Photon-emitting Brachytherapy Sources Research Articles

Friday, June 17, 20222:30 PM - 3:30 PM PHSPP01 Presentation Time: 2:30 PM: Dosimetry for Beta Emitting Brachytherapy Sources

<h3>Purpose</h3> Dosimetry for photon-emitting brachytherapy sources is well established, to the point of commercial software for clinical treatment planning to account for material heterogeneities and patient-specific radiation scatter conditions. However, dosimetry standards for beta sources are simpler and have not been recently investigated. While the AAPM TG-149 and ICRU 72 Reports issue clinical guidance and reference data, a modern evaluation of beta-source dosimetry is missing. This investigation strives to identify the potential role for beta-emitting radionuclides as well as to examine theoretical sources for a deeper understanding of beta dosimetry. <h3>Materials and Methods</h3> Available beta-emitting brachytherapy sources include P-32, Sr/Y-90, and Ru/Rh-106 with Y-90 commonly used for selective internal radiation therapy (SIRT) of cancers in the liver. Energy spectra of these sources were taken from ICRU 72 with dose simulations performed using the MCNP v6.2 Monte Carlo radiation transport code. From ICRU 72, the maximum energies for P-32, Sr/Y-90, Y-90, and Ru/Rh-106 were 1.71, 2.28, 2.28, and 3.54 MeV, respectively. Monoenergetic sources of 0.5, 1, 1.5, 2, 3, and 4 MeV were also simulated to extend the energy range and scrutinize dose-distribution dependence on electron energy. Since 2D dose distribution are highly dependent on the design of a source, point sources were simulated to evaluate the depth-dose distribution as a function of radius, <i>r</i>, as well radial dose functions that removed the inverse-square effect. Dose was sampled in 15 cm diameter spheres comprised of water, tissue (ICRU 44 skeletal muscle), or bone (ICRU 44 cortical bone). To mass density effect was quantified in water for 0.5, 1, and 2 g/cm³ with 1 and 2 g/cm³ for tissue and bone, respectively. Observed dose differences were then ascribed to medium differences and not confounded by small differences in mass density. Dose was sampled with radial increments from 0.001 to 0.02 cm for direct comparisons to ICRU 72 results and to evaluate the effect of volume averaging. While only electron sources were considered, dose contributions from bremsstrahlung photons were quantified through comparing results of electron- and electron:photon-transport. Energy deposition was calculated using the MCNP *F8 pulse-height tally, then dividing by the voxel mass to obtain absorbed dose per electron history. With 10⁷ source electrons, statistical uncertainties (<i>k</i>=1) were <0.1% for <i>r</i><0.7 CSDA. When studying bremsstrahlung, 10⁸ source electrons produced 4% statistical uncertainties for <i>r</i>>1.2 CSDA. <h3>Results</h3> In the high dose-gradient region for radionuclide-based beta emitters, the calculated dose distributions in water were within 20% of those from the ICRU 72 Report, which used binned monoenergetic sources to approximate the continuous beta spectra. The radionuclide-based sources exhibited radial dose functions in water that diminished much more steeply than Pd-103, similar to a <0.01 MeV photon source. Sr/Y-90 had a bimodal distribution. Radial dose functions for radionuclide-based sources were inversely proportional to changes in mass density, differing from the scaling-factor models by Cross (1967) and the ICRU 56 Report over the large range of media and densities examined herein. Further, radial dose functions for monoenergetic sources demonstrated a Bragg peak with dose enhancement at <i>r</i>∼0.7 CSDA for all studied energies and media. A sampling of results for radionuclides and monoenergetic sources in water is given in the figure. <h3>Conclusions</h3> Beta dosimetry is largely governed by the mass density with medium composition being a much lesser effect, unlike for low-energy photons where the photoelectric effect is highly sensitive to <i>Z</i>_eff. Unlike for high-energy photon dosimetry, beta dosimetry is negligibly impacted by radiation scatter conditions due to their short range. While Ru/Rh-106 and Sr/Y-90 are proven for shallow plaque brachytherapy and Y-90 for SIRT, beta-emitting radionuclides do not have adequate range for interstitial implants like prostate brachytherapy since dose uniformity is much worse than with HDR Ir-192 or LDR Pd-103 brachytherapy.

GEC-ESTRO ACROP recommendations on calibration and traceability of HE HDR-PDR photon-emitting brachytherapy sources at the hospital level

The vast majority of radiotherapy departments in Europe using brachytherapy (BT) perform temporary implants of high- or pulsed-dose rate (HDR-PDR) sources with photon energies higher than 50 keV. Such techniques are successfully applied to diverse pathologies and clinical scenarios. These recommendations are the result of Working Package 21 (WP-21) initiated within the BRAchytherapy PHYsics Quality Assurance System (BRAPHYQS) GEC-ESTRO working group with a focus on HDR-PDR source calibration. They provide guidance on the calibration of such sources, including practical aspects and issues not specifically accounted for in well-accepted societal recommendations, complementing the BRAPHYQS WP-18 Report dedicated to low energy BT photon emitting sources (seeds). The aim of this report is to provide a European-wide standard in HDR-PDR BT source calibration at the hospital level to maintain high quality patient treatments.

