Browsing by Author "Vaz, Pedro"
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- 131I therapy in thyroid cancer and benign thyroid diseases: personal dose equivalent HP(10) assessment in patient’s close family membersPublication . Raminhas Carapinha, Maria João; Costa, Gracinda; Ferreira, Teresa C.; Salgado, Lucília; Vaz, Sofia; Ferreira, Rui; Isidoro, Jorge; Rézio, Teresa; Nunes, Carla; Tavares, António Barata; Vaz, PedroIntroduction - The aim is to quantify the personal dose equivalent HP(10) in the family members (FMs) of the patients (PATs) undergoing iodine-131 thyroid cancer (TC) therapy and benign thyroid diseases (BTD) and to compare the HP(10) values of children and adults. Methods - An observational study with convenience sampling was performed, including 83 FMs (59% ♂) of 48 PATs (72.9% ♀). All FMs wore a whole body TLD for 21 days and received instructions on radiation protection, based on Euratom recommendations. All FMs were provided with relevant instructions for TLD use and answered a questionnaire. Two groups were defined: Group-TC, included 65 FMs (5 children below the age of 10) of 37 PATs treated for TC with average (ᾱ) activity of 3434MBq (range 1110–5920MBq); Group-BTD included 18 FMs adults of 11 PATs treated for BTD with ᾱ activity of 336.4MBq (range 185–555MBq). The in-PATs of Group-TC were discharged 48h after therapy. All ethical principles of the investigation were respected. Results - When the PATs of Group-TC were discharged the ᾱ effective dose rate measured at a 1-metre distance was 10.4μSv/h (range 2–28μSv/h). The ᾱ value of HP(10) in FMs were: 0.14mSv (range 0.00-3.37mSv) for Group-TC and 0.37mSv (range 0.01-2.40mSv) for Group-BTD. The HP(10) value depended on the degree of relationship (p=0.008) and the age of the FMs (p=0.007). HP(10) of the FMs were moderately associated to administered activity (ρsp=-0.319; p=0.010) in Group-TC. No association was found between HP(10) FMs and the administered activity in Group-BTD (ρsp=0.139; p=0.583). Conclusions - The FMs of the PATs submitted 131I therapy for BTD received higher doses when compared to FMs of TC PATs. The HP(10) of the FMs depended to the degree of relationship and the age of the FMs. In the PATs submitted 131I therapy for BTD, the HP(10) of the FMs is not associated with the administered activity. The personal dose equivalent in these FMs does not reach the dose limits recommended by ICRP 97 and ICRP 94.
- Alternative regimens for treating prostate cancer using equivalent uniform dose and Monte Carlo methodsPublication . Oliveira, Susana; Rosmanets, Yuriy; Teles, Pedro; Fernandes, Lisete; Teixeira, Nuno; Vaz, PedroIntroduction - Conventional radiotherapy treatments are administrated with 2 Gy external beam radiotherapy (EBRT) fractions. It has been postulated that prostate cancer would respond to radiotherapy as a slowly proliferating late-responding normal tissue, benefiting from hypo-fractionated regimens. Highly conformed brachytherapy is a treatment option either alone or combined with EBRT. Purpose - To identify alternative radiotherapy regimens for treating prostate cancer using EBRT and low dose-rate brachytherapy (LDRBT) with 125I implants, biologically equivalent to conventional treatments in terms of uniform equivalent dose (EUD). Materials and methods - The EUD concept was used, together with Monte Carlo (MC) methods. Two voxel phantoms were segmented from the computed tomography of patients to obtain the energy deposition derived from the MC simulations of EBRT and LDRBT treatments on a voxel-by-voxel basis. The energy deposition was converted in EUD. Equivalent regimens to EUDs of 72 Gy, 80 Gy, 90 Gy, and 100 Gy were determined for increasing fractions of 1.8–5.0 Gy and amounts of LDRBT from 0 Gy (EBRT exclusive) to 145 Gy. The resulting EUD for rectum was also evaluated. Results - Alternative schemes equivalent, in terms of EUD, were obtained. For example, it is equivalent to an EUD of 72 Gy, 38 × 2 Gy, 20 × 3 Gy or 9 × 5 Gy of EBRT, or 6 × 5 Gy of EBRT plus 50 Gy of LDRBT. The rectum benefits of higher amounts of LDRBT for EBRT fractionations <2.5 Gy and larger fractions for LDRBT dose <50 Gy. Conclusion - Alternative regimens for the treatment of prostate cancer with EBRT and LDRBT are proposed. The rational for the use of brachytherapy becomes less relevant with the increasing therapeutic ratio achieved with hypo-fractionated EBRT.
