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Purpose: To compare TG43-based and Acuros deterministic radiation transport-based calculations of the BrachyVision treatment planning system (TPS) with corresponding Monte Carlo (MC) simulation results in heterogeneous patient geometries, in order to validate Acuros and quantify the accuracy improvement it marks relative to TG43., Methods: Dosimetric comparisons in the form of isodose lines, percentage dose difference maps, and dose volume histogram results were performed for two voxelized mathematical models resembling an esophageal and a breast brachytherapy patient, as well as an actual breast brachytherapy patient model. The mathematical models were converted to digital imaging and communications in medicine (DICOM) image series for input to the TPS. The MCNP5 v.1.40 general-purpose simulation code input files for each model were prepared using information derived from the corresponding DICOM RT exports from the TPS., Results: Comparisons of MC and TG43 results in all models showed significant differences, as reported previously in the literature and expected from the inability of the TG43 based algorithm to account for heterogeneities and model specific scatter conditions. A close agreement was observed between MC and Acuros results in all models except for a limited number of points that lay in the penumbra of perfectly shaped structures in the esophageal model, or at distances very close to the catheters in all models., Conclusions: Acuros marks a significant dosimetry improvement relative to TG43. The assessment of the clinical significance of this accuracy improvement requires further work. Mathematical patient equivalent models and models prepared from actual patient CT series are useful complementary tools in the methodology outlined in this series of works for the benchmarking of any advanced dose calculation algorithm beyond TG43.

Purpose: The aim of this work is the dosimetric validation of a deterministic radiation transport based treatment planning system (BRACHYVISION v. 8.8, referred to as TPS in the following) for multiple 192Ir source dwell position brachytherapy applications employing a shielded applicator in homogeneous water geometries., Methods: TPS calculations for an irradiation plan employing seven VS2000 192Ir high dose rate (HDR) source dwell positions and a partially shielded applicator (GM11004380) were compared to corresponding Monte Carlo (MC) simulation results, as well as experimental results obtained using the VIP polymer gel-magnetic resonance imaging three-dimensional dosimetry method with a custom made phantom., Results: TPS and MC dose distributions were found in agreement which is mainly within +/- 2%. Considerable differences between TPS and MC results (greater than 2%) were observed at points in the penumbra of the shields (i.e., close to the edges of the "shielded" segment of the geometries). These differences were experimentally verified and therefore attributed to the TPS. Apart from these regions, experimental and TPS dose distributions were found in agreement within 2 mm distance to agreement and 5% dose difference criteria. As shown in this work, these results mark a significant improvement relative to dosimetry algorithms that disregard the presence of the shielded applicator since the use of the latter leads to dosimetry errors on the order of 20%-30% at the edge of the "unshielded" segment of the geometry and even 2%-6% at points corresponding to the potential location of the target volume in clinical applications using the applicator (points in the unshielded segment at short distances from the applicator)., Conclusions: Results of this work attest the capability of the TPS to accurately account for the scatter conditions and the increased attenuation involved in HDR brachytherapy applications employing multiple source dwell positions and partially shielded applicators.

Purpose: The aim of this work is to validate a deterministic radiation transport based treatment planning system (TPS) for single 192Ir brachytherapy source dosimetry in homogeneous water geometries., Methods: TPS results were obtained using the deterministic radiation transport option of a BRACHYVISION v. 8.8 system for three characteristic source designs (VS2000, GMPlus HDR, and GMPlus PDR) with each source either centered in a 15 cm radius spherical water phantom, or positioned at varying distance away from the phantom center. Corresponding MC simulations were performed using the MCNPX code v.2.5.0 and source geometry models prepared using information provided by the manufacturers., Results: Comparison in terms of the AAPM TG-43 dosimetric formalism quantities, as well as dose rate distributions per unit air kerma strength with a spatial resolution of 0.1 cm, yielded close agreement between TPS and MC results for the sources centered in the phantom. Besides some regions close to the source longitudinal axes where discrepancies could be characterized as systematic, overall agreement for all three sources studied is comparable to the statistical (type A) uncertainty of MC simulations (1% at the majority of points in the geometry increasing to 2%-3% at points lying both away from the source center and close to the source longitudinal axis). A corresponding good agreement was also found between TPS and MC results for the sources positioned away from the phantom center., Conclusions: Results of this work attest the capability of the TPS to accurately account for the scatter conditions regardless of the size or shape of a given geometry of dosimetric interest, and the position of a source within it. This is important since, as shown in the literature and summarized also in this work, these factors could introduce a significant dosimetric effect that is currently ignored in clinical treatment planning. It is concluded that the implementation of the deterministic radiation transport option of the BRACHYVISION v. 8.8 system for 192Ir brachytherapy dosimetry in homogeneous water geometries yields results of comparable accuracy to the golden standard of Monte Carlo simulation, in clinically viable calculation times.

