Assessment of skin dose in breast cancer radiotherapy: on-phantom measurement and Monte Carlo simulation.

AIM: The main purpose of the present study is assessment of skin dose in breast cancer radiotherapy. BACKGROUND: Accurate assessment of skin dose in radiotherapy can provide useful information for clinical considerations. MATERIALS AND METHODS: A RANDO phantom was irradiated using a 6 MV Siemens Primus linac with medial and tangential radiotherapy fields for simulating breast cancer treatment. Dosimetry was also performed on various positions across the fields using an EBT3 radiochromic film. Similar conditions of measurement on the RANDO phantom including field size, irradiation angle, number of fields, etc. were subsequently simulated via the Monte Carlo N-Particle Transport code (MCNP). Ultimately, dose values for corresponding points from both methods were compared. RESULTS: Considering dosimetry using radiochromic films on the RANDO phantom, there were points having underdose and overdose based on the prescribed dose and skin tolerance levels. In this respect, 81.25% and 18.75% of the points had underdose and overdose, respectively. In some cases, several differences were observed between the measurement and the MCNP simulation results associated with skin dose. CONCLUSION: Based on the results of the points which had underdose, it was suggested that a bolus should be used for the given points. With regard to overdose points, it was advocated to consider skin tolerance dose in treatment planning. Differences between the measurement and the MCNP simulation results might be due to voxel size of tally cells in simulations, effect of beam's angle of incidence, validation time of linac's head, lack of electronic equilibrium in the build-up region, as well as MCNP tally type.

Dosimetric investigation of a new high dose rate 192Ir brachytherapy source, IRAsource, by Monte Carlo method.

PURPOSE: The purpose of the present study was to perform an independent calculation of dosimetric parameters associated with a new 192Ir brachytherapy source model, IRAsource. MATERIALS AND METHODS: The parameters of air kerma strength (AKS), dose rate constant (DRC), geometry function (GF), radial dose function (RDF), as well as two-dimensional (2D) anisotropy function (AF) of IRAsource 192Ir source model were calculated in this study. The MC n-particle extended (MCNPX) code was also employed for simulating high dose rate (HDR), IRAsource and 192Ir source; and formalism was used for calculating dosimetry parameters based on task group number 43 updated report (TG-43 U1). RESULTS: The results of this study were consistent with the ones reported about the IRAsource source by Sarabiasl et al. The AKS per 1 mCi activity and the DRC values were also equal to 3.65 cGycm2 h-1 mCi-1 and 1.094 cGyh-1U-1; respectively. The comparison of the results of the DRC and the RDF reported by Sarabiasl et al. also validated the 192Ir IRAsource simulation in this study. Moreover, the AFs of IRAsource source model were in a good agreement with those of Sarabiasl et al. at different distances, which could be attributed to identical geometries. CONCLUSION: In line with those reported by Sarabiasl et al., the results of this study confirmed the IRAsource 192Ir source for clinical uses. The calculated dosimetric parameters of the IRAsource source could be utilized in clinical practices as input data sets or for validation of treatment planning system calculations.

A Monte Carlo evaluation of dose distribution of commercial treatment planning systems in heterogeneous media.

