SECONDARY RADIATION MAPPING

Radiation protection for personnel working with X-rays is of vital importance. Several studies have been published regarding the secondary radiation and the shielding requirements to areas that are adjacent to the X-ray units. In this work, secondary radiation in a conventional radiographic room, in terms of dose rate (mSv/hr), as a function of different radiographic exposure factors has been studied. The measurements were performed with a 451P Fluke Biomedical survey meter on a Philips Medio 65 CP-H X-ray generator with a cylindrical water phantom. It was found that the dose rate from the scatter radiation decreases with distance. An added filtration of 2.0 mmAl at 100 kVp reduced the secondary dose rate further by 21.4%. The results of this study may be of value during exposure of personnel that are not protected by shielding materials. Highlights Ÿ It was found that the dose rate from the scatter radiation decreases with distance. An added filtration of 2.0 mmAl at 100 kVp reduced the secondary dose rate further by 21.4%. Ÿ The mean secondary X-ray energies for 60, 80, 100 and 100 kV with 2 mmAl added, were calculated as 34.41, 51.12, 69.03 and 71.29 keV respectively. Ÿ The results of this study are of value during exposure of people such as radiographers, and patients during the use of mobile X-ray units.

Evaluation of MU2net as an Online Secondary Dose Check for MR Guided Radiation Therapy with the Elekta Unity MR Linac

During the adaptive workflow associated with MRgRT, a secondary dose calculation is required and MU2net (DOSIsoft, France) is one commercial option. The suitability of MU2net to be used in conjunction with the online Monaco treatment planning system of the Elekta Unity (Elekta AB, Stockholm, Sweden), is evaluated in this work. Monaco and MU2net point doses are compared for various fields on and off axis and at different SSDs. To investigate the comparative effects of attenuation due to the cryostat, couch and posterior coil, measured, MU2net and Monaco dose outputs at the isocentre, as a function of gantry angle, were compared. Point doses for the beams of nine step and shoot IMRT (SSIMRT) test plans (courtesy Elekta) were calculated with Monaco v5.4 and compared to corresponding doses computed with MU2net. In addition, Monaco v5.4 and MU2net point doses were compared for 1552 beams treated on the Unity at our facility. For the on-axis fields investigated the agreement between MU2net and measured data is acceptable. MU2net and Monaco point doses for the Elekta SSIMRT test plans were within ± 5.0 % and ± 6.4 % for beams delivered from gantry zero and at planned beam angles, respectively. For the 1552 beams delivered approximately 80.0 % of MU2net and Monaco point doses agree within ± 5.0 %, therefore it is recommended to correlate MU2net Dose Reference Points (DRPs )with pre and post treatment dosimetry verification. Computational accuracy of MU2net could be enhanced with improved modelling of attenuation due to the couch, cryostat and posterior MR imaging coil.