Monte Carlo simulation dosimetry is used to compare 169Yb to 192Ir for breast high dose rate (HDR) brachytherapy applications using multiple catheter implants. Results for bare point sources show that while 169Yb delivers a greater dose rate per unit air kerma strength at the radial distance range of interest to brachytherapy in homogeneous water phantoms, it suffers a greater dose rate deficit in missing scatter conditions relative to 192Ir. As a result of these two opposing factors, in the scatter conditions defined by the presence of the lung and the finite patient dimensions in breast brachytherapy the dose distributions calculated in a patient equivalent mathematical phantom by Monte Carlo simulations for the same implant of either 169Yb or 1921r commercially available sources are found comparable. Dose volume histogram results support that 169Yb could be at least as effective as 192Ir delivering the same dose to the lung and slightly reduced dose to the breast skin. The current treatment planning systems' approach of employing dosimetry data precalculated in a homogeneous water phantom of given shape and dimensions, however, is shown to notably overestimate the delivered dose distribution for 169Yb. Especially at the skin and the lung, the treatment planning system dose overestimation is on the order of 15%-30%. These findings do not undermine the potential of 169Yb HDR sources for breast brachytherapy relative to the most commonly used 192Ir HDR sources. They imply, however, that there could be a need for the amendment of dose calculation algorithms employed in clinical treatment planning of particular brachytherapy applications, especially for intermediate photon energy sources such as 169Yb.

169Yb has received a renewed focus lately as an alternative to 192Ir sources for high dose rate (HDR) brachytherapy. Following the results of a recent work by our group which proved 169Yb to be a good candidate for HDR prostate brachytherapy, this work seeks to quantify the radiation shielding requirements for 169Yb HDR brachytherapy applications in comparison to the corresponding requirements for the current 192Ir HDR brachytherapy standard. Monte Carlo simulation (MC) is used to obtain 169Yb and 192Ir broad beam transmission data through lead and concrete. Results are fitted to an analytical equation which can be used to readily calculate the barrier thickness required to achieve a given dose rate reduction. Shielding requirements for a HDR brachytherapy treatment room facility are presented as a function of distance, occupancy, dose limit, and facility workload, using analytical calculations for both 169Yb and 192Ir HDR sources. The barrier thickness required for 169Yb is lower than that for 192Ir by a factor of 4-5 for lead and 1.5-2 for concrete. Regarding 169Yb HDR brachytherapy applications, the lead shielding requirements do not exceed 15 mm, even in highly conservative case scenarios. This allows for the construction of a lead door in most cases, thus avoiding the construction of a space consuming, specially designed maze. The effects of source structure, attenuation by the patient, and scatter conditions within an actual treatment room on the above-noted findings are also discussed using corresponding MC simulation results.

In this work, a polymer gel-magnetic resonance (MR) imaging method is employed for the dosimetric characterization of a new 125I low dose rate seed (IsoSeed model I25.S17). Two vials filled with PABIG gel were prepared in-house and one new seed as well as one commercially available 125I seed of similar dose rate and well-known dosimetric parameters (IsoSeed model I25.S06) were positioned in each vial. Both seeds in each vial were MR scanned simultaneously on days 11 and 26 after implantation. The data obtained from the known seed in each vial are used to calibrate the gel dose response which, for the prolonged irradiation duration necessitated by the investigated dose rates, depends on the overall irradiation time. Data for this study are presented according to the AAPM TG-43 dosimetric formalism. Polymer gel results concerning the new seed are compared to corresponding, published dosimetric results obtained, for the purpose of the new seed clinical implementation, by our group using the established methods of Monte Carlo (MC) simulation and thermo-luminescence dosimetry (TLD). Polymer gel dosimetry yields an average dose rate constant value of lambda = (0.921 +/- 0.031) cGy h(-1) U(-1) relative to (MC)lambda = (0.929 +/- 0.014) cGy h(-1) U(-1), (TLD)lambda = (0.951 +/- 0.044) cGy h(-1) U(-1) and the average value of Lambda = (0.940 +/- 0.051) cGy h(-1) U(-1) proposed for the clinical implementation of the new seed. Results for radial dose function, g(L)(r), and anisotropy function, F(r, theta), also agree with corresponding MC calculations within experimental uncertainties which are smaller for the polymer gel method compared to TLD. It is concluded that the proposed polymer gel-magnetic resonance imaging methodology could be used at least as a supplement to the established techniques for the dosimetric characterization of new low energy and low dose rate interstitial brachytherapy seeds.

