TG-43 Dose Calculation Research Articles

Retrospective assessment of HDR brachytherapy dose calculation methods in locally advanced cervical cancer patients: AcurosBV vs. AAPM TG43 formalism.

This retrospective analysis was completed to investigate the use of a model-based dose calculation algorithm (MBDCA) AcurosBV, for use in HDR BT treatments for locally advanced cervical cancer treated with tandem and ovoid applicators with interstitial needles. A cohort of 32 patients receiving post-EBRT HDR brachytherapy boost with a prescription dose of 5.5Gy × 5 fractions to the high-risk clinical target volume (CTVHR) were selected for this study. For standard TG43 dose calculation, applicators were manually digitized on the planning images, while for AcurosBV calculations, solid renderings of Titanium Fletcher Suite Delclos (FSD) applicators included in BrachyVision were matched to those used clinically and Ti needles were manually digitized. The dose was recalculated using Varian's AcurosBV 13.5 and dose-to-medium-in-medium (Dm,m) was reported. EQD2 values for targets and organs at risk were compared between dose calculation formalisms. D90% and D98% values were reported for the high and intermediate-risk CTVs, and values were reported for OARs including bladder, rectum, sigmoid, bowel, and vagina. Due to variability within the patient cohort, the dosimetric impact of AcurosBV was investigated corresponding to planning image modality (CT vs. CBCT), presence of Ti needles, and contrast within vaginal balloons used to stabilize implants. AcurosBV showed lower dosimetric values for all plans compared to TG43. The average±standard deviation of dosimetric reduction in D90% was 4.33±0.09% for CTVHR and 4.12±0.09% for CTVIR. The reduction to OARs was: 4.99±0.15% for bladder, 7.87±0.16% for rectum, 5.79±0.17% for sigmoid, 6.91±0.14% for bowel, and 4.55±0.14% for vagina. AcurosBV should be utilized for HDR BT GYN cases, treated with tandem and ovoid applicators, with high degrees of heterogeneity and calculated in tandem with TG43.

A comparison of TG-43 and TG-186 dose calculation algorithms for treatment planning of intra-cavitary brachytherapy using tandem and ovoid applicator

A comparison of TG-43 and TG-186 dose calculation algorithms for treatment planning of intra-cavitary brachytherapy using tandem and ovoid applicator

Generation and comparison of 3D dosimetric reference datasets for COMS eye plaque brachytherapy using model-based dose calculations.

A joint Working Group of the American Association of Physicists in Medicine (AAPM), the European Society for Radiotherapy and Oncology (ESTRO), and the Australasian Brachytherapy Group (ABG) was created to aid in the transition from the AAPM TG-43 dose calculation formalism, the current standard, to model-based dose calculations. This work establishes the first test cases for low-energy photon-emitting brachytherapy using model-based dose calculation algorithms (MBDCAs). Five test cases are developed: (1) a single model 6711 125 I brachytherapy seed in water, 13 seeds (2) individually and (3) in combination in water, (4) the full Collaborative Ocular Melanoma Study (COMS) 16 mm eye plaque in water, and (5) the full plaque in a realistic eye phantom. Calculations are done with four Monte Carlo (MC) codes and a research version of a commercial treatment planning system (TPS). For all test cases, local agreement of MC codes was within ∼2.5% and global agreement was ∼2% (4% for test case 5). MC agreement was within expected uncertainties. Local agreement of TPS with MC was within 5% for test case 1 and ∼20% for test cases 4 and 5, and global agreement was within 0.4% for test case 1 and 10% for test cases 4 and 5. Dose distributions for each set of MC and TPS calculations are available online (https://doi.org/10.52519/00005) along with input files and all other information necessary to repeat the calculations. These data can be used to support commissioning of MBDCAs for low-energy brachytherapy as recommended by TGs 186 and 221 and AAPM Report 372. This work additionally lays out a sample framework for the development of test cases that can be extended to other applications beyond eye plaque brachytherapy.