- Assessment of iodine-131 in the urine of the patient’s family members after differentiated thyroid carcinoma therapyPublication . Raminhas Carapinha, Maria João; Costa, Gracinda; Ferreira, Teresa C.; Salgado, Lucília; Carvalho, Inês; Sofia, Monica; Isidoro, Jorge; Rézio, Teresa; Silva, Lidia; Reis, Mário; Santos, Marta; Nunes, Carla; Tavares, António Barata; Vaz, PedroIntroduction - The aim is to evaluate the internal exposure of the family members (FMs) of the patients (PATs) undergoing iodine-131 (131I) thyroid cancer (TC) therapy and quantify the amount of 131I in the FMs, excreted through the urinary. Methods - An observational study with convenience sampling was performed, including 25 PATs and 34 FMs. The PATs, who underwent 131I treatments for TC, were discharged from hospital 48h after therapy. All FMs received instructions on radiation protection, based on Euratom recommendations use and submitted to a questionnaire. A urine sample was collected from every FMs about 70h after discharge of the PAT. Samples of urine were analyzed by gamma spectrometry and counted for 24h. All ethical principles of the investigation were respected. Results - The average activity of 131I given to the PATs (52.9% ♀) was 3266.4 ±1120.2MBq. When the PATs have discharged the average (ᾱ) effective dose rate measured at a 1-metre distance was 7.9±5.8μSv/hr (range 1-25μSv/hr). In the 34 FMs (52.9% ♂) with ᾱ of 48.1±18.6years, only in 3FMs 131I wasn’t detected in the urine. In the other 31 samples urines, the specific activities of 131I have ᾱ of 97.4Bq/L (range 0.0-1146Bq/L). The specific activity of 131I in urine: it is not the same among the classes of the administered activity (p=0.019); don’t is the same on the different classes of FMs ages (p=0.470) and the different degree of relationship (p=0.744). We observed a moderate correlation between the specific activity of 131I in the urine and the activity administered to the PATs (ρsp=0.540; p=0.001) and also between the effective dose rate in the PATs (ρsp=0.730; p<0.001). With a CI of 95%. Conclusions - The PATs are a radioactive source that can cause exposure of the FMs to ionizing radiation. The specific activity of 131I in the urines of the FMs is related to the activity administered to the PAT. It is clear that FMs of PATs submitted to radioiodine therapy can be subject to internal contamination.
- Assessment of out-of-field doses in radiotherapy treatments of paediatric patients using Monte Carlo methods and measurementsPublication . Sá, Ana Cravo; Barateiro, Andreia; Bednarz, Bryan; Borges, Cecília; Pereira, Joana; Baptista, Mariana; Pereira, Miguel; Zarza-Moreno, Miriam; Almeida, Pedro; Vaz, Pedro; Madaleno, Tiago; Romanets, YuriyPurpose: To assess out-of-field doses in radiotherapy treatments of pediatric patients, using Monte Carlo methods to implement a new model of the linear accelerator validated against measurements and developing a voxelized anthropomorphic pediatric phantom. Methods: CT images of a physical anthropomorphic pediatric phantom were acquired and dosimetric planning using a TPS was obtained. The CT images were used to perform the voxelization of the physical phantom using the ImageJ software and later implemented in MCNP. In order to validate the Monte Carlo model, dose measurements of the 6 MV beam and Linac with 120 MLC were made in a clinical setting, using ionization chambers and a water phantom. afterward, TLD measurements in the physical anthropomorphic phantom were performed in order to assess the out-of-field doses in the eyes, thyroid, c-spine, heart, and lungs. Results: The Monte Carlo model was validated for in-field and out-of-field doses with average relative differences below 3%. The average relative differences between TLD measurements and Monte Carlo is 14,3% whilst the average relative difference between TLD and TPS is 55,8%. Moreover, organs up to 22.5 cm from PTV center show TLD and MCNP6 relative differences and TLD and TPS relative differences up to 21.2% and 92.0%, respectively. Conclusions: Our study provides a novel model that could be used in clinical research, namely in dose evaluation outside the treatment fields. This is particularly relevant, especially in pediatric patients, for studying new radiotherapy treatment techniques, since it can be used to estimate the development of secondary tumors.
