جستجوی مقالات مرتبط با کلیدواژه « dosimetry » در نشریات گروه « پزشکی »

Organ dose distribution calculation in radiotherapy and knowledge about its side effects in cancer etiology is the most concern for medical physicists. Calculation of organ dose distribution for breast cancer treatment plans with Monte Carlo (MC) simulation is the main goal of this study.

Elekta Precise linear accelerator (LINAC) photon mode was simulated and verified using the GEANT4 application for tomographic emission. Eight different radiotherapy treatment plans on RANDO’s phantom left breast were produced with the ISOgray treatment planning system (TPS). The simulated plans verified photon dose distribution in clinical tumor volume (CTV) with TPS dose volume histogram (DVH) and gamma index tools. To verify photon dose distribution in out‑of‑field organs, the point dose measurement results were compared with the same point doses in the MC simulation. Eventually, the DVHs for out‑of‑field organs that were extracted from the TPS and MC simulation were compared.

Based on the implementation of gamma index tools with 2%/2 mm criteria, the simulated LINAC output demonstrated high agreement with the experimental measurements. Plan simulation for in‑field and out‑of‑field organs had an acceptable agreement with TPS and experimental measurement, respectively. There was a difference between DVHs extracted from the TPS and MC simulation for out‑of‑field organs in low‑dose parts. This difference is due to the inability of the TPS to calculate dose distribution in out‑of‑field organs. Conclusion and

Based on the results, it was concluded that the treatment plans with the MC simulation have a high accuracy for the calculation of out‑of‑field dose distribution and could play a significant role in evaluating the important role of dose distribution for second primary cancer estimation.

Esophageal cancer, a highly aggressive and often fatal gastrointestinal disease, frequently reaches advanced unresectable stages. The standard treatment involves definitive chemoradiation due to concerns about regional failure. To address this, intensified radiation dosages and advanced techniques like Intensity-Modulated Radiation Therapy (IMRT) and Three-Dimensional Conformal Radiation Therapy (3D-CRT) are being explored. This study aimed to compare dosimetric factors in patients with esophageal carcinoma undergoing IMRT versus 3D-CRT treatments.

Twenty patients were alternately assigned to receive either treatment. Each patient’s alternate virtual plan resulted in a total of forty plans. Dosimetric evaluations included coverage of the Planning Target Volume (PTV) and dose-volumes of lungs, heart, and spinal cord. Treatment consisted of 50.4 Gy radiation with concurrent weekly paclitaxel and carboplatin chemotherapy. Statistical analysis was conducted using the two-tailed Paired t-Test.

Dosimetric evaluations revealed no significant distinctions in PTV parameters such as maximum dose, minimum dose, mean dose, D2%, D50%, and V95% between IMRT and 3D-CRT plans. However, IMRT exhibited improvements in D98% and Homogeneity Index. While Conformity Index did not differ significantly, IMRT displayed reduced lung irradiation in various aspects such as Dmean, V20, and V30, while 3D-CRT showed lower irradiation in V5 and V10. IMRT effectively spared the heart with lowered heart irradiation in V30. Spinal cord Dmax remained consistent across both techniques.

IMRT demonstrated better dose homogeneity and superior lung and heart sparing capabilities compared to 3D-CRT in treating esophageal carcinoma. While both techniques had similar dose conformity, IMRT’s potential to reduce longterm radiation-induced lung and heart complications through improved sparing of these organs is noteworthy.

