Ii Dosimetric Characterization Output Verify
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Dosimetric characterization and output verification for conical brachytherapy surface applicators. Part II. High dose rate 192Ir sources Regina K. Fulkerson, John A. Micka, and Larry A. DeWerd Citation: Medical Physics 41, 022104 (2014); doi: 10.1118/1.4862506 View online: http://dx.doi.org/10.1118/1.4862506 View Table of Contents: http://scitation.aip.org/content/aapm/journal/medphys/41/2?ver=pdfcov Published by the American Association of Physicists in Medicine

Dosimetric characterization and output verification for conical brachytherapy surface applicators. Part II. High dose rate 192 Ir sources Regina K. Fulkerson,a) John A. Micka, and Larry A. DeWerd Department of Medical Physics, University of Wisconsin–Madison, Madison, Wisconsin 53705 (Received 31 July 2013; revised 20 November 2013; accepted for publication 9 December 2013; published 23 January 2014) Purpose: Historically, treatment of malignant surface lesions has been achieved with linear accelerator based electron beams or superficial x-ray beams. Recent developments in the field of...

Fulkerson, Micka, and DeWerd: Surface applicator output verification F IG . 1. VariSource iX and GammaMedplus iX. (a) VariSource iX source geometry, units in mm. (b) GammaMedplus iX source geometry, units in mm. Images courtesy of Rasmussen et al. (Ref. 14). Varian offers two types of applicators manufactured out of a stainless-tungsten alloy (Fig. 2) for use with the GammaMedplus iX and the VariSource iX. One applicator type positions the source parallel to the treatment surface inside a source guide tube with a nominal source to surface distance (SSD) of 12.5 mm. The other applicator...

Fulkerson, Micka, and DeWerd: Surface applicator output verification F IG . 3. Schematic of source dwell positions within Varian surface applicators. (a) Varian surface applicator with VariSource iX. (b) Close-up of VariSource iX in Varian surface applicator showing dwell index. (c) Varian surface applicator with GammaMedplus iX. (d) Close-up of GammaMedplus iX in Varian surface applicator showing dwell index. While standard dosimetry protocols exist for brachytherapy sources and low-energy external photon beams, the geometric and scatter conditions observed with the HDR 192 Ir and...

Fulkerson, Micka, and DeWerd: Surface applicator output verification determined as Kair = M · NK · P elec · PTP ·P cham · PPOM , where the air kerma, Kair is determined through: M is the measured charge reading over a collecting period; Pelec is the electrometer calibration coefficient; PTP is the correction for ambient temperature and pressure; and NK is an applicatorspecific calibration coefficient. Pcham = Kair vol is a chamber Kcham replacement factor, where Kair vol is the Monte Carlo calculated kerma to air-volume at the point of measurement and Kcham is the Monte Carlo calculated kerma...

Fulkerson, Micka, and DeWerd: Surface applicator output verification 2.B. Correction factors for determination of absorbed dose to water F IG . 4. Modified seven-distance apparatus with surface applicator. Positioning of the applicator and chamber was achieved with two alignment lasers. Once a nominal distance of 10 cm between the applicator exit window and center of the ionization chamber was achieved, charge readings were collected with a Standard Imaging Supermax electrometer at distances ranging from 5 to 30 cm from the exit window of the surface applicator. Unlike the traditional...

Fulkerson, Micka, and DeWerd: Surface applicator output verification 2.C.2. Relative dose distributions Relative surface dose distributions, profiles, and distributions at depth were measured using a combination of radiochromic films and TLDs for all source and applicator combinations. Details regarding the experimental methods for the TLD and film measurements can be found in Part I. Solid poly-methyl methacrylate (PMMA) ρ = (1.18 ± 0.01) g cm−3 phantoms were constructed to hold TLD-100 microcubes and position radiochromic film for surface and at-depth measurements. Monte Carlo simulations in...

Fulkerson, Micka, and DeWerd: Surface applicator output verification TABLE II. Air-kerma rate for the Varian surface applicators with the VariSource iX. Chamber measured air-kerma rate (mGy • s-1) Exradin A3 54.6 55.1 54.5 55.1 TABLE IV. Measured and calculated air-kerma rate at the surface of the 30 mm diameter applicator and GammaMedplus iX. Values have been normalized to a reference date. Method Air-kerma rate (cGy) % difference Monte Carlo calculated 6.05 Table II shows the measured air-kerma rate at the exit window for each Varian surface applicator with the...

Fulkerson, Micka, and DeWerd: Surface applicator output verification TABLE VI. Uncertainty budget for Exradin A3 measurements of air-kerma rate for the Varian surface applicators with the GammaMedplus iX. Component Type A % Type B % Chamber position relative to applicator exit window 1.2 Source position within applicator 0.31 0.16 Expanded uncertainty (k = 2) 4.2 applicator was dependent on the afterloader deployment mechanics as described in Sec. 1.A. The manufacturer quotes a ±1 mm uncertainty in the source position for any source/applicator combination. However, this...

Fulkerson, Micka, and DeWerd: Surface applicator output verification 022104-9 TableVII. Uncertainty budget for Exradin A20 measurements of air-kerma rate for the Varian surface applicators with the VariSource iX. Table IX. Calculated Pcham for the Exradin A20 and the surface applicators of interest. These values were derived from MCNP5 simulations. Varian surface applicators with VariSource iX Diameter (mm) Pcham Varian surface applicators with GammaMedplus iX Applicator diameter (mm) Pcham Component Type A % Type B % Chamber positioning on applicator exit window 0.04 Source...

Fulkerson, Micka, and DeWerd: Surface applicator output verification TABLE X. Calculated PDw values for the surface applicators of interest. PDw : Varian surface applicators with VariSource iX Depth (mm) Diameter (mm) PDw : Varian surface applicators with GammaMedplus iX Depth (mm) Diameter (mm) 30 35 40 45 measured calculated measured calculated F IG . 7. Percentage depth dose curves in water for the Varian surface applicators and VariSource iX. Medical Physics, Vol. 41, No. 2, February 2014