Modern Tools for Modern Brachytherapy

This review aims to showcase the brachytherapy tools and technologies that have emerged during the last 10 years. Soft-tissue contrast using magnetic resonance and ultrasound imaging has seen enormous growth in use to plan all forms of brachytherapy. The era of image-guided brachytherapy has encouraged the development of advanced applicators and given rise to the growth of individualised 3D printing to achieve reproducible and predictable implants. These advances increase the quality of implants to better direct radiation to target volumes while sparing normal tissue. Applicator reconstruction has moved beyond manual digitising, to drag and drop of three-dimensional applicator models with embedded pre-defined source pathways, ready for auto-recognition and automation. The simplified TG-43 dose calculation formalism directly linked to reference air kerma rate of high-energy sources in the medium water remains clinically robust. Model-based dose calculation algorithms accounting for tissue heterogeneity and applicator material will advance the field of brachytherapy dosimetry to become more clinically accurate. Improved dose-optimising toolkits contribute to the real-time and adaptive planning portfolio that harmonises and expedites the entire image-guided brachytherapy process. Traditional planning strategies remain relevant to validate emerging technologies and should continue to be incorporated in practice, particularly for cervical cancer. Overall, technological developments need commissioning and validation to make the best use of the advanced features by understanding their strengths and limitations. Brachytherapy has become high-tech and modern by respecting tradition and remaining accessible to all.

Update of the CLRP Monte Carlo TG-43 parameter database for high-energy brachytherapy sources.

To update and extend version 2 of the Carleton Laboratory for Radiotherapy Physics (CLRP) TG-43 dosimetry database (CLRP_TG43v2) for high-energy (HE, ≥50 keV) brachytherapy sources (1 169 Yb, 23 192 Ir, 5 137 Cs, and 4 60 Co) using egs_brachy, an open-source EGSnrc application. A comprehensive dataset of TG-43 parameters is compiled, including detailed source descriptions, dose-rate constants, radial dose functions, 1D and 2D anisotropy functions, along-away dose-rate tables, Primary and Scatter Separated (PSS) dose tables, and mean photon energies escaping each source. The database also documents the source models which are freely distributed with egs_brachy. Datasets are calculated after a recoding of the source geometries using the egs++ geometry package and its egs_brachy extensions. Air kerma per history is calculated in a 10 0.05cm3 voxel located 100cm from the source along the transverse axis and then corrected for the lateral and thickness dimensions of the scoring voxel to give the air kerma on the central axis at a point 100cm from the source's mid-point. Full-scatter water phantoms with varying voxel resolutions in cylindrical coordinates are used for dose calculations. Most data (except for 60 Co) are based on the assumption of charged particle equilibrium and ignore the potentially large effects of electron transport very close to the source and dose from initial beta particles. These effects are evaluated for four representative sources. For validation, data are compared to those from CLRP_TG43v1 and publisheddata. Data are available at https://physics.carleton.ca/clrp/egs_brachy/seed_database_v2 or http://doi.org/10.22215/clrp/tg43v2 including in Excel (.xlsx) spreadsheets, and are presented graphically in comparisons to previously published data for each source. The CLRP_TG43v2 database has applications in research, dosimetry, and brachytherapy planning. This comprehensive update provides the medical physics community with more precise and in some cases more accurate Monte Carlo (MC) TG-43 dose calculation parameters, as well as fully benchmarked and described source models which are distributed with egs_brachy.

Assessment of dose to vaginal mucosa for gynecologic template interstitial high-dose-rate brachytherapy using Monte Carlo simulation.

