جستجوی مقالات مرتبط با کلیدواژه "organ dose" در نشریات گروه "پزشکی"

Computed tomography (CT) imaging has a large portion in the dose of patients from radiological procedures; therefore, accurate calculation of radiation risk estimation in this modality is inevitable. In this study, a method for determining the patient‑specific effective dose using the dose–length product (DLP) index in lung CT scan using Monte Carlo (MC) simulation is introduced.

EGSnrc/BEAMnrc MC code was used to simulate a CT scanner. The DOSxyznrc simulation code was used to simulate a specific voxelized phantom from the patient’s lungs and irradiate it according to X‑ray parameter of routing lung CT scan, and dose delivered to thorax organs was calculated. Three types of phantoms were simulated according to three different body habits (slim, standard, and fat patients) in two groups of men and women. A factor was used to convert the relative dose per particle in MC code to the absolute dose. The dose was calculated in all lung organs, and the effective dose was calculated for all three groups of patient body habits. DLP index and volume CT dose index (CTDIvol) were extracted from the patient’s dose report in the CT scanner. The DLP to effective dose conversion factor (k‑factor) for patients with different body habitus was calculated.

Lung radiation dose in slim, standard, and fat patients in men was 0.164, 0.103, and 0.078 mGy/mAs and in women was 0.164, 0.105, and 0.079 mGy/mAs, respectively. The k‑factor in the group of slim patients, especially in women, was higher than in other groups.

CT scan dose indexes for slim patients are reported to be underestimated in studies. The dose report in CT scan systems should be modified in proportion to the patient’s body habitus, to accurately estimate the radiation risk.

Radiotherapy (RT), which is considered one of the critical treatments for cancer patients is also known as adjuvant therapy and palliative care, and can be attempted alone or concurrent with chemotherapy. Although RT reduces the risk of recurrence, the scattered dose may enhance the risk of secondary cancer induction; this is raising some challenges in clinical practice. To the best of our knowledge, few studies to date have assessed such effects of brain cancer adjuvant radiotherapy.

We estimated the RT-induced risk of secondary cancer for a 45-year-old patient who had undergone radiotherapy of the head and pelvis with a 6 MV photon beam in 15 and 10 sessions, respectively. The absorbed dose by the thyroid, breast, eye lenses, region overlying ovaries, and parotids was measured using Thermoluminescent Dosimeters (TLD). Since the patient was scanned before radiotherapy, it was decided to calculate their risk as well. To evaluate the cancer risk, radiobiological models for Excess Absolute Risk (EAR), as well as Excess Relative Risk (ERR) published by the Committee on the Biological Effects of Ionizing Radiation (BEIR) in report VII, were implemented. This study thus aimed to estimate the Risk of Exposure-Induced Death (REID) and assess the radiation dose delivered to patients from Computed Tomography (CT) scans and common diagnostic nuclear medicine examinations.

The mean risk of secondary cancer for sensitive organs was calculated 3 years after radiotherapy. The highest estimated ERR was related to the region overlying right and left ovaries for pelvic radiotherapy (47.82) and (51.17), and the next highest EAR followed by right and left eye lenses for brain radiotherapy (18.09) and (15.43), respectively. In addition, other cancers arising from CT scans had the highest REID values for solid cancer (0.0015) and bone scans revealed the highest REID values for other cancers (0.00121).

Calculating the corresponding risks of RT is of great significance for the patients in procedural change. Choosing proper field sizes and adapted techniques to avoid excessive doses to healthy organs can thus be a great assistance in this regard.

 The purpose of this study was to evaluate the risk of gonad cancer induction attributable to pelvic radiation therapy in adult patients. 

 By characterizing the peripheral dose the TLDs were placed on the testis and ovary in two fractions of radiotherapy. All patients delivered a 45 Gy total dose in 4 fields in the prone position with 3D planning. The doses from a linear accelerator at 18 MV photon beam, were investigated.

 The mean excess relative risk (ERR) based on the BEIR IIV models of men and women after 5 and 10 year of radiotherapy treatment for pelvic radiotherapy was 0.825±0.168, 0.948±0.504, 0.700±0.135, and 0.803±0.407 respectively.

 Estimating the second cancer risk of untargeted organs is crucial in radiotherapy. Using the single-energy mode linear accelerator and proper shields can be minimized the out-of-field doses.

The computed tomography (CT) scan delivers a relatively high radiation dose to the patient. One of the critical factors that affects the absorbed dose is the intensity of tube current. The aim of this study is to measure and compare the radiation dose of three radiation-sensitive organs in constant current mode and tube current modulation (TCM) modes.

CT-scans from the chest and abdomen-pelvis regions of adults in three different current modes were obtained. The absorbed doses of thyroid, lungs, and ovaries were measured using the thermoluminescent dosimeter (TLD) chips embedded in the RANDO phantom. Furthermore, the confirmation of the organ doses was simulated using the Monte Carlo (MC) simulation. The measured doses were evaluated and confirmed by comparison with the simulated doses.

The relative differences between the measured and simulated doses for thyroid, lung, and ovary were -4.7%, -1.3%, and -11.7% for constant current mode, -2.2%, -11.2%, and -6.3% for longitudinal modulation mode, and 0.0%, -14.6%, and -9.9% for angular modulation mode, respectively. With longitudinal modulation mode, thyroid, lung, and ovary doses were reduced by 34.0%, 19.0%, and 19.0% for the measured doses and 32.0%, 26.0%, and 13.0% for the simulated doses, respectively. The longitudinal modulation mode resulted in a greater dose reduction compared to the angular modulation for both measured and simulated doses.

Using TCM resulted in reducing does received by the organs in both measured and simulated doses. The TCM reduces organ dose, which is more evident in the longitudinal modulation.

The study aimed to assess absorbed and effective doses in organs through computed tomography (CT) examinations using automatic exposure control (AEC) and fixed tube current (FTC) techniques.

Scanning parameters were obtained for routine adult CT examinations and used to estimate the organ absorbed and effective doses using CT-Expo software. The estimated effective doses were based on International Commission on Radiological Protection publication 103 recommendations.

Regarding the scans performed with AEC, doses to head, chest, abdomen and pelvic organs were within the range of 19.7-41.8, 6.4-17.4, 19.2-20.9, and 10.5-24.9 mGy respectively. Moreover, the effective doses for the mentioned organs were 1.6, 6.1, 6.4 and 5.4 mSv respectively. Considering FTC technique, doses to organs ranged 16.7-75.5, 4.1-52.2, 10.6-33.2 and 5.2-38.7 mGy respectively. Moreover, the mean effective doses of FTC were 2.1, 6.9, 9.4 and 6.1 mSv, respectively. Examinations performed with AEC technique induced a dose reduction of 9% and 34% for head organs, 52, 62 and 25% for chest organs, 16% and 14% for abdomen organs, and 11% and 10% for pelvic organs, compared to the FTC. A dose increase of 3% was observed for testes. The mean effective doses for scans with AEC were 13-46% lower than those obtained by FTC.

According to the obtained results of the current study, the estimated doses for scans with AEC technique were in a lower level compared to FTC technique. Accordingly, it is recommended to utilize this technique for CT examinations to ensure optimal dose reduction to radiosensitive organs.