimator and secondary collimator. The dose was calculated using Monte Carlo simulation in both homogenous and inhomogeneous geometries rebuilt from patient CT data with identical beam parameters. A small volume was created around the iso‐center for DVH comparison. The doses in a 16cm diameter spherical QA phantom were also measured and calculated with and without 1.5mm Lead‐covering. Results: For QA phantom, the dose ratios with and without 1.5mm Lead covering are 89.8% from measurement and 89.2% from Monte Carlo. For patient's CT phantoms, Monte Calor results show that although the isodose lines remain almost the same with and without inhomogeneity correction, the difference in absolute dose has been observed. The dose in CT phantom is about 4.1% lower than the dose in water replaced CT phantom. With various skull densities, the inhomogeneity effect could reach as high as 8.0%. Conclusion: Monte Carlo has been applied to dose comparison for CT image with and without inhomogeneity correction. Monte Carlo simulation matches very well with measurement for the spherical QA phantom. It shows that the implementation of Monte Carlo simulation for Gamma Knife is accurate. It shows that the inhomogeneity effect should be considered for gamma knife treatment planning.