Technical note: Dosimetric study of a new Co-60 source used in brachytherapy

Feasibility of using micro silica bead TLDs for in-Vivo dosimetry of CT-based HDR prostate brachytherapy: An experimental and simulation study

PURPOSE

Feasibility of silica-based dosimeters for IVD of HDR prostate brachytherapy.

MATERIAL AND METHODS

Plastic dosimeter holders and a water-fillable prostate phantom were built in-house. Interstitial prostate brachytherapy and Monte Carlo simulations were performed. The treatment planning, Monte-Carlo simulation, and dosimetry results were compared.

RESULTS

The relative differences between TLD-TPS, TLD-MCNP, and TPS-MCNP were 0.2-6.9 %, 0.5-6.5 %, and 0.6-6.3 %, respectively.

CONCLUSION

Micro-silica bead dosimeters can perform offline in situ quality assurance in HDR prostate brachytherapy.

Assessing Heterogeneity Effects on Points A, B, and Organs at Risk Doses in High-dose-Rate Brachytherapy for Cervical Cancer - A Comparison of 192Ir and 60Co Sources Using Monte Carlo N-Particle 5

Purpose

The present article deals with investigating the effects of tissue heterogeneity consideration on the dose distribution of 192Ir and 60Co sources in high-dose-rate brachytherapy (HDR-BT).

Materials and Methods

A Monte Carlo N-Particle 5 (MCNP5) code was developed for the simulation of the dose distribution in homogeneous and heterogeneous phantoms for cervical cancer patients. The phantoms represented water-equivalent and human body-equivalent tissues. Treatment data for a patient undergoing HDR-BT with a 192Ir source were used as a reference for validation, and for 60Co, AAPM Task Group 43 methodology was also applied. The dose values were calculated for both source types in the phantoms.

Results

The results showed a good agreement between the calculated dose in the homogeneous phantom and the real patient's treatment data, with a relative difference of less than 5% for both sources. However, when comparing the absorbed doses at critical points such as Point A right, Point A left, Point B right, Point B left, bladder International Commission on Radiation Units and Measurement (ICRU) point, and recto-vaginal ICRU point, the study revealed significant percentage differences (approximately 5.85% to 12.02%) between the homogeneous and heterogeneous setups for both 192Ir and 60Co sources. The analysis of dose-volume histograms (DVH) indicated that organs at risk, notably the rectum and bladder, still received doses within recommended limits.

Conclusions

The study concludes that 60Co and 192Ir sources can be effectively used in HDR-BT, provided that careful consideration is given to tissue heterogeneity effects during treatment planning to ensure optimal therapeutic outcomes.

Monte Carlo dosimetry of the 60Co sources of a new GZP3 HDR afterloading system

BACKGROUND

The purpose of this work was to obtain the dosimetric parameters of the new GZP3 ⁶⁰Co high-dose-rate afterloading system launched by the Nuclear Power Institute of China, which is comprised of two different ⁶⁰Co sources.

METHODS

The Monte Carlo software Geant4 and EGSnrc were employed to derive accurate calculations of the dosimetric parameters of the new GZP3 ⁶⁰Co brachytherapy source in the range of 0-10 cm, following the formalism proposed by American Association of Physicists in Medicine reports TG43 and TG43U1. Results of the two Monte Carlo codes were compared to verify the accuracy of the data. The source was located in the center of a 30-cm-radius theoretical sphere water phantom.

RESULTS

For channels 1 and 2 of the new GZP3 ⁶⁰Co afterloading system, the results of the dose-rate constant (Λ) were 1.115 cGy h^-1 U^-1 and 1.112 cGy h^-1 U^-1, and for channel 3 they were 1.116 cGy h^-1 U^-1 and 1.113 cGy h^-1 U^-1 according to the Geant4 and EGSnrc, respectively. The radial dose function in the range of 0.25-10.0 cm in a longitudinal direction was calculated, and the fitting formulas for the function were obtained. The polynomial function for the radial dose function and the anisotropy function (1D and 2D) with a [Formula: see text] of 0°-175° and an r of 0.5-10.0 cm were obtained. The curves of the radial function and the anisotropy function fitted well compared with the two Monte Carlo software.

CONCLUSION

These dosimetric data sets can be used as input data for TPS calculations and quality control for the new GZP3 ⁶⁰Co afterloading system.

Radiobiological and dosimetric comparison of 60Co versus 192Ir high-dose-rate intracavitary-interstitial brachytherapy for cervical cancer

BACKGROUND

High-dose-rate (HDR) intracavitary-interstitial brachytherapy (IC-ISBT) is an effective treatment for bulky, middle, and advanced cervical cancer. In this study, we compared the differences between 60Co and 192Ir HDR IC-ISBT plans in terms of radiobiological and dosimetric parameters, providing a reference for clinical workers in brachytherapy.

METHODS

A total of 30 patients with cervical cancer receiving HDR IC-ISBT were included in this study, and IC-ISBT plans for each individual were designed with both 60Co and 192Ir at a prescribed dose of CTV D90 = 6 Gy while keeping the dose to OARs as low as possible. Physical dose and dose-volume parameters of CTV and OARs were extracted from TPS. The EQD2, EUBED, EUD, TCP, and NTCP were calculated using corresponding formulas. The differences between the 60Co and 192Ir IC-ISBT plans were compared using the paired t-test.

RESULTS

In each patient's 60Co and 192Ir IC-ISBT plan, the average physical dose and EQD2 of 60Co were lower than those of 192Ir, and there were statistically significant differences in D2cc and D1cc for the OARs (p < 0.05); there were statistically significant differences in D0.1 cc for the bladder (p < 0.05) and no significant differences in D0.1 cc for the rectum or intestines (p > 0.05). The EUBED ratio (60Co/192Ir) at the CTV was mostly close to 1 when neither 60Co or 192Ir passed their half-lives or when both passed two half-lives, and the difference between them was not significant; at the OARs, the mean value of 60Co was lower than that of 192Ir. There was no statistical difference between 60Co and 192Ir in the EUD (93.93 versus 93.92 Gy, p > 0.05) and TCP (97.07% versus 97.08%, p > 0.05) of the tumors. The mean NTCP value of 60Co was lower than that of 192Ir.

CONCLUSIONS

Considering the CTV and OARs, the dosimetric parameters of 60Co and 192Ir are comparable. Compared with 192Ir, the use of 60Co for HDR IC-ISBT can ensure a similar tumor control probability while providing better protection to the OARs. In addition, 60Co has obvious economic advantages and can be promoted as a good alternative to 192Ir.

Comparative Analysis of 60Co and 192Ir Sources in High Dose Rate Brachytherapy for Cervical Cancer

High-dose-rate (HDR) brachytherapy (BT) is an essential treatment for cervical cancer, one of the most prevalent gynecological malignant tumors. In HDR BT, high radiation doses can be delivered to the tumor target with the minimum radiation doses to organs at risk. Despite the wide use of the small HDR 192Ir source, as the technique has improved, the HDR 60Co source, which has the same miniaturized geometry, has also been produced and put into clinical practice. Compared with 192Ir (74 days), 60Co has a longer half-life (5.3 years), which gives it a great economic advantage for developing nations. The aim of the study was to compare 60Co and 192Ir sources for HDR BT in terms of both dosimetry and clinical treatment. The results of reports published on the use of HDR BT for cervical cancer over the past few years as well as our own research show that this treatment is safe and it is feasible to use 60Co as an alternative source.

BEBIG 60Co HDR brachytherapy source dosimetric parameters validation using GATE Geant4-based simulation code

Purpose

This study aims to validate the dosimetric characteristics of High Dose Rate (HDR) ⁶⁰Co source (Co0.A86 model) using GATE Geant4-based Monte Carlo code. According to the recommendation of the American Association of Physicists in Medicine (AAPM) task group report number 43, the dosimetric parameters of a new brachytherapy source should be verified either experimentally or by Monte Carlo calculation before clinical applications. The validated ⁶⁰Co source in this study will be used for the simulation of intensity-modulated brachytherapy (IMBT) of vaginal cancer using the same GATE Geant4-based Monte Carlo code in the future.

Materials and methods

GATE (version 9.0) simulation code was used to model and calculate the required TG-43U1 dosimetric data of the ⁶⁰Co HDR source. DoseActors were defined for calculation of dose rate constant, radial dose function, and anisotropy function in a water phantom with an 80 cm radius.

