Dosimetric evaluation of the Leksell GammaPlan™ Convolution dose calculation algorithm.

The dosimetric accuracy of the Leksell GammaPlan Convolution calculation algorithm was evaluated through comparison with corresponding Monte Carlo (MC) dosimetric results. MC simulations were based on generated sector phase space files for the 4 mm, 8 mm and 16 mm collimator sizes, using a previous comprehensive Gamma Knife Perfexion™ source model and validated using film dosimetry. Test cases were designed for the evaluation of the Convolution algorithm involving irradiation of homogeneous and inhomogeneous phantom geometries mimicking clinical cases, with radiation fields created using one sector (single sector), all sectors with the same (single shot) or different (composite shot) collimator sizes. Dose calculations using the Convolution algorithm were found to be in excellent agreement (gamma pass rate greater than 98%, applying 1%/1 mm local dose difference and distance agreement criteria), with corresponding MC calculations, indicating the accuracy of the Convolution algorithm in homogeneous and heterogeneous model geometries. While of minor clinical importance, large deviations were observed for the voxels laying inside air media. The calculated beam on times using the Convolution algorithm were found to increase (up to 7%) relative to the TMR 10 algorithm currently used in clinical practice, especially in a test case mimicking a brain metastasis close to the skull, in excellent agreement with corresponding MC calculations.

DOSE COEFFICIENTS FOR LIVER CHEMOEMBOLISATION PROCEDURES USING MONTE CARLO CODE.

The aim of the present study is the estimation of radiation burden during liver chemoembolisation procedures. Organ dose and effective dose conversion factors, normalised to dose-area product (DAP), were estimated for chemoembolisation procedures using a Monte Carlo transport code in conjunction with an adult mathematical phantom. Exposure data from 32 patients were used to determine the exposure projections for the simulations. Equivalent organ (HT) and effective (E) doses were estimated using individual DAP values. The organs receiving the highest amount of doses during these exams were lumbar spine, liver and kidneys. The mean effective dose conversion factor was 1.4 Sv Gy-1 m-2 Dose conversion factors can be useful for patient-specific radiation burden during chemoembolisation procedures.

Dual-energy contrast-enhanced digital mammography: patient radiation dose estimation using a Monte Carlo code.

Mammography is a standard procedure that facilitates breast cancer detection. Initial results of contrast-enhanced digital mammography (CEDM) are promising. The purpose of this study is to assess the CEDM radiation dose using a Monte Carlo code. EGSnrc MC code was used to simulate the interaction of photons with matter and estimate the glandular dose (Dg). A voxel female human phantom with a 2-8-cm breast thickness range and a breast glandular composition of 50 % was applied. Dg values ranged between 0.96 and 1.45 mGy (low and high energy). Dg values for a breast thickness of 5.0 cm and a glandular fraction of 50 % for craniocaudal and mediolateral oblique view were 1.12 (low energy image contribution is 0.98 mGy) and 1.07 (low energy image contribution is 0.95 mGy), respectively. The low kV part of CEDM is the main contributor to total glandular breast dose.

Dual-energy contrast-enhanced digital mammography: Glandular dose estimation using a Monte Carlo code and voxel phantom.

PURPOSE: To estimate the mean glandular dose of contrast enhanced digital mammography, using the EGSnrc Monte Carlo code and female adult voxel phantom. METHODS: Automatic exposure control of full field digital mammography system was used for the selection of the X-ray spectrum and the exposure settings for dual energy imaging. Measurements of the air-kerma and of the half value layers were performed and a Monte Carlo simulation of the digital mammography system was used to compute the mean glandular dose, for breast phantoms of various thicknesses, glandularities and for different X-ray spectra (low and high energy). RESULTS: For breast phantoms of 2.0-8.0 cm thick and 0.1-100% glandular fraction, CC view acquisition, from AEC settings, can result in a mean glandular dose of 0.450 ± 0.022 mGy -2.575 ± 0.033 mGy for low energy images and 0.061 ± 0.021 mGy - 0.232 ± 0.033 mGy for high energy images. In MLO view acquisition mean glandular dose values ranged between 0.488 ± 0.007 mGy - 2.080 ± 0.021 mGy for low energy images and 0.065 ± 0.012 mGy - 0.215 ± 0.010 mGy for high energy images. CONCLUSION: The low kV part of contrast enhanced digital mammography is the main contributor to total mean glandular breast dose. The results of this study can be used to provide an estimated mean glandular dose for individual cases.