This study investigated reliable vaginal mucosa dose-volume histogram (DVH) metrics in gynecologic template interstitial high-dose-rate brachytherapy (HDR-BT) for the purpose of standardized dose reporting. Gynecologic template (Syed/Neblett) interstitial HDR-BT patients treated from September 2016 to November 2022 at the study institute were included in the cohort. Each patient implant included a vaginal mucosa contour defined by a 5 mm expansion from vaginal cylinder, then another volume with clinical target volume subtracted. DVH metrics were investigated between D0.1cc to D4cc. Clinical plans were re-calculated using Monte Carlo (MC) simulations both in heterogeneous material and in water. The patient cohort included 61 patients with clinical plans using conventional homogeneous dose calculation (TG43). Heterogeneous vs. water MC dose differences were between -1.1% and -1.4% for all metrics investigated. DVH metrics D1cc and smaller resulted in > 5% discrepancies between TG43 and MC dose (to water) calculation due to the proximity of source positions in/nearby the vaginal mucosa. Reliability improved when DVH metric volume was larger (D2cc and D4cc). Both D2cc and D4cc presented very high linear correlation between TG43 and MC reported doses for the vagina, and average ± standard deviation dose difference was 4.6 ±2.9% and -3.0 ±1.9%, respectively. Dose differences decreased when the clinical target volume was removed: -1.5 ±3.5% and -0.8 ±2.1% for D2cc and D4cc, respectively. For perineal template gynecologic HDR-BT procedures, the 2 cc volume is the smallest representative volume that reliably reports vaginal dose and at minimum should be reported to establish dose and outcome evaluation.

PHSOR08 Presentation Time: 1:05 PM: Retrospective Comparison of TG43 vs. AcurosBV Model-Based Dose Calculation Algorithm (MBDCA) in Cervical Cancer Patients Treated with HDR Brachytherapy Boost

<h3>Purpose</h3> To evaluate dosimetric impact of heterogeneity from applicators and patient tissue between plans treated with tandem and ovoid applicators with interstitial needles calculated with the TG43 formalism and Acuros®BV MBDCA (Varian Medical Systems (VMS), Inc). <h3>Materials Methods</h3> For this retrospective analysis, HDR plans prescribing 5.5 Gy to high-risk clinical target volume (CTV) D_90% for locally advanced cervical cancer patients were selected. The implants consisted of tandem and ovoid (T&O) with or without interstitial needles, treated using a GammaMedPlus™ iX afterloader with a ¹⁹²Ir source. Implants were stabilized by Alatus vaginal balloons (Angiodynamics) filled with a 5% IsoVue to 95% saline ratio. Imaging for applicator digitization and planning was done using either Acuity CBCT (VMS, Inc), or AIRO CT (BrainLab AG). For standard TG43 clinical dose calculation, all applicators were manually digitized on the CT or CBCT images. Solid renderings of Fletcher-Suit Delclos applicators included in BrachyVision (VMS, Inc) were matched to those used clinically. The composition of the applicators was assigned from the applicator library. Titanium needles were left unchanged, as there is no solid applicator model available. The dose was recalculated using Varian's Acuros®BV 13.5 and dose-to-medium-in-medium (D_m,m) was reported. Equivalent dose in 2 Gy per fraction (EQD2) values for targets and organs at risk (OARs) were compared between TG43 formalism and the Acuros®BV plans. D_90% and D_98% values were reported for the high and intermediate-risk CTVs, and D_2cm3 values were reported for OARs including bladder, rectum, sigmoid, bowel, and vagina. In a separate analysis, we compared dosimetric endpoint differences between TG43 and Acuros®BV plans imaged with CT versus CBCT, and also between plans with T&O applicators with and without needles. Linear regression and Bland Altman Analysis (BAA) were performed between the two plans to show the correlation and dosimetric differences between both methods. <h3>Results</h3> Thirty-two patients with a total of 156 fractions were included in this study, 70 planned on CBCT, and 86 planned on AIRO CT. Consistently, Acuros®BV plans showed lower dosimetric values for all plans compared to TG43. The average ± standard deviation of dosimetric reduction in D_90% was 4.33 ± 0.09% (0.41 ± 0.13 Gy) for CTV_HR and 4.12 ± 0.09% (0.21 ± 0.07Gy) for CTV_IR . Fig.1 shows an example BAA plot for differences between TG43 and Acuros®BV D_90% for the targets. The reduction to OARs D_2cm3 was: 4.99 ± 0.15% (0.34 ± 0.17 Gy) for bladder, 7.87 ± 0.16% (0.20 ± 0.09 Gy) for rectum, 5.79 ± 0.17% (0.21 ± 0.09 Gy) for sigmoid, 6.91 ± 0.14% (0.25 ± 0.13 Gy) for bowel, and 4.55 ± 0.14% (0.46 ± 0.27 Gy) for vagina. There was no statistically significant difference between TG43 and Acuros®BV plans calculated on CBCT versus CT images (p value = 0.24). A set of 5 patients with a total of 24 fractions planed with T&O applicators without needles was used for comparison with plans with interstitial needles, and no statistically significant difference between TG43 and Acuros®BV plans was observed (p value = 0.35). <h3>Conclusion</h3> This large patient cohort study confirms that plans calculated using Acuros®BV MBDCA show a reduction in dose to all structures when compared to the standard TG43 formalism. This is expected mainly due to more photon attenuation by high-density material of the applicators, as well as tissue heterogeneities. Clinical implementation of Acuros®BV can be challenging due to increased calculation time, alteration of the clinical flow, and increased planning complexity. These factors must be evaluated, and further investigation should be conducted in order to understand the effects of its utilization as a primary dose calculation method.

