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Sci‐Sat AM (2) Therapy‐01: A rotational total skin electron irradiation technique using a linear accelerator with a commercially available high dose rate total body electron mode
Author(s) -
Evans M,
Olivares M,
Seuntjens J,
Parker W,
Devic S,
Poli E,
Freeman C,
Podgorsak E
Publication year - 2006
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2244697
Subject(s) - linear particle accelerator , ionization chamber , dosimetry , monitor unit , bremsstrahlung , irradiation , beam (structure) , betatron , percentage depth dose curve , electron , cathode ray , nuclear medicine , dose profile , physics , materials science , ionization , atomic physics , optics , nuclear physics , medicine , ion , quantum mechanics
We have transferred and modernized our 25‐year‐old rotational total skin electron irradiation (RTSEI) technique from a linac (Varian Clinac‐18) with a custom modified beam line to a linac (Varian 21EX) with a commercially available electron mode intended for total skin electron irradiation. The new technique uses a “high dose rate” mode and a “high dose per Monitor Unit” mode in conjunction with a custom‐made flattening filter to produce a uniform beam at an extended SSD of 378 cm. Reference dosimetry for the stationary and rotational electron fields was performed to allow delivery of the prescription dose using the linac's transmission ionization chamber. The accessory tray holds the custom‐made flattening filter and automatically selects the beam energy (6 MeV) and high dose rate (888 MU/min) while moving the collimators to the maximum 40 × 40 cm 2 field size. Beam parameters are monitored using the record‐and‐verify (VARIS) system. Patients are treated on a rotating platform with a high dose rate electron beam having a z max at the skin surface, an R 50 at 15 mm and a bremsstrahlung contamination of the order of 3%. The nominal dose rate to water at z max (surface) for the rotational technique was determined to be 24.1 cGy/1000 MU, and beam delivery is monitored with a secondary Farmer‐type ionization chamber located near the patient in the treatment field. Treatment times for a daily dose of 2.0 Gy are of the order of 9.5 minutes and to date we have treated 15 patients with this technique.