Effect of saccharide additives on response of ferrous–agarose–xylenol orange radiotherapy gel dosimeters

Abstract

Glucose, sucrose, starch, and locust bean gum have been used as additives to the ferrous-agarose-xylenol orange (FAX) gel dosimeter. The saccharide enhanced dosimeters were found to have a higher dose sensitivity over a standard FAX gel as measured by both optical density change and magnetic resonance imaging (MRI). With optical density measurement, OD-dose sensitivity increases were up to 55% for glucose, 122% for sucrose and 43% for starch, while locust bean gum did not give a consistent response. With MRI, R1-dose sensitivity increases were up to 178% with sucrose addition. The FAX gel with sucrose was studied in greatest detail. The OD-dose sensitivity dependence on cooling rate was reduced for the sucrose FAX gel over the standard FAX gel, which has significant implications for uniform dose sensitivity in large gel phantoms. The thermal oxidation rate in the sucrose FAX gel was up to 2.3 times higher than in the standard gel. The OD-dose sensitivity of oxygenated sucrose FAX gels was 4.3 times greater than standard FAX gels, while continued enhancement in OD-dose sensitivity with increased sucrose concentrations beyond 2.0 g/l was found only for the oxygenated sucrose FAX gels. Both the molar absorption coefficient of the ferric ion-xylenol orange complex at 543 nm and gel pH were not affected by the presence of sucrose, with the implication that the higher OD-dose sensitivity of gels with saccharides is due to increased chain reaction production of ferric ions.

Characterisation of a Ferrous Agarose Xylenol ( FAX ) gel for radiotherapy dose measurement

“…The standard deviation is less than 0.4% of the calculated extinction coefficient. Healy et al 15 The variations in molar extinction coefficients have been attributed to variations in impurities in the xylenol orange from different manufacturers. In this study the xylenol orange was from Acros Organic which has not been included in the reported work.…”

A dosimetric evaluation of tissue equivalent phantom prepared using 270 Bloom gelatin for absorbed dose imaging in Gamma knife radiosurgery

“…Phantoms can easily be obtained and used as dosimeter to obtain 3-D dose distribution. Different kinds of gel dosimeters have been developed, the two main investigated groups are the aqueous gels, the Fricke gel dosimeters [4,5,6,7,8,9] and the based on radiation-induced polymerization and cross-linking of acrylic monomers, the polymer gels [3,10,11,12,13]. Imaging techniques such us spectrophotometry and MRI scanning, have been proposed [14,15,16,17].…”

3D dosimetry fundamentals: gels and plastics

“…The elevated temperature has been problematic for many of the radiation chemistries that were investigated. For example, heating reduces the amount of dissolved oxygen and increases auto-oxidation rates [14]. This can lead to chemically nonuniform gels with unnecessarily elevated background levels for optical studies.…”