Film dosimetry of small elongated electron beams for treatment planning.
The characteristics of 5, 7, 10, 12, 15, and 18 Mev electron beams for small elongated fields of dimensions L X 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 electron 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 agreement to within 1% with the measured film values.
Niroomand-Rad
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Department of Radiation Medicine, Georgetown University Medical Center, Washington, D.C. 20007.
D004583:Electrons; D005373:Film Dosimetry; D006801:Humans; D010315:Particle Accelerators; D011880:Radiotherapy Planning, Computer-Assisted; D011881:Radiotherapy, Computer-Assisted; D011882:Radiotherapy, High-Energy