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Clinical radiotherapy applications of low energy electrons in the treatment of total skin
involvement is a complex and rarely practiced modality world over. The physics and technical aspects
of execution of the techniques involve clear understanding of the use of relevant parameters. After
finalizing the treatment geometry and characterizing the parameters of total skin electron treatment
(TSET) beam in a linear accelerator, the treatment has to be delivered using 3 pairs of fields in the
Stanford technique. There is need to find out the integrated effect of 6 fields by further dosimetric
measurements to derive monitor units for single field. Measurements were performed using humanoid
phantom in simulated treatment position on a rotating stool. The factor for 6 pairs' of field related from
single field calibrated dose per MU is found out using a 0.6 cc Farmer chamber at two selected
positions on the humanoid phantom. The overdose ratio at the junction is also quantified. Monitor
units are calculated using the single field output and the 6 pairs dosimetric factor. A factor of 4.26 is
derived for the 6 pairs of wide angle electron fields of the Stanford technique. The overdose ratio at
the junction of 12.20 tilted upper and lower halfrbody fields is found to be 1.09. For the treatment
delivery of planned dose of 1 Gy, the required mohitor units for the 6 MeV beams were 428 MU for 3
pairs of fields on alternate days. Ameasured value of 0.1063 cGy/MU on humanoid phantom'with 0.6
cc is in agreement with measured 0.1092 cGy/MU with parallel plate chamber with cubic phantom.
The value of dose for 6 pairs of fields to 1 pair of fields D6p/lD1p=2.79 which agrees with the factor
between 2.5 to 3.0 reported by AAPM. Our methodology in implementation of TSET will be helpful for
other centers rendering this rare radiotherapy practice.
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