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Evaluation Output Dose of Electron Beams Based On Monte Carlo

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c gao

D Liu, Z Chi, c gao*, C Han, The Fourth Hospital of HeBei Medical University, Shijiazhuang, Hebei Province

SU-E-T-513 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: The purpose of this study is to investigate the influence factor of output dose for electron beams used in radiotherapy by Monte Carlo technique.

Methods: MCTP code was used to calculate a group of output dose from Varian Clinac 23EX. According to the contributions, the calculated output dose was divided into four parts which can help to identify the physical reasons for the variation of output dose, dose from direct particles which was arisen from the machine head directly, dose from indirect particles which was arisen from the collimation devices, including jaws, scrapers and shielding.

Results: 1. Appling same cones and same jsw settings but different field inserts, considering the 6 Mev beams, due to direct particles as well as indirect particles the output dose increases from the smallest to the largest field insert. 2. Different cones with same jaw settings and field size, for 6MeV electron beams, the use of a wider cone resulted in a higher output dose, which is mainly because of the direct particles. 3. Same field size with different cones and jaw settings, considering the 18 MeV beams, the wider cone exhibits a reduced output dose, which is attributed to indirect particles, and jaw contributes more than others. 4. Open cone, for the 6 MeV beams the wider cones that also has wider jaw settings showed an increased contribution to the output dose majorly from the indirect particles compared with the smaller cones. Similar trends were seen from the 9 MeV beams, although they were diminished. A reverse result was indicated for the 18 MeV beams.

Conclusion: The variation of output dose depends in a complicated manner on the characteristics of the beams and the modifications that the various cone-insert combinations introduce to these characteristics.

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