Preliminary Dose Measurements on the SCANNEX Low Dose X-Ray Unit

A modified version of the SCANNEX X-ray unit for medical diagnostic purposes has been developed by DEBEX, a Division of De Beers Mining Co. The unit was designed using technology developed for the detection of diamonds in mine workers. One of the prime features of this scanning, slit imaging X-ray unit is the low radiation dose to the patient and personnel. 

A prototype of this unit was installed in the trauma department of Groote Schuur Hospital for clinical and physics trials, enabling us to measure the radiation doses in the primary beam and around the unit. 

Dose measurements were carried out for all possible kV and mA settings with different collimators and added filtration, full and partial scans. 

The doses around the unit were about 3% of those for conventional X-ray units, whereas the patient surface entrance doses ranged from 0.3 to 13% of those for conventional X-rays. 
back...

Effect of Evening Primrose Oil (EPO) Supplementation on Mouse Tissue Radiation Response

Aim:

1. To determine the effect of EPO supplementation on mouse skin response to radiation.
2. To determine the effect of EPO supplementation on mouse tumour response to radiation.

Method:

Results:

The tumour radiation growth delay of mice receiving EPO supplementation increased and was statistically different when compared to that of control mice. 

Conclusion:

The Effect of Inhibitors of Energy Metabolism on the Radiation Response of Tumours In Vivo

Inhibitors of energy metabolism, 2-deoxyglucose (2DG) and aminooxyacetic acid (AOA) have been used to inhibit energy metabolism, the former inhibiting glycolysis and the latter inhibiting glutaminolysis. Since a supply of energy is required for repair of radiation damage to take place, it was proposed that the presence of these inhibitors would inhibit such repair. Experiments were performed using tumour growth delay assay in 3 tumour types. Contrary to results by previous workers, no statistically significant change in growth delay was found for tumours in mice administered 2DG prior to radiation relative to that for tumours in mice given saline prior to radiation. However, when, AOA was administered together with 2DG a reduction in radiation induced growth delay was found. This suggests that some kind of interaction may exist between glycolysis and glutaminolysis, which may influence energy supply and possibly repair. 
back...

Rays of Hope: A Radiotherapy Information Video

Purpose:

Methods:

Results:

• What is cancer?
• What is radiotherapy?
• What can a patient expect when radiotherapy is prescribed?
• What side effects or reactions can occur due to radiotherapy?
• What other support systems are available to patients?
• What happens behind the scenes?

Conclusion:

Fetal Dose Estimation during Three Different Diagnostic Radiology Procedures.

Purpose:

Introduction:

Method:

1. ) Existing tabulated data [ NCRP report No. 54, Fetal Dose Estimates for CT Pelvimetry, M.M Moore, D.R. Shearer, Radiology 1989;171 ]
2. ) TLD’s

Results:

Conclusion:

Dose Area Product (DAP) Measurement for Determining Reference Doses in Radiology

Purpose:

Method:

Conclusion:

Implementation of Revised Dosimetric Quantities and Dose Limits for Radiation Protection in Medicine

Objective:

Method:

Results:

Conclusion:

Radiation dosimetry of craniopagus twins during Tc^99m-DTPA and Tc^99m-HMPAO studies.

Introduction:

Aim:

Method:

Results:

Simple Method of Measuring Glomerular Filtration Rate below 30 ml/min

The recommended technique for measurment of glomerular filtration rate (GFR) less than 30 ml/min requires the counting of plasma and urine samples. An alternative method is described to give a body surface area (BSA) normalised GFR measurement (GFR_n) which requires a single injection of Tc-99m DTPA and the counting of two blood plasma samples. No other measurement such as BSA or injected dose is needed. 

The theoretical background was described and mathematical analysis of errors due to enlarged or reduced patients extracellular volume (ECV) was performed. 