In systemic radionuclide therapy such as radioiodine (I-131) for differentiated thyroid cancer, post-therapy dosimetry is essential to verify pre-therapy predictions, which in turn informs the next treatment. However, post-therapy multi-time point dosimetry is resource intensive and unfeasible in many institutions. We devised a schema of rapid predictive dosimetry by circumventing post-First Strike multi-time point dosimetry with carefully assigned gestalt values of predicted kinetics to personalise the Second Strike prescription. Verification is performed after the First Strike. Patient-specific time-activity curve is plotted from serial measurements of whole body exposure rates to obtain its decay constant; its inverse is the whole body Time Integrated Activity Coefficient (TIAC). The percentage of whole body TIAC attributed to blood is carefully assigned by gestalt based on population kinetics tabulated in Part 1, adjusted by any metastasis on I-131 whole body scintigraphy. Marrow absorbed dose is calculated by EANM formularism. Lung safety threshold at 48h post-therapy is linearly scaled by height, where the patient’s risk of lung radiotoxicity is revealed from the whole body time-activity curve value at 48h. Predictive prescription for the second I-131 fraction (Second Strike) is by careful gestalt assessment based on predicted kinetics, remaining marrow and lung tolerance, marrow dose rate constraint per fraction (0.265 Gy/h), local regulatory and facility requirements in relation to radiation protection. Tumour dosimetry is obviated under the assumption of severe tumour absorbed dose heterogeneity. The final prescription for the Second Strike is usually the lowest I-131 activity amongst all clinical, dosimetric and regulatory constraints. This schema is incorporated into a Predictive Calculator spreadsheet for rapid predictive dosimetry, and is freely available. Calculations may be completed within minutes to generate personalised predictive prescriptions, making it feasible for routine clinical implementation. Our innovative schema of rapid verification and predictive dosimetry bridges the technological gap between empiric vs theranostic prescription to help institutions modernise. Its expeditious design makes this schema feasible to be integrated into the routine clinical workflow. Its predictive estimates provide invaluable dosimetric insight to inform the next I-131 fraction, allowing every prescription to be scientifically rationalised and personalised according to individual circumstances.

The scattered radiation from the treatment volume might be more significant for children than for adults because of life expectancy. The present study used biological effects of ionizing radiation (BEIR) VII models to estimate radiation-induced secondary cancer risks in irradiated organs following three-dimensional conformal radiation therapy (3D-CRT) of Acute Lymphocytic Leukemia (ALL) in children. Both excess absolute risk (EAR) and excess relative risk (ERR) models were used to estimate the secondary cancer risks of eye lenses, thyroid, parotid, breast, and region overlying ovaries.

In this expository cross-sectional study, from 45 patients who were examined, 16 patients age under 18 years (mean age of 9.6) met the criteria for entering the study in Shahid Ramezanzadeh Hospital in Yazd underwent whole brain radiotherapy (WBRT) using COMPACT accelerator. Measurement was performed using thermoluminescent dosimeters (TLD). After radiation therapy, the secondary cancer risk in these organs was calculated.

The organ dose mean values in female patients were 1.8±0.1, 1.65±0.61, 1.47±0.04, 0.1±0.03, and 1.58±0.52 cGy in the eye lenses, parotid, thyroid, breast, and region overlying ovaries, respectively and 2.7±0.6, 0.76±0.17, 0.6±0.05, and 0.005±0.002 cGy for eye lens, parotid, thyroid, breast, and testis of male patient, respectively. The ERR and EAR were estimated after 3, 5, 10, 15 and 20 years for eye lens, parotid breast, and ovary/testis for female/male.

Higher risk values were found for eye lenses and thyroid. The scattered rays decreased by increasing the organ distance from the treatment radiation field.

Percutaneous vertebroplasty employs bone cement for injecting into the fractured vertebral body (VB) caused by spinal metastases. Radioactive bone cement and also brachytherapy seeds have been utilized to suppress the tumor growth in the VB.
This study aims to investigate the dose distributions of low-energy brachytherapy seeds, and to compare them to those of radioactive bone cement, by Monte Carlo simulation.
In this simulation study, nine CT scan images were imported in Geant4. For the simulation of brachytherapy, I-125, Cs-131, or Pd-103 seeds were positioned in the VB, and for the simulation of vertebroplasty, the VB was filled by a radioactive cement loaded by P-32, Ho-166, Y-90, or Sm-153 radioisotopes. The dose-volume histograms of the VB, and the spinal cord (SC) were obtained after segmentation, considering that the reference dose is the minimum dose covered 95% of the VB.
The SC sparing was improved by using beta-emitting cement because of their steep gradient dose distribution. I-125 seeds and Y-90 radioisotope showed better VB coverage for brachytherapy and vertebroplasty techniques, respectively. Pd-103 seeds and P-32 radioisotope showed better SC sparing for brachytherapy and vertebroplasty, respectively. The minimum mean doses that covered 100% of the VB were 62.0%, 56.5%, and 45.0% for I-125, Cs-131, and Pd-103 seeds, and 28.3%, 28.6%, 32.9%, and 17.7%, for P-32, Ho-166, Y-90, and Sm-153 sources, respectively. 
I-125 and Cs-131 seeds may be useful for large tumors filling the entire VB, and also for the extended tumors invading multiple vertebrae. Beta-emitting bone cement is recommended for tumors located near the SC.