Comparison of Dose Distribution around Central Vaginal Applicator Brachytherapy Treatment Calculated with Water Based TG43 &amp; Model Based TG186

Aim: The focus of this research was to look at the dosimetric effect and evaluate the dose difference between TG-186 and TG-43 plans for cervical carcinoma using central vaginal applicators, in order to help clinicians to choose right algorithm. Introduction: TG-43 protocol is for calculation of dose-rate distributions around photon-emitting brachytherapy sources. The radiation is assumed to be carried out through an infinite homogeneous water phantom in the TG-43 dose calculation approach. Thus any heterogeneities within or outside the patient are not taken into account. As a result the accuracy of dose calculations in places near to air or bone may be impacted. The recently published AAPM Radiation Therapy Committee Task Group 186 (TG-186) report has provided new guidelines for dose calculation and reporting in brachytherapy to address the shortcomings of the current TG-43U1 dose calculation methodology. Heterogeneity correction algorithms have only recently been made available to the BT community in contrary to external beam radiotherapy. Materials and Methods: A retrospective study including 15 patients with cervical cancer who had undergone postoperative brachytherapy was performed. External Beam Radiotherapy (EBRT) was performed with a total dose of 50 Gy in 25 fractions as 2 Gy/per fraction using conventional fractionation schedule.Based on TG-43 and TG-186 algorithms plans were done for 15 cervical patients on the Nucletron- oncentra planning system and treated with Ir-192 brachytherapy source. The plans were not re optimized and therefore the dwell positions and dwell times were identical between the two plans. Retrospectively the plans were recalculated using the TG-186 algorithms. For each patient DVH is used to calculate dose in 0.1cc CGy, 1cc CGy, 2cc CGy and 5cc CGy of OAR doses as well as prescription point doses. Results: D w,m, found small changes in Prescription doses and in D0.1 cc, D1 cc, D2 cc, D5 cc for rectum and bladder with all dose parameters for individual patients differing from TG-43 values by &lt; 1%. Conclusion: The dose difference between TG43 and TG186 algorithms is for most clinical cases not significant for target volumes and OARs. Cylinder applicators although TG43 algorithm overestimated the tissue dose the difference of dose distribution caused by the two algorithms was almost negligible because the difference of dose distribution was not much (less than 1%) and both were located around the applicator.

Update of the CLRP eye plaque brachytherapy database for photon-emitting sources.

To update and extend the Carleton Laboratory for Radiotherapy Physics (CLRP) Eye Plaque (EP) dosimetry database for low-energy photon-emitting brachytherapy sources using egs_brachy, an open-source EGSnrc application. The previous database, CLRP_EPv1, contained datasets for the Collaborative Ocular Melanoma Study (COMS) plaques (10-22mm diameter) with 103 Pd or 125 I seeds (BrachyDose-computed, 2008). The new database, CLRP_EPv2, consists of newly calculated three-dimensional (3D) dose distributions for 17 plaques [eight COMS, five Eckert & Ziegler BEBIG, and four others representative of models used worldwide] for 103 Pd, 125 I, and 131 Cs seeds. Plaque models are developed with egs_brachy, based on published/manufacturer dimensions and material data. The BEBIG plaques (modeled for the first time) are identical in dimensions to COMS plaques but differ in elemental composition and/or density. Previously benchmarked seed models are used. Eye plaques and seeds are simulated at the center of full-scatter water phantoms, scoring in (0.05cm)3 voxels spanning the eye for scenarios: (a) "HOMO": simulated TG43 conditions; (b) "HETERO": eye plaques and seeds fully modeled; (c) "HETsi" (BEBIG only): one seed is active at a time with other seed geometries present but not emitting photons (inactive); summation over all seeds in a plaque then yields "HETsum" (includes interseed effects). For validation, doses are compared to those from CLRP_EPv1 and published data. Data are available at https://physics.carleton.ca/clrp/eye_plaque_v2, http://doi.org/10.22215/clrp/EPv2. The data consist of 3D dose distributions (text-based EGSnrc "3ddose" file format) and graphical presentations of the comparisons to previously published data. The CLRP_EPv2 database provides accurate reference 3D dose distributions to advance ocular brachytherapy dose evaluations. The fully-benchmarked eye plaque models will be freely distributed with egs_brachy, supporting adoption of model-based dose evaluations as recommended by TG-129, TG-186, and TG-221.