INTRODUCTION: Calculations from a treatment planning system (TPS) in heterogeneous regions may present significant inaccuracies due to loss of electronic equilibrium. The purpose of this study is to evaluate and quantify the differences of dose distributions computed by some of the newest dose calculation algorithms, including collapsed cone convolution (CCC), fast Fourier transform (FFT) convolution, and superposition convolution, in heterogeneity of the lung. MATERIALS AND METHODS: A 6-MV Siemens Primus linear accelerator was simulated by MCNPX Monte Carlo (MC) code, and the results of percentage depth dose (PDD) and dose profile values were compared with measured data. The ISOgray TPS was used and PDDs of CCC, FFT, and superposition convolution algorithms were compared with the results obtained by MCNPX code. CT2MCNP software was used to convert the computed tomography images of the lung tissue to MC input files, and dose distributions from the three algorithms were compared to MC method. RESULTS: For PDD curves in buildup region, the maximum underdosage of ISOgray TPS was at the surface (19%) and comes in closer agreement when depth increases (average 7.08%). Dose differences (DD) between different algorithms and MC were typically 4.81% (range: 1.95% to 7.30%), -1.55% (range: -5.14% to 5.26%) and 4.96% (range: 2.00% to 7.4%) in the lung for the CCC, FFT, and superposition algorithms, respectively. The difference between monitor units and maximum dose calculated using the three algorithms were 0.5% and 1.61%, respectively. The maximum DD of 7% was observed between MC and TPS results. CONCLUSION: Significant differences were found when the calculation algorithms were compared with MC method in lung tissue, and this difference is not negligible. It is recommended to use of MC-based TPS for the treatment fields including lung tissue.

Effect of computed tomography number-relative electron density conversion curve on the calculation of radiotherapy dose and evaluation of Monaco radiotherapy treatment planning system.

The accuracy of a computed tomography (CT)-relative electron density (RED) curve may have an indirect impact on the accuracy of dose calculation by a treatment planning system (TPS). This effect has not been previously quantified for input of different CT-RED curves from different CT-scan units in the Monaco TPS. This study aims to evaluate the effect of CT-RED curve on the dose calculation by the Monaco radiotherapy TPS. Four CT images of the CIRS phantom were obtained by different CT scanners. The accuracy of the dose calculation in the three algorithms of the Monaco TPS (Monte Carlo, collapse cone, and pencil beam) is also evaluated based on TECDOC 1583. The CT-RED curves from the CT scanners were transferred to the Monaco TPS to audit the different algorithms of the TPS. The dose values were measured with an ionization chamber in the CIRS phantom. Then, the dose values were calculated by the Monaco algorithms in the corresponding points. For the Monaco TPS and based on TECDOC 1583, the accuracy of the dose calculation in all the three algorithms is within the agreement criteria for most of the points evaluated. For low dose regions, the differences between the calculated and measured dose values are higher than the agreement criteria in a number of points. For the majority of the points, the algorithms underestimate the calculated dose values. It was also found that the use of different CT-RED curves can lead to minor discrepancies in the dose calculation by the Monaco TPS, especially in low dose regions. However, it appears that these differences are not clinically significant in most of the cases.

Effect of Beta Particles Spectrum on Absorbed Fraction in Internal Radiotherapy.

OBJECTIVES: The purpose of this research is to study the effect of beta spectrum on absorbed fraction (ϕ) and to find suitable analytical functions for beta spectrum absorbed fractions in spherical and ellipsoidal volumes with a uniform distribution for several radionuclides that are commonly used in nuclear medicine. METHODS: In order to obtain the beta particle absorbed fraction, Monte Carlo simulations were performed by using the MCNPX code. The validation of the simulations was performed by calculating the absorbed fractions in spheres and comparing the results with the data published by other investigators. The absorbed fractions were calculated and compared by using an actual beta energy spectrum with those obtained through the mean beta energy of 14C, 199Au, 177Lu, 131I, 90Sr, 153Sm, 186Re, 32P, 90Y, 38Cl and 88Rb radionuclides. RESULTS: The maximum difference between the absorbed fractions for beta particles accounting for the whole beta spectrum of all the considered nuclides was 29.62% with respect to the mean beta energy case. Suitable analytical relationships were found between the absorbed fraction and the generalized radius, and the dependence of the fitting parameters from beta spectrum energy was discussed and fitted by appropriate parametric functions. CONCLUSION: The results allowed the calculation of the absorbed fractions from the above stated beta sources uniformly distributed in spherical and ellipsoidal volumes of any ellipticity and volume, in a wide range of practical volumes that are not only used for internal dosimetry in nuclear medicine applications, but also in radiological protection estimates of doses from internal contamination.

