RADIOMETRIC EFFECTS CAUSED BY THE INCORPORATION OF COPPER IN POLYMERIC GEL DOSIMETERS

A. WOLFEL; I. SCARINCI; P. PÉREZ; F. MATTEA; M. VALENTE

Sao Paulo

Congreso; LASSSD - Latin American Symposium of Solida-date Dosimetry; 2021

LASSD - USP

Introduction: Radiotherapy is broadly applied inthe treatment of cancer. Therefore, novel equipment andtechniques for precise delivery of high doses of ionizingradiation are constantly under development. Consequently,it is necessary to develop reliable devices forthe spatially-defined quantification of the absorbed doseto guarantee treatment planning quality. In this regard,polymer gel dosimeters (PGDs) are tissue-equivalentand radiosensitive devices used to precisely quantify,with spatial resolution, the absorption of ionizing radiation.However, it is still necessary to optimize the radiosensitivityof PGDs to achieve better time-stability andspatial resolution of the dosimetric response [1]. Thepresent study hypothesizes that the incorporation of copper(Cu) atoms into a PGD formulation could improveits performance while maintaining tissue-equivalence.Cu may promote a local enhancement in the depositeddose through the emission of secondary electrons. In addition,Cu2+ ions could be formed by the effect of the ionizingradiation, which might be useful to improve theoptical sensitivity of PGDs through the formation ofhighly-coloured metal-organic complexes [2]. Thesetwo effects may be useful for improving the characterizationof low levels of deposited dose.This work reports on the radiological effects of incorporatingCu atoms into PGDs. In particular, dose-responseand water-equivalence were characterized.Materials and methods: Dedicated Monte Carlosubroutines were adapted from the PENELOPE andFLUKA main codes. PGDs composition was: 89% w/wwater; 3% w/w N-isopropylacrylamide (NIPAm); 3%w/w N,N′-methylenebisacrylamide (MBA); 5% w/wGelatin and 10 mM THPC. Cu concentration was variedbetween 0 and 1.5% w/w and water was reduced accordingly.Phantom dimensiones were 4x1x1 cm and sourcephantomdistance was set to 80 cm. X-ray beam fieldsize was 1x1 cm, using a experimentally measured spectrumfrom a 44 kVp W anode.Results: The presence of Cu changed the absorptionbehavior of the PGDs, as compared with liquid water(Fig 1). In general terms, an increase in Cu concentrationcaused a proportional increase in the local absorption ofradiation. This phenomenon could be caused by: i) thehigher attenuation coefficient of Cu and/or ii) a local dosimetricreinforcement caused by the emission of secondary(mainly Auger and Coster-Kronig) electrons.Therefore, this issue should be accounted for when dealingwith potential variations of the sensitivity of the experimentaldose-response curve.Conclusions: The incorporation of Cu increases thelocal deposition of radiation and thus could improve thesensitivity of PGDs, while representing a potentiallysuitable scheme to evaluate the local dose enhancement.-0,2 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,60,951,001,051,101,151,201,25Water Equivalency[PGD/Water]Cu (% w/w)Fig 1: Water equivalency of PGDs vs. Cu concentration.References:1. C. Baldock and Y. De Deene, Phys. Med. Biol. 55(5),1-63 (2010).2. A. Wolfel et. al., Radiat. Phys. Chem. 180, 109295(2021).