Clay as thermoluminescence dosemeter in diagnostic radiology applications.

BACKGROUND: As part of efforts to isolate and utilize local and naturally occurring materials for development of thermoluminescece dosemeters and other technologies, an earlier report had shown that Nigerian clay showed prospects of utility as a thermoluminescence dosemeter (TLD). This paper reports the investigation of the basic thermoluminescence properties of clay at x-rays in the diagnostic radiology range, including dose monitoring in abdominal radiography. METHODOLOGY: Clay sourced from Calabar, Nigeria, was tested for thermoluminescence response after irradiation at diagnostic radiology doses, including application in abdominal radiography dose monitoring in a clinical setting. RESULTS: Results show that thermoluminescence (TL) output in natural clay is very low, but demonstrates enhanced performance with the addition of common salt. Specific TL characteristics of good repeatability for individual and batched pellets (variability index of 3.08%) and a high degree of trap emptying were observed. It had a glow curve peak at 275 degrees C; with traces of spurious thermoluminescence emission at the reader anneal temperature. There was evidence of good batch homogeneity (< 30%) and a similar pattern of dose absorption in abdominal radiography with commercial Lithium Fluoride (LiF TLD-100). A high fading rate (over 30% in twelve hours) and low sensitivity (12 times less than LiF TLD-100) however, signal the unacceptability of clay as a TLD in diagnostic radiology in the forms studied. CONCLUSION: Clay demonstrates poor TL response at diagnostic radiology doses. However, it's water absorbing property offers a means of overcoming the hygroscopic nature of common salt. This could be explored to improve the use of sodium chloride as a radiation detector.

An on-line replanning scheme for interfractional variations.

Ability of online adaptive replanning is desirable to correct for interfraction anatomic changes. A full-scope replanning/reoptimization with the current planning techniques takes too long to be practical. A novel online replanning strategy to correct for interfraction anatomic changes in real time is presented. The scheme consists of three steps: (1) rapidly delineating targets and organs at risk on the computed tomography of the day by modifying original planning contours using robust tools in a semiautomatic manner, (2) online segment aperture morphing (SAM) (adjusting beam/ segment apertures) by applying the spatial relationship between the planning target contour and the apertures to the new target contour, and (3) performing segment weight optimization (SWO) for the new apertures if necessary. The entire scheme was tested for direct-aperture-based IMRT on representative prostate and abdomen cases. Dose volume histograms obtained with the online scheme are practically equivalent to those obtained with full-scope reoptimization. For the days of small to moderate organ deformations, only the SAM is necessary, while for the large deformation days, both SAM and SWO are required to adequately account for the deformation. Both the SAM and SWO programs can be completed within 1 min, and the overall process can be completed within 10 min. The proposed SAM-SWO scheme is practically comparable to full-scope reoptimization, but is fast enough to be implemented for on-line adaptive replanning, enabling dose-guided RT.

Consequences of modern anthropometric dimensions for radiographic techniques and patient radiation exposures.

Radiographic techniques are devised on the basis of anatomic dimensions. Inaccurate dimensions can cause radiographs to be exposed inappropriately and patient radiation exposures to be calculated incorrectly. The source of anatomic dimensions in common usage dates back to 1948. The objective of this study was to compare traditional and modern anthropometric data, use modern dimensions to estimate potential errors in patient exposure, and suggest modified technique guidelines. Anthropometry software was used to derive modern anatomic dimensions. Data from routine annual testing were analyzed to develop an x-ray generator output curve. Published tabulated data were used to determine the relationship between tissue half-value layer and kilovoltage. These relationships were used to estimate entrance skin exposure and create a provisional technique guide. While most anatomic regions were actually larger than previously indicated, some were similar, and a few were smaller. Accordingly, exposure estimates were higher, similar, or lower, depending on the anatomic region. Exposure estimates using modern dimensions for clinically significant regions of the trunk were higher than those calculated with traditional dimensions. Exposures of the postero-anterior chest, lateral chest, antero-posterior (AP) abdomen, male AP pelvis, and female AP pelvis were larger by 48%, 31%, 54%, 52%, and 112%, respectively. The dimensions of bony regions of the anatomy, such as the joints and skull, were unchanged. These findings are consistent with the idea that anatomic areas where fat is deposited are larger in the modern U.S. population than they were in previous years. Exposure techniques for manual radiography and calculations of patient dose for automatic exposure control radiography should be adjusted according to the modern dimensions. Population radiation exposure estimates calculated in national surveys should also be modified appropriately.