Results

The dose rate constant was obtained as 1.070±0.008cGy.h−1.U−1 which shows a relative difference of 2.01% compared to the consensus value, 1.092  ​cGy.h−1.U−1. The calculated results of anisotropy and radial dose functions starting from 0.1 cm to 10 cm around the source showed excellent agreement with the results of published studies. The mean variation of the radial dose and anisotropy functions values from the consensus data were 1% and 0.9% respectively.

Conclusion

Findings from this investigation revealed that the validation of the HDR ⁶⁰Co source is feasible by the GATE Geant4-based Monte Carlo code. As a result, the GATE Monte Carlo code can be used for the verification of the brachytherapy treatment planning system.

Evaluation of bone dose arising from skin cancer brachytherapy: A comparison between 192Ir and 60Co sources through Monte Carlo simulations

PURPOSE

This study aimed to calculate and compare absorbed dose to bone following exposure to ¹⁹²Ir and ⁶⁰Co sources in high dose rate (HDR) skin brachytherapy. Moreover, effects of the bone thickness and soft tissue thickness before the bone on absorbed dose to the bone are evaluated .

MATERIALS AND METHODS

¹⁹²Ir and ⁶⁰Co sources inserted in Leipzig applicators with internal diameters of 1, 2 and 3 cm with/without their optimal flattening filters were simulated by MCNPX Monte Carlo code. Then, heterogeneous phantoms (including skin, soft tissue before and after the bone, cortical bone and bone marrow) were defined. Finally, relative depth dose values for the bone and other tissues in the heterogeneous phantoms were obtained and compared.

RESULTS

The average relative depth dose values of the skin, soft tissue before and after bone and bone marrow were almost similar for both ¹⁹²Ir and ⁶⁰Co sources, with a maximum difference less than 2%. However, a 0.1-6.8% difference was observed between average relative depth dose values of these two sources for the cortical bone. The results showed that with increasing the bone thickness and bone distance from the skin surface, the average relative depth dose values of the bone marrow and cortical bone decreased for both ¹⁹²Ir and ⁶⁰Co sources inserted in the applicators without/with their optimal flattening filters. For most of evaluated the applicators without/with their flattening filters, the average relative depth dose values of the bone marrow arisen from the ⁶⁰Co source were higher than those obtained from the ¹⁹²Ir source, while an opposite trend was observed for the cortical bone .

CONCLUSION

The obtained findings showed that the average relative depth dose values of ¹⁹²Ir and ⁶⁰Co sources at the corresponding depths of the designed heterogeneous phantoms were almost similar (expect for the cortical bone). Hence, it is concluded that ⁶⁰Co source can be used instead of ¹⁹²Ir source in HDR skin brachytherapy, particularly in developing countries.

APPLICABILITY OF PURE PROPANE GAS FOR MICRODOSIMETRY AT BRACHYTHERAPY ENERGIES: A FLUKA STUDY

Applicability of pure propane gas for microdosimetric measurements at photon energies relevant in brachytherapy is studied using the Monte Carlo-based FLUKA code. Monoenergetic photons in the energy range of 20-1250 keV and brachytherapy sources such as 103Pd, 125I, 169Yb, 192Ir, 137Cs and 60Co are considered in the study. Using the calculated values of energy deposited in the sensitive region of LET-1/2 tissue-equivalent proportional counter filled with pure propane gas and tissue-equivalent propane gas, values of density scaling factor for the site sizes of 1 and 8 μm are obtained. The study shows that density of propane gas should be lowered by a factor of about 0.93 for 169Yb, 192Ir, 137Cs and 60Co sources for the site sizes of 1-8 μm. For 125I source, the density of propane gas requires a scaling of 0.93 for 1 μm site size, whereas for site sizes 2-8 μm, density need not be altered. 103Pd source does not require density scaling for site sizes 1-8 μm.

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.

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, θ)) 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, θ) remained nearly unaffected by the magnetic field for all investigated strengths. For the ⁶⁰Co source, the differences for the g(r) and F (r,θ) 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.

Measurements and Monte Carlo calculation of radial dose and anisotropy functions of BEBIG 60Co high-dose-rate brachytherapy source in a bounded water phantom

Purpose

The study compared the experimentally measured radial dose function, g(r), and anisotropy function, F(r,θ), of a BEBIG ⁶⁰Co (Co0.A86) high-dose-rate (HDR) source in an in-house designed water phantom with egs_brachy Monte Carlo (MC) calculated values. MC results available in the literature were only for unbounded phantoms, and there are no currently published data in the literature for experimental data compared to MC calculations for a bounded phantom.

Material and methods

egs_brachy is a fast EGSnrc application designed for brachytherapy applications. For unbounded phantom calculation, we considered a cylindrical phantom with a length and diameter of 80 cm and used liquid water. These egs_brachy calculated TG43U1 parameters were compared with the consensus data. Upon its validation, we experimentally measured g(r) and F(r,θ) in a precisely machined 30 × 30 × 30 cm³ water phantom using TLD-100 and EBT2 Gafchromic Film and compared it with the egs_brachy results of the same geometry.

Results

The TG43U1 dosimetric dataset calculated using egs_brachy was compared with published data for an unbounded phantom, and found to be in good agreement within 2%. From our experimental results of g(r) and F(r,θ), the observed variation with the egs_brachy code calculation is found to be within the acceptable experimental uncertainties of 3%.

Conclusions

In this study, we validated the egs_brachy calculation of the TG43U1 dataset for the BEBIG ⁶⁰Co source for an unbounded geometry. Subsequently, we measured the g(r) and F(r,θ) for the same source using an in-house water phantom. In addition, we validated these experimental results with the values calculated using the egs_brachy MC code, with the same geometry and similar phantom material as used in the experimental methods.

MONTE CARLO-BASED INVESTIGATION OF MICRODOSIMETRIC DISTRIBUTION OF HIGH ENERGY BRACHYTHERAPY SOURCES

FLUKA-based Monte Carlo calculations were carried out to study microdosimetric distributions in air and in water for encapsulated high energy brachytherapy sources (60Co, 137Cs, 192Ir and 169Yb) by simulating a Tissue Equivalent Proportional Counter (Model LET1/2) having sensitive diameter of 1. 27 cm for a site size of 1 μm. The study also included microdosimetric distributions of bare sources. When the sources are in air, for a given source, the source geometry does not affect the y¯F and y¯D values significantly. When the encapsulated 192Ir, 137Cs and 60Co sources are in water, y¯F and y¯D values increase with distance in water which is due to degradation in the energy of photons. Using the calculated values of y¯D, relative biological effectiveness (RBE) was obtained for the investigated sources. When 60Co, 137Cs and 192Ir sources are in water, RBE increases from 1.03 ± 0.01 to 1.17 ± 0.01, 1.24 ± 0.01 to 1.46 ± 0.02 and 1.50 ± 0.01 to 1.75 ± 0.03, respectively, when the distance was increased from 3-15 cm, whereas for 169Yb, RBE is about 2, independent of distance in water.

Experimental Determination of Radial Dose Function and Anisotropy Function of GammaMed Plus 192Ir High-Dose-Rate Brachytherapy Source in a Bounded Water Phantom and its Comparison with egs_brachy Monte Carlo Simulation

OBJECTIVE

The aim of the present study is to experimentally measure the radial dose function g(r) and anisotropy function F(r,θ) of GammaMed Plus 192Ir high-dose-rate source in a bounded water phantom using thermoluminescent dosimeter (TLD) and film dosimetry and compare the obtained results with egs_brachy Monte Carlo (MC)-calculated values for the same geometry.

MATERIALS AND METHODS

The recently developed egs_brachy is a fast Electron Gamma Shower National Research Council of Canada MC application which is intended for brachytherapy applications. The dosimetric dataset recommended by Task Group 43 update (TG43U1) is calculated using egs_brachy for an unbounded phantom. Subsequently, radial dose function g(r) and anisotropy function F(r,θ) are measured experimentally in a bounded water phantom using TLD-100 and Gafchromic EBT2 film.

RESULTS

The TG43U1 dosimetric parameters were determined using the egs_brachy MC calculation and compared with published data which are found to be in good agreement within 2%. The experimentally measured g(r) and F(r,θ) and its egs_brachy MC code-calculated values for a bounded phantom geometry are found to be good in agreement within the acceptable experimental uncertainties of 3%.

CONCLUSION

Our experimental phantom size represents the average patient width of 30 cm; hence, results are closer to scattering conditions in clinical situations. The experimentally measured g(r) and F(r,θ) and egs_brachy MC calculations for bounded geometry are well in agreement within experimental uncertainties. Further, the confidence level of our comparative study is enhanced by validating the egs_brachy MC code for the unbounded phantom with respect to consensus data.