Evaluation of electron dose calculations accuracy of a treatment planning system in radiotherapy of breast cancer with photon-electron technique.

AIM: The aim of this study was to assess the accuracy of electron dose calculations of Prowess Panther treatment planning system (TPS) for abutting photon-electron (PE) technique. In this work, we have assessed the accuracy of electron dose calculations in a simulated internal mammary field because this field is irradiated with electron in PE technique. MATERIALS AND METHODS: In this study, regions of in-field, under electron shield, and outside the internal mammary field were evaluated. Thermoluminescent dosimeter (TLD-700) chips were used within RANDO phantom for dose measurement. Prowess Panther TPS was also applied for dose calculation. Finally, confidence limit values were obtained to quantify the TPS electron dose calculation accuracy of an internal mammary field. RESULTS: The results show that for outside of field and under shield regions, Prowess Panther TPS underestimated the dose compared to the measured doses by TLD-700, whereas for in-field regions, the calculated doses by Prowess Panther TPS compared to the measured doses by TLD-700, for some points are overestimated and other points are underestimated. Finally, the confidence limit values were obtained for various regions of the internal mammary field. Confidence limits for in-field, outside of field, and under shield regions were 54.23, 108.19, and 80.51, respectively. CONCLUSIONS: It is concluded that the accuracy of electron dose calculations of Prowess Panther TPS is not adequate for internal mammary field treatment. Therefore, it is recommended that for fields with electron beams Prowess Panther TPS calculations should not be entirely relied upon.

A comparison between skin dose of breast cancer patients at the breast region, measured by thermoluminescent dosimeter in the presence and absence of bolus.

AIM: The aim of this study was to measure entrance skin dose (ESD) on the breast of patients who had undergone radiotherapy following surgery, in the presence and absence of bolus. MATERIALS AND METHODS: In this study, the ESD on the breast of 22 female patients was measured using thermoluminescent dosimeter-100 chips. For each patient, the ESD was measured 3 times (once without bolus and twice using bolus). The bolus types used in this study include super flab and wax. RESULTS: The average ESDs on the breast of patients (from both medial and lateral tangential fields) in the presence of the super flab bolus and absence of bolus were 225.8 and 148.17 cGy, respectively, that when using the bolus, around 52% increasing in ESD was observed. The results showed a significant relationship between the ESD on the breast of patients and bolus types (P = 0.002); in addition, correlation coefficient between the two boluses (super flab and wax) was 0.615 (r = 0.615). CONCLUSION: When using the bolus in postmastectomy irradiation, it is noted that in dose delivery to the chest wall, surgical scar or skin of the treated region should be considered. The use of the bolus as a substance that increases of the skin dose can sometimes cause an excessive increase in skin dose that may cause severe skin reactions and underdosing of underlying tissues. Furthermore, using wax bolus in regions that do not require a lot of shaping of bolus is affordable.

Physical, dosimetric and clinical aspects and delivery systems in neutron capture therapy.

Neutron capture therapy (NCT) is a targeted radiotherapy for cancer treatment. In this method, neutrons with a spectra/specific energy (depending on the type of agent used for NCT) are captured with an agent that has a high cross-section with these neutrons. There are some agents that have been proposed in NCT including 10B, 157Gd and 33S. Among these agents, only 10B is used in clinical trials. Application of 157Gd is limited to in-vivo and in-vitro research. In addition, 33S has been applied in the field of Monte Carlo simulation. In BNCT, the only two delivery agents which are presently applied in clinical trials are BPA and BSH, but other delivery systems are being developed for more effective treatment in NCT. Neutron sources used in NCT are fission reactors, accelerators, and 252Cf. Among these, fission reactors have the most application in NCT. So far, BNCT has been applied to treat various cancers including glioblastoma multiforme, malignant glioma, malignant meningioma, liver, head and neck, lung, colon, melanoma, thyroid, hepatic, gastrointestinal cancer, and extra-mammary Paget's disease. This paper aims to review physical, dosimetric and clinical aspects as well as delivery systems in NCT for various agents.