Radiation therapy, the most common form of cancer treatment, can result in late complications, such as secondary breast and thyroid cancers.

This study aimed to evaluate the risk of secondary cancers using two radiobiological models of Excess Absolute Risk (EAR) and Excess Relative Risk (ERR) in patients with brain cancer undergoing radiotherapy for improved survival rates of cancer patients.

In this expository cross-sectional study, 45 patients under the age of 40 years underwent Whole Brain Radiotherapy (WBRT) using a compact accelerator in Shahid Ramezanzadeh Hospital, Yazd, Iran. Out-of-field organ dose measurement was performed using a Thermoluminescent Dosimeter (TLD) to determine the dose to thyroid and breast tissues. The risk of secondary cancers in these organs was calculated 3, 5, 10, 15, and 20 years after radiation therapy.

The mean values of thyroid cancer risk in men and women were 0.418±0.509 and 0.274±0.306, respectively. ERR values of breast cancer in 3-, 5-, 10-, 15-, and 20-year women undergoing radiation therapy were 1.084±2.938, 0.594±1.407, 0.248±0.497, 0.138±0.248, and 0.091±0.148, respectively. EAR values of breast cancer in 3-, 5-, 10-, 15-, and 20-year women following radiation therapy were 0.064±0.060, 0.077±0.071, 0.119±0.100, 0.178±0.248, and 0.259±0.178, respectively. 

After irradiation, the risk of secondary cancer is affected by factors, such as the patient’s age and gender. The secondary thyroid cancer is higher than that of other organs, such as the breast, in the patients undergoing WBRT.

Ophthalmic brachytherapy using radioactive plaques is an effective technique for the treatment of uveal melanoma. Ru-106 eye plaques are considered as interesting issue due to their steep gradient dose. The pre-planning evaluation of dosimetric parameters is essential for the treatment planning system.
The current study aims at providing dose distributions of six Ru-106 eye plaques (CCA, CCB, CGD, CIB, COB and COD) using radiochromic EBT3 film, Geant4 Monte Carlo toolkit and the treatment planning software (Plaque Simulator).
In this experimental study, an in-house phantom was employed for depth dose measurements with EBT3 films. Also, Geant4.10.5 scoring mesh was implemented to obtain the 2D dose distribution of the plaques. The results were compared with Plaque Simulator software and the manufacturer’s (BEBIG) data. The gamma index criterion (3%/3 mm) was used to evaluate dose distributions obtained by the film measurements and Geant4 simulation.
A good agreement was achieved between simulation and experimental results. Gamma index passing rate was 94.2%, 89.3%, 88.2%, 82.2%, 92.2% and 90.1% for CCA, CCB, CGD, CIB, COB and COD plaques, respectively. Absolute dose rate (mGy/min) obtained by EBT3 film at the depth of 2 mm was 79.4 mGy/min, 81.0 mGy/min, 78.6 mGy/min, 62.2 mGy/min, 75.2 mGy/min and 81.2 mGy/min for CCA, CCB, CGD, CIB, COB and COD plaques, respectively.  
The measured dose distributions and lateral dose profiles may be utilized in the treatment planning system to cover clinical volumes such as the clinical target volume and the gross tumor volume.