Determination of TG-43 Dosimetric Parameters for Photon Emitting Brachytherapy Sources

Objective:

Brachytherapy sources are widely used for the treatment of cancer. The report of Task Group No. 43 (TG-43) of American Association of Physicists in Medicine is known as the most common method for the determination of dosimetric parameters for brachytherapy sources. The aim of this study is to obtain TG-43 dosimetric parameters for ⁶⁰Co, ¹³⁷Cs, ¹⁹²Ir and ¹⁰³Pd brachytherapy sources by Monte Carlo simulation.

Methods:

In this study, ⁶⁰Co (model Co0.A86), ¹³⁷Cs (model 6520-67), ¹⁹²Ir (model BEBIG) and ¹⁰³Pd (model OptiSeed) brachytherapy sources were simulated using MCNPX Monte Carlo code. To simulate the sources, the exact geometric characterization of each source was defined in Monte Carlo input programs. Dosimetric parameters including air kerma strength, dose rate constant, radial dose function and anisotropy function were calculated for each source. Each input program was run with sufficient number of particle histories. The maximum type A statistical uncertainty in the simulation of the ⁶⁰Co, ¹³⁷Cs, ¹⁹²Ir and ¹⁰³Pd sources, were equal to 4%, 4%, 3.19% and 6.50%, respectively.

Results:

The results for dosimetry parameters of dose rate constant, radial dose function and anisotropy function for the ⁶⁰Co, ¹³⁷Cs, ¹⁹²Ir and ¹⁰³Pd sources in this study demonstrated good agreement with other studies.

Conclusion:

Based on the good agreement between the results of this study and other studies, the TG-43 results for Co0.A86 ⁶⁰Co, 67-65200 ¹³⁷Cs, BEBIG ¹⁹²Ir and OptiSeed ¹⁰³Pd sources are validated and can be used as input data in treatment planning systems (TPSs) and to validate the TPS calculations.

Treatment outcomes of high-dose-rate intracavitary brachytherapy for cervical cancer: a comparison of Ir-192 versus Co-60 sources

Objective

To determine and compare treatment outcomes between cobalt-60 (Co-60) and iridium-192 (Ir-192) high dose rate (HDR) brachytherapy in stage IB2–IIIB cervical cancer patients at Department of Radiology, Faculty of Medicine Vajira Hospital, Navamindrahiraj University.

Methods

A retrospective cohort study of patients diagnosed with cervical cancer and treated with radiotherapy at the Department of Radiation Oncology, Faculty of Medicine Vajira Hospital between 2004 and 2014. Survival rate was analyzed by Kaplan-Meier method and were compared between groups with log-rank test. Multivariate analysis was performed using Cox proportional hazards model.

Results

A total of 480 patients with cervical cancer and treated with radiotherapy were included, 274 patients for Ir-192 group and 206 patients for Co-60 group. The 2- and 5-year disease-free survival rate in Ir-192 group were 80.4% and 73.1% and in Co-60 group were 82.5% and 74.7%, respectively (p=0.365). Overall survival rates at 2 and 5 years were 89.4% and 77% of the Ir-192 group, and 91.6% and 81.9% in the Co-60 group, respectively (p=0.238). The complications were primarily grade 1 or 2. Grade 3 and 4 complications were found in 13 of 274 and 7 of 206 in Ir-192 and Co-60 groups, respectively (p=0.232). Grade and clinical stage of cancer significantly affected the survival outcome.

Conclusion

Cervical cancer patients who were treated with HDR Co-60 brachytherapy were comparable in survival and toxicity outcomes of those with HDR Ir-192 brachytherapy. Co-60 source has lots of economic advantages over Ir-192 and hence suitable for low resource radiotherapy setting.

Monte carlo study of organ doses and related risk for cancer in Tanzania from scattered photons in cervical radiation treatment involving Co-60 source

PURPOSE

The present work aimed to evaluate organ doses and related risk for cancer from external beam radiation treatment (EBRT) and high-dose-rate (HDR) brachytherapy (BT) involving Co-60 source for patients with cervical carcinoma in Tanzania based on Monte Carlo methods and to evaluate the secondary cancer risks in their lifetime.

METHODS

EBRT and HDR-BR were modelled by using the MCNPX Monte Carlo (MC) code. The MC simulations were performed by using validated models and isocentric irradiation of an adult female computational phantom. The organ doses and cancer risks estimates were obtained.

RESULTS

The highest absorbed doses of 6.98 × 10^-2 and 5.74 × 10^-2 Sv/Gy were recorded in the bladder for BT and EBRT. The higher risk was found for colon at 1.06 × 10^-3 in the HDR-BT and 9.75 × 10^-5 in the EBRT per 100,000 population at exposure age of 35 years than in the other organs. The risk magnitude decreased with increasing age at exposure. In general, the secondary cancer risks in all sites considered from EBRT and HDR-BR for cervical cancer patient were lower than the baseline risks.

CONCLUSIONS

The chances of developing secondary cancer take years following radiation therapy are extremely low, but the results of present study can support to establish a future database on secondary cancer risks involving radiation therapy in patients with cervical cancer by using HDR-BR and EBRT with Co-60 source in Tanzania and other developing countries.

Postoperative endometrial cancer treatments with electronic brachytherapy source

Purpose

This study is a dosimetric and acute toxicity comparison of endometrial cancer patients treated with either Axxent (Xoft, Inc., San José, CA, USA) electronic and interstitial brachytherapy versus interstitial high dose rate brachytherapy (HDRBT).

Materials and Methods

Between 2015 and 2017, 94 patients with postoperative endometrial cancer were treated in our centre with the Axxent electronic brachytherapy (eBT) system. The V150 and V200 are evaluated prospectively for each plan. The mean age of patients was 65.9 years (age range 33–84 years), with different tumour staging. Of the 94 patients, 37 received exclusive adjuvant brachytherapy (25 Gy in five sessions); the remaining patients received external beam radiotherapy (EBRT) with a regimen of 23 sessions of 2 Gy each to the entire pelvis, followed by eBT (15 Gy in three sessions). Additionally, the absorbed doses received by the organs at risk (OAR), urinary bladder, rectum and sigmoid colon were compared with HDRBT plans, evaluating D2cc, V50% and V35%. Median follow-up was done for each of the 94 patients to assess the toxicity of the treatment: vaginal mucosa toxicity, rectal and urinary toxicity; and results are presented for acute toxicity, toxicity at 1 month after the end of treatment and follow-up after 12 months for a portion of patients according to the Radiation Therapy Oncology Group (RTOG) toxicity criteria.

Results

The doses in OAR for eBT plans were lower than that for HDRBT plans, both Ir-192 and Co-60 plans, whose doses were similar. The dose in bladder with eBT was 63.8% of the prescribed dose for D2cc versus 70.1% for HDRBT Ir-192, for V50% was 7.2% versus 12.7% and for V35% was 15.2% versus 28.2%. In rectum the D2cc was 61.2% versus 68.4%, for V50% was 7.9% versus 14.3% and for V35% was 16.7% versus 32%. Results demonstrated lower doses to OAR in all eBT plans. Acute toxicity in eBT was very low in cases of mucositis, with only one case of toxicity greater than grade 1, rectal toxicity and urinary toxicity; results at 1 month are equally good, toxicity symptoms disappeared and no relapses have occurred to date.

Conclusions

The results of treatment with the Axxent eBT unit for 94 patients are very good, as no recurrence has been observed and the toxicity of the treatment is very low. The increase in V150 and V200 has not produced an increase in vaginal mucosa toxicity, and the doses in the OAR are lower than in the plans implemented for HDRBT with Ir-192 or Co-60. eBT is a good alternative to treat endometrial cancer in centres without conventional HDR availability. To date, there are limited published studies reporting on outcomes from patients treated with eBT.

A revised dosimetric characterization of 60Co BEBIG source: From single-source data to clinical dose distribution

PURPOSE

Although the dosimetric characterization of ⁶⁰Co BEBIG source can be found in several literature studies, the data sets show major discrepancies and the lack of uncertainty analyses. This study tried to determine an accurate dosimetric data set for this source using Monte Carlo (MC) simulations along with detailed uncertainty analysis. To explore how different dosimetric data sets can make changes in practical situations, clinical dose distributions based on our results were compared with the dose distributions derived from Granero et al. and consensus data sets.

METHODS AND MATERIALS

The MC simulations were performed with Monte Carlo N-Particle eXtended code (MCNPX) version 2.6.0 and the TG-43 parameters were estimated adhering to the American Association of Physicists in Medicine (AAPM) and European SocieTy for Radiotherapy and Oncology (ESTRO) 229 report. The dose rate distributions for single-source and two typical clinical cases, including one intracavitary and one interstitial, were calculated using an in-house code on the basis of the TG-43 formalism.