Assessment the accuracy of dose calculation in build-up region for two radiotherapy treatment planning systems.

AIM: Our objective is to quantify dose calculation accuracy in the build-up region using TiGRT and Prowess Panther treatment planning systems (TPSs). MATERIALS AND METHODS: Thermoluminescent dosimeter-100 chips were used in a phantom for dose measurement. TiGRT Version 1.2 (LinaTech, Sunnyvale, CA, USA) and Prowess Panther version 5.1 (Prowess Inc., Concord, CA, USA) TPSs were also used for dose calculations. Finally, the confidence limit values obtained to quantify dose calculation accuracy of the TPSs at build-up region for different field sizes and various gantry angles. RESULTS: For 8 cm × 10 cm, 10 cm × 10 cm, and 15 cm × 10 cm field sizes, the confidence limit values for TiGRT TPS were 16.64, 16.56, and 25.85; for Prowess TPS with fast photon effective (FPE) algorithm were 15.17, 14.22, and 9.73; and for Prowess TPS with collapsed cone convolution superposition (CCCS) algorithm were 10.53, 9.97, and 9.76, respectively. For wedged field with gantry angles of 15°, 30°, and 60°, the confidence limit values for TiGRT TPS were 12.11, 12.96, and 22.69 and for Prowess TPS with FPE algorithm were 24.50, 22.07, and 7.82, respectively. CONCLUSIONS: It is concluded that for open field sizes without gantry angulation, dose calculation accuracy in Prowess TPS with CCCS algorithm is better than TiGRT and Prowess TPSs with FPE algorithm. Furthermore, it is concluded that for wedged field with large gantry angle, dose calculation accuracy of Prowess TPS with FPE algorithm is better than TiGRT TPS while, for medium and small gantry angles, dose calculation accuracy of TiGRT TPS is better than Prowess TPS with FPE algorithm.

Evaluation of the effect of soft tissue composition on the characteristics of spread-out Bragg peak in proton therapy.

AIM: The aim of this study is to evaluate the effect of soft tissue composition on dose distribution and spread-out Bragg peak (SOBP) characteristics in proton therapy. SUBJECTS AND METHODS: Proton beams with nominal energies of 70, 120 and 210 MeV were considered. The soft tissues and tissue equivalent materials implemented in this study are: 9-component soft tissue, 4-component soft tissue, adipose tissue, muscle (skeletal), lung tissue, breast tissue, A-150 tissue equivalent plastic, perspex and water. Each material was separately defined inside a 20 cm × 20 cm × 40 cm phantom. A multilayer phantom was evaluated as well. The effect of tissue composition on the relative dose in SOBP region (relative to the dose in SOBP region in water), range of SOBP, length of SOBP, and uniformity index of SOBP was evaluated. RESULTS: Various soft tissues and tissue equivalent materials have shown different dose level in SOBPs, ranges of SOBPs, lengths of SOBPs and uniformity indices. CONCLUSIONS: Based on the obtained results, various soft tissues and tissue equivalent materials have quite different SOBP characteristics. Since in clinical practice with proton therapy, only the range of SOBP is corrected for various tissues, omission of the above effects may result in major discrepancies in proton beam radiotherapy. To improve treatment accuracy, it is necessary to introduce such effects in treatment planning in proton therapy.

Evaluation of the accuracy of various dose calculation algorithms of a commercial treatment planning system in the presence of hip prosthesis and comparison with Monte Carlo.