With the introduction of Intensity Modulated Radiotherapy (IMRT) approach, better dosimetry results and patient outcomes has been attained for various anatomical sites. In present study, a comparative dosimetric evaluation of Volumetric-Modulated Arc Therapy (VMAT) versus two techniques of IMRT i.e. Dynamic IMRT (d-IMRT) and step & shoot IMRT (ss-IMRT) was done for thoracic esophageal cancer. VMAT, ss-IMRT, and d-IMRT plans were generated on the Computed Tomography Simulator data sets of 13 Patients with thoracic esophageal carcinoma who had been treated earlier. The prescription dose for each patient was 50.4 Gy in 28 fractions. All the plans were optimized to achieve greater or equal to 95% of the prescribed dose to the Planning Target Volume (PTV). Dose to PTV and organ at risk (OAR) were compared with the help of Dose Volume Histogram (DVH). VMAT and d-IMRT plans were nearly equivalent for PTV coverage, homogeneity index (HI), and uniformity index (UI) (p> 0.05). However, VMAT and d-IMRT plans had superior PTV coverage, HI, and UI, (p < 0.01) than ss-IMRT. For PTV, the Dmean, D98, and D95 values in ss-IMRT were significantly less than VMAT and d-IMRT (p< 0.05). All three techniques are able to provide a homogeneous and conformal dose distribution. VMAT offers better homogeneous dose distribution and may be preferred for treating thoracic esophageal carcinoma. Thus, the multi-arc VMAT technique may be a better option with equivalent or superior dose distribution, uniformity, and homogeneity.

The patient-specific 3D printed anthropomorphic phantom is used for breast cancer after mastectomy developed by the laboratory of medical physics and biophysics, Department of Physics, Institut Teknologi Sepuluh Nopember, Indonesia. This phantom is applied to simulate and measure the radiation interactions occurring in the human body either using the treatment planning system (TPS) or direct measurement with external beam therapy (EBT) 3 film. This study aimed to provide dose measurements in the patient-specific 3D printed anthropomorphic phantom using a TPS and direct measurements using single-beam three-dimensional conformal radiation therapy (3DCRT) technique with electron energy of 6 MeV. In this experimental study, the patient-specific 3D printed anthropomorphic phantom was used for post-mastectomy radiation therapy. TPS on the phantom was conducted using a 3D-CRT technique with RayPlan 9A software. The single-beam radiation was delivered to the phantom with an angle perpendicular to the breast plane at 337.3° at 6 MeV with a total prescribed dose of 5000 cGy/25 fractions with 200 cGy per fraction. The doses at planning target volume (PTV) and right lung confirmed a non-significant difference both for TPS and direct measurement with P-values of 0.074 and 0.143, respectively. The dose at the spinal cord showed statistically significant differences with a P-value of 0.002. The result presented a similar skin dose value using either TPS or direct measurement.  The patient-specific 3D printed anthropomorphic phantom for breast cancer after mastectomy on the right side has good potential as an alternative to the evaluation of dosimetry for radiation therapy.

The traditional practice of empiric radioiodine (I-131) prescription is scientifically obsolete and inappropriate for inoperable metastatic differentiated thyroid cancer. However, theranostically guided prescription is still years away for many institutions. A personalized predictive method of radioiodine prescription that bridges the gap between empiric and theranostic methods is presented. It is an adaptation of the “maximum tolerated activity” method, where serial blood sampling is replaced by population kinetics carefully chosen by the user. It aims to maximize crossfire benefits within safety constraints to overcome tumour absorbed dose heterogeneity for a safe and effective first radioiodine fraction i.e., the First Strike.

The EANM method of blood dosimetry was incorporated with population kinetics, marrow and lung safety constraints, body habitus and clinical assessment of metastatic extent. Population data of whole body and blood kinetics in patients with and without metastases, prepared by recombinant human thyroid stimulating hormone or thyroid hormone withdrawal, and the maximum safe marrow dose rate were deduced from published data. For diffuse lung metastases, the lung safety limit was linearly scaled by height and separated into lung and remainder-of-body components.