Dosimetric comparison of AcurosBV with AAPM TG43 dose calculation formalism in cervical intraductal high‐dose‐rate brachytherapy using three different applicators

AbstractPurposeTo compare the dosimetric effects of American Association of Physicists in Medicine (AAPM) TG43 dose formalism and AcurosBV (grid‐based Boltzmann solver, GBBS) formalism on high‐dose‐rate (HDR) brachytherapy planning for cervical cancer patients irradiated using three different applicators.MethodsA TG43 plan and a AcurosBV plan were generated for each of the 30 patients. Twenty patients who had undergone whole pelvic radiotherapy followed by cervical HDR brachytherapy and the remaining 10 patients who underwent total hysterectomy only gave HDR brachytherapy also were enrolled in this study. The patients were divided into three groups according to the types of applicators used: tandem and ovoid (T&amp;O), tandem and ring (T&amp;R), and cylinder. To compare the dosimetric parameters, the cumulative dose‐volume histograms (DVHs) were measured. We also compared the doses at 90% of the volume (D90%), the volume receiving 100% and 150% of the prescribed dose (V100% and V150%) for the clinical target volume (CTV‐HR), and the doses of point A, the dose receiving 0.1 and 2 cc of the volume (D0.1cc and D2cc) for the organs‐at‐risk (OARs).ResultsCompared with the AcurosBV plans, TG43 plans predicted higher D90%, V100%, and V150% of CTV‐HR, dose of point A, and D0.1cc and D2cc of OARs in three types of applicators. Except D2cc of sigmoid in T&amp;R and cylinder applicators, the D90%, V100%, and V150% of CTV‐HR; the dose of point A and the D0.1cc and D2cc of bladder, rectum, and small bowel exhibited significant discrepancies (all p &lt; 0.05). The effects of the three types of applicators on the dose distribution were quite different due to the differences in the materials: The dose difference of CTV‐HR and OARs was greatest (around 10%) for T&amp;O applicators but only 1–5% for T&amp;R and cylinder applicators.ConclusionsAcurosBV was more accurate in calculating the doses in the air cavity and high‐density substance than TG43. In the clinical setting, AcurosBV exhibited different dosimetric distributions in the cervix plans for HDR brachytherapy, especially in treatment planning when using T&amp;O applicators. The AcurosBV algorithm should be considered when using T&amp;O applicators or other materials with a much higher or lower density (metal or air) than soft tissue. However, If the density is close to that of soft tissue, considering AcurosBV algorithm requires more calculation time, TG43 could still be selected when using applicators in clinical.

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.

Recommendations for intraoperative mesh brachytherapy: Report of AAPM Task Group No. 222.