- Comparison of 3DCRT and IMRT out-of-field doses in pediatric patients using Monte Carlo simulations with treatment planning system calculations and measurementsPublication . Sá, Ana Cravo; Barateiro, Andreia; Bednarz, Bryan P.; Almeida, Pedro; Vaz, Pedro; Madaleno, TiagoPurpose: Out-of-field doses are given to healthy tissues, which may allow the development of second tumors. The use of IMRT in pediatric patients has been discussed, as it leads to a "bath" of low doses to large volumes of out-of-field organs and tissues. This study aims to compare out-of-field doses in pediatric patients comparing IMRT and 3DCRT techniques using measurements, Monte Carlo (MC) simulations, and treatment planning system (TPS) calculations. Materials and methods: A total dose of 54 Gy was prescribed to a PTV in the brain of a pediatric anthropomorphic phantom, for both techniques. To assess the out-of-field organ doses for both techniques, two treatment plans were performed with the 3DCRT and IMRT techniques in TPS. Measurements were carried out in a LINAC using a pediatric anthropomorphic phantom and thermoluminescent dosimeters to recreate the treatment plans, previously performed in the TPS. A computational model of a LINAC, the associated multileaf collimators, and a voxelized pediatric phantom implemented in the Monte Carlo N-Particle 6.1 computer program were also used to perform MC simulations of the out-of-field organ doses, for both techniques. Results: The results obtained by measurements and MC simulations indicate a significant increase in dose using the IMRT technique when compared to the 3DCRT technique. More specifically, measurements show higher doses with IMRT, namely, in the right eye (13,041 vs. 593 mGy), left eye (6,525 vs. 475 mGy), thyroid (79 vs. 70 mGy), right lung (37 vs. 28 mGy), left lung (27 vs. 20 mGy), and heart (31 vs. 25 mGy). The obtained results indicate that out-of-field doses can be seriously underestimated by TPS. Discussion: This study presents, for the first time, out-of-field dose measurements in a realistic scenario and calculations for IMRT, centered on a voxelized pediatric phantom and an MC model of a medical LINAC, including MLC with log file-based simulations. The results pinpoint significant discrepancies in out-of-field doses for the two techniques and are a cause of concern because TPS calculations cannot accurately predict such doses. The obtained doses may presumably increase the risk of the development of second tumors.
- Corrigendum: Comparison of 3DCRT and IMRT out-of-field doses in pediatric patients using Monte Carlo simulations with treatment planning system calculations and measurementsPublication . Sá, Ana Cravo; Barateiro, Andreia; Bednarz, Bryan P.; Almeida, Pedro; Vaz, Pedro; Madaleno, TiagoThis article is a correction to: Comparison of 3DCRT and IMRT out-of-field doses in pediatric patients using Monte Carlo simulations with treatment planning system calculations and measurements.
- Dosimetric effect of tissue heterogeneity for 125I prostate implantsPublication . Oliveira, Susana Maria; Teixeira, Nuno; Fernandes, Lisete; Teles, Pedro; Vaz, PedroAim - To use Monte Carlo (MC) together with voxel phantoms to analyze the tissue heterogeneity effect in the dose distributions and equivalent uniform dose (EUD) for (125)I prostate implants. Background - Dose distribution calculations in low dose-rate brachytherapy are based on the dose deposition around a single source in a water phantom. This formalism does not take into account tissue heterogeneities, interseed attenuation, or finite patient dimensions effects. Tissue composition is especially important due to the photoelectric effect. Materials and Methods - The computed tomographies (CT) of two patients with prostate cancer were used to create voxel phantoms for the MC simulations. An elemental composition and density were assigned to each structure. Densities of the prostate, vesicles, rectum and bladder were determined through the CT electronic densities of 100 patients. The same simulations were performed considering the same phantom as pure water. Results were compared via dose-volume histograms and EUD for the prostate and rectum. Results - The mean absorbed doses presented deviations of 3.3-4.0% for the prostate and of 2.3-4.9% for the rectum, when comparing calculations in water with calculations in the heterogeneous phantom. In the calculations in water, the prostate D 90 was overestimated by 2.8-3.9% and the rectum D 0.1cc resulted in dose differences of 6-8%. The EUD resulted in an overestimation of 3.5-3.7% for the prostate and of 7.7-8.3% for the rectum. Conclusions - The deposited dose was consistently overestimated for the simulation in water. In order to increase the accuracy in the determination of dose distributions, especially around the rectum, the introduction of the model-based algorithms is recommended.
- Tissue composition and density impact on the clinical parameters for 125I prostate implants dosimetryPublication . Oliveira, Susana Maria; Teixeira, Nuno; Fernandes, Lisete; Teles, Pedro; Vieira, Guy; Vaz, PedroThe MCNPX code was used to calculate the TG-43U1 recommended parameters in water and prostate tissue in order to quantify the dosimetric impact in 30 patients treated with (125)I prostate implants when replacing the TG-43U1 formalism parameters calculated in water by a prostate-like medium in the planning system (PS) and to evaluate the uncertainties associated with Monte Carlo (MC) calculations. The prostate density was obtained from the CT of 100 patients with prostate cancer. The deviations between our results for water and the TG-43U1 consensus dataset values were -2.6% for prostate V100, -13.0% for V150, and -5.8% for D90; -2.0% for rectum V100, and -5.1% for D0.1; -5.0% for urethra D10, and -5.1% for D30. The same differences between our water and prostate results were all under 0.3%. Uncertainties estimations were up to 2.9% for the gL(r) function, 13.4% for the F(r,θ) function and 7.0% for Λ, mainly due to seed geometry uncertainties. Uncertainties in extracting the TG-43U1 parameters in the MC simulations as well as in the literature comparison are of the same order of magnitude as the differences between dose distributions computed for water and prostate-like medium. The selection of the parameters for the PS should be done carefully, as it may considerably affect the dose distributions. The seeds internal geometry uncertainties are a major limiting factor in the MC parameters deduction.