Introduction: There have been no significant changes in anal cancer treatment options in 4 decades. In this study, we highlight two preclinical models designed to assess anal cancer treatments. Materials and methods: Transgenic K14E6/E7 mice were treated with 7, 12-dimethylbenz(a) anthracene until anal tumors developed. Mice were treated with localized radiation in addition to chemotherapy (combined-modality therapy [CMT]) and compared to no treatment control (NTC). K14E6/E7 mouse anal spheroids with and without Pik3ca mutations were isolated and treated with vehicle, LY3023414 (LY3) (a drug previously shown to be effective in cancer prevention), CMT, or CMT + LY3. Results: In the in vivo model, there was a significant increase in survival in the CMT group compared to the NTC group (P = 0.0392). In the ex vivo model, there was a significant decrease in the mean diameter of CMT and CMT + LY3-treated spheroids compared to vehicle (P <= 0.0001). For LY3 alone compared to vehicle, there was a statistically significant decrease in spheroid size in the K14E6/E7 group without mutation (P = 0.0004).Conclusions: We have provided proof of concept for two preclinical anal cancer treatment models that allow for the future testing of novel therapies for anal cancer. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

PURPOSE This work seeks to investigate new methods to determine the absorbed dose to water from kilovoltage x rays. Current methods are based on measurements in air and rely on correction factors in order to account for differences between the photon spectrum in air and at depth in phantom, between the photon spectra of the calibration beam and the beam of interest, or in the radiation absorption properties of air and water. This work aims to determine the absorbed dose to water in the NIST-matched x-ray beams at the University of Wisconsin Accredited Dosimetry Calibration Laboratory (UWADCL). This will facilitate the use of detectors in terms of dose to water, which will allow for a simpler determination of dose to water in clinical kilovoltage x-ray beams. MATERIALS AND METHODS A model of the moderately filtered x-ray beams at the UWADCL was created using the BEAMnrc user code of the EGSnrc Monte Carlo code system. This model was validated against measurements and the dose to water per unit air kerma was calculated in a custom built water tank. Using this value and the highly precise measurement of the air kerma made by the UWADCL, the dose to water was determined in the water tank for the x-ray beams of interest. The dose to water was also determined using the formalism defined in the report of AAPM Task Group 61 and using a method that makes use of a 60 Co absorbed dose-to-water calibration coefficient and a beam quality correction factor to account for differences in beam quality between the 60 Co calibration and kilovoltage x-ray beam of interest. The dose to water values as determined by these different methods was then compared. RESULTS The BEAMnrc models used in this work produced simulations of transverse and depth dose profiles that agreed with measurements with a 2%/2 mm criteria gamma test. The dose to water as determined from the different methods used here agreed within 3.5% at the surface of the water tank and agreed within 1.8% at a depth of 2 cm in phantom. The dose-to-water values all agreed within the associated uncertainties of the methods used in this work. Both the Monte Carlo-based method and the 60 Co-based method had a lower uncertainty than the TG-61 methodology for all of the x-ray beams used in this work. CONCLUSION Two new dose determination methods were used to determine the dose to water in the NIST-matched x-ray beams at the UWADCL and they showed good agreement with previously established techniques. Due to the improved Monte Carlo calculation techniques used in this work, both of the methods have lower uncertainties compared to TG-61. The methods presented in this work compare favorably with calorimetry-based standards established at other institutions.

Background: Locally recurrent rectal cancer (LRRC) is a major problem after curative resection of rectal cancer. Extensive pelvic surgery can achieve complete resection of LRRC. Such surgery is often associated with extensive blood loss and severe postoperative complications. Especially pelvic abscess (PA) frequently develops after such radical surgeries with large pelvic defect. Since 2012, laparoscopic surgery has been performed to reduce surgical stress in our institutions. The aim of this study was to assess the safety and feasibility of laparoscopic surgery for LRRC. Method: The medical records of 177 patients who underwent curative-intent resection for LRRC between 2000 and 2016 were reviewed. Among them, 50 patients underwent laparoscopic surgery. Surgical outcomes were compared between laparoscopic surgery group (Lap group) and open surgery group (Open group). Results: In the total cohort, LRRC resection with concomitant sacrectomy (n = 76) was significantly invasive procedure compared to resection without sacrectomy (n = 101) in terms of extensive blood loss (5176 4339 ml vs 3039 6673 ml, respectively, P = 0.016), prolonged operative time (916 708 min vs 554 253 min, respectively, P < 0.0001), and high incidence of PA [40/76 (53%) vs 23/78 (29%), respectively, P < 0.0001]. The number of cases with concomitant sacrectomy did not differ significantly between Lap group and Open group: 16/50 (32%) versus 60/127 (47%), respectively, P = 0.091. The rate of pathologically confirmed curative resection was not different between Lap group and Open group: 42/50 (84%) versus 107/125 (85%), respectively, P = 0.816. There were no significant differences between Lap group and the Open group in terms of operation time: 589 237 min versus 757 604 min, respectively, P = 0.060. Lap group had significantly less intraoperative blood loss than Open group: 548 527 ml versus 5334 6422 ml, respectively, P < 0.0001. The incidence of pelvic abscess was significantly lower in Lap group than in Open group: 9/50 (18%) versus 54/127 (43%), respectively, P = 0.0028. Conclusion: Laparoscopic surgery for LRRC can be a safe and feasible procedure.

