A novel phantom design for brachytherapy quality Assurance

Background: One major challenge in brachytherapy is to verify the accuracy of dose distributions calculated by the treatment planning system. In this project, a new phantom design has been introduced for quality assurance of dose distributions in gynocological (GYN) brachytherapy implants using EBT GafChromic film. Materials and Methods: This phantom has been designed and fabricated from 90 slabs of 18�16�0.2 cm3 Perspex to accommodate a tandem and ovoids assembly, which is normally used for GYN brachytherapy treatment. In addition, this phantom design is allowing the use EBT GafChromic films for dosimetric verification of GYN implants with Cs-137 Selectron LDR system. With this assembly, GafChromic films were exposed using a plan designed to deliver 2.5 Gy dose to point "A" in Manchester system for tandem and ovoids configurations and to deliver 1.5 Gy of dose to 0.5 cm distance from the lateral surface of ovoids for using ovoid-pair. The measured dose distributions with GafChromic films were compared with the TPS isodose lines both numerically and spatially. For a quantitative analysis of the results, the measured doses values at several points of interest were evaluated with the treatment planning data and values obtained following the TG-43 dose calculation formalism. Results: The results of these investigations have indicated that the new phantom design enables us to measure differences of greater than ±6 for LDR brachytherapy GYN treatments. Conclusion: The new phantom design could be utilized for the QA procedure of the brachytherapy remote after loading systems to confirm the accuracy of dose distribution in GYN implants

Salvage Brachytherapy for Biochemically Recurrent Prostate Cancer Following Primary Brachytherapy

Purpose. In this study, we evaluated our experience with salvage brachytherapy after discovery of biochemical recurrence after a prior brachytherapy procedure. Methods and Materials. From 2001 through 2012 twenty-one patients treated by brachytherapy within University of Kentucky or from outside centers developed biochemical failure and had no evidence of metastases. Computed tomography (CT) scans were evaluated; patients who had an underseeded portion of their prostate were considered for reimplantation. Results. The majority of the patients in this study (61.9%) were low risk and median presalvage PSA was 3.49 (range 17.41–1.68). Mean follow-up was 61 months. At last follow-up after reseeding, 11/21 (52.4%) were free of biochemical recurrence. There was a trend towards decreased freedom from biochemical recurrence in low risk patients (p = 0.12). International Prostate Symptom Scores (IPSS) increased at 3-month follow-up visits but decreased and were equivalent to baseline scores at 18 months. Conclusions. Salvage brachytherapy after primary brachytherapy is possible; however, in our experience the side-effect profile after the second brachytherapy procedure was higher than after the first brachytherapy procedure. In this cohort of patients we demonstrate that approximately 50% oncologic control, low risk patients appear to have better outcomes than others

Dose distribution verification for GYN brachytherapy using EBT Gafchromic film and TG-43 calculation

Aim Verification of dose distributions for gynecological (GYN) brachytherapy implants using EBT Gafchromic film. Background One major challenge in brachytherapy is to verify the accuracy of dose distributions calculated by a treatment planning system. Materials and methods A new phantom was designed and fabricated using 90 slabs of 18 cm � 16 cm � 0.2 cm Perspex to accommodate a tandem and Ovoid assembly, which is normally used for GYN brachytherapy treatment. This phantom design allows the use of EBT Gafchromic films for dosimetric verification of GYN implants with a cobalt-60 HDR system or a LDR Cs-137 system. Gafchromic films were exposed using a plan that was designed to deliver 1.5 Gy of dose to 0.5 cm distance from the lateral surface of ovoids from a pair of ovoid assembly that was used for treatment vaginal cuff. For a quantitative analysis of the results for both LDR and HDR systems, the measured dose values at several points of interests were compared with the calculated data from a commercially available treatment planning system. This planning system was utilizing the TG-43 formalism and parameters for calculation of dose distributions around a brachytherapy implant. Results The results of these investigations indicated that the differences between the calculated and measured data at different points were ranging from 2.4 to 3.8 for the LDR Cs-137 and HDR Co-60 systems, respectively. Conclusion The EBT Gafchromic films combined with the newly designed phantom could be utilized for verification of the dose distributions around different GYN implants treated with either LDR or HDR brachytherapy procedures. © 2016 Greater Poland Cancer Centr