Technical note: Dosimetric study for the new BEBIG 60Co HDR source used in brachytherapy in water and different media using Monte Carlo N-Particle eXtended code

This work aims to study the dosimetrc parameters of the new 60Co-source model Co0.A86 used in high dose rate brachytherapy and manufactured by BEBIG (Eckert & Ziegler BEBIG GmbH, Germany). The radial dose function, 2D along&away dose rates and the dose rate constant were investigated in a water phantom. Accordingly, we use the recommendations from the AAPM and ESTRO on dose calculation for high-energy (average energy higher than 50 keV) photon-emitting brachytherapy sources cited in the HEBD working group report. Furthermore, we compared the obtained results with the quoted values in the previous studies. The value of air-kerma strength calculated in this work was 3.030 ± 0.002 UBq-1. Moreover, the radial dose function and 2D along&away dose rates are evaluated in different tissues and compared with the results obtained in the water and we found a notable difference. To reach the goal we have used MCNPX code for simulation.

GEC-ESTRO ACROP recommendations on calibration and traceability of LE-LDR photon-emitting brachytherapy sources at the hospital level

Prostate brachytherapy treatment using permanent implantation of low-energy (LE) low-dose rate (LDR) sources is successfully and widely applied in Europe. In addition, seeds are used in other tumour sites, such as ophthalmic tumours, implanted temporarily. The calibration issues for LE-LDR photon emitting sources are specific and different from other sources used in brachytherapy. In this report, the BRAPHYQS (BRAchytherapy PHYsics Quality assurance System) working group of GEC-ESTRO, has developed the present recommendations to assure harmonized and high-quality seed calibration in European clinics. There are practical aspects for which a clarification/procedure is needed, including aspects not specifically accounted for in currently existing AAPM and ESTRO societal recommendations. The aim of this report has been to provide a European wide standard in LE-LDR source calibration at end-user level, in order to keep brachytherapy treatments with high safety and quality levels. The recommendations herein reflect the guidance to the ESTRO brachytherapy users and describe the procedures in a clinic or hospital to ensure the correct calibration of LE-LDR seeds.

Supplement 2 for the 2004 update of the AAPM Task Group No. 43 Report: Joint recommendations by the AAPM and GEC-ESTRO.

Since the publication of the 2004 update to the American Association of Physicists in Medicine (AAPM) Task Group No. 43 Report (TG-43U1) and its 2007 supplement (TG-43U1S1), several new low-energy photon-emitting brachytherapy sources have become available. Many of these sources have satisfied the AAPM prerequisites for routine clinical purposes and are posted on the Brachytherapy Source Registry managed jointly by the AAPM and the Imaging and Radiation Oncology Core Houston Quality Assurance Center (IROC Houston). Given increasingly closer interactions among physicists in North America and Europe, the AAPM and the Groupe Européen de Curiethérapie-European Society for Radiotherapy & Oncology (GEC-ESTRO) have prepared another supplement containing recommended brachytherapy dosimetry parameters for eleven low-energy photon-emitting brachytherapy sources. The current report presents consensus datasets approved by the AAPM and GEC-ESTRO. The following sources are included: 125 I sources (BEBIG model I25.S17, BEBIG model I25.S17plus, BEBIG model I25.S18, Elekta model 130.002, Oncura model 9011, and Theragenics model AgX100); 103 Pd sources (CivaTech Oncology model CS10, IBt model 1031L, IBt model 1032P, and IsoAid model IAPd-103A); and 131 Cs (IsoRay Medical model CS-1 Rev2). Observations are included on the behavior of these dosimetry parameters as a function of radionuclide. Recommendations are presented on the selection of dosimetry parameters, such as from societal reports issuing consensus datasets (e.g., TG-43U1, AAPM Report #229), the joint AAPM/IROC Houston Registry, the GEC-ESTRO website, the Carleton University website, and those included in software releases from vendors of treatment planning systems. Aspects such as timeliness, maintenance, and rigor of these resources are discussed. Links to reference data are provided for radionuclides (radiation spectra and half-lives) and dose scoring materials (compositions and mass densities). The recent literature is examined on photon energy response corrections for thermoluminescent dosimetry of low-energy photon-emitting brachytherapy sources. Depending upon the dosimetry parameters currently used by individual physicists, use of these recommended consensus datasets may result in changes to patient dose calculations. These changes must be carefully evaluated and reviewed with the radiation oncologist prior to their implementation.

Absolute measurement of LDR brachytherapy source emitted power: Instrument design and initial measurements.