We would like to thank Dr. Brivio et al. [Med. Phys.] for their comment on our recent paper. Miller et al. [Med. Phys. 43 (2016) 2141-2152] determined the primary cause of voltage-dependent polarity effects in microchambers to be a potential difference between the guard and collecting electrodes. In their comment, Brivio et al., offer an explanation for the cause of such potential differences. Brivio et al. attribute the potential difference to the disparity in the work functions between guard and collecting electrodes composed of different materials. However, all of the microchambers investigated in Miller et al. contained a guard and collecting electrode which were composed of the same material. Therefore, the explanation offered by Brivio et al. that "the electric potential perturbation arises from the work function difference of the disparate materials electrodes" does not explain the polarity effects exhibited by the microchambers investigated in Miller et al., all of which contain electrodes composed of the same materials.

PurposeTo perform an in‐air air‐kerma strength () calibration of the Bebig model Ir2.A85‐2 high‐dose rate (HDR) brachytherapy source manufactured by Mallinckrodt Medical (Westerduinweg, Germany) with the NIST‐traceable seven‐distance technique established by the University of Wisconsin. A comparison was made between the reference air‐kerma rate (RAKR) reported on a certificate from the Physikalisch‐Technische Bundesanstalt (Berlin, Germany) (PTB) primary laboratory and the determined at the University of Wisconsin Madison Radiation Research Center (UWMRRC). A theoretical sensitivity study was performed to investigate the impact that variations in the experimental setup have on the computed from the seven‐distance algorithm in order to determine if the uncertainty budget for the seven‐distance method should be expanded.MethodsThe manufacturer‐reported for the source was compared to the determined from the University of Wisconsin Accredited Dosimetry Calibration Laboratory (UWADCL) transfer standard well chambers and the seven‐distance technique. Monte Carlo techniques (MCNP6) were employed to compare the theoretical calibration coefficients of a Standard Imaging (Middleton, WI) HDR1000 Plus well chamber using Standard Imaging model 70010 and model 70110 source holders to determine if a holder dependence was present. Radiochromic film (EBT3, Ashland) exposures were performed to assess the dose distribution of the source in phantom. The seven‐distance algorithm was coded in MATLAB®(R2013b) and benchmarked with MCNP6 with the capacity to model distance offset behaviors among nominal positions. This offset model was used in a Monte Carlo simulation coded in MATLAB to determine the average uncertainty in the calculations from the seven‐distance algorithm.ResultsThe measured using the seven‐distance technique at the UWMRRC agreed with the RAKR reported on the PTB source certificate and the on the Mallinckrodt source certificate to within 0.28% and −0.79%, respectively. It was found that the difference between the measured from the transfer standard well chambers at the UWADCL and the seven‐distance method was between 0.13% and 0.30% at the 95% confidence level. Monte Carlo results showed negligible differences between the simulated calibration coefficient for an HDR1000 Plus well chamber using the model 70010 or model 70110 source holder. The autoradiographs from the source in Virtual Water showed that the dose distribution is symmetric. Additionally, the sensitivity study performed in MATLAB showed that the calculated with the seven‐distance algorithm could deviate by 0.24% from randomly generated distance offsets within 1mm in magnitude.ConclusionThe differences between the measurements determined from the seven‐distance technique and the accredited UWADCL measurement results were within the k = 2 uncertainty reported for an accredited calibration. Excellent agreement was found between the measured and RAKR methods used at the UWMRRC and PTB, respectively. Additionally, the sensitivity study has shown that the seven‐distance algorithm accurately determines the of a source while having a variable chamber offset among nominal positions; the uncertainty budget for the seven‐distance method does not need to be expanded at this time. It has been determined that the current standard used by the UWADCL for well chamber calibrations is valid for the Bebig model Ir2.A85‐2 brachytherapy source.

