Application of high-resolution radiochromic film dosimetry in verifying a small-field stereotactic radiosurgery plan.

A high-resolution radiochromic film dosimetry (Hr-RCFD) method has been applied to verify a small-field stereotactic radiosurgery (SRS) plan. This was done by exposing a RCF in a Perspex head phantom undergoing the same treatment plan as the patient. The dose distribution obtained by the Hr-RCFD was verified against that calculated by the stereotactic treatment planning system and the result was satisfactory. The Hr-RCFD method has been found to be an accurate and practical tool in verifying small-field SRS plans.

Dose Optimization in Lumbar Spine Radiographic Examination by Air Gap Method at CR and DR Systems: A Phantom Study.

OBJECTIVE: This study aims at investigating the feasibility of replacing an antiscatter grid with an air gap to achieve dose reduction for lumbar spine radiography while retaining image quality at an acceptable diagnostic level. METHODS: Frontal and lateral projections of lumbar spine radiographic examinations were performed on an anthropomorphic phantom. Nongrid images of both the computed radiography (CR) and digital radiography (DR) systems with air gap thickness ranging from 0 to 25 cm were produced and compared with their corresponding grid images. Dose measurements using thermoluminescent dosimeters at the ovary and testes regions of the phantom were conducted. The image quality of all the images was evaluated by five radiographers using image quality score and visual grading analysis tests. Data on dose measurements and image quality tests were input for statistical analysis. The dose area product (DAP) of all the examinations was recorded and input for the computation of effective doses using a PC-based Monte Carlo program (PCXMC 2.0; STUK, Helsinki, Finland). RESULTS: Significant dose reduction effects on the ovaries of 60.2%-74.1% and 55.1%-73.3% were found, respectively, at the frontal and lateral projections of nongrid lumbar spine examinations compared with their corresponding grid ones in both the CR and DR systems. Results on the image quality score and visual grading analysis tests showed that nongrid images with 10-cm and 5-cm of air gap thicknesses respective to the frontal and lateral images of the lumbar spine were rated with the highest scores. In general, a dose reduction effect using the air gap method was found to be more pronounced in the CR system compared with the DR system. Nevertheless, the CR system delivered a 2.4-4.5 times higher ovary dose respective to the frontal and lateral projections of lumbar spine examinations compared with the DR system. CONCLUSIONS: Ten and 5 centimeters were found to be the optimal air gap thicknesses respective to the frontal and lateral lumbar spine radiographic examinations of the tested Rando phantom (Alderson Laboratories, Stamford, CT) in both the CR and DR systems. Significant dose reduction effects on both the ovary and testes regions of the nongrid examinations were shown. The effective dose computed from PCMCX 2.0 reflected that the risk of cancer induction was halved when an antiscatter grid was replaced by the nongrid method with an optimal air gap thickness in the tested examinations. Further reduction on cancer risk could be achieved by using DR instead of the CR system.

An Investigation on the Non-uniform Distribution of Radiation Intensity Output of Diagnostic X-ray Tubes.

OBJECTIVE: This study aimed at investigating the air kerma distribution of the radiation output in two and three dimensions of three general radiographic units by physical measurements. METHODS: A 6-cm3 ionization chamber was placed at 5-cm intervals of 225 locations in a 70 × 70 cm2 x-ray beam field. The chamber was placed at a level of 30 cm above the x-ray table to measure the air kerma intensity of the x-ray output across the whole area. Three different brands of radiographic units with different anode target angles and at different tube aging stages were studied. The same exposure parameters were used for each location, and measurements were made for three different tube potentials at 60, 85, and 110 kilovoltage peaks (kV[p]). RESULTS: At the tube potential of 85 kV(p), the relative maximum percentage differences on the average air kerma measured along the central anode-cathode axis (x-axis) of the x-ray tube were found to be 31.5%, 15.5%, and 43.1% more at the cathode ends than those at the anode ends of the three radiographic units. Results of a paired samples t test (confidence intervals at 95%, two-tailed) on three of the four fixed pair-wise sampling points along the x-axis were found to be statistically significant in their relative percentage differences in air kerma intensity with respect to the central point (labeled as 35 cm) with a P value ≤.03. However, those measured at four fixed pair-wise points at 90° across the anode-cathode direction were all found to be statistically nonsignificant (P ≥ .29). Similar trends were observed for the other two tube potentials tested. From the three-dimensional displays of radiation output intensity, a similar unique pyramidal shape pattern with a skewed peak toward the cathode end was observed for all three diagnostic x-ray tubes tested. CONCLUSIONS: The anode heel effect was found to be enhanced in the x-ray tube with a smaller anode target angle, more aging, and higher tube potentials. Three-dimensional air kerma distribution maps of the three x-ray units tested were found to be similar in pattern, and this was displayed in detail regarding the extent of the anode heel effect.