The use of magnetic resonance imaging as a readout method for polymer gel dosimetry commonly involves long imaging sessions, particularly when high spatial resolution is required in all three dimensions, for the investigation of dose distributions with steep dose gradients and stringent dose delivery specifications. In this work, a volume selective turbo spin echo (TSE) pulse sequence is compared to the established Carr-Purcell-Meiboom-Gill (CPMG) multiecho acquisition with regard to providing accurate dosimetric results in significantly reduced imaging times. Polyethylene glycol diacrylate based (PABIG) gels were irradiated and subsequently scanned to obtain R2 relaxation rate measurements, using a CPMG multiecho sequence and a dual echo TSE utilizing an acceleration (turbo) factor of 64. R2 values, plotted against corresponding Monte Carlo dose calculations, provided calibration data of PABIG gels dose response over a wide dose range. A linear R2 versus dose relationship was demonstrated for both sequences with TSE results presenting reduced dose sensitivity. Although TSE data were found to deviate from linearity at lower doses compared to CPMG data, a relatively wide dynamic dose range of response extending up to approximately 100 Gy was observed for both sequences. The TSE and CPMG sequences were evaluated with a brachytherapy irradiation using a high dose rate 192Ir source and a gamma knife stereotactic radiosurgery irradiation with a single 4 mm collimator helmet shot. Dosimetric results obtained with the TSE and CPMG are shown to compare equally well with the expected dose distributions for these irradiations. The 60-fold scan time reduction achieved with TSE implies that this sequence could prove to be a useful tool for the introduction of polymer gel dosimetry in clinical radiation therapy applications involving high doses and steep dose gradients.

Purpose: The aim of this work is to validate a deterministic radiation transport based treatment planning system (TPS) for single 192Ir brachytherapy source dosimetry in homogeneous water geometries. Methods: TPS results were obtained using the deterministic radiation transport option of a BRACHYVISION v. 8.8 system for three characteristic source designs (VS2000, GMPlus HDR, and GMPlus PDR) with each source either centered in a 15 cm radius spherical water phantom, or positioned at varying distance away from the phantom center. Corresponding MC simulations were performed using the MCNPX code v.2.5.0 and source geometry models prepared using information provided by the manufacturers. Results: Comparison in terms of the AAPM TG-43 dosimetric formalism quantities, as well as dose rate distributions per unit air kerma strength with a spatial resolution of 0.1 cm, yielded close agreement between TPS and MC results for the sources centered in the phantom. Besides some regions close to the source longitudinal axes where discrepancies could be characterized as systematic, overall agreement for all three sources studied is comparable to the statistical (type A) uncertainty of MC simulations (1% at the majority of points in the geometry increasing to 2%–3% at points lying both away from the source center and close to the source longitudinal axis). A corresponding good agreement was also found between TPS and MC results for the sources positioned away from the phantom center. Conclusions: Results of this work attest the capability of the TPS to accurately account for the scatter conditions regardless of the size or shape of a given geometry of dosimetric interest, and the position of a source within it. This is important since, as shown in the literature and summarized also in this work, these factors could introduce a significant dosimetric effect that is currently ignored in clinical treatment planning. It is concluded that the implementation of the deterministic radiation transport option of the BRACHYVISION v. 8.8 system for 192Ir brachytherapy dosimetry in homogeneous water geometries yields results of comparable accuracy to the golden standard of Monte Carlo simulation, in clinically viable calculation times. [ABSTRACT FROM AUTHOR]

Ample literature exists on the dose overestimation by commercially available treatment planning systems in MammoSite® applications using high dose rate 192Ir sources for partial breast brachytherapy as monotherapy, due to their inability to predict the dose reduction caused by the radiographic contrast solution in the balloon catheter. In this work Monte Carlo simulation is used to verify the dose rate reduction in a balloon breast applicator which does not vary significantly with distance and it is 1.2% at the prescription distance for the reference simulated geometry of 10% diluted radiographic contrast media and 2.5 cm balloon radius. Based on these findings and the minimal hardening of the initially emitted photon spectrum for 192Ir, a simple analytical method is proposed and shown capable for correcting dosimetry planning in clinical applications. Simulations are also performed to assess the corresponding dose reduction in applications of balloon breast applicators using high dose rate 169Yb sources that have recently become available. Results yield a far more significant and distance dependent dose reduction for 169Yb (on the order of 20% at the prescription distance for the abovementioned reference simulation geometry). This dose reduction cannot be accounted for using simple analytical methods as for 192Ir due to the significant hardening of the initially emitted 169Yb photons within the diluted radiographic contrast media. Combined with results of previous works regarding the effect of altered scatter conditions (relative to treatment planning system assumptions) on breast treatment planning accuracy, which is more pronounced for 169Yb relative to 192Ir, these findings call for the amendment of dose treatment planning systems before using 169Yb high dose rate sources in balloon breast applicators. [ABSTRACT FROM AUTHOR]