PURPOSEMicrochambers demonstrate anomalous voltage-dependent polarity effects. Existing polarity and ion recombination correction factors do not account for these effects. As a result, many commercial microchamber models do not meet the specification of a reference-class ionization chamber as defined by the American Association of Physicists in Medicine. The purpose of this investigation is to determine the cause of these voltage-dependent polarity effects.METHODSA series of microchamber prototypes were produced to isolate the source of the voltage-dependent polarity effects. Parameters including ionization-chamber collecting-volume size, stem and cable irradiation, chamber assembly, contaminants, high-Z materials, and individual chamber components were investigated. Measurements were performed with electrodes coated with graphite to isolate electrode conductivity. Chamber response was measured as the potential bias of the guard electrode was altered with respect to the collecting electrode, through the integration of additional power supplies. Ionization chamber models were also simulated using comsol Multiphysics software to investigate the effect of a potential difference between electrodes on electric field lines and collecting volume definition.RESULTSInvestigations with microchamber prototypes demonstrated that the significant source of the voltage-dependent polarity effects was a potential difference between the guard and collecting electrodes of the chambers. The voltage-dependent polarity effects for each prototype were primarily isolated to either the guard or collecting electrode. Polarity effects were reduced by coating the isolated electrode with a conductive layer of graphite. Polarity effects were increased by introducing a potential difference between the electrodes. comsol simulations further demonstrated that for a given potential difference between electrodes, the collecting volume of the chamber changed as the applied voltage was altered, producing voltage-dependent polarity effects in the chamber response. Ionization chamber measurements and comsol simulations demonstrated an inverse relationship between the chamber collecting volume size and the severity of voltage-dependent polarity effects on chamber response. The effect of a given potential difference on chamber polarity effects was roughly ten times greater for microchambers as compared to Farmer-type chambers. Stem and cable irradiations, chamber assembly, contaminants, and high-Z materials were not found to be a significant source of the voltage-dependent polarity effects.CONCLUSIONSA potential difference between the guard and collecting electrodes was found to be the primary source of the voltage-dependent polarity effects demonstrated by microchambers. For a given potential difference between electrodes, the relative change in the collecting volume is smaller for larger-volume chambers, illustrating why these polarity effects are not seen in larger-volume chambers with similar guard and collecting electrode designs. Thus, for small-volume chambers, it is necessary to reduce the potential difference between the guard and collecting electrodes in order to reduce polarity effects for reference dosimetry measurements.

A new directional Pd-103 source has been developed by CivaTech Oncology Inc. (Durham, NC) for use in low-dose rate (LDR) brachytherapy. As with any new LDR brachytherapy source, a calibration method and a National Institute of Standards and Technology (NIST)-traceable calibration standard must be established for a clinical user to perform air-kerma strength measurements and verify the manufacturer stated source strength. For typical LDR brachytherapy sources, the Wide-Angle Free-Air Chamber at NIST (NIST WAFAC) is used to determine the air-kerma strength of an individual source, and then a well-type ionization chamber with an ADCL-supplied calibration coefficient is used by the clinical user for source strength verification. However, with the unique directional nature and spectral characteristics of this source, additional experiments are necessary before establishing a NIST-traceable calibration technique. In this work we examine the results of air-kerma strength measurements performed with two different free-air chamber designs, as well as the directionality effects and batch-to-batch variations on calibration coefficients determined with a commercial well-type ionization chamber. The new Pd-103 source is referred to as a CivaDot and consists of a disk-shaped polymer capsule containing radioactive Pd-103 and a gold shield. The CivaDot is intended to be used in a planar source array called a CivaSheet® consisting of multiple CivaDots encased in a bioabsorbable membrane. In this investigation two different free-air chambers were used to determine the air-kerma strength of three CivaDots. One is the University of Wisconsin Variable-Aperture Free-Air Chamber (UW VAFAC) and the second is the NIST WAFAC. Measurements and spectra-dependent correction factors were determined independently and the results compared once all measurements were complete. Additionally, two different Standard Imaging Inc. (Middleton, WI) HDR1000 Plus well-type ionization chambers and a CivaDot-specific source holder insert have been calibrated using the CivaDots from multiple batches and for multiple orientations within the chambers. For each measurement, the CivaDot orientation is indexed to the well chamber and the calibration coefficient compared at four cardinal angles. The average calibration coefficient (averaged over all four cardinal angles) has been compared between three different batches of sources over a one year period. The agreement between the UW VAFAC and NIST WAFAC air-kerma strength determinations was within 0.5% for all three sources, which was well within the estimated uncertainties for each measurement. The rotational effects of a CivaDot within a well chamber were significant (+/- 1.5%), but can be accounted for by averaging the results from four cardinal angles. One well chamber showed more rotational anisotropy than the other. The CivaDot calibration coefficients from multiple batches produced over a one year period showed < 2% variations, which is typical for other LDR brachytherapy seeds.Table 1Air-kerma strength (SK) comparison results as measured by two different free-air chambers. Results are decay-corrected to the reference time of 8/21/2015 at 00:00:01 EST.Source IDUW VAFAC SK (U)NIST WAFAC SK (U)UW/NIST005 A5.2655.2710.999005 B5.3045.2841.004005 C5.1695.1601.002 Open table in a new tab Good agreement and reproducibility between independent primary measurements of air-kerma strength supports the accuracy of each technique, as shown in Table 1. The rotational dependence of the well chamber calibration coefficients can be accounted for by averaging the results over four cardinal angles.