The slowest whole body Time Integrated Activity Coefficient (TIAC) amongst patients with any metastases was 33.5±17.0 h and the highest percentage of whole body TIAC attributed to blood was 16.6±7.9%, prepared by thyroid hormone withdrawal. A variety of other average radioiodine kinetics is tabulated. Maximum safe marrow dose rate was deduced to be 0.265 Gy/h per fraction, where blood TIAC is normalised to administered activity. An easy-to-use calculator was developed which only requires height, weight and gender to populate recommendations for personalized First Strike prescription. The user decides by clinical gestalt whether the prescription is to be constrained by marrow or lung, then selects an activity depending on how extensive the metastases are likely to be. A Standard Female with oligometastasis and good urine output without diffuse lung metastasis is expected to safely tolerate 8.03 GBq of radioiodine as the First Strike.

This predictive method will help institutions rationalise the First Strike prescription based on radiobiologically sound principles, personalised to individual circumstances.

Calibration of Thermo Luminescent Dosimetry (TLD) in eye lens dosimeter requires a standard phantom. The use of anthropomorphic phantoms in calibration needs evaluation.    This study aimed to analyze the angular response of the TLD on the fabricated 3D anthropomorphic head phantom and Computerized Imaging Reference Systems (CIRS)- Computed Tomography (CT) dose phantom as a standard phantom irradiated with Cs-137 and to compare the absorbed dose and linear attenuation for both phantoms. Hp(3) analysis, conversion coefficient (hpK(3)), and calibration factor (CF) are also investigated. In this experimental study, the fabricated 3D printed anthropomorphic head phantom was analyzed using polylactic acid (PLA) with the skull and then filled with the artificial brain and cerebrospinal fluid (CSF) as a test phantom. TLD-700H and TLD Reader Harshaw 6600 plus were used to analyze the angular response of Cs-137 radiation and to determine the absorbed dose and linear attenuation coefficient of test and standard phantoms.  The effect of the angle of radiation source towards TLD reading at the anthropomorphic head phantom has a similar value to the standard phantom with a calibration factor ranging from 0.82 to 1. The absorbed dose measurement and the linear attenuation coefficient of the anthropomorphic head phantom with the standard phantom have different values of 2.52 and 3.78%, respectively.   The fabricated 3D printed anthropomorphic head phantom has good potential as an alternative to standard phantoms for TLD calibration in eye lens dosimeter.

In this study, Radiomic features analysis of CT scan images of the irradiated breast compared to the contralateral breast after a 12 Gy boost radiation dose in IOERT was conducted to obtain radiation-sensitive indicators (parameters) biological markers or biological dosimeters. 35 contrast chest CT scans (with unilateral ductal carcinoma in situ (DCIS) who had undergone boost IOERT) were used in this study. The total number of 259 CT radiomic features (first-order, textural, gradient, and autoregressive model-based features) were extracted using Mazda software. The features that were significantly different in the two breasts were selected. A score was assigned to each of the features and the highest scores were characterized (according to the level of significant differences). The feature selection process was performed using the hybrid feature selection method. CT Texture analysis indicated that radiation dose causes significant changes in some radiomic features of the breast tissue.  With more research in the future, we can fit the Delta-Radiomics values with the received radiation dose and achieve a biological dosimeter to detect low-dose radiation.

Dosimetric comparison between 3D-conformal radiation therapy (3D-CRT) and helical tomotherapy (HT) in pediatric Medulloblastoma (MB) receiving craniospinal irradiation (CSI). This was a retrospective dosimetric study on five pediatric male patients diagnosed as MB, who were planned to receive CSI post-surgery. Treatment plans for 3D-CRT and HT were generated. Comparison was made in terms of planning target volume (PTV) coverage, homogeneity index (HI), conformity index (CI), organs at risk (OAR) dose, and treatment time (TT). HT increased the minimum dose up to PTV (81% vs. 74%) with better CI and HI (1.024 vs. 0.36 and 1.078 vs. 1.21, respectively). HT decreased the mean and maximum dose to OAR, except for higher mean dose of larynx, oral cavity, pharynx, and comparable V5 of lungs. TT of 3D CRT was shorter than HT (76 seconds vs. 545 seconds). HT was found to be a better treatment option in all the MB cases receiving CSI regarding PTV, conformity, homogeneity, and most of OAR, while TT was shorter in 3D-CRT plan.