PURPOSE: High atomic number elements are commonly used in a hip prosthesis which can cause uncertainty in accurate dose calculations in radiation therapy. The aim of this study is to assess the accuracy of the three various algorithms of ISOgray treatment planning system in the presence of hip prosthesis by Monte Carlo (MC). MATERIALS AND METHODS: A MC model of Siemens PRIMUS linear accelerator has been built and verified by the measured data of the different algorithms of ISOgray treatment planning systems (TPS) in 6 and 15 MV photon beam energies. Two types of hip prosthesis have been used: stainless steel and titanium. The accuracy of mentioned dose calculation algorithms in the presence of hip prosthesis was evaluated. RESULTS: There were 24.78%, 27.68%, and 27.72% errors in fast Fourier transform (FFT) Convolution, collapsed cone (CC), and superposition in 6 MV photon beam and 26.45%, 30.45%, and 28.63% in 15 MV photon beam for titanium type, respectively. However, there were 32.84%, 35.89%, and 35.57% in 6 MV photon beam and 38.81%, 47.31%, and 39.91% errors in 15 MV photon beam in steel type, respectively. In addition, the ISOgray TPS algorithms are not able to predict the dose enhancement and reduction at the proximal and distal prosthesis interfaces, respectively. CONCLUSIONS: Hip prosthesis creates a considerable disturbance in dose distribution which cannot be predicted accurately by the FFT convolution, CC, and superposition algorithms. It is recommended to use of MC-based TPS for the treatment fields including the hip prosthesis.

Comparison of the hypothetical (57)Co brachytherapy source with the (192)Ir source.

AIM OF THE STUDY: The (57)Co radioisotope has recently been proposed as a hypothetical brachytherapy source due to its high specific activity, appropriate half-life (272 days) and medium energy photons (114.17 keV on average). In this study, Task Group No. 43 dosimetric parameters were calculated and reported for a hypothetical (57)Co source. MATERIAL AND METHODS: A hypothetical (57)Co source was simulated in MCNPX, consisting of an active cylinder with 3.5 mm length and 0.6 mm radius encapsulated in a stainless steel capsule. Three photon energies were utilized (136 keV [10.68%], 122 keV [85.60%], 14 keV [9.16%]) for the (57)Co source. Air kerma strength, dose rate constant, radial dose function, anisotropy function, and isodose curves for the source were calculated and compared to the corresponding data for a (192)Ir source. RESULTS: The results are presented as tables and figures. Air kerma strength per 1 mCi activity for the (57)Co source was 0.46 cGyh(-1) cm 2 mCi(-1). The dose rate constant for the (57)Co source was determined to be 1.215 cGyh(-1)U(-1). The radial dose function for the (57)Co source has an increasing trend due to multiple scattering of low energy photons. The anisotropy function for the (57)Co source at various distances from the source is more isotropic than the (192)Ir source. CONCLUSIONS: The (57)Co source has advantages over (192)Ir due to its lower energy photons, longer half-life, higher dose rate constant and more isotropic anisotropic function. However, the (192)Ir source has a higher initial air kerma strength and more uniform radial dose function. These properties make (57)Co a suitable source for use in brachytherapy applications.

A comparison study on various low energy sources in interstitial prostate brachytherapy.

PURPOSE: Low energy sources are routinely used in prostate brachytherapy. (125)I is one of the most commonly used sources. Low energy (131)Cs source was introduced recently as a brachytherapy source. The aim of this study is to compare dose distributions of (125)I, (103)Pd, and (131)Cs sources in interstitial brachytherapy of prostate. MATERIAL AND METHODS: ProstaSeed (125)I brachytherapy source was simulated using MCNPX Monte Carlo code. Additionally, two hypothetical sources of (103)Pd and (131)Cs were simulated with the same geometry as the ProstaSeed (125)I source, while having their specific emitted gamma spectra. These brachytherapy sources were simulated with distribution of forty-eight seeds in a phantom including prostate. The prostate was considered as a sphere with radius of 1.5 cm. Absolute and relative dose rates were obtained in various distances from the source along the transverse and longitudinal axes inside and outside the tumor. Furthermore, isodose curves were plotted around the sources. RESULTS: Analyzing the initial dose profiles for various sources indicated that with the same time duration and air kerma strength, (131)Cs delivers higher dose to tumor. However, relative dose rate inside the tumor is higher and outside the tumor is lower for the (103)Pd source. CONCLUSIONS: The higher initial absolute dose in cGy/(h.U) of (131)Cs brachytherapy source is an advantage of this source over the others. The higher relative dose inside the tumor and lower relative dose outside the tumor for the (103)Pd source are advantages of this later brachytherapy source. Based on the total dose the (125)I source has advantage over the others due to its longer half-life.