The method was tested on patients referred for conventional Tc-99m DTPA renography and a Cr-51 EDTA BSA normalised GFR measurement (GFR_{n a}) by the slope intercept technique. Simultaneous measurement of GFR_n with Tc-99m DTPA and GFR_{n a} on 28 patients whose GFR was less than 50 ml/min were selected for analysis. Taking GFR_{n a} as standard, the GFR_n method was found to be accurate for a normal size ECV but was in error for an enlarged or reduced ECV. For GFR less than 30 ml/min these errors were acceptably small. 

The GFR_n method may be useful when poor renal function is observed during conventional scintigraphic renography and a GFR measurement is required for confirmation. The injected renographic dose can be used for the measurement and at least 15 minutes will be available after renography to arrange for blood sampling. 
back...

Normalisation of Glomerular Filtration Rate in Adults and Children: Body Surface Area or Extracellular Fluid?

Introduction:

Method:

Results:

Conclusion:

1. The Du Bois formula for the calculation of body surface area correlates well with the Haycock formula in children and in adults and can therefore be used for the normalisation of GFR.
2. Extracellular volume can be used as the normalisation variable in adults.
3. Body surface area is the most accurate parameter for the normalisatiion of GFR in children.

References:

1. Russell CD, Bischoff PG, Kontzen FN, et al: Measurement of glomerular filtration rate: Single injection plasma clearance method without urine collection. Journal of Nuclear Medicine 26: 1243-1247,1985
2. Du Bois D and Du Bois EF: A formula to estimate the approximate surface area if height and weight are known. Arch Intern Med 17: 863,1916
3. Haycock GB, Chir B, Schwartz GJ, Wisotsky DH: Geometric method for measuring body surface area. Journal of Pediatrics 93: 62,1978

Left Ventricular Ejection Fraction Normal Values

Introduction:

Method:

Results:

Conclusion:

References:

1. Franken, P.R.; Deconinck, F.; Bourguignon, M.H.; Busemann Sokole, E. and contributors to the ENCD, European variability of left ventricular ejection fraction from gated blood pool studies. J. Nuc. Med. Proceedings, Proceedings of 44th Annual Congress, San Antonio, Texas, No. 725, 168P, June 1997.
2. Siemens Operating Instructions. Clinical Protocols for ICON-Volume 1, Rev. 06, February 1996.

I am a Medical Physicist

Aim:

Content:

Poster 2 contains more information and is slightly less accessible. The information gives more insight into making on career choices. 

Poster 3 is a more formal presentation of the profession of Medical Physics. A brief outline of the scope of practice is included (2). An example calculation is also given (3). 

Conclusion:

References:

1. Institute of Physics and Engineering in Medicine, "Physics in Engineering and Medicine", Ed. P.N.T. Wells, 1997.
2. Department of National Health and Population Developement, "Regulations Defining The Scope Of The Profession Of Medical Physicist", Government Gazette No. 11152, pg. 46-47, 26 February 1988.
3. Johns, H.E.; Cunningham, J.R. "The Physics of Radiology", IV Ed., 1983, Charles C Thomas.

Quality Control for Diffusion Imaging in MRI

Introduction

Method

Specific imaging parameter (1) used are : 

1. Resonance Frequency
2. Signal to Noise ratio
3. Spatial linearity
4. Spatial resolutio
5. Slice thickness 
6. Slice separation
7. a 5 step diffusion gradient in all 3 planes simultaneously (x,y,z) and in individual plane x,y,z in steps of 0.4 mT m^-1.

Results

Discussion

Conclusion

References:

1. Price R R, Axel L, et al, Med Phys 11.7(2) Mar/Apr 1990 287 - 295

Progressively Reduced Sm-153-EDTMP Uptake in Normal Bone after Multiple Applications; A Non-Human Primate Study

Re-application of Sm-153-EDTMP for maintained palliation of metastatic bone pain in patients was found to be progressively less effective. Does EDTMP exert a blocking function, limiting access to bone tissue on re-application? 