Salvage Brachytherapy for Biochemically Recurrent Prostate Cancer following Primary Brachytherapy

. Purpose. In this study, we evaluated our experience with salvage brachytherapy after discovery of biochemical recurrence after a prior brachytherapy procedure. Methods and Materials. From 2001 through 2012 twenty-one patients treated by brachytherapy within University of Kentucky or from outside centers developed biochemical failure and had no evidence of metastases. Computed tomography (CT) scans were evaluated; patients who had an underseeded portion of their prostate were considered for reimplantation. Results. The majority of the patients in this study (61.9%) were low risk and median presalvage PSA was 3.49 (range 17.41-1.68). Mean follow-up was 61 months. At last follow-up after reseeding, 11/21 (52.4%) were free of biochemical recurrence. There was a trend towards decreased freedom from biochemical recurrence in low risk patients ( = 0.12). International Prostate Symptom Scores (IPSS) increased at 3-month follow-up visits but decreased and were equivalent to baseline scores at 18 months. Conclusions. Salvage brachytherapy after primary brachytherapy is possible; however, in our experience the side-effect profile after the second brachytherapy procedure was higher than after the first brachytherapy procedure. In this cohort of patients we demonstrate that approximately 50% oncologic control, low risk patients appear to have better outcomes than others

Is grid therapy useful for all tumors and every grid block design?

Grid therapy is a treatment technique that has been introduced for patients with advanced bulky tumors. The purpose of this study is to investigate the effect of the radiation sensitivity of the tumors and the design of the grid blocks on the clinical response of grid therapy. The Monte Carlo simulation technique is used to determine the dose distribution through a grid block that was used for a Varian 2100C linear accelerator. From the simulated dose profiles, the therapeutic ratio (TR) and the equivalent uniform dose (EUD) for different types of tumors with respect to their radiation sensitivities were calculated. These calculations were performed using the linear quadratic (LQ) and the Hug-Kellerer (H-K) models. The results of these calculations have been validated by comparison with the clinical responses of 232 patients from different publications, who were treated with grid therapy. These published results for different tumor types were used to examine the correlation between tumor radiosensitivity and the clinical response of grid therapy. Moreover, the influence of grid design on their clinical responses was investigated by using Monte Carlo simulations of grid blocks with different hole diameters and different center-to-center spacing. The results of the theoretical models and clinical data indicated higher clinical responses for the grid therapy on the patients with more radioresistant tumors. The differences between TR values for radioresistant cells and radiosensitive cells at 20 Gy and 10 Gy doses were up to 50% and 30%, respectively. Interestingly, the differences between the TR values with LQ model and H-K model were less than 4%. Moreover, the results from the Monte Carlo studies showed that grid blocks with a hole diameters of 1.0 cm and 1.25 cm may lead to about 19% higher TR relative to the grids with hole diameters smaller than 1.0 cm or larger than 1.25 cm (with 95% confidence interval). In summary, the results of this study indicate that grid therapy is more effective for tumors with radioresistant characteristics than radiosensitive tumors

Coupled-channel analysis of neutron scattering from /sup 12/C between 9 and 15 MeV

A deformed and energy dependent phenomenological optical model potential and coupled-channel formalism for deformed nuclei have been used in the analysis of elastic and inelastic (Q = 4.439 MeV) scattering, and analyzing power for neutrons scattered from /sup 12/C in the energy range of 9 to 15 MeV. 6 refs., 1 fig., 1 tab

Grid therapy: Impact of radiobiological models on calculation of therapeutic ratio