Energy-based source strength metrics may find use with model-based dose calculation algorithms, but no instruments exist that can measure the energy emitted from low-dose rate (LDR) sources. This work developed a calorimetric technique for measuring the power emitted from encapsulated low-dose rate, photon-emitting brachytherapy sources. This quantity is called emitted power (EP). The measurement methodology, instrument design and performance, and EP measurements made with the calorimeter are presented in this work. A calorimeter operating with a liquid helium thermal sink was developed to measure EP from LDR brachytherapy sources. The calorimeter employed an electrical substitution technique to determine the power emitted from the source. The calorimeter's performance and thermal system were characterized. EP measurements were made using four (125)I sources with air-kerma strengths ranging from 2.3 to 5.6 U and corresponding EPs of 0.39-0.79 μW, respectively. Three Best Medical 2301 sources and one Oncura 6711 source were measured. EP was also computed by converting measured air-kerma strengths to EPs through Monte Carlo-derived conversion factors. The measured EP and derived EPs were compared to determine the accuracy of the calorimeter measurement technique. The calorimeter had a noise floor of 1-3 nW and a repeatability of 30-60 nW. The calorimeter was stable to within 5 nW over a 12 h measurement window. All measured values agreed with derived EPs to within 10%, with three of the four sources agreeing to within 4%. Calorimeter measurements had uncertainties ranging from 2.6% to 4.5% at the k = 1 level. The values of the derived EPs had uncertainties ranging from 2.9% to 3.6% at the k = 1 level. A calorimeter capable of measuring the EP from LDR sources has been developed and validated for (125)I sources with EPs between 0.43 and 0.79 μW.

Second primary malignancies after radiotherapy including HDR (252)Cf brachytherapy for cervical cancer.

Second primary malignancies (SPMs) are among the most serious late adverse effects after radiotherapy experienced over time by the increasing population of cancer survivors worldwide. The study aim was to determine the rate and distribution of SPMs for neutron- and photon-emitting brachytherapy (BT) sources for patients treated for cervical cancer. The cohort comprised 662 patients with invasive cervical cancer (Stages IIB and IIIB) and contributed 5,224 patient-years (PY) of observation. These patients were treated by radiotherapy during the 1989-1999 year period with cobalt-60 source ((60)Co) teletherapy. The first group of patients (N = 375; 3,154 PY) received high-dose-rate (HDR) californium-252 source ((252)Cf) BT, whereas the second group (N = 287; 2,070 PY) received HDR (60)Co BT. Over a 25-year period, 35 SPMs were observed, amounting to 5.3% of all observed patients: in 16 (2.4%) heavily, 2 (0.3%) moderately, 14 (2.1%) lightly irradiated body sites, and 3 (0.5%) other sites. Of these, 21 cases (5.6%) were observed in the HDR (252)Cf BT group, whereas 14 cases (4.9%) were observed in the HDR (60)Co BT group. Exposures received during (60)Co teletherapy and HDR BT with either (252)Cf or (60)Co had statistically equivalent (p = 0.68) effects on SPM development. Cure rates are improving, and therefore, there are more long-term survivors from cervical cancer. This study shows no significant difference in rates or distribution of SPMs in women treated with neutron BT compared with photon BT (p = 0.68). After reviewing related literature and our research results, it is evident that a detailed investigation of SPM frequency, localization, and dose to adjacent organs is a suitable topic for further research.

Of the use of new EBT3 for dose profile and dose-area product measurements in small fields