This investigation concerns the pharmaconetics and bone localisation of Sm-153-EDTMP in the normal baboon during three successive applications (6 week intervals) each with two different concentrations of EDTMP (0.7 EDTMP mg/kg, normal; and 1.4 EDTMP mg/kg). Two groups of six baboons were used, one for each concentration. Scintigraphy included a two hour dynamic study (1 min frames) following 111 MBq Sm-153-EDTMP i.v. Static images (4 min) followed hourly at 2 till 5 hours. Time-activity curves were obtained for the heart, kidney and liver, and relative bone to background uptake from the static images. Blood and urine clearance curves were obtained. Comparisons were drawn (Student’s t-test) between successive applications, and between the two concentrations. Partial blocking appears with the lower EDTMP concentration, significant after the third application (P<0.05). The first application of the high concentration indicates lower uptake in the bone than the lower one, pointing to blocking by the high concentration, however not with subsequent re-applications. Re-application of the high EDTMP-concentration could reduce levels of serum calcium, increase parathyroid hormone level, triggering osteoblastic activity and bone remodeling, thus partially off-setting blocking which was hence clearer at the low concentration. 
back...

Re-188-HEDP as a Therapeutic Bone Agent - Preparation, Experimental Pharmocokinetic and Biodistribution Studies in the Normal Baboon Model

A variety of bone-seeking radiopharmaceuticals, including ³²P, ⁸⁹Sr, ¹⁵³Sm-EDTMP and ¹⁸⁶Re-HEDP have been used to treat patients with skeletal metastases. ¹⁸⁸Re-HEDP (Rhenium-188-hydroxyethylidene diphosphonate) is an attractive alternative for therapeutic use. ¹⁸⁸Re (t_½ 16.9 hr; b ^- 2.1 MeV, g 103 keV 15%) has a shorter physical half-life than both ¹⁵³Sm and ¹⁸⁶Re which allows for higher doses (compared with the longer lived radionuclides). ¹⁸⁸Re is also available from an in-house generator system (similar to the current ^99mTc-generator). Na ¹⁸⁸ReO_4- was obtained from an 185 000 MBq ORNL alumina-based ¹⁸⁸W/¹⁸⁸Re-generator system by elution with 0.9% NaCl. To make ¹⁸⁸Re-HEDP, 1.0 ml K ReO₄^- solution (1.0 mg/ml) and up to 2960 MBq, 188ReO₄^- in 5.0 ml eluate was added to a vial containing 75.0 mg HEDP, 10.0 mg ascorbic acid and 20 mg SnCl₂•2H₂O. The whole mixture (pH 3.5) was heated for 15 min (» 100 ° C), allowed to cool, whereafter 3.0 ml of 1.0 M sodium citrate (pH 7.0) was added to adjust the pH to 5 - 6. Radiochemical purity (> 99.0%) was determined by instant thin-layer chromatography on silica gel impregnated glass fibre sheets using acetone as solvent. (¹⁸⁸Re-HEDP stays at the origin (Rf = 0) while ReO₄^- was at Rf 0.8). 

In this study the pharmocokinetics and biodistribution of ¹⁸⁸Re-HEDP was investigated using the baboon experimental model (which answers many of the criteria of parallelism to the human). With the baboons (n = 6) under pentobaritone anaesthesia both dynamic (one frame/min for 30 min) and subsequent static scintigraphic studies (5 min acquisition; hourly form 2 - 4 hours), were performed after bolus i.v. injection of sterilised 185 MBq ¹⁸⁸Re-HEDP, with the HEDP adjusted to a dose of 1.0 mg/kg body weight. Blood and urine samples were collected at 120 min and later at 20 min intervals for 4 hours and then analysed. Time-activity curves were obtained for the heart, kidney, liver, and relative bone to background uptake from the static images. Blood and urine clearance curves were obtained. 