Purpose:The aim of this work is to determine the TG-43 dose-rate constant analog for a new directional low-dose rate brachytherapy source based on experimental methods and comparison to Monte Carlo simulations. The CivaSheet™ is a new commercially available planar source array comprised of a variable number of discrete directional source elements called “CivaDots”. Given the directional nature and non-conventional design of the source, modifications to the AAPM TG-43 protocol for dosimetry are required. As a result, various parameters of the TG-43 dosimetric formalism have to be adapted to accommodate this source. This work focuses on the dose-rate constant analog determination for a CivaDot.Methods:Dose to water measurements of the CivaDot were performed in a polymethyl methacrylate phantom (20×20×12 cm3) using thermoluminescent dosimeters (TLDs) and Gafchromic EBT3 film. The source was placed in the center of the phantom, and nine TLD micro-cubes were irradiated along its central axis at a distance of 1 cm. For the film measurements, the TLDs were substituted by a (3×3) cm2 EBT3 film. Primary air-kerma strength measurements of the source were performed using a variable-aperture free-air chamber. Finally, the source was modeled using the Monte Carlo N-Particle Transport Code 6.Results:Dose-rate constant analog observed for a total of eight CivaDots using TLDs and five CivaDots using EBT3 film was within ±7.0% and ±2.9% of the Monte Carlo predicted value respectively. The average difference observed was −4.8% and −0.1% with a standard deviation of 1.7% and 2.1% for the TLD and the film measurements respectively, which are both within the comparison uncertainty.Conclusion:A preliminary investigation to determine the doserate constant analog for a CivaDot was conducted successfully with good agreement between experimental and Monte Carlo based methods. This work will aid in the eventual realization of a clinically-viable dosimetric framework for the CivaSheet.This work was partially supported by NCI contract (HHSN261201200052C) through CivaTech Oncology Inc.

