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1
Effect of low magnetic field on single-diode dosimetry for clinical use

Choi, Chang Heon,Park, Jong Min,An, Hyun Joon,Kim, Jung-in NUCLITAL S.R.L. GRUPPO NUCLETRON HOLDING-OLANDA 2019 PHYSICA MEDICA Vol.60 No.-
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Abstract Purpose To evaluate the effect of a low magnetic field (B-field, 0.35 T) on QED™ for clinical use. Methods Black and Blue QED were irradiated using tri-Co-60 magnetic resonance image-guided radiation therapy systems with and without the B-field. For both detectors, angular dependence of the beam orientation was evaluated by rotating the gantry and detector in parallel and perpendicular directions to the B-field. Angular dependence betweenthe directions of both QED and B-field was also measured. Response on the depth and output factor of both detectors was investigated for parallel and perpendicular setups, respectively. Results When Black QED was placed on a surface, detector response decreased by 1.8% and 4.5% for parallel and perpendicular setups, respectively, owing to the B-field. The angular dependence of the beam orientation was not affected by B-field for both detectors. There was a significant angular dependence between Black QED and B-field direction and for the Black QED when the gantry was rotated. Owing to the B-field, the detector response at 90° decreased by 2.4%, response of Black QED on the depth was changed only on the surface, and output factor of Black QED was changed only on the surface. The response of Blue QED was not affected by the B-field for all examined situations. Conclusions Using Black QED on a surface in the same position as that in the calibration requires some correction to the B-field. Blue QED does not require correction as it is not affected by the B-field. Highlights <UL> <LI> The effect of magnetic field on two QED™ detector was investigated for clinical use. </LI> <LI> Angular dependence, response on depth, and output factor were evaluated. </LI> <LI> Black QED on surface requires the correction for directions and magnetic-field. </LI> <LI> Blue QED does not require correction for clinical use. </LI> </UL>
2
Monte Carlo simulation of neutron dose equivalent by photoneutron production inside the primary barriers of a radiotherapy vault

Choi, Chang Heon,Park, So-Yeon,Park, Jong Min,Chun, Minsoo,Kim, Jung-in NUCLITAL S.R.L. GRUPPO NUCLETRON HOLDING-OLANDA 2018 PHYSICA MEDICA Vol.48 No.-
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Abstract Purpose To evaluate the neutron dose equivalent produced by photoneutrons inside the primary barriers of a radiotherapy vault. Methods Monte Carlo simulations were performed for investigating the production of photoneutrons as well as neutron shielding requirements. Two photon beams of 15 and 18 MV struck sheets of steel and lead, and the neutron doses were calculated at the isocenter (Piso) and at a distance of 50 cm from the inside wall (Pwall) while delivering 1 Gy to the patient. The proper thicknesses of borated polyethylene (BPE) and concrete were simulated to reduce neutron contamination. Results When the primary barrier consisted of a concrete alone, the neutron doses at Piso were 0.5 μSv/Gy and 12.8 μSv/Gy for 15- and 18-MV, respectively. At Pwall, the neutron doses were 15.8 μSv/Gy and 318.4 μSv/Gy for 15- and 18-MV, respectively. When 15 MV photons interacted with metal sheets, the neutron doses were 0.4–22.2 μSv/Gy at Piso and 15.8–812.5 μSv/Gy at Pwall, depending on the thickness and material of the metal sheets and neutron shielding. In the case of 18 MV photons with the same configuration, the neutron doses were 0.9–59.5 μSv/Gy and 73.9–5006.1 μSv/Gy for Piso and Pwall, respectively. The neutron dose delivered to the patient was reduced to the level of the dose delivered with a concrete barrier by including a 10-cm-thick BPE for each beam. Conclusions When the primary barrier shielding is designed with a metal sheet inside for high energy, proper neutron shielding should be constructed to avoid undesirable photoneutron dose. Highlights <UL> <LI> Monte Carlo simulation for the photoneutron of photon interaction with metal. </LI> <LI> Evaluation of the neutron ambient dose equivalent by photoneutron inside bunker. </LI> <LI> Calculation of neutron dose for metal shielding material and neutron shielding. </LI> <LI> Proper laminated primary barrier design suggestion. </LI> </UL>
3
High-precision quality assurance of robotic couches with six degrees of freedom

Cheon, Wonjoong,Cho, Junsang,Ahn, Sung Hwan,Han, Youngyih,Choi, Doo Ho NUCLITAL S.R.L. GRUPPO NUCLETRON HOLDING-OLANDA 2018 PHYSICA MEDICA Vol.49 No.-
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The mean error and standard deviation of linear and rotational motions, as well as couch sagging were analyzed from continuously acquired images in the moving couch. The accuracy of VTS was 0.024 mm deviation for the sinusoidal motion, and the accuracy of the transformation matrix was 0.02 mm. In a cross-comparison, the difference between Laser Tracker (FARO) measurements was 0.14 +/- 0.12 mm for translation and 0.032 +/- 0.026 degrees on average for yaw rotation. The new system provides QA of yaw, pitch and roll motion as well as sagging of the couch and sub-millimeter/degree accuracy together with precision.

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