Mesh brachytherapy is a special type of a permanent brachytherapy implant: it uses low-energy radioactive seeds in an absorbable mesh that is sutured onto the tumor bed immediately after a surgical resection. This treatment offers low additional risk to the patient as the implant procedure is carried out as part of the tumor resection surgery. Mesh brachytherapy utilizes identification of the tumor bed through direct visual evaluation during surgery or medical imaging following surgery through radiographic imaging of radio-opaque markers within the sources located on the tumor bed. Thus, mesh brachytherapy is customizable for individual patients. Mesh brachytherapy is an intraoperative procedure involving mesh implantation and potentially real-time treatment planning while the patient is under general anesthesia. The procedure is multidisciplinary and requires the complex coordination of multiple medical specialties. The preimplant dosimetry calculation can be performed days beforehand or expediently in the operating room with the use of lookup tables. In this report, the guidelines of American Association of Physicists in Medicine (AAPM) are presented on the physics aspects of mesh brachytherapy. It describes the selection of radioactive sources, design and preparation of the mesh, preimplant treatment planning using a Task Group (TG) 43-based lookup table, and postimplant dosimetric evaluation using the TG-43 formalism or advanced algorithms. It introduces quality metrics for the mesh implant and presents an example of a risk analysis based on the AAPM TG-100 report. Recommendations include that the preimplant treatment plan be based upon the TG-43 dose calculation formalism with the point source approximation, and the postimplant dosimetric evaluation be performed by using either the TG-43 approach, or preferably the newer model-based algorithms (viz., TG-186 report) if available to account for effects of material heterogeneities. To comply with the written directive and regulations governing the medical use of radionuclides, this report recommends that the prescription and written directive be based upon the implanted source strength, not target-volume dose coverage. The dose delivered by mesh implants can vary and depends upon multiple factors, such as postsurgery recovery and distortions in the implant shape over time. For the sake of consistency necessary for outcome analysis, prescriptions based on the lookup table (with selection of the intended dose, depth, and treatment area) are recommended, but the use of more advanced techniques that can account for real situations, such as material heterogeneities, implant geometric perturbations, and changes in source orientations, is encouraged in the dosimetric evaluation. The clinical workflow, logistics, and precautions are also presented.

PHSOR05 Presentation Time: 10:20 AM: Commissioning and Clinical Use of Shielded Brachytherapy Applicators Using a Hybrid TG-43 Dosimetry Technique

Purpose: Brachytherapy (BT) treatment planning systems (TPSs) generally rely on the AAPM TG-43 dose calculation formalism, which approximates patient composition as water for all radionuclides and clinical applications. This approach does not produce accurate results for BT applicators that include high-Z shielding to collimate the radiation for protecting healthy tissues. While advanced dose calculation algorithms beyond the TG-43 formalism are on the market, the software is not readily available and not all applicators are modeled.

Developing A Method for Inter-Seed Effect Correction in 125I Interstitial Brachytherapy Using Artificial Neural Network

Introduction: Treatment planning systems use TG-43 dose calculation protocol for brachytherapy sources. Dose calculations based on TG-43 formalism do not correct the perturbations due to the presence of tissue inhomogeneity, applicators, and inter-seed effects. Inter-seed attenuation has an important effect on dosimetry in permanent implant brachytherapy. The aim of this study is to evaluate the inter-seed attenuation effect for I-125 permanent implants. Then, a software was developed to find the real dose distribution for different combinations of sources. Materials and methods: In the first step, a hypothetical generic source model was designed based on the configurations of different commercial source types. MCNP5 Monte Carlo code was utilized to simulate the single active generic source at the center of the phantom, and an inactive placed at various positions inside the phantom. An algorithm was introduced using artificial neural network models that can estimate the dose distribution in presence of inactive sources. Results: The Monte Carlo calculation results showed that the dose distribution is clearly affected by the inter-seed attenuation effect. Comparison of the artificial neural network results with the Monte Carlo simulation results show that the artificial neural networks can predict the inter-seed attenuation with acceptable accuracy, and with not much greater than 3% deviation.Discussion and conclusions: Inter-seed effect is dependent on the distance between the seeds. Decreasing distances would cause more effect. According to the results, it seems that the artificial neural network can be used as a tool for correction of inter-seed attenuation effect in treatment planning systems.