RESULTS

The total uncertainties for water dose rate on source transverse axis at 1 cm and 5 cm, air kerma strength, and dose rate constant were evaluated to be 0.10%, 0.09%, 0.04%, and 0.11%, respectively. Meaningful differences were found for the interstitial case in which 22% of clinical target volume (CTV) showed differences from ±1% to ±10% or even larger.

CONCLUSIONS

The MC uncertainty was derived about 16 times smaller than the typical MC component stated in TG-138, partly because of large number of histories and partly because the spectra of ⁶⁰Co and also its photons' attenuation coefficients are adequately accurate. The results showed that in the clinical situations, the applicator geometry and the superposition of single-source dose distributions can reduce the differences observed between several data sets.

Dosimetric study of GZP6 60 Co high dose rate brachytherapy source

The purpose of this study was to obtain dosimetric parameters of GZP6 ⁶⁰Co brachytherapy source number 3. The Geant4 MC code has been used to obtain the dose rate distribution following the American Association of Physicists in Medicine (AAPM) TG‐43U1 dosimetric formalism. In the simulation, the source was centered in a 50 cm radius water phantom. The cylindrical ring voxels were 0.1 mm thick for r ≤ 1 cm, 0.5 mm for 1 cm < r ≤ 5 cm, and 1 mm for r > 5 cm. The kerma‐dose approximation was performed for r > 0.75 cm to increase the simulation efficiency. Based on the numerical results, the dosimetric datasets were obtained. These results were compared with the available data of the similar ⁶⁰Co high dose rate sources and the detailed dosimetric characterization was discussed.

A Monte Carlo investigation of the dose distribution for 60Co high dose rate brachytherapy source in water and in different media

In this study, the dosimetric characterization for The BEBIG ⁶⁰Co High Dose Rate (HDR) brachytherapy source model Co0.A86 was investigated and the validity of the EGS5 Monte Carlo code to reproduce the dosimetric parameters in water phantom was checked. In addition, the dose distribution for different tissue phantoms was calculated. The BEBIG ⁶⁰Co HDR brachytherapy source was modeled using EGS5 Monte Carlo simulation code. A description of the source design, geometry and materials used in this work were provided. According to the update TG43-U1 formalism of AAPM, the air kerma strength, the dose rate constant, 2D rectangular dose distribution in water were calculated, moreover, the results of the radial dose function were obtained in water and different tissue phantoms; bone, lung, adipose tissue, breast and muscle. The obtained results were tabulated and presented in graphical formats for the comparison with available data. The calculated value of the air kerma strength of this study, 3.0419 U Bq^-1, agree well with that of the other Monte Carlo calculation. The 2D look-up along-away rectangular dose were obtained in water, the results were similar to the published data for all distances larger than 1 cm, for the distances near to the source region on the transversal source axis small differences are apparent. The radial dose function were presented in graphical format for the comparison between the dose distribution in water and different tissue phantoms. The EGS5 results obtained in this study shows good consistency with the published data for the dosimetric parameters of the of the BEBIG ⁶⁰Co HDR brachytherapy source. It seems that the radial dose function calculated in water differed in tissue phantoms due to the atomic composition and densities for media that are not taken account by the TG43-U1 formalism.

A comparative assessment of inhomogeneity and finite patient dimension effects in 60Co and 192Ir high-dose-rate brachytherapy

Purpose

To perform a comparative study of heterogeneities and finite patient dimension effects in ⁶⁰Co and ¹⁹²Ir high-dose-rate (HDR) brachytherapy.

Material and methods

Clinically equivalent plans were prepared for 19 cases (8 breast, 5 esophagus, 6 gynecologic) using the Ir2.A85-2 and the Co0.A86 HDR sources, with a TG-43 based treatment planning system (TPS). Phase space files were obtained for the two source designs using MCNP6, and validated through comparison to a single source dosimetry results in the literature. Dose to water, taking into account the patient specific anatomy and materials (D_w,m), was calculated for all plans using MCNP6, with input files prepared using the BrachyGuide software tool to analyze information from DICOM RT plan exports.

Results

A general TG-43 dose overestimation was observed, except for the lungs, with a greater magnitude for ¹⁹²Ir. The distribution of percentage differences between TG-43 and Monte Carlo (MC) in dose volume histogram (DVH) indices for the planning target volume (PTV) presented small median values (about 2%) for both ⁶⁰Co and ¹⁹²Ir, with a greater dispersion for ¹⁹²Ir. Regarding the organs at risk (OARs), median percentage differences for breast V_50% were 3% (5%) for ⁶⁰Co (¹⁹²Ir). Differences in median skin D_2cc were found comparable, with a larger dispersion for ¹⁹²Ir, and the same applied to the lung D_10cc and the aorta D_2cc. TG-43 overestimates D_2cc for the rectum and the sigmoid, with median differences from MC within 2% and a greater dispersion for ¹⁹²Ir. For the bladder, the median of the difference is greater for ⁶⁰Co (~2%) than for ¹⁹²Ir (~0.75%), demonstrating however a greater dispersion again for ¹⁹²Ir.

Conclusions

The magnitude of differences observed between TG-43 based and MC dosimetry and their smaller dispersion relative to ¹⁹²Ir, suggest that ⁶⁰Co HDR sources are more amenable to the TG-43 assumptions in clinical treatment planning dosimetry.

A multicentre audit of HDR/PDR brachytherapy absolute dosimetry in association with the INTERLACE trial (NCT015662405)

A UK multicentre audit to evaluate HDR and PDR brachytherapy has been performed using alanine absolute dosimetry. This is the first national UK audit performing an absolute dose measurement at a clinically relevant distance (20 mm) from the source. It was performed in both INTERLACE (a phase III multicentre trial in cervical cancer) and non-INTERLACE brachytherapy centres treating gynaecological tumours. Forty-seven UK centres (including the National Physical Laboratory) were visited. A simulated line source was generated within each centre's treatment planning system and dwell times calculated to deliver 10 Gy at 20 mm from the midpoint of the central dwell (representative of Point A of the Manchester system). The line source was delivered in a water-equivalent plastic phantom (Barts Solid Water) encased in blocks of PMMA (polymethyl methacrylate) and charge measured with an ion chamber at 3 positions (120° apart, 20 mm from the source). Absorbed dose was then measured with alanine at the same positions and averaged to reduce source positional uncertainties. Charge was also measured at 50 mm from the source (representative of Point B of the Manchester system). Source types included 46 HDR and PDR ¹⁹²Ir sources, (7 Flexisource, 24 mHDR-v2, 12 GammaMed HDR Plus, 2 GammaMed PDR Plus, 1 VS2000) and 1 HDR ⁶⁰Co source, (Co0.A86). Alanine measurements when compared to the centres' calculated dose showed a mean difference (±SD) of  +1.1% (±1.4%) at 20 mm. Differences were also observed between source types and dose calculation algorithm. Ion chamber measurements demonstrated significant discrepancies between the three holes mainly due to positional variation of the source within the catheter (0.4%-4.9% maximum difference between two holes). This comprehensive audit of absolute dose to water from a simulated line source showed all centres could deliver the prescribed dose to within 5% maximum difference between measurement and calculation.

Direction modulated brachytherapy (DMBT) for treatment of cervical cancer: A planning study with 192 Ir, 60 Co, and 169 Yb HDR sources

PURPOSE

To evaluate plan quality of a novel MRI-compatible direction modulated brachytherapy (DMBT) tandem applicator using ¹⁹² Ir, ⁶⁰ Co, and ¹⁶⁹ Yb HDR brachytherapy sources, for various cervical cancer high-risk clinical target volumes (CTV_HR ).

MATERIALS AND METHODS

The novel DMBT tandem applicator has six peripheral grooves of 1.3-mm diameter along a 5.4-mm thick nonmagnetic tungsten alloy rod. Monte Carlo (MC) simulations were used to benchmark the dosimetric parameters of the ¹⁹² Ir, ⁶⁰ Co, and ¹⁶⁹ Yb HDR sources in a water phantom against the literature data. 45 clinical cases that were treated using conventional tandem-and-ring applicators with ¹⁹² Ir source (¹⁹² Ir-T&R) were selected consecutively from intErnational MRI-guided BRAchytherapy in CErvical cancer (EMBRACE) trial. Then, for each clinical case, 3D dose distribution of each source inside the DMBT and conventional applicators were calculated and imported onto an in-house developed inverse planning optimization code to generate optimal plans. All plans generated by the DMBT tandem-and-ring (DMBT T&R) from all three sources were compared to the respective ¹⁹² Ir-T&R plans. For consistency, all plans were normalized to the same CTV_HR D90 achieved in clinical plans. The D_2 cm3 for organs at risk (OAR) such as bladder, rectum, and sigmoid, and D90, D98, D10, V100, and V200 for CTV_HR were calculated.