Purpose: To investigate ion recombination and polarity effects in scanning and microionization chambers when used with digital electrometers and high‐dose‐rate linac beams such as flattening‐filter‐free (FFF) fields, and to compare results against conventional pulsed and continuous photon beams. Methods: Saturation curves were obtained for one Farmer‐type ionization chamber and eight small‐volume chamber models with volumes ranging from 0.01 to 0.13 cm3 using a Varian TrueBeam™ STx with FFF capability. Three beam modes (6 MV, 6 MV FFF, and 10 MV FFF) were investigated, with nominal dose‐per‐pulse values of 0.0278, 0.0648, and 0.111 cGy/pulse, respectively, at dmax. Saturation curves obtained using the Theratronics T1000 60Co unit at the UWADCL and a conventional linear accelerator (Varian Clinac iX) were used to establish baseline behavior. Jaffé plots were fitted to obtain Pion, accounting for exponential effects such as charge multiplication. These values were compared with the two‐voltage technique recommended in TG‐51, and were plotted as a function of dose‐per‐pulse to assess the ability of small‐volume chambers to meet reference‐class criteria in FFF beams. Results: Jaffé‐ and two‐voltage‐determined Pion values measured for high‐dose‐rate beams agreed within 0.1% for the Farmer‐type chamber and 1% for scanning and microionization chambers, with the exception of the CC01 which agreed within 2%. With respect to ion recombination and polarity effects, the Farmer‐type chamber, scanning chambers and the Exradin A26 microchamber exhibited reference‐class behavior in all beams investigated, with the exception of the IBA CC04 scanning chamber, which had an initial recombination correction that varied by 0.2% with polarity. All microchambers investigated, with the exception of the A26, exhibited anomalous polarity and ion recombination behaviors that make them unsuitable for reference dosimetry in conventional and high‐dose‐rate photon beams. Conclusions: The results of this work demonstrate that recombination and polarity behaviors seen in conventional pulsed and continuous photon beams trend accordingly in high‐dose‐rate FFF linac beams. Several models of small‐volume ionization chambers used with a digital electrometer have been shown to meet reference‐class requirements with respect to ion recombination and polarity, even in the high‐dose‐rate environment. For such chambers, a two‐voltage technique agreed well with more rigorous methods of determining Pion. However, the results emphasize the need for careful reference detector selection, and indicate that ionization chambers ought to be extensively tested in each beam of interest prior to their use for reference dosimetry.

PURPOSE: To propose a modification of the current dose calculation formalism introduced in the Task Group No. 43 Report (TG-43) to accommodate an air-kerma rate standard for electronic brachytherapy sources as an alternative to an air-kerma strength standard.METHODS: Electronic brachytherapy sources are miniature x-ray tubes emitting low energies with high-dose-rates. The National Institute of Standards and Technology (NIST) has introduced a new primary air-kerma rate standard for one of these sources, in contrast to air-kerma strength. A modification of the TG-43 protocol for calculation of dose-rate distributions around electronic brachytherapy sources including sources in an applicator is presented. It cannot be assumed that the perturbations from sources in an applicator are negligible, and thus, the applicator is incorporated in the formalism. The modified protocol mimics the fundamental methodology of the original TG-43 formalism, but now incorporates the new NIST-traceable source strength metric of air-kerma rate at 50 cm and introduces a new subscript, i, to denote the presence of an applicator used in treatment delivery. Applications of electronic brachytherapy sources for surface brachytherapy are not addressed in this Technical Note since they are well documented in other publications.RESULTS: A modification of the AAPM TG-43 protocol has been developed to accommodate an air-kerma rate standard for electronic brachytherapy sources as an alternative to an air-kerma strength standard.CONCLUSIONS: The modified TG-43 formalism allows dose calculations to be performed using a new NIST-traceable source strength metric and introduces the concept of applicator-specific formalism parameters denoted with subscript, i. (C) 2015 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.

PURPOSE:This work presents the development of a phantom to verify the treatment planning system (TPS) algorithms used for high-dose-rate (HDR) brachytherapy. It is designed to measure the relative dose in a heterogeneous media. The experimental details used, simulation methods, and comparisons with a commercial TPS are also provided.METHODS:To simulate heterogeneous conditions, four materials were used: Virtual Water™ (VM), BR50/50™, cork, and aluminum. The materials were arranged in 11 heterogeneity configurations. Three dosimeters were used to measure the relative response from a HDR (192)Ir source: TLD-100™, Gafchromic(®) EBT3 film, and an Exradin™ A1SL ionization chamber. To compare the results from the experimental measurements, the various configurations were modeled in the penelope/penEasy Monte Carlo code. Images of each setup geometry were acquired from a CT scanner and imported into BrachyVision™ TPS software, which includes a grid-based Boltzmann solver Acuros™. The results of the measurements performed in the heterogeneous setups were normalized to the dose values measured in the homogeneous Virtual Water™ setup and the respective differences due to the heterogeneities were considered. Additionally, dose values calculated based on the American Association of Physicists in Medicine-Task Group 43 formalism were compared to dose values calculated with the Acuros™ algorithm in the phantom. Calculated doses were compared at the same points, where measurements have been performed.RESULTS:Differences in the relative response as high as 11.5% were found from the homogeneous setup when the heterogeneous materials were inserted into the experimental phantom. The aluminum and cork materials produced larger differences than the plastic materials, with the BR50/50™ material producing results similar to the Virtual Water™ results. Our experimental methods agree with the penelope/penEasy simulations for most setups and dosimeters. The TPS relative differences with the Acuros™ algorithm were similar in both experimental and simulated setups. The discrepancy between the BrachyVision™, Acuros™, and TG-43 dose responses in the phantom described by this work exceeded 12% for certain setups.CONCLUSIONS:The results derived from the phantom measurements show good agreement with the simulations and TPS calculations, using Acuros™ algorithm. Differences in the dose responses were evident in the experimental results when heterogeneous materials were introduced. These measurements prove the usefulness of the heterogeneous phantom for verification of HDR treatment planning systems based on model-based dose calculation algorithms.

