Experimental investigation of GafChromic® EBT3 intrinsic energy dependence with kilovoltage x rays, 137Cs, and 60Co

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141567/1/mp12682_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/141567/2/mp12682.pd

Improved image quality for x-ray CT imaging of gel dosimeters

Purpose: This study provides a simple method for improving precision of x-ray computed tomography (CT) scans of irradiated polymer gel dosimetry. The noise affecting CT scans of irradiated gels has been an impediment to the use of clinical CT scanners for gel dosimetry studies. Method: In this study, it is shown that multiple scans of a single PAGAT gel dosimeter can be used to extrapolate a ‘zero-scan’ image which displays a similar level of precision to an image obtained by averaging multiple CT images, without the compromised dose measurement resulting from the exposure of the gel to radiation from the CT scanner. Results: When extrapolating the zero-scan image, it is shown that exponential and simple linear fits to the relationship between Hounsfield unit and scan number, for each pixel in the image, provides an accurate indication of gel density. Conclusions: It is expected that this work will be utilised in the analysis of three-dimensional gel volumes irradiated using complex radiotherapy treatments

Electronic structure calculations of defect states in Ti-doped LiF

This work investigates, using density functional theory (DFT), the localization of electrons and holes produced by irradiation in LiF crystals doped with Ti. We show that the Ti can act either as an electron trap, when located at an interstitial position of the LiF lattice, or as a trap for holes by substituting a Li atom. We also observe that an excess electron is localized in a Ti p-state while a hole localizes in a Ti d-state. The localization of the hole in this state when the Ti substitutes a Li is supported by results reported in the literature where it was assumed that the Ti substitute is a hole trap. The defect energy levels obtained in this work agree quite well with those reported in experiments.</p

Figure 3. 2D dose distributions in the 18 mm diameter LGK field.

<p>a. Axial plane relative to the patient position. b. Coronal plane relative to the patient position.</p

Reference absorbed dose to water rate computed in the modified accelerator for SRS compared with CD following TRS-398 [1].

a<p>µm thickness,</p>b<p>mm³,</p>c<p>mm diameter,</p>d<p>mm thickness.</p

Reference absorbed dose to water rate computed in the Leksell Gamma Knife® unit compared with CD following the AAPM-TG21 [8].

a<p>µm thickness,</p>b<p>mm³,</p>c<p>mm diameter,</p>d<p>mm thickness.</p

Figure 2. Calibration curves for each dosimeter exposed to 60Co gamma and 6 MV x-ray beams as a function of the absorbed dose to water.

<p>The symbols represent the data and the lines are linear fits: a. MD-V2-55 for the three color channels (red, green and blue). b. TLD-100. c. Alanine dosimeters and for the 60Co data, we only compare the dose determined with our ionization chamber and that provided by NIST.</p