Individualized mould-based high-dose-rate brachytherapy for perinasal skin tumors: technique evaluation from a dosimetric point of view.

PurposeDosimetric treatment planning evaluations concerning patient-adapted moulds for iridium-192 high-dose-rate brachytherapy are presented in this report.Material and methodsSix patients with perinasal skin tumors were treated with individual moulds made of biocompatible epithetic materials with embedded plastic applicators. Treatment plans were optimized with regard to clinical requirements, and dose was calculated using standard water-based TG-43 formalism. In addition, retrospective material-dependent collapsed cone calculations according to TG-186 protocol were evaluated to quantify the limitations of TG-43 protocol for this superficial brachytherapy technique.ResultsThe dose-volume parameters D90, V100, and V150 of the planning target volumes (PTVs) for TG-43 dose calculations yielded 92.2% to 102.5%, 75.1% to 93.1%, and 7.4% to 41.7% of the prescribed dose, respectively. The max- imum overall dose to the ipsilateral eyeball as the most affected organ at risk (OAR) varied between 8.9 and 36.4 Gy. TG-186 calculations with Hounsfield unit-based density allocation resulted in down by –6.4%, –16.7%, and –30.0% lower average D90, V100, and V150 of the PTVs, with respect to the TG-43 data. The corresponding calculated OAR doses were also lower. The model-based TG-186 dose calculations have considered reduced backscattering due to environmental air as well as the dose-to-medium influenced by the mould materials and tissue composition. The median PTV dose was robust within 0.5% for simulated variations of mould material densities in the range of 1.0 g/cm3 to 1.26 g/cm3 up to 7 mm total mould thickness.ConclusionsHDR contact BT with individual moulds is a safe modality for routine treatment of perinasal skin tumors. The technique provides good target coverage and OARs’ protection, while being robust against small variances in mould material density. Model-based dose calculations (TG-186) should complement TG-43 dose calculations for verification purpose and quality improvement.

Validation of American Association of Physicists in Medicine TG 43 Dosimetry Data in Commercial Treatment Planning System.

AimsThis study aimed to validate the dosimetric data of low-energy photon-emitting low-dose rate (LE-LDR) brachytherapy seed sources in commercial treatment planning system (TPS).Materials and MethodsThe LE-LDR seed sources dosimetric data were published in the American Association of Physicists in Medicine (AAPM) Task Group reports TG-43 (1995), TG-43U1 (2004), TG-43U1S1 (2007), and TG-43U1S2. The Bhabha Atomic Research centre (BARC) 125I Ocu-Prosta seed dosimetry data are also available in the literature. The commercially available TPSs are using both two-dimensional (cylindrically symmetric line-source) and one-dimensional (1D) (point source) dose-calculation formalisms. TPS used in this study uses only 1D dose-calculation formalism for permanent implant dosimetry. The point-dose calculation, dose summation, isodose representation, and dose–volume histogram quality assurance tests were performed in this study. The point-source dose-calculation tests were performed for all the available sources in the literature. The others tests were performed for the I-125 BARC Ocu-Prosta seeds. The TPS-calculated doses were validated using manual calculation.Results and DiscussionIn point-source calculation test, the TPS-calculated point-dose values are within ±2% agreement with manually calculated dose for all the seeds studied. The agreement between the TPS and manually calculated dose is 0.5% for the dose summation test. The isodose line pass through the grid points at an equal distance was verified visually on the computer screen for seed used clinically. In dose–volume histogram test, the TPS-determined volume was compared with the real volume.ConclusionMisinterpretation of the TPS test and/or misunderstanding of the TG-43 dose-calculation formalism may cause large errors. It is very important to validate the TPS using literature provided dosimetric data. The dosimetric data of BARC 125I Ocu-Prosta Seed are validated with other AAPM TG-43-recommended seeds. The dose calculation of Best® NOMOS permanent implant TPS is accurate for all permanent implant seeds studied.

