Film dosimetry of small elongated electron beams for treatment planning

Publisher Website
Google Scholar
Abstract
The characteristics of 5, 7, 10, 12, 15, and 18 Mev electron beams for small elongated fields of dimensions L .RTM. W (where L = 1,2,3,4,5, and 10 cm; and W = 1,2,3,4,5, and 10 cm) have been studied. Film dosimetry and parallel-plate ion chamber measurements have been used to obtain various dose parameters. Selective results of a series of systematic measurements for central axis depth dose data, uniformity index, field flatness, and relative output factors of small elongated electron beams are reported. The square-root method is employed to predict the beam data of small elongated electron fields from corresponding small square electron fields using film dosimetry. The single parameter area/perimeter radio A/P is used to characterize the relative output factors of elongated electron beams. It is our conclusion that for clinical treatment planning square-root method may be applied with caution in determining the beam characteristics of small elongated fields from film dosimetry. The calculated and estimated relative output factors from square-root method and A/P ratio are in good agreement and show aggreement to within 1% with the measured film values.