)coupled through optical fibers to a two-channel photodetection module.The module is basically composed of two silicon photomultipliers syn-chronized together by a FPGA card. The two probes are positioned in aPMMA cylinder, at 18 mm away from its axis and spaced apart by 29 mm.A 2 mm diameter source transfer catheter is inserted into the cylinderaxis.Testing results have shown that, the seed activity can be estimated with aprecision better than 5 % when it is positioned in front of one of the twodosimetric probes. This positioning is chosen to estimate the dose with thehighest measurement SNR and the lowest sensitivity on seed positioningerrors (There is a low dose rate gradient when the seed is facing the probe).With the acquisition of a treatment plan used as a reference, the dwell posi-tion can be estimated with sub-milimetric accuracy over a range of 20 mm,and the dwell time with a mean error of 24 ms. It also integrates measure-ments of thetransit timeduringtheintroduction andremovalof the source.Thus, it is possible to define the dose at any point in space from the activityreferencesourcebyusingthedosecalculationformalismTG-43AAPM-ESTROconsensus [2]. The difference between the dose calculated by the systemsoftware and the TPS is less than 4% for the consideredpoints of interest.Theproposedsystemallowsanentirequalitycheckoftheafterloaderbeforetreatment.Bycomparingmeasuredvalueswithexpectedones,italsoallowsreal-time detection of different types of errors such as bad source activity,treatment protocol error, in-catheter curvature-induced position errors [3].Keywords: Brachytherapy, DoRGaN, Quality assuranceReferences[1]R.Nath,L.L.Anderson,J.A.Meli,A.J.Olch,J.A.Stitt,andJ.F.Williamson,“Code of practice for brachytherapy physics: Reportof the AAPM RadiationTherapy Committee Task Group No. 56,”Med. Phys. Vol 24 (1997),p.1557 e1598.[2] J. Perez-Calatayud, F. Ballester, R.K. Das, L.A. Dewerd, G.S. Ibbott, A.S.Meigooni, Z. Ouhib Z.M.J. Rivard, R.S. Sloboda, J.F. Williamson, “Dosecalculation for photon-emitting brachytherapy sources with average en-ergy higher than 50 keV: full report of the AAPM and ESTRO report of thehigh energy brachytherapy source dosimetry (HEBD) working group,”august 2012, ISBN: 978-1-936366-17-0, ISSN: 0271-7344.[3] A. Palmer, B. Mzenda, “Performance assessment of the BEBIG Multi-Source high dose rate brachytherapy treatment unit, “Phys Med Biol. Vol 54(2009) p. 7417-34.http://dx.doi.org/10.1016/j.ejmp.2014.10.048ESTABLISHMENT OF DOSIMETRIC REFERENCES IN SMALL FIELDSTHANKS TO A NEW QUANTITY OF INTERESTS. Dufreneix, J.M. Bordy, F. Delaunay, J. Daures, J. Gouriou, M. Le Roy, A.Ostrowsky, B. Rapp, L. Sommier CEA, LIST, Laboratoire National HenriBecquerel, 91191 Gif-sur-Yvette, FranceIntroduction: The output factor ratio measurement assumes that thecalibration factor of the ionization chamber in terms of absorbed dose towater is invariant with field size. A new approach was suggested in orderto verify that this hypothesis is true for a parallel-plate chamber whichsensitive volume is larger than the beam’s section. The quantity of interestis then no longer a dose at a point but a dose integrated over a surface.Methods: A graphite calorimeter and a parallel-plate ionization chamberwith the same sensitive volume (3 cm diameter) were built. They werefully characterized in a large 60Co beam and then used in small circularfields of 2, 1 and 0.75 cm diameter. The ratio of calorimetric againstionometric measurements was considered as a good approximation of thecalibration factor and thus studied.Results: The dose rate established in a large 60Co field with the newcalorimeter is in agreement within 0.4% with previous calorimeters. Theionization chamber shows good characteristics except for a 0.06% drift perhourinwater.Insmallfields,statisticaluncertaintyontheratioconsideredincreases with decreasing field size but stays under 0.5%. A difference of1.3% of this ratio was found for the three field sizes of interest.Conclusion: Results presented here highlight the possibility of measuringcalibration factors in small fields using a dose-area product. Monte Carlosimulations are underway in order to precisely determine the calibrationfactor of the parallel plate chamber in the three small fields studied.Keywords: Radiotherapy; Dosimetric reference; Small fields; Dose-areaproducthttp://dx.doi.org/10.1016/j.ejmp.2014.10.049

Dosimetric characterization of the GammaClip™169Yb low dose rate permanent implant brachytherapy source for the treatment of nonsmall cell lung cancer postwedge resection

A novel (169)Yb low dose rate permanent implant brachytherapy source, the GammaClip™, was developed by Source Production & Equipment Co. (New Orleans, LA) which is designed similar to a surgical staple while delivering therapeutic radiation. In this report, the brachytherapy source was characterized in terms of "Dose calculation for photon-emitting brachytherapy sources with average energy higher than 50 keV: Report of the AAPM and ESTRO" by Perez-Calatayud et al. [Med. Phys. 39, 2904-2929 (2012)] using the updated AAPM Task Group Report No. 43 formalism. Monte Carlo calculations were performed using Monte Carlo N-Particle 5, version 1.6 in water and air, the in-air photon spectrum filtered to remove photon energies below 10 keV in accordance with TG-43U1 recommendations and previously reviewed (169)Yb energy cutoff levels [D. C. Medich, M. A. Tries, and J. M. Munro, "Monte Carlo characterization of an Ytterbium-169 high dose rate brachytherapy source with analysis of statistical uncertainty," Med. Phys. 33, 163-172 (2006)]. TG-43U1 dosimetric data, including SK, Ḋ(r,θ), Λ, gL(r), F(r, θ), φan(r), and φan were calculated along with their statistical uncertainties. Since the source is not axially symmetric, an additional set of calculations were performed to assess the resulting axial anisotropy. The brachytherapy source's dose rate constant was calculated to be (1.22±0.03) cGy h(-1) U(-1). The uncertainty in the dose to water calculations, Ḋ(r,θ), was determined to be 2.5%, dominated by the uncertainties in the cross sections. The anisotropy constant, φan, was calculated to be 0.960±0.011 and was obtained by integrating the anisotropy factor between 1 and 10 cm using a weighting factor proportional to r(-2). The radial dose function was calculated at distances between 0.5 and 12 cm, with a maximum value of 1.20 at 5.15±0.03 cm. Radial dose values were fit to a fifth order polynomial and dual exponential regression. Since the source is not axially symmetric, angular Monte Carlo calculations were performed at 1 cm which determined that the maximum azimuthal anisotropy was less than 8%. With a higher photon energy, shorter half-life and higher initial dose rate 169Yb is an interesting alternative to 125I for the treatment of nonsmall cell lung cancer.