Gold nanoparticle-based brachytherapy enhancement in choroidal melanoma using a full Monte Carlo model of the human eye.

The effects of gold nanoparticles (GNPs) in 125I brachytherapy dose enhancement on choroidal melanoma are examined using the Monte Carlo simulation technique. Usually, Monte Carlo ophthalmic brachytherapy dosimetry is performed in a water phantom. However, here, the compositions of human eye have been considered instead of water. Both human eye and water phantoms have been simulated with MCNP5 code. These simulations were performed for a fully loaded 16 mm COMS eye plaque containing 13 125I seeds. The dose delivered to the tumor and normal tissues have been calculated in both phantoms with and without GNPs. Normally, the radiation therapy of cancer patients is designed to deliver a required dose to the tumor while sparing the surrounding normal tissues. However, as the normal and cancerous cells absorbed dose in an almost identical fashion, the normal tissue absorbed radiation dose during the treatment time. The use of GNPs in combination with radiotherapy in the treatment of tumor decreases the absorbed dose by normal tissues. The results indicate that the dose to the tumor in an eyeball implanted with COMS plaque increases with increasing GNPs concentration inside the target. Therefore, the required irradiation time for the tumors in the eye is decreased by adding the GNPs prior to treatment. As a result, the dose to normal tissues decreases when the irradiation time is reduced. Furthermore, a comparison between the simulated data in an eye phantom made of water and eye phantom made of human eye composition, in the presence of GNPs, shows the significance of utilizing the composition of eye in ophthalmic brachytherapy dosimetry Also, defining the eye composition instead of water leads to more accurate calculations of GNPs radiation effects in ophthalmic brachytherapy dosimetry.

Neutron capture therapy: a comparison between dose enhancement of various agents, nanoparticles and chemotherapy drugs.

The aim of this study is to compare dose enhancement of various agents, nanoparticles and chemotherapy drugs for neutron capture therapy. A (252)Cf source was simulated to obtain its dosimetric parameters, including air kerma strength, dose rate constant, radial dose function and total dose rates. These results were compared with previously published data. Using (252)Cf as a neutron source, the in-tumour dose enhancements in the presence of atomic (10)B, (157)Gd and (33)S agents; (10)B, (157)Gd, (33)S nanoparticles; and Bortezomib and Amifostine chemotherapy drugs were calculated and compared in neutron capture therapy. Monte Carlo code MCNPX was used for simulation of the (252)Cf source, a soft tissue phantom, and a tumour containing each capture agent. Dose enhancement for 100, 200 and 500 ppm of the mentioned media was calculated. Calculated dosimetric parameters of the (252)Cf source were in agreement with previously published values. In comparison to other agents, maximum dose enhancement factor was obtained for 500 ppm of atomic (10)B agent and (10)B nanoparticles, equal to 1.06 and 1.08, respectively. Additionally, Bortezomib showed a considerable dose enhancement level. From a dose enhancement point of view, media containing (10)B are the best agents in neutron capture therapy. Bortezomib is a chemotherapy drug containing boron and can be proposed as an agent in boron neutron capture therapy. However, it should be noted that other physical, chemical and medical criteria should be considered in comparing the mentioned agents before their clinical use in neutron capture therapy.

Effect of tissue composition on dose distribution in brachytherapy with various photon emitting sources.