RESULTS

In general, plan quality significantly improved when a conventional tandem (Con.T) is replaced with the DMBT tandem. The target coverage metrics were similar across ¹⁹² Ir-T&R and DMBT T&R plans with all three sources (P > 0.093). ⁶⁰ Co-DMBT T&R generated greater hot spots and less dose homogeneity in the target volumes compared with the ¹⁹² Ir- and ¹⁶⁹ Yb-DMBT T&R plans. Mean OAR doses in the DMBT T&R plans were significantly smaller (P < 0.0084) than the ¹⁹² Ir-T&R plans. Mean bladder D_2 cm3 was reduced by 4.07%, 4.15%, and 5.13%, for the ¹⁹² Ir-, ⁶⁰ Co-, and ¹⁶⁹ Yb-DMBT T&R plans respectively. Mean rectum (sigmoid) D_2 cm3 was reduced by 3.17% (3.63%), 2.57% (3.96%), and 4.65% (4.34%) for the ¹⁹² Ir-, ⁶⁰ Co-, and ¹⁶⁹ Yb-DMBT T&R plans respectively. The DMBT T&R plans with the ¹⁶⁹ Yb source generally resulted in the greatest OAR sparing when the CTV_HR were larger and irregular in shape, while for smaller and regularly shaped CTV_HR (<30 cm³ ), OAR sparing between the sources were comparable.

CONCLUSIONS

The DMBT tandem provides a promising alternative to the Con.T design with significant improvement in the plan quality for various target volumes. The DMBT T&R plans generated with the three sources of varying energies generated superior plans compared to the conventional T&R applicators. Plans generated with the ¹⁶⁹ Yb-DMBT T&R produced best results for larger and irregularly shaped CTV_HR in terms of OAR sparing. Thus, this study suggests that the combination of the DMBT tandem applicator with varying energy sources can work synergistically to generate improved plans for cervical cancer brachytherapy.

Monte Carlo Calculation of Beam Quality and Phantom Scatter Corrections for Lithium Formate Electron Paramagnetic Resonance Dosimeter for High-energy Brachytherapy Dosimetry

Purpose:

To investigate beam quality correction, K_QQ0 (r) and phantom scatter correction, K_phan (r) for lithium formate dosimeter as a function of distance r along the transverse axis of the high-energy brachytherapy sources ⁶⁰Co, ¹³⁷Cs, ¹⁹²Ir and ¹⁶⁹Yb using the Monte Carlo-based EGSnrc code system.

Materials and Methods:

The brachytherapy sources investigated in this study are BEBIG High Dose Rate (HDR) ⁶⁰Co (model Co0.A86), ¹³⁷Cs (model RTR), HDR ¹⁹²Ir (model Microselectron) and HDR ¹⁶⁹Yb (model 4140). The solid phantom materials investigated are PMMA, polystyrene, solid water, virtual water, plastic water, RW1, RW3, A150 and WE210.

Result:

K_QQ0 (r) is about unity and distance independent fo ⁶⁰Co, ¹³⁷Cs and ¹⁹²Ir brachytherapy sources, whereas for the ¹⁶⁹Yb source, K_QQ0 (r) increases gradually to about 4 % larger than unity at a distance of 15 cm along the transverse axis of the source. For ⁶⁰Co source, phantoms such as polystyrene, plastic water, solid water, virtual water, RW1, RW3 and WE210 are water-equivalent but PMMA and A150 phantoms show distance-dependent K_phan (r) values. For ¹³⁷Cs and ¹⁹²Ir sources, phantoms such as solid water, virtual water, RW1, RW3 and WE210 are water-equivalent. However, phantoms such as PMMA, plastic water, polystyrene and A150 showed distance-dependent K_phan (r) values, for these sources. For ¹⁶⁹Yb source, all the investigated phantoms show distance-dependent K_phan (r) values.

Conclusion:

K_QQ0 (r) is about unity and distance independent for ⁶⁰Co, ¹³⁷Cs and ¹⁹²Ir brachytherapy sources. Phantoms such as solid water, virtual water, RW1, RW3 and WE210 are water-equivalent for ⁶⁰Co, ¹³⁷Cs and ¹⁹²Ir brachytherapy sources. For ¹⁶⁹Yb source, all the investigated phantoms show distance-dependent K_phan (r) values.

Monte Carlo dosimetric characterization of the Flexisource Co-60 high-dose-rate brachytherapy source using PENELOPE

PURPOSE

⁶⁰Co sources have been commercialized as an alternative to ¹⁹²Ir sources for high-dose-rate (HDR) brachytherapy. One of them is the Flexisource Co-60 HDR source manufactured by Elekta. The only available dosimetric characterization of this source is that of Vijande et al. [J Contemp Brachytherapy 2012; 4:34-44], whose results were not included in the AAPM/ESTRO consensus document. In that work, the dosimetric quantities were calculated as averages of the results obtained with the Geant4 and PENELOPE Monte Carlo (MC) codes, though for other sources, significant differences have been quoted between the values obtained with these two codes. The aim of this work is to perform the dosimetric characterization of the Flexisource Co-60 HDR source using PENELOPE.

METHODS AND MATERIALS

The MC simulation code PENELOPE (v. 2014) has been used. Following the recommendations of the AAPM/ESTRO report, the radial dose function, the anisotropy function, the air-kerma strength, the dose rate constant, and the absorbed dose rate in water have been calculated.

RESULTS

The results we have obtained exceed those of Vijande et al. In particular, the absorbed dose rate constant is ∼0.85% larger. A similar difference is also found in the other dosimetric quantities. The effect of the electrons emitted in the decay of ⁶⁰Co, usually neglected in this kind of simulations, is significant up to the distances of 0.25 cm from the source.

CONCLUSIONS

The systematic and significant differences we have found between PENELOPE results and the average values found by Vijande et al. point out that the dosimetric characterizations carried out with the various MC codes should be provided independently.

Guidelines by the AAPM and GEC-ESTRO on the use of innovative brachytherapy devices and applications: Report of Task Group 167

Although a multicenter, Phase III, prospective, randomized trial is the gold standard for evidence-based medicine, it is rarely used in the evaluation of innovative devices because of many practical and ethical reasons. It is usually sufficient to compare the dose distributions and dose rates for determining the equivalence of the innovative treatment modality to an existing one. Thus, quantitative evaluation of the dosimetric characteristics of innovative radiotherapy devices or applications is a critical part in which physicists should be actively involved. The physicist's role, along with physician colleagues, in this process is highlighted for innovative brachytherapy devices and applications and includes evaluation of (1) dosimetric considerations for clinical implementation (including calibrations, dose calculations, and radiobiological aspects) to comply with existing societal dosimetric prerequisites for sources in routine clinical use, (2) risks and benefits from a regulatory and safety perspective, and (3) resource assessment and preparedness. Further, it is suggested that any developed calibration methods be traceable to a primary standards dosimetry laboratory (PSDL) such as the National Institute of Standards and Technology in the U.S. or to other PSDLs located elsewhere such as in Europe. Clinical users should follow standards as approved by their country's regulatory agencies that approved such a brachytherapy device. Integration of this system into the medical source calibration infrastructure of secondary standard dosimetry laboratories such as the Accredited Dosimetry Calibration Laboratories in the U.S. is encouraged before a source is introduced into widespread routine clinical use. The American Association of Physicists in Medicine and the Groupe Européen de Curiethérapie-European Society for Radiotherapy and Oncology (GEC-ESTRO) have developed guidelines for the safe and consistent application of brachytherapy using innovative devices and applications. The current report covers regulatory approvals, calibration, dose calculations, radiobiological issues, and overall safety concerns that should be addressed during the commissioning stage preceding clinical use. These guidelines are based on review of requirements of the U.S. Nuclear Regulatory Commission, U.S. Department of Transportation, International Electrotechnical Commission Medical Electrical Equipment Standard 60601, U.S. Food and Drug Administration, European Commission for CE Marking (Conformité Européenne), and institutional review boards and radiation safety committees.