Accurate assessment of surface and build-up doses has a key role in radiotherapy, especially for the superficial lesions with uncertainties involved while performing measurements in the build-up region. This study aimed to assess surface and build-up doses for 6 MV photon beam from linear accelerator using parallel plate ionization chamber, EBT3 Gafchromic films, and PRIMO Monte Carlo (MC) simulation code. In this experimental study, parallel plate chamber (PPC05) and EBT3 Gafchromic films were used to measure doses in a build-up region for 6 MV beam from the linear accelerator for different field sizes at various depths ranging from 0 to 2 cm from the surface with 100 cm source to surface distance (SSD) in a solid water phantom. Measured results were compared with Monte Carlo simulated results using PENELOPE-based PRIMO simulation code for the same setup conditions. Effect of gantry angle incidence and SSD were also analyzed for depth doses at the surface and build-up regions using PPC05 ion chamber and EBT3 Gafchromic films. Doses measured at the surface were 14.78%, 19.87%, 25.83%, and 31.54% for field sizes of 5×5, 10×10, 15×15, and 20×20 cm2, respectively for a 6 MV photon beam with a parallel plate chamber and 14.20%, 19.14%, 25.149%, and 30.90%, respectively for EBT3 Gafchromic films. Both measurement sets were in good agreement with corresponding simulated results from the PRIMO MC simulation code; doses increase with the increase in field sizes.  Good agreement was observed between the measured depth doses using parallel plate ionization chamber, EBT3 Gafchromic films, and the simulated depth doses using PRIMO Monte Carlo simulation code.

To compare the dosimetric parameters, clinical complications, and efficacy of helical tomotherapy (HT) and fixed-field intensity-modulated radiotherapy (f-IMRT) in radical radiotherapy for cervical cancer.

From November 2016 to December 2018, 77 cervical cancer patients in radical irradiation were selected, 38 patients undergoing treatment with HT and 39 with f-IMRT. The dosimetic parameters, clinical complications, and efficacy were compared.

The homogeneity index (HI) and conformity index (CI) of HT plans were both superior to those of f-IMRT plans(P=0.000). HT plans resulted in a reduction in the dosimetric parameters of organs at risk (OARs) (P<0.05) except the V10 of small intestine (P=0.682). The incidence of myelosuppression showed no significant differences (P=0.265).The patients with HT had no radiocystitis, grade 2 or above radiation proctitis. The complete remission (CR) rates, efficacy rates (CR+PR) and local control rates of two years were 81.58%,100% and 97.37%.

HT showed advantages in dosimetry, and provided more superior clinical results. It has a good application prospect in radical irradiation for cervical cancer.

The concept of Quality Control (QC) is considered a regular method to control, stabilize, and inspect the function of the diagnostic imaging system. The objective of implementing the QC program is to produce high-quality images by applying a minimum dose of radiation based on the As Low As Reasonably Achievable (ALARA) principle. Therefore, this study aimed to evaluate the status of radiation protection in diagnostic radiology wards of educational hospitals affiliated with Hamadan University of Medical Sciences.

In order to implement the QC programs, standard QC tests were performed for 11 devices at educational hospitals affiliated with Hamadan University of Medical Sciences. A Sweden QC kit called Pirranha was used to carry out the QC tests of X-ray devices, and the dosimetry of controlled areas. Also, the measurement of ambient dose in different places was performed by Graetz dosimeter made in Germany.

Voltage Reproducibility, Exposure time reproducibility, tube outlet Linearity, and tube outlet reproducibility tests in all radiology departments which were in accordance with standard criteria were accepted; however, about 10% of the total filtration resulted in different centers needed to be corrected. In terms of radiation protection, 5% of the centers had problems related to warning signs, dimensions of radiology rooms were not standard at 7% of wards and also required protection was not sufficient at 9 percent. Moreover, there were problems with 12% of radiology centers in terms of dosimetry results and the efficiency of different parts of the radiology device.

QC programs performed by authorized companies are costly. But if these programs are done by qualified physicists in addition to reducing costs, we will see a significant increase in the accuracy and precision of the obtained results.