PURPOSE: The aim of this study is to compare the dose in various soft tissues in brachytherapy with photon emitting sources. MATERIAL AND METHODS: (103)Pd, (125)I, (169)Yb, (192)Ir brachytherapy sources were simulated with MCNPX Monte Carlo code, and their dose rate constant and radial dose function were compared with the published data. A spherical phantom with 50 cm radius was simulated and the dose at various radial distances in adipose tissue, breast tissue, 4-component soft tissue, brain (grey/white matter), muscle (skeletal), lung tissue, blood (whole), 9-component soft tissue, and water were calculated. The absolute dose and relative dose difference with respect to 9-component soft tissue was obtained for various materials, sources, and distances. RESULTS: There was good agreement between the dosimetric parameters of the sources and the published data. Adipose tissue, breast tissue, 4-component soft tissue, and water showed the greatest difference in dose relative to the dose to the 9-component soft tissue. The other soft tissues showed lower dose differences. The dose difference was also higher for (103)Pd source than for (125)I, (169)Yb, and (192)Ir sources. Furthermore, greater distances from the source had higher relative dose differences and the effect can be justified due to the change in photon spectrum (softening or hardening) as photons traverse the phantom material. CONCLUSIONS: The ignorance of soft tissue characteristics (density, composition, etc.) by treatment planning systems incorporates a significant error in dose delivery to the patient in brachytherapy with photon sources. The error depends on the type of soft tissue, brachytherapy source, as well as the distance from the source.

A Monte Carlo evaluation of dose enhancement by cisplatin and titanocene dichloride chemotherapy drugs in brachytherapy with photon emitting sources.

Some chemotherapy drugs contain a high Z element in their structure that can be used for tumour dose enhancement in radiotherapy. In the present study, dose enhancement factors (DEFs) by cisplatin and titanocene dichloride agents in brachytherapy were quantified based on Monte Carlo simulation. Six photon emitting brachytherapy sources were simulated and their dose rate constant and radial dose function were determined and compared with published data. Dose enhancement factor was obtained for 1, 3 and 5 % concentrations of cisplatin and titanocene dichloride chemotherapy agents in a tumour, in soft tissue phantom. The results of the dose rate constant and radial dose function showed good agreement with published data. Our results have shown that depending on the type of chemotherapy agent and brachytherapy source, DEF increases with increasing chemotherapy drug concentration. The maximum in-tumour averaged DEF for cisplatin and titanocene dichloride are 4.13 and 1.48, respectively, reached with 5 % concentrations of the agents, and (125)I source. Dose enhancement factor is considerably higher for both chemotherapy agents with (125)I, (103)Pd and (169)Yb sources, compared to (192)Ir, (198)Au and (60)Co sources. At similar concentrations, dose enhancement for cisplatin is higher compared with titanocene dichloride. Based on the results of this study, combination of brachytherapy and chemotherapy with agents containing a high Z element resulted in higher radiation dose to the tumour. Therefore, concurrent use of chemotherapy and brachytherapy with high atomic number drugs can have the potential benefits of dose enhancement. However, more preclinical evaluations in this area are necessary before clinical application of this method.

Dose enhancement by various nanoparticles in prostate brachytherapy.