Study of the dosimetric differences between (192)Ir and (60)Co sources of high dose rate brachytherapy for breast interstitial implant

AIM

The study intends to compare (192)Ir source against the (60)Co source for interstitial breast metal implant in high dose rate brachytherapy.

BACKGROUND

Few studies have been reported to compare (60)Co and (192)Ir on HDR brachytherapy in gynaecology and prostate cancer and very few with reference to breast cancer.

MATERIALS AND METHODS

Twenty patients who had undergone interstitial template guided breast implant were treated in HDR (192)Ir brachytherapy unit. Plans were generated substituting (60)Co source without changing the dwell positions and optimization. Cumulative dose volume histograms were compared.

RESULTS

The reference isodose line enclosing CTV (CTVref) and the 2.34% difference seen in the volume enclosed by the reference isodose line (V ref) between the two isotopes show small but statistically significant difference (p < 0.05). In DHI, no difference was observed in the relative dose between the two sources (p = 0.823). The over dose volume index showed 11% difference. The conformity index showed 2.32% difference compared to (192)Ir (p < 0.05). D mean (%) and D max (%) for the heart, ipsilateral lung, ipsilateral ribs, skin presented very small difference. V 5% and V 10% of the heart shows 25% and 32% difference in dose. D 2cc (%) and D 0.1cc (%) for the contralateral breast, contralateral lung and D 2cc (%) of the skin displayed significant difference (p < 0.05). However, D 0.1cc (%) of the skin indicated no noteworthy difference with p = 0.343.

CONCLUSION

Based on the 3D dosimetric analysis of patient plans considered in this study, most of the DVH parameters showed statistically significant differences which can be reduced by treatment planning optimization techniques. (60)Co isotope can be used as a viable alternative because of its long half-life, logistic advantages in procurement, infrequent need of source replacement and disposal of used source.

A generic high-dose rate (192)Ir brachytherapy source for evaluation of model-based dose calculations beyond the TG-43 formalism

PURPOSE

In order to facilitate a smooth transition for brachytherapy dose calculations from the American Association of Physicists in Medicine (AAPM) Task Group No. 43 (TG-43) formalism to model-based dose calculation algorithms (MBDCAs), treatment planning systems (TPSs) using a MBDCA require a set of well-defined test case plans characterized by Monte Carlo (MC) methods. This also permits direct dose comparison to TG-43 reference data. Such test case plans should be made available for use in the software commissioning process performed by clinical end users. To this end, a hypothetical, generic high-dose rate (HDR) (192)Ir source and a virtual water phantom were designed, which can be imported into a TPS.

METHODS

A hypothetical, generic HDR (192)Ir source was designed based on commercially available sources as well as a virtual, cubic water phantom that can be imported into any TPS in DICOM format. The dose distribution of the generic (192)Ir source when placed at the center of the cubic phantom, and away from the center under altered scatter conditions, was evaluated using two commercial MBDCAs [Oncentra(®) Brachy with advanced collapsed-cone engine (ACE) and BrachyVision ACUROS™ ]. Dose comparisons were performed using state-of-the-art MC codes for radiation transport, including ALGEBRA, BrachyDose, GEANT4, MCNP5, MCNP6, and PENELOPE2008. The methodologies adhered to recommendations in the AAPM TG-229 report on high-energy brachytherapy source dosimetry. TG-43 dosimetry parameters, an along-away dose-rate table, and primary and scatter separated (PSS) data were obtained. The virtual water phantom of (201)(3) voxels (1 mm sides) was used to evaluate the calculated dose distributions. Two test case plans involving a single position of the generic HDR (192)Ir source in this phantom were prepared: (i) source centered in the phantom and (ii) source displaced 7 cm laterally from the center. Datasets were independently produced by different investigators. MC results were then compared against dose calculated using TG-43 and MBDCA methods.

RESULTS

TG-43 and PSS datasets were generated for the generic source, the PSS data for use with the ace algorithm. The dose-rate constant values obtained from seven MC simulations, performed independently using different codes, were in excellent agreement, yielding an average of 1.1109 ± 0.0004 cGy/(h U) (k = 1, Type A uncertainty). MC calculated dose-rate distributions for the two plans were also found to be in excellent agreement, with differences within type A uncertainties. Differences between commercial MBDCA and MC results were test, position, and calculation parameter dependent. On average, however, these differences were within 1% for ACUROS and 2% for ace at clinically relevant distances.

CONCLUSIONS

A hypothetical, generic HDR (192)Ir source was designed and implemented in two commercially available TPSs employing different MBDCAs. Reference dose distributions for this source were benchmarked and used for the evaluation of MBDCA calculations employing a virtual, cubic water phantom in the form of a CT DICOM image series. The implementation of a generic source of identical design in all TPSs using MBDCAs is an important step toward supporting univocal commissioning procedures and direct comparisons between TPSs.

Dosimetric comparison of brachytherapy sources for high-dose-rate treatment of endometrial cancer: (192)Ir, (60)Co and an electronic brachytherapy source

OBJECTIVE

To compare high-dose-rate (HDR) brachytherapy systems with (192)Ir, (60)Co and electronic brachytherapy source (EBS) for treatment of endometrial cancers.

METHODS

Two additional plans were generated per patient fraction using a (60)Co source and Xoft-EBS on 10 selected patients, previously treated with a vaginal cylinder applicator using a (192)Ir source. Dose coverage of "PTV_CYLD", a 5-mm shell surrounding the cylinder, was evaluated. Doses to the following organs at risk (OARs) the rectum, bladder and sigmoid were evaluated in terms of V35% and V50%, the percentage volume receiving 35% and 50% of the prescription dose, respectively, and D2cm(3), the highest dose to a 2-cm(3) volume of an OAR.

RESULTS

Xoft-EBS reduces doses to all OARs in the lower dose range, but it does not always provide better sparing of the rectum in higher dose range as does evaluation using D2cm3. V150% and V200% for PTV_CYLD was up to four times greater for Xoft-EBS plans than for plans generated with (192)Ir or (60)Co. Surface mucosal (vaginal cylinder surface) doses were also 23% higher for Xoft-EBS than for (192)Ir or (60)Co plans.

CONCLUSION

Xoft-EBS is a suitable HDR source for vaginal applicator treatment with advantages of reducing radiation exposure to OARs in the lower dose range, while simultaneously increasing the vaginal mucosal dose.

ADVANCES IN KNOWLEDGE

This work presents newer knowledge in dosimetric comparison between (192)Ir or (60)Co and Xoft-EBS sources for endometrial vaginal cylinder HDR planning.

Evaluation of BEBIG HDR (60)Co system for non-invasive image-guided breast brachytherapy

Purpose

HDR ⁶⁰Co system has recently been developed and utilized for brachytherapy in many countries outside of the U.S. as an alternative to ¹⁹²Ir. In addition, the AccuBoost^® technique has been demonstrated to be a successful non-invasive image-guided breast brachytherapy treatment option. The goal of this project is to evaluate the possibility of utilizing the BEBIG HDR ⁶⁰Co system for AccuBoost treatment. These evaluations are performed with Monte Carlo (MC) simulation technique.

Material and methods

In this project, the MC calculated dose distributions from HDR ⁶⁰Co for various breast sizes have been compared with the simulated data using an HDR ¹⁹²Ir source. These calculations were performed using the MCNP5 code. The initial calculations were made with the same applicator dimensions as the ones used with the HDR ¹⁹²Ir system (referred here after as standard applicator). The activity of the ⁶⁰Co source was selected such that the dose at the center of the breast would be the same as the values from the ¹⁹²Ir source. Then, the applicator wall-thickness for the HDR ⁶⁰Co system was increased to diminish skin dose to levels received when using the HDR ¹⁹²Ir system. With this geometry, dose values to the chest wall and the skin were evaluated. Finally, the impact of a conical attenuator with the modified applicator for the HDR ⁶⁰Co system was analyzed.

Results

These investigations demonstrated that loading the ⁶⁰Co sources inside the thick-walled applicators created similar dose distributions to those of the ¹⁹²Ir source in the standard applicators. However, dose to the chest wall and breast skin with ⁶⁰Co source was reduced using the thick-walled applicators relative to the standard applicators. The applicators with conical attenuator reduced the skin dose for both source types.

Conclusions

The AccuBoost treatment can be performed with the ⁶⁰Co source and thick-wall applicators instead of ¹⁹²Ir with standard applicators.