Overview on the dosimetric uncertainty analysis for photon-emitting brachytherapy sources, in the light of the AAPM Task Group No 138 and GEC-ESTRO report

In 2011, the American Association of Physicists in Medicine (AAPM) and the Groupe Européen de Curiethérapie–European Society for Radiotherapy and Oncology (GEC-ESTRO) published a report pertaining to uncertainties in brachytherapy single-source dosimetry preceding clinical use. The International Organization for Standardization's Guide to the Expression of Uncertainty in Measurement and Technical Note 1297 by the National Institute of Standards and Technology are taken as reference standards for uncertainty formalism. Uncertainties involved in measurements or Monte Carlo methods to estimate brachytherapy dose distributions are provided with discussion of the components intrinsic to the overall dosimetric assessment. The uncertainty propagation from the primary calibration standard through transfer to the clinic for air-kerma strength is given with uncertainties in each of the brachytherapy dosimetry parameters of the AAPM TG-43 dose-calculation formalism. For low-energy and high-energy brachytherapy sources of low dose-rate and high dose-rate, a combined dosimetric uncertainty <5% (k = 1) is estimated, which is consistent with prior literature estimates. Recommendations are provided for clinical medical physicists, dosimetry investigators, and manufacturers of brachytherapy sources and treatment planning systems. These recommendations reflect the guidance of the AAPM and GEC-ESTRO for their members, and may also be used as guidance to manufacturers and regulatory agencies in developing good manufacturing practices for conventional brachytherapy sources used in routine clinical treatments.

Dose calculation for photon‐emitting brachytherapy sources with average energy higher than 50 keV: Report of the AAPM and ESTRO

Recommendations of the American Association of Physicists in Medicine (AAPM) and the European Society for Radiotherapy and Oncology (ESTRO) on dose calculations for high-energy (average energy higher than 50 keV) photon-emitting brachytherapy sources are presented, including the physical characteristics of specific (192)Ir, (137)Cs, and (60)Co source models. This report has been prepared by the High Energy Brachytherapy Source Dosimetry (HEBD) Working Group. This report includes considerations in the application of the TG-43U1 formalism to high-energy photon-emitting sources with particular attention to phantom size effects, interpolation accuracy dependence on dose calculation grid size, and dosimetry parameter dependence on source active length. Consensus datasets for commercially available high-energy photon sources are provided, along with recommended methods for evaluating these datasets. Recommendations on dosimetry characterization methods, mainly using experimental procedures and Monte Carlo, are established and discussed. Also included are methodological recommendations on detector choice, detector energy response characterization and phantom materials, and measurement specification methodology. Uncertainty analyses are discussed and recommendations for high-energy sources without consensus datasets are given. Recommended consensus datasets for high-energy sources have been derived for sources that were commercially available as of January 2010. Data are presented according to the AAPM TG-43U1 formalism, with modified interpolation and extrapolation techniques of the AAPM TG-43U1S1 report for the 2D anisotropy function and radial dose function.

Evaluation of brachytherapy lung implant dose distributions from photon‐emitting sources due to tissue heterogeneities

Photon-emitting brachytherapy sources are used for permanent implantation to treat lung cancer. However, the current brachytherapy dose calculation formalism assumes a homogeneous water medium without considering the influence of radiation scatter or tissue heterogeneities. The purpose of this study was to determine the dosimetric effects of tissue heterogeneities for permanent lung brachytherapy. The MCNP5 v1.40 radiation transport code was used for Monte Carlo (MC) simulations. Point sources with energies of 0.02, 0.03, 0.05, 0.1, 0.2, and 0.4 MeV were simulated to cover the range of pertinent brachytherapy energies and to glean dosimetric trends independent of specific radionuclide emissions. Source positions from postimplant CT scans of five patient implants were used for source coordinates, with dose normalized to 200 Gy at the center of each implant. With the presence of fibrosis (around the implant), cortical bone, lung, and healthy tissues, dose distributions and (PTV)DVH were calculated using the MCNP ∗FMESH4 tally and the NIST mass-energy absorption coefficients. This process was repeated upon replacing all tissues with water. For all photon energies, 10(9) histories were simulated to achieve statistical errors (k = 1) typically of 1%. The mean PTV doses calculated using tissue heterogeneities for all five patients changed (compared to dose to water) by only a few percent over the examined photon energy range, as did PTV dose at the implant center. The (PTV)V(100) values were 81.2%, 90.0% (as normalized), 94.3%, 93.9%, 92.7%, and 92.2% for 0.02, 0.03, 0.05, 0.1, 0.2, and 0.4 MeV source photons, respectively. Relative to water, the maximum bone doses were higher by factors of 3.7, 5.1, 5.2, 2.4, 1.2, and 1.0 The maximum lung doses were about 0.98, 0.94, 0.91, 0.94, 0.97, and 0.99. Relative to water, the maximum healthy tissue doses at the mediastinal position were higher by factors of 9.8, 2.2, 1.3, 1.1, 1.1, and 1.1. However, the maximum doses to these healthy tissues were only 3.1, 7.2, 11.3, 10.9, 9.0, and 8.1 Gy while maximum bone doses were 66, 177, 236, 106, 49, and 39 Gy, respectively. Similarly, maximum lung doses were 55, 66, 73, 74, 73, and 73 Gy, respectively. The current brachytherapy dose calculation formalism overestimates PTV dose and significantly underestimates doses to bone and healthy tissue. Further investigation using specific brachytherapy source models and patient-based CT datasets as MC input may indicate whether the observed trends can be generalized for low-energy lung brachytherapy dosimetry.

