The effective dose (Deff) for electron beams.
OBJECTIVE
Calculation of the effective dose and proposal of a dose specification method for the electron beams.


METHODS
In a homogenous water phantom the 3D dose distributions for electron beams of energy 6, 9, 12, 15, 18 and 21 MeV and beam size 10x10 cm were calculated. For a volume encompassed with 80, 85 and 90% isodose, the mean dose and the SD were calculated for each energy. Using the Brahme's formulae, the effective dose was calculated.


RESULTS
The larger the minimum dose (value of the encompassing isodose), the larger the mean dose and the smaller the SD. The mean doses and SD to the volume encompassed with 80, 85 and 90% are in the range of 91-94%, and 5.1-6.2%, 93-96% and 4.2-4.6%, 94-96% and 3.0-3.2%, respectively. Thus the effective dose for the volume encompassed with 80, 85 and 90% are about 90, 93 and 95%, respectively.


CONCLUSIONS
Taking into account the requirements regarding dose uniformity within the PTV and the sparing effect for normal tissue situated under the PTV, we propose to keep the 85% isodose as a minimum one and to prescribe the dose to the 90% isodose. The present method may be applied for single electron beams and typical cases.
Kukolowicz
Pawel Franciszek
PF
Medical Physics Department, Holycross Cancer Centre, Artwinskiego 3, 25-734 Kielce, Poland.
Gil-Ulkowska
Malgorzata
M
Bulski
Wojciech
W
D004583:Electrons / Q000627:therapeutic use*; D006801:Humans; D021621:Imaging, Three-Dimensional; D008962:Models, Theoretical; D009369:Neoplasms / Q000532:radiotherapy*; D011874:Radiometry; D014867:Water
D014867:Water