Monte Carlo Dosimetry of the 60Co BEBIG High Dose Rate for Brachytherapy

INTRODUCTION

The use of high-dose-rate brachytherapy is currently a widespread practice worldwide. The most common isotope source is 192Ir, but 60Co is also becoming available for HDR. One of main advantages of 60Co compared to 192Ir is the economic and practical benefit because of its longer half-live, which is 5.27 years. Recently, Eckert & Ziegler BEBIG, Germany, introduced a new afterloading brachytherapy machine (MultiSource®); it has the option to use either the 60Co or 192Ir HDR source. The source for the Monte Carlo calculations is the new 60Co source (model Co0.A86), which is referred to as the new BEBIG 60Co HDR source and is a modified version of the 60Co source (model GK60M21), which is also from BEBIG.

OBJECTIVE AND METHODS

The purpose of this work is to obtain the dosimetry parameters in accordance with the AAPM TG-43U1 formalism with Monte Carlo calculations regarding the BEBIG 60Co high-dose-rate brachytherapy to investigate the required treatment-planning parameters. The geometric design and material details of the source was provided by the manufacturer and was used to define the Monte Carlo geometry. To validate the source geometry, a few dosimetry parameters had to be calculated according to the AAPM TG-43U1 formalism. The dosimetry studies included the calculation of the air kerma strength Sk, collision kerma in water along the transverse axis with an unbounded phantom, dose rate constant and radial dose function. The Monte Carlo code system that was used was EGSnrc with a new cavity code, which is a part of EGS++ that allows calculating the radial dose function around the source. The spectrum to simulate 60Co was composed of two photon energies, 1.17 and 1.33 MeV. Only the gamma part of the spectrum was used; the contribution of the electrons to the dose is negligible because of the full absorption by the stainless-steel wall around the metallic 60Co. The XCOM photon cross-section library was used in subsequent simulations, and the photoelectric effect, pair production, Rayleigh scattering and bound Compton scattering were included in the simulation. Variance reduction techniques were used to speed up the calculation and to considerably reduce the computer time. The cut-off energy was 10 keV for electrons and photons. To obtain the dose rate distributions of the source in an unbounded liquid water phantom, the source was immersed at the center of a cube phantom of 100 cm3. The liquid water density was 0.998 g/cm3, and photon histories of up to 1010 were used to obtain the results with a standard deviation of less than 0.5% (k = 1). The obtained dose rate constant for the BEBIG 60Co source was 1.108±0.001 cGyh-1U-1, which is consistent with the values in the literature. The radial dose functions were compared with the values of the consensus data set in the literature, and they are consistent with the published data for this energy range.

A radiation quality correction factor k for well-type ionization chambers for the measurement of the reference air kerma rate of (60)Co HDR brachytherapy sources

PURPOSE

The aim of this study was to investigate whether a chamber-type-specific radiation quality correction factor kQ can be determined in order to measure the reference air kerma rate of (60)Co high-dose-rate (HDR) brachytherapy sources with acceptable uncertainty by means of a well-type ionization chamber calibrated for (192)Ir HDR sources.

METHODS

The calibration coefficients of 35 well-type ionization chambers of two different chamber types for radiation fields of (60)Co and (192)Ir HDR brachytherapy sources were determined experimentally. A radiation quality correction factor kQ was determined as the ratio of the calibration coefficients for (60)Co and (192)Ir. The dependence on chamber-to-chamber variations, source-to-source variations, and source strength was investigated.

RESULTS

For the PTW Tx33004 (Nucletron source dosimetry system (SDS)) well-type chamber, the type-specific radiation quality correction factor kQ is 1.19. Note that this value is valid for chambers with the serial number, SN ≥ 315 (Nucletron SDS SN ≥ 548) onward only. For the Standard Imaging HDR 1000 Plus well-type chambers, the type-specific correction factor kQ is 1.05. Both kQ values are independent of the source strengths in the complete clinically relevant range. The relative expanded uncertainty (k = 2) of kQ is UkQ = 2.1% for both chamber types.

CONCLUSIONS

The calibration coefficient of a well-type chamber for radiation fields of (60)Co HDR brachytherapy sources can be calculated from a given calibration coefficient for (192)Ir radiation by using a chamber-type-specific radiation quality correction factor kQ. However, the uncertainty of a (60)Co calibration coefficient calculated via kQ is at least twice as large as that for a direct calibration with a (60)Co source.

Comparison of Axxent-Xoft, (192)Ir and (60)Co high-dose-rate brachytherapy sources for image-guided brachytherapy treatment planning for cervical cancer

OBJECTIVE

To evaluate the dosimetric differences and similarities between treatment plans generated with Axxent-Xoft electronic brachytherapy source (Xoft-EBS), (192)Ir and (60)Co for tandem and ovoids (T&O) applicators.

METHODS

In this retrospective study, we replanned 10 patients previously treated with (192)Ir high-dose-rate brachytherapy. Prescription was 7 Gy × 4 fractions to Point A. For each original plan, we created two additional plans with Xoft-EBS and (60)Co. The dose to each organ at risk (OAR) was evaluated in terms of V(35%) and V(50%), the percentage volume receiving 35% and 50% of the prescription dose, respectively, and D(2cc), highest dose to a 2 cm(3) volume of an OAR.

RESULTS

There was no difference between plans generated by (192)Ir and (60)Co, but the plans generated using Xoft-EBS showed a reduction of up to 50% in V(35%), V(50%) and D(2cc). The volumes of the 200% and 150% isodose lines, however, were 74% and 34% greater than the comparable volumes generated with the (192)Ir source. Point B dose was on average only 16% of the Point A dose for plans generated with Xoft-EBS compared with 30% for plans generated with (192)Ir or (60)Co.

CONCLUSION

The Xoft-EBS can potentially replace either (192)Ir or (60)Co in T&O treatments. Xoft-EBS offers either better sparing of the OARs compared with (192)Ir or (60)Co or at least similar sparing. Xoft-EBS-generated plans had higher doses within the target volume than (192)Ir- or (60)Co-generated ones.

ADVANCES IN KNOWLEDGE

This work presents newer knowledge in dosimetric comparison between Xoft-EBS, (192)Ir or (60)Co sources for T&O implants.

Phantom scatter corrections of radiochromic films in high-energy brachytherapy dosimetry: a Monte Carlo study

Our aim in this study was to calculate Monte Carlo-based phantom scatter corrections of various radiochromic films for different solid phantoms for high-energy brachytherapy sources. Brachytherapy sources (60)Co, (137)Cs, (192)Ir, and (169)Yb and radiochromic films EBT, EBT2 (lot 020609 and lot 031109), RTQA, XRT, XRQA, and HS were investigated in this study. The solid phantom materials investigated were PMMA (polymethylmethacrylate), polystyrene, solid water, virtual water, plastic water, RW1, RW3, A150, and WE210. Monte Carlo-based user codes DOSRZnrc and FLURZnrc of the EGSnrc code system were employed in the present work. For the (60)Co source, the polystyrene, plastic water, solid water, virtual water, RW1, RW3, and WE210 phantoms were water equivalent for the investigated films, but showed distance-dependent values for XRT and XRQA films. For the (137)Cs and (192)Ir sources, the solid water, virtual water, RW1, RW3, and WE210 phantoms were water equivalent for the investigated films, but showed distance-dependent values for XRT and XRQA films. For these sources, the remaining phantoms showed distance-dependent values for all of the films investigated. For the (169)Yb source, all of the investigated phantoms showed distance-dependent values for the investigated films. This study suggests that radiochromic films demonstrate distance-dependent values, but the degree of dependence is related to the types of solid phantom and film. Hence, for brachytherapy dosimetry involving radiochromic films and solid phantom materials, phantom scatter corrections need to be applied.