Utilization of recycled cathode ray tubes glass in cement mortar for X-ray radiation-shielding applications.

Recycled glass derived from cathode ray tubes (CRT) glass with a specific gravity of approximately 3.0 g/cm(3) can be potentially suitable to be used as fine aggregate for preparing cement mortars for X-ray radiation-shielding applications. In this work, the effects of using crushed glass derived from crushed CRT funnel glass (both acid washed and unwashed) and crushed ordinary beverage container glass at different replacement levels (0%, 25%, 50%, 75% and 100% by volume) of sand on the mechanical properties (strength and density) and radiation-shielding performance of the cement-sand mortars were studied. The results show that all the prepared mortars had compressive strength values greater than 30 MPa which are suitable for most building applications based on ASTM C 270. The density and shielding performance of the mortar prepared with ordinary crushed (lead-free) glass was similar to the control mortar. However, a significant enhancement of radiation-shielding was achieved when the CRT glasses were used due to the presence of lead in the glass. In addition, the radiation shielding contribution of CRT glasses was more pronounced when the mortar was subject to a higher level of X-ray energy.

Comparison of radiation dose for implant imaging using conventional spiral tomography, computed tomography, and cone-beam computed tomography.

OBJECTIVE: The objective of this study was to compare typical patient radiation dose delivered in implant imaging with spiral computed tomography (CT), conventional spiral tomography, and cone-beam CT (CBCT). STUDY DESIGN: The Scanora (Orion Corporation Soredex, Helsinki, Finland), Spiral HiSpeed/Fxi (General Electric, Milwaukee, WI), and Classic iCAT (Imaging Sciences International, Hatfield, PA) units were selected to represent conventional spiral tomography, spiral CT, and CBCT, respectively. Thermoluminescent dosimeters were used in a Rando phantom to measure radiation-absorbed doses to the lenses, parotid glands, submandibular glands, sublingual gland, and the thyroid for maxillary and mandibular implant imaging techniques. RESULTS: Spiral CT delivered the highest absorbed dose, whereas CBCT delivered the lowest in both maxillary and mandibular implant scans. The salivary glands received the highest absorbed doses. Scanora delivered lower radiation doses than CBCT when the anterior region of the maxilla or mandible was irradiated. CONCLUSION: In implant imaging, CT delivers the highest radiation dose to the salivary glands, whereas the CBCT system studied delivers the lowest dose. Irrespective of imaging modality, during implant imaging as conducted for this study, salivary glands receive most radiation.

Is eye size related to orbit size in human subjects?

The purpose of this study is to determine if there is an association between eye size and the volume of the orbit in adult subjects. Thirty-three subjects with varying degrees of ametropia (+1.00 to -12.75 D) underwent magnetic resonance scan of the orbit. Results show that the larger myopic eye was not associated with a larger orbit.

Orbital development in Hong Kong Chinese subjects.

The purpose of this study was to examine the development of the orbit in Hong Kong Chinese subjects. Orbit volume was determined from magnetic resonance images of 81 subjects aged from 1 to 42 years old. Results show that orbit volume ranged from 11.56 to 25.50 cm3. In the first year of life, the mean orbit volume was 12.36 cm3. The orbit showed rapid growth in the first 3 years of life. From about 1-3 years old, the mean volume was 15.31 cm3. The orbit grew steadily to the age of 10 years. From age 11 to 15 years old, the mean volume was 20.24 cm3. Orbit growth levelled off at about 16 years of age with the mean volume at 21.00 cm3.