Evaluation of organ and effective doses during paediatric barium meal examinations using PCXMC 2.0 Monte Carlo code.

Radiation protection and estimation of the radiological risk in paediatric radiology is essential due to children's significant radiosensitivity and their greater overall health risk. The purpose of this study was to estimate the organ and effective doses of paediatric patients undergoing barium meal (BM) examinations and also to evaluate the assessment of radiation Risk of Exposure Induced cancer Death (REID) to paediatric patients undergoing BM examinations. During the BM studies, fluoroscopy and multiple radiographs are involved. Since direct measurements of the dose in each organ are very difficult if possible at all, clinical measurements of dose-area products (DAPs) and the PCXMC 2.0 Monte Carlo code were involved. In clinical measurements, DAPs were assessed during examination of 51 patients undergoing BM examinations, separated almost equally in three age categories, neonatal, 1- and 5-y old. Organs receiving the highest amounts of radiation during BM examinations were as follows: the stomach (10.4, 10.2 and 11.1 mGy), the gall bladder (7.1, 5.8 and 5.2 mGy) and the spleen (7.5, 8.2 and 4.3 mGy). The three values in the brackets correspond to neonatal, 1- and 5-y-old patients, respectively. For all ages, the main contributors to the total organ and effective doses are the fluoroscopy projections. The average DAP values and absorbed doses to patient were higher for the left lateral projections. The REID was calculated for boys (4.8 × 10(-2), 3.0 × 10(-2) and 2.0 × 10(-2) %) for neonatal, 1- and 5-y old patients, respectively. The corresponding values for girl patients were calculated (12.1 × 10(-2), 5.5 × 10(-2) and 3.4 × 10(-2) %).

Effective dose in percutaneous transhepatic biliary drainage examination using PCXMC2.0 and MCNP5 Monte Carlo codes.

OBJECTIVES: To estimate the organ equivalent doses and the effective doses (E) in patient undergoing percutaneous transhepatic biliary drainage (PTBD) examinations, using the MCNP5 and PCXMC2 Monte Carlo-based codes. METHODS: The purpose of this study is to estimate the organ doses to patients undergoing PTBD examinations by clinical measurements and Monte Carlo simulation. Dose area products (DAP) values were assessed during examination of 43 patients undergoing PTBD examination separated into groups based on the gender and the dimensions and location of the beam. RESULTS: Monte Carlo simulation of photon transport in male and female mathematical phantoms was applied using the MCNP5 and PCXMC2 codes in order to estimate equivalent organ doses. Regarding the PTBD examination the organ receiving the maximum radiation dose was the lumbar spine. The mean calculated HT for the lumbar spine using the MCNP5 and PCXMC2 methods respectively, was 117.25 mSv and 131.7 mSv, in males. The corresponding doses were 139.45 mSv and 157.1 mSv respectively in females. The HT values for organs receiving considerable amounts of radiation during PTBD examinations were varied between 0.16% and 73.2% for the male group and between 1.10% and 77.6% for the female group. E in females and males using MCNP5 and PCXMC2.0 was 5.88 mSv and 6.77 mSv, and 4.93 mSv and 5.60 mSv. CONCLUSION: The doses remain high compared to other invasive operations in interventional radiology. There is a reasonable good coincidence between the MCNP5 and PCXMC2.0 calculation for most of the organs.

Verification of radiation dose calculations during paediatric cystourethrography examinations using MCNP5 and PCXMC 2.0 Monte Carlo codes.

The estimation of the radiological risk in the case of children is of particular importance due to their enhanced radiosensitivity when compared with that of adult patients. The purpose of this study is to estimate the organ and effective doses of paediatric patients undergoing micturating cystourethrography examinations. Since direct measurements of the dose in each organ are very difficult, dose-area products of 90 patients undergoing cystourethrography examinations were recorded and used with two Monte Carlo codes, MCNP5 and PCXMC2.0, to assess the organ doses in these procedures. The organs receiving the highest radiation doses were the urinary bladder (ranging from 1.9 mSv in the newborn to 4.7 mSv in a 5-y old patient) and the large intestines (ranging from 1.5 mSv in the newborn to 3.1 mSv in the 5-y old patient). For all ages the main contributors to the total organ or effective doses are the fluoroscopy projections compared with the radiographs. There was a reasonable agreement between the dose estimates provided by PCXMC v2.0 and MCNP5 for most of the organs considered in this study. In special cases, there were systematic disagreements in organ doses such as in the skeleton, gonads and oesophagus due to the anatomical differences between patient anatomic models employed by the two codes.

