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| Year : 2005 | Volume
: 30
| Issue : 2 | Page : 60-65 |
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Clinical Electron Beam Configuration And Physical Parameters For Total Skin Electron Treatment (Test)
R Ravichandran, K Kirshnamurthy, S S Sivakumar, C A Davis, B K Mohanti
Correspondence Address:
R Ravichandran
 Source of Support: None, Conflict of Interest: None  | Check |
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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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