The results of this study showed that there is a highly selective Re-188 uptake in the skeletal system as well as a low non-target uptake and rapid clearance in non-osseous tissue. 
back...

Breast Tangential Fields: Penumbral Dose to Lung

It has been considered best to treat breast tangential fields, either with a half-field block or independent jaws or to angle the fields so that the posterior beam edges are co-linear. This has been true on both Cobalt teletherapy units and on linear accelerators. 

However, if patients are treated with either modality on the basis of clinical skin markings, as would be the case in very advanced carcinoma of the breast, Dose-Volume Histograms, as produced by a Helax treatment planning system, show that there is very little difference between the three modes of treatment. 

Comparisons of the three possible treatments will be given for both modalities. 
back...

Calculation of Distances within and between Reconstructed SPECT Tomographic Slices

When distances have to be calculated within or between SPECT tomographic slices, the usual procedure is to obtain the distance in pixels from the image and convert it to absolute units using the pixel width, which is usually supplied as an output parameter of the reconstruction group of images. 

Unexpected results were obtained with certain combinations of acquisition and reconstruction parameters on one manufacturer's dual head gamma. These results prompted this investigation in which SPECT images were acquired of a simple arrangement of point sources, known distances apart. These images were acquired and reconstructed with a various combinations of the relevant parameters and the separation of the source images was calculated and compared with actual values. 

The results revealed two important facts: 

1. for transaxial slices the pixel width parallel with the axis of rotation is that of the acquisition group. Thus the slice width is unaffected by the values of the reconstruction parameters.
2. for slices in the coronal, sagittal and oblique planes, the pixel width is that of the expected reconstruction group except when the following combination of parameters applies:

acquisition frame size: 128 x 128 reconstruction frame size: 64 x 64 reconstruction zoom factor: less than 2.0 

The Radiotoxicity of 4-[¹²³I]-IODOANTIPYRINE in Normal and Cancer Cells

The high-LET effects of short range Auger electrons is a possible means to inactivate tumor cells. Presently it is of great interest to quantify Auger electron damage in relation to the inherent radiosensitivity of cells. In this work the induction of micronuclei from intracellular and extracellular disintegrations of ¹²³I were followed in an ovarian cancer cell type (DMBA) and a normal cell line (CHO-K1). Extracellular disintegrations of the radionuclide is effected by exposing the cells to [123I]NaI and cellular uptake ensured by using 4-[¹²³I]-iodoantipyrine. Cell exposure to 4-[¹²³I]-iodoantipyrine after 10 half- lives had no measurable effect, indicating that any biological damage from the chemical compound is insignificant. By contrast, high micronuclei frequencies were noted in both cell types when exposed to radioactive ¹²³I. Extracellular disintegrations of the nucleid consistently yield lower levels of biological damage compared to when cells were exposed to 4-[¹²³I]- iodoantipyrine. 
back...

Development of a Production Procedure for ¹³⁹Ce at NAC

Long-lived (137.64 d) ¹³⁹Ce is well-known as a laboratory standard for the calibration of g-ray detectors. Since it emits only one g-ray (165.857 keV) in the optimum energy range for detection with a gamma camera this radioisotope also has a high potential for use in calibration sources for SPET. In order to explore this possibility a production procedure for ¹³⁹Ce was developed at the NAC and an experimental ¹³⁹Ce line source was prepared for employment in a scanning line source assembly developed by the Department of Biophysics, UOFS, Bloemfontein. 

No suitable cross-section data for the cyclotron production of ¹³⁹Ce could be found in the literature. Therefore, the excitation function (see Fig. 1) for the production of ¹³⁹Ce in the bombardment of praseodymium with protons up to 100 MeV was measured in this work. Subsequently, a Pr-metal target was designed and manufactured and several high-current production runs were executed with the 66 MeV proton beam. The yields obtained agree very well with the expected thick-target yield as determined from the measured excitation function data.