Monte Carlo-based beam quality and phantom scatter corrections for solid-state detectors in 60Co and 192Ir brachytherapy dosimetry

Beam quality correction, kQQ0(r), for solid‐state detectors diamond, LiF, Li2B4O7,Al2O3, and plastic scintillator are calculated as a function of distance, r, along the transverse axis of the 60Co and 192Ir brachytherapy sources using the Monte Carlo‐based EGSnrc code system. This study also includes calculation of detector‐specific phantom scatter correction, kphan(r), for solid phantoms such as PMMA, polystyrene, solid water, virtual water, plastic water, RW1, RW3, A150, and WE210. For 60Co source, kQQ0(r) is about unity and distance‐independent for diamond, plastic scintillator, Li2B4O7 and LiF detectors. For this source, kQQ0(r) decreases gradually with r for Al2O3 detector (about 6% smaller than unity at 15 cm). For 192Ir source, kQQ0(r) is about unity and distance‐independent for Li2B4O7 detector (overall variation is about 1% in the distance range of 1–15 cm). For this source, kQQ0(r) increases with r for diamond and plastic scintillator (about 6% and 8% larger than unity at 15 cm, respectively). Whereas kQQ0(r) decreases with r gradually for LiF (about 4% smaller than unity at 15 cm) and steeply for Al2O3 (about 25% smaller than unity at 15 cm). For 60Co source, solid water, virtual water, RW1, RW3, and WE210 phantoms are water‐equivalent for all the investigated solid‐state detectors. Whereas polystyrene and plastic water phantoms are water‐equivalent for diamond, plastic scintillator, Li2B4O7 and LiF detectors, but show distance‐dependent kphan(r) values for Al2O3 detector. PMMA phantom is water‐equivalent at all distances for Al2O3 detector, but shows distance‐dependent kphan(r) values for remaining detectors. A150 phantom shows distance‐dependent kphan(r) values for all the investigated detector materials. For 192Ir source, solid water, virtual water, RW3, and WE210 phantoms are water‐equivalent for diamond, plastic scintillator, Li2B4O7 and LiF detectors, but show distance‐dependent kphan(r) values for Al2O3 detector. All other phantoms show distance‐dependent kphan(r) values for all the detector materials.

PACS numbers: 87.10.Rt, 87.53.Bn, 87.53.Jw

Limitations of the TG-43 formalism for skin high-dose-rate brachytherapy dose calculations

PURPOSE

In skin high-dose-rate (HDR) brachytherapy, sources are located outside, in contact with, or implanted at some depth below the skin surface. Most treatment planning systems use the TG-43 formalism, which is based on single-source dose superposition within an infinite water medium without accounting for the true geometry in which conditions for scattered radiation are altered by the presence of air. The purpose of this study is to evaluate the dosimetric limitations of the TG-43 formalism in HDR skin brachytherapy and the potential clinical impact.

METHODS

Dose rate distributions of typical configurations used in skin brachytherapy were obtained: a 5 cm × 5 cm superficial mould; a source inside a catheter located at the skin surface with and without backscatter bolus; and a typical interstitial implant consisting of an HDR source in a catheter located at a depth of 0.5 cm. Commercially available HDR(60)Co and (192)Ir sources and a hypothetical (169)Yb source were considered. The Geant4 Monte Carlo radiation transport code was used to estimate dose rate distributions for the configurations considered. These results were then compared to those obtained with the TG-43 dose calculation formalism. In particular, the influence of adding bolus material over the implant was studied.

RESULTS

For a 5 cm × 5 cm(192)Ir superficial mould and 0.5 cm prescription depth, dose differences in comparison to the TG-43 method were about -3%. When the source was positioned at the skin surface, dose differences were smaller than -1% for (60)Co and (192)Ir, yet -3% for (169)Yb. For the interstitial implant, dose differences at the skin surface were -7% for (60)Co, -0.6% for (192)Ir, and -2.5% for (169)Yb.

CONCLUSIONS

This study indicates the following: (i) for the superficial mould, no bolus is needed; (ii) when the source is in contact with the skin surface, no bolus is needed for either (60)Co and (192)Ir. For lower energy radionuclides like (169)Yb, bolus may be needed; and (iii) for the interstitial case, at least a 0.1 cm bolus is advised for (60)Co to avoid underdosing superficial target layers. For (192)Ir and (169)Yb, no bolus is needed. For those cases where no bolus is needed, its use might be detrimental as the lack of radiation scatter may be beneficial to the patient, although the 2% tolerance for dose calculation accuracy recommended in the AAPM TG-56 report is not fulfilled.

Dosimetric perturbations of a lead shield for surface and interstitial high-dose-rate brachytherapy

In surface and interstitial high-dose-rate brachytherapy with either (60)Co, (192)Ir, or (169)Yb sources, some radiosensitive organs near the surface may be exposed to high absorbed doses. This may be reduced by covering the implants with a lead shield on the body surface, which results in dosimetric perturbations. Monte Carlo simulations in Geant4 were performed for the three radionuclides placed at a single dwell position. Four different shield thicknesses (0, 3, 6, and 10 mm) and three different source depths (0, 5, and 10 mm) in water were considered, with the lead shield placed at the phantom surface. Backscatter dose enhancement and transmission data were obtained for the lead shields. Results were corrected to account for a realistic clinical case with multiple dwell positions. The range of the high backscatter dose enhancement in water is 3 mm for (60)Co and 1 mm for both (192)Ir and (169)Yb. Transmission data for (60)Co and (192)Ir are smaller than those reported by Papagiannis et al (2008 Med. Phys. 35 4898-4906) for brachytherapy facility shielding; for (169)Yb, the difference is negligible. In conclusion, the backscatter overdose produced by the lead shield can be avoided by just adding a few millimetres of bolus. Transmission data provided in this work as a function of lead thickness can be used to estimate healthy organ equivalent dose saving. Use of a lead shield is justified.

Monte Carlo-based investigation of absorbed-dose energy dependence of radiochromic films in high energy brachytherapy dosimetry

Relative absorbed dose energy response correction, R, for various radiochromic films in water phantom is calculated by the use of the Monte Carlo‐based EGSnrc code system for high energy brachytherapy sources 60Co, 137Cs, 192Ir and 169Yb. The corrections are calculated along the transverse axis of the sources (1‐15 cm). The radiochromic films investigated are EBT, EBT2 (lot 020609 and lot 031109), RTQA, XRT, XRQA, and HS. For the 60Co source, the value of R is about unity and is independent of distance in the water phantom for films other than XRT and XRQA. The XRT and XRQA films showed distance‐dependent R values for this source (the values of R at 15 cm from the source in water are 1.845 and 2.495 for the films XRT and XRQA, respectively). In the case of 137Cs and 192Ir sources, XRT, XRQA, EBT2 (lot 031109), and HS films showed distant‐dependent R values. The rest of the films showed no energy dependence (HS film showed R values less than unity by about 5%, whereas the other films showed R values higher than unity). In the case of 169Yb source, the EBT film showed no energy dependence and EBT2 film (lot 031109) showed a distance‐independent R value of 1.041. The rest of the films showed distance‐dependent R values (increases with distance for the films other than HS). The solid phantoms PMMA and polystyrene enhance the R values for some films when compared the same in the water phantom.

PACS number: 87.53.Jw

Using mean dose rate to compare relative dosimetric efficiency with respect to source type and source change schedules for HDR brachytherapy

Remote afterloading devices used for high‐dose‐rate (HDR) brachytherapy may be supplied with different sources, and these sources typically have differing initial source strengths. In addition, the proposed frequency for source changes may also vary, depending upon the source type. Dosimetric parameters unique to each source are often used to compare source types. However, when considering the relative dosimetric efficiency between two HDR sources, the combined effect of source type, initial source strength, and source change scheme must be considered. A method of quantifying this combined effect by calculating mean dose rate from specific dosimetric source data is discussed. This method suggests an objective manner of comparing source scheme equivalency to facilitate performing a cost ratio analysis between different HDR sources and source change schemes.

PACS numbers: 87.53.Jw, 87.56.bg

EGSnrc Monte Carlo-aided dosimetric studies of the new BEBIG (60)Co HDR brachytherapy source

PURPOSE

The purpose of this study is to obtain the dosimetric parameters of the new BEBIG (60)Co brachytherapy source following by TG-43U1 recommendation with appropriate electron cutoff energy (0.521 MeV).

MATERIAL AND METHODS

The new BEBIG (60)Co brachytherapy source is used to calculate the TG-43U1 parameters. EGSnrc-based Monte Carlo simulation code has been used to calculate the radial dose functions and anisotropy functions. 2D dose rate table is obtained with Cartesian coordinate system for surrounding the source.

RESULTS

The radial dose functions are calculated for the distance of 0.06 cm to 100 cm from the source center with different cutoff energies and compared. The anisotropy functions values are calculated with the range of 1° to 179°, and apart from 0.2 cm to 20 cm of radial distances. The along-away dose rate data are calculated for quality assurance purposes. The calculated values are compared with the consensus data set and previous published results.

CONCLUSIONS

The radial dose function values from 0.06 cm to 0.16 cm are low, and these values gradually increased up to 0.3 cm radial distance. The radial dose function values are compared with the values of consensus data set using EGSnrc code system, and it is in good agreement with the published data range. The data for < 0.1 cm is not available in consensus data set, and extrapolated value is included for 0 distances which is the same as the value of 0.1 cm. In this study, the obtained values are strictly fall-off to < 0.1 cm distances. Good agreement with the published data was observed, except the values less than 40° angle at 0.5 cm distance for anisotropy function values.