Dosimetric parameters for small field sizes using Fricke xylenol gel, thermoluminescent and film dosimeters, and an ionization chamber

Abstract

Dosimetric measurements in small therapeutic x-ray beam field sizes, such as those used in radiosurgery, that have dimensions comparable to or smaller than the build-up depth, require special care to avoid incorrect interpretation of measurements in regions of high gradients and electronic disequilibrium. These regions occur at the edges of any collimated field, and can extend to the centre of small fields. An inappropriate dosimeter can result in an underestimation, which would lead to an overdose to the patient. We have performed a study of square and circular small field sizes of 6 MV photons using a thermoluminescent dosimeter (TLD), Fricke xylenol gel (FXG) and film dosimeters. PMMA phantoms were employed to measure lateral beam profiles (1 x 1, 3 x 3 and 5 x 5 cm2 for square fields and 1, 2 and 4 cm diameter circular fields), the percentage depth dose, the tissue maximum ratio and the output factor. An ionization chamber (IC) was used for calibration and comparison. Our results demonstrate that high resolution FXG, TLD and film dosimeters agree with each other, and that an ionization chamber, with low lateral resolution, underestimates the absorbed dose. Our results show that, when planning small field radiotherapy, dosimeters with adequate lateral spatial resolution and tissue equivalence are required to provide an accurate basic beam data set to correctly calculate the absorbed dose in regions of electronic disequilibrium.

Evaluation of MRI-based MAGIC polymer gel dosimeter in small photon fields

“…The difference between measurements and calculations is reduced by increasing ield sizes due to decreasing of lateral electronic disequilibrium. The same result has been reported by Oliveira and Calcina for The Fricke Xylenol Gel dosimeter (FXG) compared with other dosimeters in small photon ields (5,18) .…”

Analysis Of Small Field Dosimetry For 6 MV Photon Beams

“…Küçük alan RDF'lerinde TLD ve PinPoint iyon odası benzer okumalar göstermiştir. Bu sonuçlar literatürle uyumlu bulunmuştur 14,17 . Çalışmamız ve diğer literatürlerdeki benzer çalışmaların sonuçlarını dikkate aldığımızda, küçük alanların dozimetrik parametrelerini değerlendirirken karşılaştığımız lateral elektron dengesizliği ve dozimetre hacminin alan boyutuna uygun olacak şekilde seçimi önem taşımaktadır.…”

3D Dosimetric Tools in Radiotherapy for Photon Beams

“…Other complication is the perturbation of the level of disequilibrium, which is inducted bye the dosimeter when introduced in the track of the radiation fields. Thus, due these characteristics of the small fields, an accurate dose verification of the delivery dose of the small radiation fields is required [42][43][44][45].…”