Journal of Medical Physics
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Year : 2005  |  Volume : 30  |  Issue : 2  |  Page : 60-65

Clinical Electron Beam Configuration And Physical Parameters For Total Skin Electron Treatment (Test)

Correspondence Address:
R Ravichandran

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Source of Support: None, Conflict of Interest: None

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Total skin electron treatment(TSET) using electrons of energy about 2 - 4 MeV are widely practiced in the treatment of cutaneous T cell lymphomas. In high energy electron accelerators, the treatment technique needs to be designed using 6 MeV to 9 MeV electron beams. The physical parameters of these low energy electron beams should be characterized after high energy electron beam is degraded. At the new linac facility installed at our center we have standardized the above technique. A 10 mm plexiglass beam spoiler has been locally designed which provides 4.25 M focusto- skin distance (FSD) at the Clinac-2300 CD linear accelerator. Measurements were performed with high dose rate mode 2500 MU/min. The beam energy and absorbed dose measurements were carried out with plane parallel chamber (PPC 40) and solid water phantom. Beam flatness measurements were performed using 0.6 cc Farmer chamber. Using this flatness profile for single beam, the beam tilt was calculated so as to provide homogeneity at the junction. The mean energy of the direct electron beam is 2.28 MeV, most probable energy 3.4 MeV, and practical range 15 mm. The measured bremsstrahlung background is less than 0.5% for the horizontal single beam. Two wide angle electron beams with 12.20 tilts against horizontal direction provided large field size of 260 cm x 75 cm at FSD, with dose uniformity within + 8%. The measured absorbed dose rate is 0.109 cGy/MU at FSD. The treatment room dimensions provided large treatment distance. To achieve 130 cm distance between field centers, required tilt of the beam was 12.20. Assuming that one primary electron produces another scattered electron, doubling of the calculated dose by inverse square law, showed good agreement with measured dose/MU within 5%. Additional phantom measurements are required to apply the horizontal beam measurements for executing Stanford technique of TSET.

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