Evaluation of BrachyDose Monte Carlo code for HDR brachytherapy: dose comparison against Acuros®BV and TG-43 algorithms

AbstractAim:The aim of this study is to investigate the accuracy of dose distributions calculated by the BrachyDose Monte Carlo (MC) code in heterogeneous media for high-dose-rate (HDR) brachytherapy and to evaluate its usability in the clinical brachytherapy treatment planning systems.Materials and methods:For dose comparisons, three different dose calculation algorithms were used in this study. Namely, BrachyDose MC code, Eclipse TG-43 dose calculation tool and Acuros®BV model-based dose calculation algorithm (MBDCA). Dose distributions were obtained using any of the above codes in various scenarios including ‘homogenous water medium scenario’, an ‘extreme case heterogeneous media scenario’ and clinically important ‘a patient with a cervical cancer scenario’. In the ‘extreme case, heterogeneous media scenario’, geometry is a rare combination of unusual high-density and low-density materials and it is chosen to provide a test environment for the propagation of photons in the interface of two materials with different absorption and scattering properties. GammaMed192Ir Model 12i Source is used as the HDR brachytherapy source in this study. Dose calculations were performed for the cases where there is either a single source or five sources planted into the phantom geometry in all homogenous water phantom and extreme case heterogeneous media scenarios. For the scenario a patient with a cervical cancer, dose calculations were performed in a voxelized rectilinear phantom, which is constructed from a series of computed tomography (CT) slices of a patient, which are obtained from a CT device.Results:In homogeneous water phantom scenario, we observed no statistically significant dose differences among the dose distributions calculated by any of the three algorithms at almost every point in the geometry. In the extreme case heterogeneous media scenario, the dose calculation engines Acuros®BV and BrachyDose are agreed well within statistics in every region of the geometry and even in the points close to the interfaces of low-density and high-density materials. On the other hand, the dose values calculated by these two codes are significantly different from those calculated by the TG-43 algorithm. In the ‘a patient with a cervical cancer scenario’, the calculated D2ccdose difference between Acuros®BV and BrachyDose codes is within 2% in the rectum and 11% for the bladder and sigmoid. There was no meaningful difference in the mean dose values between MBDCAs in the bone structures.Conclusions:In this study, the accurate dose calculation capabilities of the BrachyDose program in HDR brachytherapy were investigated on various scenarios and, as a MC dose calculation tool, its effectiveness in HDR brachytherapy was demonstrated by comparative dose analysis.

The validity of Acuros BV and TG-43 for high-dose-rate brachytherapy superficial mold treatments

PurposeThe purpose of this work is to validate the Acuros BV dose calculation algorithm for high-dose-rate (HDR) brachytherapy superficial mold treatments in the absence of full scatter conditions and compare this with TG-43 dose calculations. We also investigate the impact of additional back scatter material (bolus) applied above surface molds to the dose distributions under the mold. Methods and MaterialsThe absorbed dose at various depths was compared for simulations performed using either TG-43 or Acuros BV dose calculations. Parameter variations included treatment area, thickness of the bolus, and surface shape (flat or spherical). Film measurements were carried out in a flat phantom. ResultsAcuros BV calculations and film measurements agreed within 1.5% but were up to 15% lower than TG-43 dose calculations when no bolus was applied above the treatment catheters. The difference in dose at the prescription depth (1 cm below the central catheter) increased with increasing treatment area: 3.3% difference for a 3 × 3.5 cm2 source loading area, 7.4% for 8 × 9 cm2, and 13.4% for 18 × 19 cm2. The dose overestimation of the TG-43 model decreased when bolus was added above the treatment catheters. ConclusionsThe TG-43 dosimetry formalism cannot model surface mold treatments in the absence of full scatter conditions within 5% for loading areas larger than approximately 5 × 5 cm2. The TG-43 model results in an overestimation of the delivered dose, which increases with treatment area. This confirms the need for model-based dose calculation algorithms as discussed in TG-186.