The purpose of this study is evaluation of the impact of radiobiological models in therapeutic ratio (TR) calculation of spatially fractionated (Grid) radiotherapy for different tumor cells. A Monte Carlo technique was employed to calculate the dose distributions of a Grid collimator in a 6 MV beam. The linear-quadratic (LQ) and modified linear quadratic (MLQ) models were used separately to evaluate the therapeutic ratio for different tumor cells (Melanoma, Squamous cell carcinoma (SCC), Adenocarcinoma and Sarcoma). Different maximum dose sizes (10 Gy, 15 Gy and 20 Gy) are considered. For each dose the equivalent uniform dose (EUD) is obtained. The EUDs and TRs for all different doses were derived through the LQ and MLQ models. Calculated therapeutic ratios from two models were compared. The results of TRs calculations from both LQ and MLQ have less than 5% difference. EUDs were varied between 2.19 Gy and 3.87 Gy. The TR was dependent on the prescribed dose, cell survival fraction at 2Gy dose (SF2) and radiobiological model parameters

Impact of magnetic fields on calculated AAPM TG-43 parameters for 192Ir and 60Co HDR brachytherapy sources: A Monte Carlo study

Purpose: The aim of this work is to investigate the influence of an external magnetic field (MF) on The American Association of Physicists in Medicine (AAPM) No. 43 Report (TG-43) parameters for 192Ir and 60Co high dose rate (HDR) brachytherapy sources using Monte Carlo (MC) simulation methods. Materials and methods: We used the Geant4 toolkit (version 10.1. p01) to simulate the geometry of 192Ir and 60Co brachytherapy sources. AAPM TG-43 parameters (the radial dose function, g(r), and the anisotropy function, F (r, \u3b8)) of both 192Ir and 60Co sources were calculated in the presence of a magnetic field with strengths of 1.5T, 3T, and 7T in the X, Y, and Z directions in a voxelized water phantom. Results: For the 192Ir source, the calculated values g(r) and F (r, \u3b8) remained nearly unaffected by the magnetic field for all investigated strengths. For the 60Co source, the differences for the g(r) and F (r,\u3b8) under the 1.5T, 3T, and 7T magnetic field strengths along the direction parallel with the MF were found to be an increase of up to 5%, 15%, and 33%, respectively. However, for the directions perpendicular with the magnetic field, there was a decrease of up to 3%, 6% and 15% under 1.5T, 3T and 7T strengths, respectively. Conclusion: Our results highlight the necessity of a Monte Carlo-based treatment planning system (TPS) if cobalt HDR treatments are performed under a magnetic field, especially for strengths greater than 1.5T

Dose enhancement in brachytherapy in the presence of gold nanoparticles : a Monte Carlo study on the size of gold nanoparticles and method of modelling

The aim of this study was to evaluate the effect of the size of gold nanoparticles (GNPs) on dose enhancement in brachytherapy with photon emitting sources. Four photon emitting sources, 125I, 169Yb, 103Pd, and 192Ir were simulated and dose rate constant and radial dose functions were compared with published corresponding data for these sources. Dose enhancement factor in the presence of gold nanoparticles of 30 mg/ml concentration was calculated separately for nanoparticles with a diameter of 50, 100 and 200 nm. Gold nanoparticles were simulated precisely as nanospheres utilizing a lattice option in the MCNPX Monte Carlo code and the results were compared with those obtained with a simple model in which gold atoms are distributed uniformly in tumor volume as a simple mixture. Among the four mentioned sources, the dose enhancement related to 125I source is higher. Our results have shown that with gold nanoparticles of higher diameter, the level of dose enhancement is higher in the tested tumor. It has been also observed that the simple model overestimates the dose enhancement factor when compared with the precise model in which nanoparticles are defined according to the Monte Carlo code. In the energy range produced by the brachytherapy sources, the dose enhancement is higher when using brachytherapy sources with lower energy. Among the size range of gold nanoparticles used in medicine, it is predicted that nanoparticles with higher diameter can be more useful when are utilized in brachytherapy. It is also recommended that when calculating dose enhancements, a precise model be used for modelling of nanoparticles in the Monte Carlo simulations