AbstractID: 8049 Title: Total Body Skin Irradiation With Electrons Utilizing a Modified
12 Field Technique on a Varian EX Linear Accelerator: Dosimetry and Technique
Mycosis fungoides is a rare disease with an annual incidence of about 3 cases per million
people. Treatment of small lesions with focused electron beams has proven to be a useful
form of therapy which provides good local control. When the disease becomes more
widespread, however, total body skin irradiation with electron beams is often the
treatment of choice.
We report our experience utilizing a modified Stanford technique which incorporates 12
fields treated daily two times per week to a total dose of 32 Gy in 16 fractions. A 6 MeV
High Dose-Rate electron beam produced by our Varian Model EX linear accelerator (s/n
1826) is used for treatments. The patient is treated at a distance of 3 meters behind a 1
cm thick beam degrading screen. The use of “upper” and “lower” fields requires precise
beam overlap by adjusting the gantry angle to provide a uniform dose in the vertical
direction. The six rotational positions require measurement of an “over-lap factor” to
provide accurate dosimetry circumferentially.
Dosimetric data such as variation of dose as a function of a) distance from absorbing
screen, b) gantry angle and c) distance away from central axis are presented as well as a
“dose mapping” of our treatment technique. TLD and film data measured on a Rando
phantom as well as patient monitoring dosimetry will be presented. Techniques for beam
calibration and measurements of equivalent electron beam energy behind the degrading
screen will also be presented.