PURPOSE Three-dimensional (3D) dosimeters are particularly useful for verifying the commissioning of treatment planning and delivery systems, especially with the ever-increasing implementation of complex and conformal radiotherapy techniques such as volumetric modulated arc therapy. However, currently available 3D dosimeters require extensive experience to prepare and analyze, and are subject to large measurement uncertainties. This work aims to provide a more readily implementable 3D dosimeter with the development and characterization of a radiochromic film stack dosimeter for megavoltage photon beam dosimetry. METHODS A film stack dosimeter was developed using Gafchromic(®) EBT2 films. The dosimeter consists of 22 films separated by 1 mm-thick spacers. A Virtual Water™ phantom was created that maintains the radial film alignment within a maximum uncertainty of 0.3 mm. The film stack dosimeter was characterized using simulations and measurements of 6 MV fields. The absorbed-dose energy dependence and orientation dependence of the film stack dosimeter were investigated using Monte Carlo simulations. The water equivalence of the dosimeter was determined by comparing percentage-depth-dose (PDD) profiles measured with the film stack dosimeter and simulated using Monte Carlo methods. Film stack dosimeter measurements were verified with thermoluminescent dosimeter (TLD) microcube measurements. The film stack dosimeter was also used to verify the delivery of an intensity-modulated radiation therapy (IMRT) procedure. RESULTS The absorbed-dose energy response of EBT2 film differs less than 1.5% between the calibration and film stack dosimeter geometries for a 6 MV spectrum. Over a series of beam angles ranging from normal incidence to parallel incidence, the overall variation in the response of the film stack dosimeter is within a range of 2.5%. Relative to the response to a normally incident beam, the film stack dosimeter exhibits a 1% under-response when the beam axis is parallel to the film planes. Measured and simulated PDD profiles agree within a root-mean-square difference of 1.3%. In-field film stack dosimeter and TLD measurements agree within 5%, and measurements in the field penumbra agree within 0.5 mm. Film stack dosimeter and TLD measurements have expanded (k = 2) overall measurement uncertainties of 6.2% and 5.8%, respectively. Film stack dosimeter measurements of an IMRT dose distribution have 98% agreement with the treatment planning system dose calculation, using gamma criteria of 3% and 2 mm. CONCLUSIONS The film stack dosimeter is capable of high-resolution, low-uncertainty 3D dose measurements, and can be readily incorporated into an existing film dosimetry program.

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 brachytherapy now allow for the treatment of surface lesions with specialized conical applicators placed directly on the lesion. Applicators are available for use with high dose rate (HDR)(192)Ir sources, as well as electronic brachytherapy sources. Part I of this paper discussed the applicators used with electronic brachytherapy sources. Part II will discuss those used with HDR (192)Ir sources. Although the use of these applicators has gained in popularity, the dosimetric characteristics have not been independently verified. Additionally, there is no recognized method of output verification for quality assurance procedures with applicators like these.METHODS:This work aims to create a cohesive method of output verification that can be used to determine the dose at the treatment surface as part of a quality assurance/commissioning process for surface applicators used with HDR electronic brachytherapy sources (Part I) and(192)Ir sources (Part II). Air-kerma rate measurements for the (192)Ir sources were completed with several models of small-volume ionization chambers to obtain an air-kerma rate at the treatment surface for each applicator. Correction factors were calculated using MCNP5 and EGSnrc Monte Carlo codes in order to determine an applicator-specific absorbed dose to water at the treatment surface from the measured air-kerma rate. Additionally, relative dose measurements of the surface dose distributions and characteristic depth dose curves were completed in-phantom.RESULTS:Theoretical dose distributions and depth dose curves were generated for each applicator and agreed well with the measured values. A method of output verification was created that allows users to determine the applicator-specific dose to water at the treatment surface based on a measured air-kerma rate.CONCLUSIONS:The novel output verification methods described in this work will reduce uncertainties in dose delivery for treatments with these kinds of surface applicators, ultimately improving patient care.