Evaluating the performance of TG-43 protocol in esophageal HDR brachytherapy viewpoint to trachea inhomogeneity.

The aim of this study is to evaluate the effect of air within trachea on dose calculations of esophageal HDR brachytherapy treatment planning. Dose calculations in esophageal HDR brachytherapy treatment planning systems are greatly based on TG-43 protocol which in all materials are considered to be water equivalent. A cylindrical PMMA phantom with a tube in the center (neck equivalent phantom) accompanied by Flexitron HDR brachytherapy system was used in this study. Brachytherapy applicators with various diameters were placed inside the esophageal tube and EDR2 film was used for dosimetry. The absorbed dose by reference point of esophageal HDR brachytherapy and anterior wall of trachea were measured and compared with those calculated by Flexiplan treatment planning system. Based on the performed statistical analysis (t-test) with 95% confidence level (t-value >1.96), there was a meaningful difference between the results of film dosimetry and treatment planning at all of the points understudy. The meaningful difference between the results of film dosimetry and treatment planning indicates that the trachea inhomogeneity has a considerable effect on dose calculations of Flexiplan treatment planning software featuring the TG-43 dose calculation algorithm. This mismatch can affect the accuracy of performed treatment plan and irradiation.

Clinical transition to model-based dose calculation algorithm: A retrospective analysis of high-dose-rate tandem and ring brachytherapy of the cervix

PurposeTo retrospectively compare clinical dosimetry of CT-based tandem–ring treatment plans using a model-based dose calculation algorithm (MBDCA) with the standard TG-43–based dose formalism. Methods and MaterialsA cohort of 10 cervical cancer cohorts treated using the tandem and ring high-dose-rate applicators were evaluated. The original treatment plans were created using the department CT-based volume optimization clinical standards. All plans originally calculated with TG-43 dose calculation formalism were recalculated using the MBDCA algorithm. The gross target volume and organs at risk (OARs) were contoured on each data set along with significant heterogeneities like air in cavity and high-density plastic tandem and ring components. The patient tissue was modeled as homogenous liquid water. D90, D95, and D100 for gross target volume, D0.1cm3, D1.0cm3, and D2.0cm3 for bladder, rectum, and sigmoid were extracted from dose–volume histograms for TG-43 and MBDCA calculated plans. Mean absolute difference ± 2σ in the above metrics was calculated for each plan. ResultsUsing the manual applicator contouring method, MBDCA plans (n = 10) showed 2.1 ± 1.1% reduction in dose to Point A average, 2.6 ± 0.9% reduction in Target D90 dose, and 2.1 ± 0.3% dose reduction to OARs. Results from plans using vendor supplied solid applicator models (n = 5) showed 2.2 ± 1.10% reduction in dose to Point A average, 2.7 ± 0.2% reduction in Target D90 dose, and 2.7 ± 1.0% dose reduction on average to OARs. ConclusionFor unshielded plastic gynecologic applicators, minimal dosimetric changes (<5%) were found using MBDCA relative to standard TG-43. Use of solid applicator model is more efficient than manual applicator contouring and also yielded similar MBDCA dosimetric results. Currently, TG-186 dose calculations should be reported along TG-43 until we obtain studies with larger cohorts to fully realize the potential of MBDCA dosimetry.

Session 29: Comparison of TG-43 and advanced dose calculation algorithms

Session 29: Comparison of TG-43 and advanced dose calculation algorithms

A Modified TG-43 Dose Calculation Formalism for Direction Modulation Brachytherapy (DMBT) Tandem Applicator

A Modified TG-43 Dose Calculation Formalism for Direction Modulation Brachytherapy (DMBT) Tandem Applicator