Measurements of backscattered radiation from Therac‐20 collimator and trimmer jaws into beam monitor chamber | Zendy

Kubo Hideo | Zendy; Lo Koon Kai | Zendy

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Measurements of backscattered radiation from Therac‐20 collimator and trimmer jaws into beam monitor chamber

Author(s) -

Kubo Hideo,

Lo Koon Kai

Publication year - 1989

Publication title -

medical physics

Language(s) - English

Resource type - Journals

SCImago Journal Rank - 1.473

H-Index - 180

eISSN - 2473-4209

pISSN - 0094-2405

DOI - 10.1118/1.596380

Subject(s) - collimator , linear particle accelerator , optics , beam (structure) , physics , dosimetry , radiation , photon , backscatter (email) , materials science , collimated light , monte carlo method , nuclear medicine , computer science , mathematics , medicine , telecommunications , wireless , laser , statistics

The field size dependent photon output is known to be influenced by the existence of backscattered radiation (BSR) generated in the collimator or trimmer jaws of a linear accelerator. This paper describes the results of measurements made to study the existence of such backscatter by simulating the geometry of the treatment head of a Therac‐20 linear accelerator. The machine's monitor chamber, flattening filter, and collimator jaws were simulated by another real monitor chamber, a 1‐cm thick lead sheet and 2.5‐cm thick low‐melting‐point alloy divergent blocks, respectively. BSR from the simulated collimator jaws (SCJ) was measured with the simulated monitor chamber (SMC) as a function of the openings of the SCJ and as a function of distance between SMC and SCJ. The present results demonstrate the presence of BSR in an 18‐MV photon beam from a Therac‐20 linear accelerator.

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