Purpose:To determine the intrinsic energy dependence of LiF:Mg,Ti thermoluminescent dosimeters (TLD‐100) for 125I and 103Pd brachytherapy sources relative to 60Co.Methods:LiF:Mg,Ti TLDs were irradiated with low‐energy brachytherapy sources and with a 60Co teletherapy source. The brachytherapy sources measured were the Best 2301 125I seed, the OncoSeed 6711 125I seed, and the Best 2335 103Pd seed. The TLD light output per measured air‐kerma strength was determined for the brachytherapy source irradiations, and the TLD light output per air kerma was determined for the 60Co irradiations. Monte Carlo (MC) simulations were used to calculate the dose‐to‐TLD rate per air‐kerma strength for the brachytherapy source irradiations and the dose to TLD per air kerma for the 60Co irradiations. The measured and MC‐calculated results for all irradiations were used to determine the TLD intrinsic energy dependence for 125I and 103Pd relative to 60Co.Results:The relative TLD intrinsic energy dependences (relative to 60Co) and associated uncertainties (k = 1) were determined to be 0.883 ± 1.3%, 0.870 ± 1.4%, and 0.871 ± 1.5% for the Best 2301 seed, OncoSeed 6711 seed, and Best 2335 seed, respectively.Conclusions:The intrinsic energy dependence of TLD‐100 is dependent on photon energy, exhibiting changes of 13%–15% for 125I and 103Pd sources relative to 60Co. TLD measurements of absolute dose around 125I and 103Pd brachytherapy sources should explicitly account for the relative TLD intrinsic energy dependence in order to improve dosimetric accuracy.

PURPOSE: To determine the in-air azimuthal anisotropy and in-water dose distribution for the 1 cm length of a new elongated Pd-103 brachytherapy source through both experimental measurements and Monte Carlo (MC) simulations. Measured and MC-calculated dose distributions were used to determine the American Association of Physicists in Medicine Task Group No. 43 (TG-43) dosimetry parameters for this source.METHODS AND MATERIALS: The in-air azimuthal anisotropy of the source was measured with a NaI scintillation detector and was simulated with the MCNP5 radiation transport code. Measured and MC results were normalized to their respective mean values and then compared. The source dose distribution was determined from measurements with LiF:Mg,Ti thermoluminescent dosimeter (TLD) microcubes and MC simulations. TG-43 dosimetry parameters for the source, including the dose-rate constant, Lambda, two-dimensional anisotropy function, F(r, theta), and line-source radial dose function, g(L)(r), were determined from the TLD measurements and MC simulations.RESULTS: NaI scintillation detector measurements and MC simulations of the in-air azimuthal anisotropy of the source showed that >= 95% of the normalized values for each source were within 1.2% of the mean value. TLD measurements and MC simulations of Lambda, F(r, theta), and g(L)(r) agreed to within the associated uncertainties.CONCLUSIONS: This new Pd-103 source exhibits a high level of azimuthal symmetry as indicated by the measured and MC-calculated results for the in-air azimuthal anisotropy. TG-43 dosimetry parameters for the source were determined through TLD measurements and MC simulations. (C) 2014 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.

This paper describes the development and characterization of a fully automated in vitro cell irradiator using an electronic brachytherapy source to perform radiation sensitivity bioassays. This novel irradiator allows complex variable dose and dose rate schemes to be delivered to multiple wells of 96-well culture plates used in standard biological assays. The Xoft Axxent® eBx™ was chosen as the x-ray source due to its ability to vary tube current up to 300 µA for a 50 kVp spectrum using clinical surface applicators. Translation of the multiwell plate across the fixed radiation field is achieved using a precision motor driven computer controlled positioning system. A series of measurements was performed to characterize dosimetric performance of the system. Measurements have shown that the radiation output measured with an end window ionization chamber is stable between operating currents of 50–300 µA. In addition, radiochromic film was used to characterize the field flatness and symmetry. The average field flatness in the in-plane and cross-plane direction was 2.9 ±1.0% and 4.0 ±1.7%, respectively. The average symmetry in the in-plane and cross-plane direction was 1.8 ±0.9% and 1.6 ±0.5%, respectively. The optimal focal spot resolution at the cellular plane was determined by measuring sequential irradiations on radiochromic film for three different well spacing schemes. It was determined that the current system can irradiate every other well with negligible impact on the radiation field characteristics. Finally, a performance comparison between this system and a common cabinet irradiator is presented.