A systematic evaluation of the dose-rate constant determined by photon spectrometry for 21 different models of low-energy photon-emitting brachytherapy sources

The aim of this study was to perform a systematic comparison of the dose-rate constant (Λ) determined by the photon spectrometry technique (PST) with the consensus value (CONΛ) recommended by the American Association of Physicists in Medicine (AAPM) for 21 low-energy photon-emitting interstitial brachytherapy sources. A total of 63 interstitial brachytherapy sources (21 different models with 3 sources per model) containing either 125I (14 models), 103Pd (6 models) or 131Cs (1 model) were included in this study. A PST described by Chen and Nath (2007 Med. Phys. 34 1412–30) was used to determine the dose-rate constant (PSTΛ) for each source model. Source-dependent variations in PSTΛ were analyzed systematically against the spectral characteristics of the emitted photons and the consensus values recommended by the AAPM brachytherapy subcommittee. The values of PSTΛ for the encapsulated sources of 103Pd, 125I and 131Cs varied from 0.661 to 0.678 cGyh−1 U−1, 0.959 to 1.024 cGyh−1U−1 and 1.066 to 1.073 cGyh−1U−1, respectively. The relative variation in PSTΛ among the six 103Pd source models, caused by variations in photon attenuation and in spatial distributions of radioactivity among the source models, was less than 3%. Greater variations in PSTΛ were observed among the 14 125I source models; the maximum relative difference was over 6%. These variations were caused primarily by the presence of silver in some 125I source models and, to a lesser degree, by the variations in photon attenuation and in spatial distribution of radioactivity among the source models. The presence of silver generates additional fluorescent x-rays with lower photon energies which caused the PSTΛ value to vary from 0.959 to 1.019 cGyh−1U−1 depending on the amount of silver used by a given source model. For those 125I sources that contain no silver, their PSTΛ was less variable and had values within 1% of 1.024 cGyh−1U−1. For the 16 source models that currently have an AAPM recommended CONΛ value, the agreement between PSTΛ and CONΛ was less than 2% for 15 models and was 2.6% for 1 103Pd source model. Excellent agreement between PSTΛ and CONΛ was observed for all source models that currently have an AAPM recommended consensus dose-rate constant value. These results demonstrate that the PST is an accurate and robust technique for the determination of the dose-rate constant for low-energy brachytherapy sources.

Monte Carlo Simulations of the Primary Air-Kerma Strength Standard for Low-Energy Photon-Emitting Brachytherapy Sources

Monte Carlo Simulations of the Primary Air-Kerma Strength Standard for Low-Energy Photon-Emitting Brachytherapy Sources

Evaluation of interpolation methods for TG-43 dosimetric parameters based on comparison with Monte Carlo data for high-energy brachytherapy sources.

PurposeThe aim of this work was to determine dose distributions for high-energy brachytherapy sources at spatial locations not included in the radial dose function gL(r) and 2D anisotropy function F(r,θ) table entries for radial distance r and polar angle θ. The objectives of this study are as follows: 1) to evaluate interpolation methods in order to accurately derive gL(r) and F(r,θ) from the reported data; 2) to determine the minimum number of entries in gL(r) and F(r,θ) that allow reproduction of dose distributions with sufficient accuracy.Material and methodsFour high-energy photon-emitting brachytherapy sources were studied: 60Co model Co0.A86, 137Cs model CSM-3, 192Ir model Ir2.A85-2, and 169Yb hypothetical model. The mesh used for r was: 0.25, 0.5, 0.75, 1, 1.5, 2–8 (integer steps) and 10 cm. Four different angular steps were evaluated for F(r,θ): 1°, 2°, 5° and 10°. Linear-linear and logarithmic-linear interpolation was evaluated for gL(r). Linear-linear interpolation was used to obtain F(r,θ) with resolution of 0.05 cm and 1°. Results were compared with values obtained from the Monte Carlo (MC) calculations for the four sources with the same grid.ResultsLinear interpolation of g L(r) provided differences ≤ 0.5% compared to MC for all four sources. Bilinear interpolation of F(r,θ) using 1° and 2° angular steps resulted in agreement ≤ 0.5% with MC for 60Co, 192Ir, and 169Yb, while 137Cs agreement was ≤ 1.5% for θ < 15°.ConclusionsThe radial mesh studied was adequate for interpolating gL(r) for high-energy brachytherapy sources, and was similar to commonly found examples in the published literature. For F(r,θ) close to the source longitudinal-axis, polar angle step sizes of 1°-2° were sufficient to provide 2% accuracy for all sources.