The aim of this Monte Carlo study is to calculate dose enhancement in tumours by various nanoparticles in prostate brachytherapy using (125)I interstitial implants. ProstaSeed (125)I brachytherapy source was simulated using MCNPX Monte Carlo code. Dose rate constant, radial dose function and anisotropy function values were calculated and compared with previously published data. Dose enhancement factors (DEFs) were calculated for Fe2O3, Ag, Gd, Pt and Au nanoparticles with concentrations of 7, 18 and 30 mg/ml. Our source simulation was validated by comparing our results with previously published data. Maximum DEF values on the central transverse line, within the tumour, for Fe2O3, Ag, Gd, Pt and Au nanoparticles with 30 mg/ml concentration were 1.27, 1.15, 1.14, 1.32, 1.79, respectively. No general trend in DEF with increasing atomic number, or concentration of nanoparticles was observed. However, DEF was the highest for 30 mg/ml concentration of Au. The 50 % isodose line tightened toward the central point of the spherical tumour and the central 100 % isodose line expanded outward. The presence of nanoparticles in a prostate tumour increases the dose inside tumour and decreases the dose outside it, thus the treatment time and source activity can be decreased due to dose enhancement in the tumour. While more preclinical studies on other aspects are necessary, using nanoparticles can be proposed as a useful tool in prostate brachytherapy. Au nanoparticles with higher concentrations can be more useful for this purpose when compared to other nanoparticles.

Investigating the dosimetric and tumor control consequences of prostate seed loss and migration.

PURPOSE: Low dose-rate brachytherapy is commonly used to treat prostate cancer. However, once implanted, the seeds are vulnerable to loss and movement. The goal of this work is to investigate the dosimetric and radiobiological effects of the types of seed loss and migration commonly seen in prostate brachytherapy. METHODS: Five patients were used in this study. For each patient three treatment plans were created using Iodine-125, Palladium-103, and Cesium-131 seeds. The three seeds that were closest to the urethra were identified and modeled as the seeds lost through the urethra. The three seeds closest to the exterior of prostatic capsule were identified and modeled as those lost from the prostate periphery. The seed locations and organ contours were exported from Prowess and used by in-house software to perform the dosimetric and radiobiological evaluation. Seed loss was simulated by simultaneously removing 1, 2, or 3 seeds near the urethra 0, 2, or 4 days after the implant or removing seeds near the exterior of the prostate 14, 21, or 28 days after the implant. RESULTS: Loss of one, two or three seeds through the urethra results in a D(90) reduction of 2%, 5%, and 7% loss, respectively. Due to delayed loss of peripheral seeds, the dosimetric effects are less severe than for loss through the urethra. However, while the dose reduction is modest for multiple lost seeds, the reduction in tumor control probability was minimal. CONCLUSIONS: The goal of this work was to investigate the dosimetric and radiobiological effects of the types of seed loss and migration commonly seen in prostate brachytherapy. The results presented show that loss of multiple seeds can cause a substantial reduction of D(90) coverage. However, for the patients in this study the dose reduction was not seen to reduce tumor control probability.

Evaluation of the effect of prostate volume change on tumor control probability in LDR brachytherapy.

PURPOSE: This study evaluates low dose-rate brachytherapy (LDR) prostate plans to determine the biological effect of dose degradation due to prostate volume changes. MATERIAL AND METHODS: In this study, 39 patients were evaluated. Pre-implant prostate volume was determined using ultrasound. These images were used with the treatment planning system (Nucletron Spot Pro 3.1(®)) to create treatment plans using (103)Pd seeds. Following the implant, patients were imaged using CT for post-implant dosimetry. From the pre and post-implant DVHs, the biologically equivalent dose and the tumor control probability (TCP) were determined using the biologically effective uniform dose. The model used RBE = 1.75 and α/ß = 2 Gy. RESULTS: The prostate volume changed between pre and post implant image sets ranged from -8% to 110%. TCP and the mean dose were reduced up to 21% and 56%, respectively. TCP is observed to decrease as the mean dose decreases to the prostate. The post-implant tumor dose was generally observed to decrease, compared to the planned dose. A critical uniform dose of 130 Gy was established. Below this dose, TCP begins to fall-off. It was also determined that patients with a small prostates were more likely to suffer TCP decrease. CONCLUSIONS: The biological effect of post operative prostate growth due to operative trauma in LDR was evaluated using the concept. The post-implant dose was lower than the planned dose due to an increase of prostate volume post-implant. A critical uniform dose of 130 Gy was determined, below which TCP begun to decline.