Electron contamination for 6 MV photon beams from an Elekta linac: Monte Carlo simulation

In external beam radiotherapy, the photons from a linear accelerator (linac) machine undergo multiple interactions, not only in the patient but also in the linac head and the air column between the linac head and the patient. Electrons are released from these interactions and contaminate the beams. The current study evaluates electron contamination for 6 MV photon beams from an Elekta linac using Monte Carlo simulation. The linac head was simulated by the BEAMnrc code and the absorbed dose in a phantom was calculated using the DOSXYZnrc code. The parameters of the initial electron beams on the target, such as mean energy and radial intensity distribution, were determined by matching the calculated dose distributions with the measured dose (at 10 x 10 cm2 field size and 90 cm source-skin distance). The central axis depth-dose curves of electron contamination were calculated for various field sizes from 5 x 5 cm2 to 40 x 40 cm2. We investigated the components that generated the electron contamination for a field size of 10 x 10 cm2. The optimal initial electron beam energy was 6.3 MeV with a full-width half maximum (FWHM) of the radial intensity distribution of 1.0 mm. These parameters were found to be in good agreement with the measured data. Electron contamination increased as the field size increased. At a depth of 1.0 mm and field sizes of 5 x 5, 10 x 10, 20 x 20, 30 x 30, and 40 x 40 cm2, the doses from electron contamination were 3.71, 5.19, 14.39, 18.97 and 20.89 %, respectively. Electron contamination decreased with increased depth. At a depth of 15 mm, the electron contamination was about 1 %. It was mainly generated in the air column between the linac head and the phantom (3.65 %), the mirror (0.99 %), and the flattening filter (0.59 %) (for the depth of 1.0 mm and the field size of 10 x 10 cm2)

Spektroskopi Inframerah Senyawa Kalsium Fosfat Hasil Presipitasi

Infrared Spectroscopy of Precipitated Calcium Phosphate Compound. Samples of calcium phosphate compounds were produced from saturated solutions containing of calcium and phosphate ions. The experiments were carried out using solutions at temperature 25 ºC and 70 ºC, combined with different pH value of 5, 7, 9 and 11. Precipitation mass from solutions at 70 ºC was relatively higher compare to that produced from solutions at 25 ºC. It was also shown that generally the mass precipitation rose with the increasing of pH. Sample analyses were performed with the use of infrared spectroscopy, particularly for the samples produced from solutions at 70 ºC. Based on the v4 phosphate absorption band, it was indicated that apatite crystals found in most samples which its amount gave rise to the increasing of pH. Infrared spectroscopy of the heated samples produced with pH 11 showed that water molecules could be present either at the surface of crystals or trapped in the crystal structure

SPEKTROSKOPI INFRAMERAH SENYAWA KALSIUM FOSFAT HASIL PRESIPITASI

Infrared Spectroscopy of Precipitated Calcium Phosphate Compound. Samples of calcium phosphate compounds were produced from saturated solutions containing of calcium and phosphate ions. The experiments were carried out using solutions at temperature 25 ºC and 70 ºC, combined with different pH value of 5, 7, 9 and 11. Precipitation massfrom solutions at 70 ºC was relatively higher compare to that produced from solutions at 25 ºC. It was also shown that generally the mass precipitation rose with the increasing of pH. Sample analyses were performed with the use of infrared spectroscopy, particularly for the samples produced from solutions at 70 ºC. Based on the ν4 phosphate absorption band, it was indicated that apatite crystals found in most samples which its amount gave rise to the increasing of pH. Infrared spectroscopy of the heated samples produced with pH 11 showed that water molecules could be present either at the surface of crystals or trapped in the crystal structure.Keywords: calcium phosphates, apatite crystals,infrared spectroscop

Occupational Dose Estimation with Field Size, Position and C-Arm Gantry Tilt Variations During Interventional Cardiology Procedures

In Interventional Cardiology, dose received by the patient is relatively higher, while the occupational would receive scattered radiation dose whose quality is relatively lower. However, the occupational received accumulative doses of all cardiovascular procedures were done over the years. Therefore, the purpose of this paper will focus to estimate the distribution of scattered dose to occupational without any protective shielding in the Cath Lab. The scattered dose rate was measured by using survey detector of Unfors Xi. The detector was placed at 6 different positions around the phantom. Each measurement position has eleven points from 25 to 175 cm above the floor with increment of 15 cm as the illustration of partial height of occupational organ. Experimentally a Rando phantom was irradiated by automatic pulsed fluoroscopy with condition varies in the range of 88-93 kV and 5.7-9.4 mA depend on gantry tilt and field size. The Philips C-arm gantry tilt was varied at 0o PA projection, 20o and 30o Caudal, 20o and 30o Cranial, and 40o and 50o Left Anterior Oblique, and also Flat Panel Detector (FPD) was varied at 20 x 20 and 25 x 25 cm2. Generally, the greatest dose rate was known at level corresponding to the waist (100 cm) of occupational and the lowest at head areas (175 cm) of occupational which is 2.49 mGv/h and 0.02 mGy/h, respectively. The given data showed that the scattered fractions are in the range of 0.001-0.060% from its primary dose at isocenter. The scattered doses tend to increase with gantry tilt for all positions. Increasing field size of FPD will decreased the scattered fraction from its dose at isocenter, and also it affects the scattered dose rate

Composition of Human Bone Mineral by FTIR and Its Relationship to the Age

Deproteinated human bone with hydrazine indicated that percentage of bone mass mineral increased with individual age in the range of child to adult, and then slowly decreased with ageing. Type of bone and sex also influenced the proportional of mineral in bone. Several information was obtained from infrared spectroscopy measurements. Calcium phosphate in bone mineral was a mixture of amorphous calcium phosphates and apatite crystals that rich of carbonates. Most crystals were carbonate apatite type B, with additional small amount of type A and AB. The splitting factor of υ4 phosphate bands indicated that crystalline degree was regulated by age, increases in the range of child to adult, then decrease up to a certain value (0.16) and finally almost constant. It is predicted that apatite crystals that was formed with less calcium phosphate will accompanied by the insertion of crystallization water in order to maintain the constancy of bone volume

Towards a Phantom for Multimodality Performance Evaluation of Breast Imaging: A 3D Structured Phantom with Simulated Lesions Tested for 2D Digital Mammography

© Springer International Publishing Switzerland 2016. The aim of this work is to test whether a 3D structured phantom with simulated lesions can be used for performance evaluation of 2D digital mammography, as a step towards a multimodality phantom. A phantom, developed for breast tomosynthesis was therefore applied on 23 digital mammography systems. Ten images were acquired at the clinically used dose and for 11 systems also at half and double dose. The images were read in a four-alternative forced choice (4-AFC) paradigm by 5 readers. CDMAM phantom acquisitions were also performed. It was possible to calculate diameter thresholds of the simulated masses and microcalcifications that guarantee 62.5% correct response. The results showed the expected sensitivity with mean glandular dose: detectability of microcalcifications improved with dose, whereas the detectability of masses was not affected. Systems of the same manufacturer and operated at similar doses had very similar detectability scores. Percentage correctly detected microcalcifications with average diameter 119 μm correlated with CDMAM based gold thickness thresholds. Present phantom, developed and tested for tomosynthesis, is also a good candidate for 2D mammography, suggesting its use for (future) benchmarking of at least two types of imaging systems.status: publishe