Dose distributions of 192Ir HDR brachytherapy in phantoms simulating water, bone, lung tissue, water-lung and bone-lung interfaces using the Monte Carlo codes EGS4, FLUKA and MCNP4C are reported. Experiments were designed to gather point dose measurements to verify the Monte Carlo results using Gafchromic film, radiophotoluminescent glass dosimeter, solid water, bone, and lung phantom. The results for radial dose functions and anisotropy functions in solid water phantom were consistent with previously reported data (Williamson and Li). The radial dose functions in bone were affected more by depth than those in water. Dose differences between homogeneous solid water phantoms and solid water-lung interfaces ranged from 0.6% to 14.4%. The range between homogeneous bone phantoms and bone-lung interfaces was 4.1% to 15.7%. These results support the understanding in dose distribution differences in water, bone, lung, and their interfaces. Our conclusion is that clinical parameters did not provide dose calculation accuracy for different materials, thus suggesting that dose calculation of HDR treatment planning systems should take into account material density to improve overall treatment quality.

The aim of this study was to understand the difference between the measured and calculated irradiation attenuations obtained using two algorithms and to identify the influence of couch attenuation on patient dose verification. We performed eight tests of couch attenuation with two photon energies, two longitudinal couch positions, and two rail positions. The couch attenuation was determined using a radiation treatment planning system. The measured and calculated attenuations were compared. We also performed 12 verifications of head-and-neck and rectum cases by using a Delta phantom. The dose deviation (DD), distance to agreement (DTA), and gamma index of pencil-beam convolution (PBC) verifications were nearly the same. The agreement was least consistent for the anisotropic analytical algorithm (AAA) without the couch for the head-and-neck case, in which the DD, DTA, and gamma index were 74.4%, 99.3%, and 89%, respectively; for the rectum case, the corresponding values were 56.2%, 95.1%, and 92.4%. We suggest that dose verification should be performed using the following three metrics simultaneously: DD, DTA, and the gamma index.

This paper describes the establishment by the Institute of Nuclear Energy Research (INER, Taiwan) of the reference air kerma rate (RAKR) calibration standard for measurement of high-dose rate (HDR) (192)Ir brachytherapy source strength. A bilateral comparison has been made in the RAKR standards for HDR (192)Ir brachytherapy sources at the INER and Physikalisch-Technische Bundesanstalt (PTB, Germany) and the measurement difference was within the overall standard uncertainty and showed good agreement between the two calibration standard systems established at the INER and the PTB. Besides, INER also worked with 20 domestic hospitals to organise an on-site measurement comparison programme to explore the status of HDR (192)Ir brachytherapy source strength determination in Taiwan. The comparison results presented the ratios of RAKR with vendor values, as determined by INER and hospitals from the programme. The ratios fall in all cases within the ± 3 % guaranteed by the vendors for a coverage factor of k = 2 or at 95 % confidence level.

Stereotactic radiosurgery (SRS) is designed for patients with small lesion areas that are not suitable for actual surgery. SRS delivers high dose to the lesion with high gradient on the irradiation margin area. In this study, radiophotoluminescent glass dosemeter (RPLGD) and radiochromic film were used to measure the output factor of a gamma knife. Also, a Monte Carlo code (OMEGA/BEAM) was applied to simulate the output factor. For 14 and 8 mm sizes of helmet collimators, the variations of output factors determined with RPLGD, radiochromic film, the Monte Carlo code and Elekta were all within 0.5 %. When helmet collimator size was 4 mm, the output factors detected from RPLGD, radiochromic film and Monte Carlo simulation were all within 3.2 % when compared with Elekta. Taken together, RPLGD, radiochromic film and Monte Carlo simulation will be used as precise tools to measure the output factor of a gamma knife.

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