Monte Carlo estimation of dose difference in lung from 192Ir brachytherapy due to tissue inhomogeneity.

Lung brachytherapy using high-dose rate (192)Ir technique is a well-established technique of radiation therapy. However, many commercial treatment planning systems do not have the ability to consider the inhomogeneity of lung in relation to normal tissue. Under such circumstances dose calculations for tissues and organs at risk close to the target are inaccurate. The purpose of the current study was to estimate the dose difference due to tissue inhomogeneity using the Monte Carlo simulation code MCNP-5. Results showed that there was a relative sub dosage by treatment planning systems calculations in neighbouring tissues around the radioactive source due to inhomogeneity ignorance. The presence of lung instead of normal tissue resulted in an increase in relative dose, which approached 8 % at 4-cm distance from the source. Additionally, the relative increase was small for the lung (2.1 %) and larger for organs at risk such as the heart (6.8 %) and bone marrow (7.6 %).

Monte Carlo estimation of radiation doses during paediatric barium meal and cystourethrography examinations.

Organ doses are important quantities in assessing the radiation risk. In the case of children, estimation of this risk is of particular concern due to their significant radiosensitivity and the greater health detriment. The purpose of this study is to estimate the organ doses to paediatric patients undergoing barium meal and micturating cystourethrography examinations by clinical measurements and Monte Carlo simulation. In clinical measurements, dose-area products (DAPs) were assessed during examination of 50 patients undergoing barium meal and 90 patients undergoing cystourethrography examinations, separated equally within three age categories: namely newborn, 1 year and 5 years old. Monte Carlo simulation of photon transport in male and female mathematical phantoms was applied using the MCNP5 code in order to estimate the equivalent organ doses. Regarding the micturating cystourethrography examinations, the organs receiving considerable amounts of radiation doses were the urinary bladder (1.87, 2.43 and 4.7 mSv, the first, second and third value in the parentheses corresponds to neonatal, 1 year old and 5 year old patients, respectively), the large intestines (1.54, 1.8, 3.1 mSv), the small intestines (1.34, 1.56, 2.78 mSv), the stomach (1.46, 1.02, 2.01 mSv) and the gall bladder (1.46, 1.66, 2.18 mSv), depending upon the age of the child. Organs receiving considerable amounts of radiation during barium meal examinations were the stomach (9.81, 9.92, 11.5 mSv), the gall bladder (3.05, 5.74, 7.15 mSv), the rib bones (9.82, 10.1, 11.1 mSv) and the pancreas (5.8, 5.93, 6.65 mSv), depending upon the age of the child. DAPs to organ/effective doses conversion factors were derived for each age and examination in order to be compared with other studies.

Magnetic resonance imaging in 120 patients with intractable partial seizures: a preoperative assessment.

The aim of this study was to describe magnetic resonance imaging (MRI) findings in patients with medically intractable epilepsy and to compare different magnetic resonance (MR) sequences in order to establish a dedicated and shorter scan time imaging protocol of choice. One hundred and twenty patients with seizures that were refractory to medical treatment were assessed by MRI with spin-echo (SE) T1, fast spin-echo (FSE) T2, fluid-attenuated inversion recovery (FLAIR), inversion recovery (IR) and contrast-enhanced T1 SE sequences. Pathological scans were acquired in 78 patients. Hippocampal sclerosis was detected in 30 patients (25%), cerebral, tumoral, mass lesions in 12 patients (10%), vascular malformations in nine patients (7.5%), cortical infarcts in eight patients (6.7%), cerebral infections in four patients (4.2%) and developmental disorders in 15 patients (12.5%). The most common location of the lesions was the temporal lobe (60%). Coronal, thin (slice thickness 4-5 mm) images have proven to be the most useful in the assessment of the hippocampus. FLAIR and IR are particularly useful in the detection of lesions abutting cerebrospinal fluid (CSF) spaces and developmental disorders, respectively, while T1 SE sequences before and after the intravenous administration of gadolinium offer great facility in identifying space-occupying lesions and infections. MRI is the most important diagnostic tool for the assessment of epileptogenic foci, thus playing the primary role in indicating the type of treatment to be applied.