Dosimetric properties of TL foils based on LiF:Mg,Cu,P (MCP-N) phosphors for clinical applications

Abstract Two prototype 2-D thermoluminescence (TL) readers: a laboratory reader equipped with a sensitive 640 × 480 pixel CCD camera and a heater planchet of 7.2 cm diameter, and a clinical reader with a 14-bit CCD PCO camera of 1024 × 1024 pixel resolution and a 20 × 20 cm 2 heater, were developed at the Institute of Nuclear Physics (IFJ PAN) in Krakow, Poland. These readers are able to produce digital images of 2-D dose distributions from exposed TL foils of sizes up to 20 × 20 cm 2 , composed of ETFE (ethylene tetrafluoroethylene) and LiF:Mg,Cu,P (MCP-N) powder, also developed and manufactured at IFJ PAN in Krakow. The clinical 2-D TL system is being developed specifically for clinical measurements of 2-D dose distributions in external photon or electron radiotherapy beams and around small sources applied in brachytherapy. We report results of our tests of basic dosimetric properties (repeatability, linearity vs. absorbed dose, signal-to-noise ratio and energy dependence) of the 2-D TL foil-reader systems using MCP-N based foils and megavolt X-ray radiotherapy beams, over a range of dose relevant to clinical radiotherapy. We conclude that the clinical 2-D TL system may be useful in clinical dosimetry of external radiotherapy beams and photon-emitting brachytherapy sources. As examples of such applications, we show verification of computer therapy planning system calculations of fields produced by multileaf collimators or stereotactic radiosurgery systems, performed as part of the quality assurance procedure in radiotherapy.

Evaluation of high‐energy brachytherapy source electronic disequilibrium and dose from emitted electrons

The region of electronic disequilibrium near photon-emitting brachytherapy sources of high-energy radionuclides (60Co, 137CS, 192Ir, and 169Yb) and contributions to total dose from emitted electrons were studied using the GEANT4 and PENELOPE Monte Carlo codes. Hypothetical sources with active and capsule materials mimicking those of actual sources but with spherical shape were examined. Dose contributions due to source photons, x rays, and bremsstrahlung; source beta-, Auger electrons, and internal conversion electrons; and water collisional kerma were scored. To determine if conclusions obtained for electronic equilibrium conditions and electron dose contribution to total dose for the representative spherical sources could be applied to actual sources, the 192Ir mHDR-v2 source model (Nucletron B.V., Veenendaal, The Netherlands) was simulated for comparison to spherical source results and to published data. Electronic equilibrium within 1% is reached for 60Co, 137CS, 192Ir, and 169Yb at distances greater than 7, 3.5, 2, and 1 mm from the source center, respectively, in agreement with other published studies. At 1 mm from the source center, the electron contributions to total dose are 1.9% and 9.4% for 60Co and 192Ir, respectively. Electron emissions become important (i.e., > 0.5%) within 3.3 mm of 60Co and 1.7 mm of 192Ir sources, yet are negligible over all distances for 137Cs and 169Yb. Electronic equilibrium conditions along the transversal source axis for the mHDR-v2 source are comparable to those of the spherical sources while electron dose to total dose contribution are quite different. Electronic equilibrium conditions obtained for spherical sources could be generalized to actual sources while electron contribution to total dose depends strongly on source dimensions, material composition, and electron spectra.

Ice as a water-equivalent solid medium for brachytherapy dosimetric measurements

Precise positioning of source and dosimeters is essential in the experimental determination of dosimetric characteristics of brachytherapy sources. Various near-water equivalent solid phantoms have been used to achieve the necessary precision in the positioning. However, the uncertainties in their chemical compositions may lead to non-negligible uncertainties in the determined doses. It is proposed here that ice may be used as an alternative to the conventional solid phantoms, since its chemical composition is identical to water while the positioning advantage associated with solid phantoms is retained. In this work, the feasibility of using ice as a solid phantom for brachytherapy dosimetry is investigated. Ice-to-water conversion factors are calculated at distances of 0.2-10 cm from the source, for six high- and low-energy photon-emitting brachytherapy sources and mono-energetic photons between 10 keV to 2.0 MeV. Practical issues and challenges associated with measuring dose in an ice phantom are discussed.