Purpose:Pulsed‐dose‐rate (PDR) brachytherapy was originally proposed to combine the therapeutic advantages of high‐dose‐rate (HDR) and low‐dose‐rate brachytherapy. Though uncommon in the United States, several facilities employ pulsed‐dose‐rate brachytherapy in Europe and Canada. Currently, there is no air‐kerma strength standard for PDR brachytherapy 192Ir sources traceable to the National Institute of Standards and Technology. Discrepancies in clinical measurements of the air‐kerma strength of the PDR brachytherapy sources using HDR source‐calibrated well chambers warrant further investigation.Methods:In this research, the air‐kerma strength for an192Ir PDR brachytherapy source was compared with the University of Wisconsin Accredited Dosimetry Calibration Laboratory transfer standard well chambers, the seven‐distance technique [B. E. Rasmussen et al., “The air‐kerma strength standard for 192Ir HDR sources,” Med. Phys. 38, – (2011)] 10.1118/1.3656683, and the manufacturer's stated value. Radiochromic film and Monte Carlo techniques were also employed for comparison to the results of the measurements.Results:While the measurements using the seven‐distance technique were within + 0.44% from the manufacturer's determination, there was a + 3.10% difference between the transfer standard well chamber measurements and the manufacturer's stated value. Results showed that the PDR brachytherapy source has geometric and thus radiological qualities that exhibit behaviors similar to a point source model in contrast to a conventional line source model.Conclusions:The resulting effect of the pointlike characteristics of the PDR brachytherapy source likely account for the differences observed between well chamber and in‐air measurements.

A three-dimensional (3D) film stack dosimeter (FSD) using Gafchromic® EBT2 film was characterized for use in external-beam radiotherapy. The FSD was found to have negligible energy dependence and orientation dependence less than 2% using Monte Carlo simulations. Percent-depth-dose measurements with the FSD aligned parallel and perpendicular to the beam axis agreed with Monte Carlo simulations within 2%. Measurements of a 60Co slit field with the FSD and thermoluminescent dosimeters agreed with a gamma passing rate of 97.6% using 1.5%/1.5 mm criteria. Edge artifacts were smaller than 2 mm, minimally affecting the usable measurement volume. The FSD is water equivalent, energy independent and orientation independent within measurement uncertainty at 60Co energies, providing a 3D dosimeter that can be analyzed with a desktop scanner.

PURPOSE:To investigate the applicability of a wide range of microionization chambers for reference dosimetry measurements in low- and medium-energy x-ray beams.METHODS:Measurements were performed with six cylindrical microchamber models, as well as one scanning chamber and two Farmer-type chambers for comparison purposes. Air-kerma calibration coefficients were determined at the University of Wisconsin Accredited Dosimetry Calibration Laboratory for each chamber for a range of low- and medium-energy x-ray beams (20-250 kVp), with effective energies ranging from 11.5 keV to 145 keV, and a (60)Co beam. A low-Z proof-of-concept microchamber was developed and calibrated with and without a high-Z silver epoxy on the collecting electrode.RESULTS:All chambers composed of low-Z materials (Z ≤ 13), including the Farmer-type chambers, the scanning chamber, and the PTW TN31014 and the proof-of-concept microchambers, exhibited air-kerma calibration coefficients with little dependence on the quality of the beam. These chambers typically exhibited variations in calibration coefficients of less than 3% with the beam quality, for medium energy beams. However, variations in air-kerma calibration coefficients of greater than 50% were measured over the range of medium-energy x-ray beams for each of the microchambers containing high-Z collecting electrodes (Z > 13). For these high-Z chambers, which include the Exradin A14SL and A16 chambers, the PTW TN31006 chamber, the IBA CC01 chamber, and the proof-of-concept chamber containing silver, the average variation in air-kerma calibration coefficients between any two calibration beams was nearly 25% over the entire range of beam qualities investigated.CONCLUSIONS:Due to the strong energy dependence observed with microchambers containing high-Z components, these chambers may not be suitable dosimeters for kilovoltage x-ray applications, as they do not meet the TG-61 requirements. It is recommended that only microchambers containing low-Z materials (Z ≤ 13) be considered for air-kerma calibrations for reference dosimetry in low- and medium-energy x-ray beams.