Sci-Sat AM(2): Brachy-06: A Comparison of MR/CT fusion versus CT alone for assessment of implant quality in permanent prostate brachytherapy.

Low dose-rate permanent implant brachytherapy is widely used in the management of patients with early stage prostate cancer. An assessment of the implant quality is usually carried out 30 days after the implant is delivered, using computed tomography (CT) to identify the prostate and seeds. This is difficult due to poor contrast of the prostate and the superposition of seeds in the CT images. Magnetic resonance (MR) imaging offers superior contrast but inferior visualization of seeds. At our centre, patients are imaged using both CT and T2 weighted MR 30 days after an implant, and the image sets are fused using a commercial software package. The seeds are identified on CT and the prostate volumes are contoured on MR, with fusion performed by matching seeds on CT with seed signal voids on MR. The purpose of this study was to compare standard prostate post-implant dosimetric parameters (D90, V100, etc.) for prostates contoured on CT alone (MR blinded) versus MR/CT fusion. 25 patients were evaluated with all contouring performed by the same physician. We found that the prostate volume was overestimated using CT alone as compared to MR/CT fusion (mean: 37.2cc vs. 35.0cc respectively, p = 0.033). We also found that dosimetric parameters were underestimated for CT alone compared to MR/CT fusion, including D90 (mean: 144.3Gy vs. 150.8Gy respectively, p = 0.005) and V100 (mean: 89.2% vs. 91.0% respectively, p = 0.01). Centres using CT alone for post-implant dosimetry may therefore be underestimating their implant quality.

Size and positioning reproducibility of an 192Ir brachytherapy stepping source.

In this paper we describe techniques for measuring the dimensions and position reproducibility of an 192Ir brachytherapy stepping source. Measurements were carried out using a 0.25x10x152 mm3 collimator placed in front of a detector of our own design. The brachytherapy source was translated past the collimator in 0.025 mm increments using a stepper motor. The source was found to be 3.58 mm long and 0.69 mm wide, which is in good agreement with the manufacturer's values of 3.5x0.6 mm2. The source position was reproducible to within 0.12 mm.

High-energy electron and photon therapy to the parotid bed: radiation dose perturbations with a titanium mandibular implant.

Adjuvant radiation therapy to the parotid bed is commonly administered following surgical resection using either a pair of angled wedged photon beams or an ipsilateral mixed-beam portal of electrons and photons. The present study seeks to determine the optimal parotid bed treatment technique in the presence of a titanium mandibular implant by investigating perturbations in the dose distribution deep to this implant for a 15-MeV electron beam and a 6-MV photon beam. A titanium mandibular plate was embedded in a tissue-equivalent phantom, and irradiated with 15-MeV electrons, and 6 MV photons. Radiation doses behind the plate were measured with both thermoluminescent dosimeters and radiographic film. With 15-MeV electrons, there is a clinically significant decrease in the dose beyond the titanium plate, which is most important at 5-mm and 10-mm depths (18-27%). With 6-MV photons the dose at the deep interface of titanium and tissue is reduced by between 15 and 18%, but rapidly drops to < 5% at a depth of 5 mm. In adjuvant treatment to the parotid bed, when the clinical target volume includes tissue positioned deep to a titanium implant, significant underdosage occurs with ipsilateral beam arrangements, especially when electrons are used.

Detection of and discrimination between total and free human interleukin-4 and free soluble interleukin-4 receptor by ELISA.

Interleukin-4 (IL-4) signaling is initiated by binding of IL-4 to the high-affinity IL-4 receptor alpha-chain and subsequent interaction with the common gamma-chain. Soluble forms of the extracellular domain of the alpha-chain (sIL-4R) were shown to be present in biological fluids and, dependent on the concentration, enhance or inhibit IL-4 activity by forming IL-4/sIL-4R complexes. To discriminate between free and potentially active IL-4 from the inactive and complexed form, we have established a set of new ELISA systems for the measurement of human IL-4 in its distinct forms. To select suitable pairs of anti-IL-4 antibodies, a chequerboard interference analysis with six highly-selective human IL-4 specific monoclonal antibodies was performed. For the determination of total IL-4, a monoclonal capture antibody was used that binds IL-4 outside the binding site of the IL-4R alpha-chain. Another antibody recognizing an epitope of the alpha-chain binding site was chosen for the detection of free IL-4. The binding of this antibody was inhibited in a dose-dependent fashion by recombinant sIL-4R. Assays for both total and free IL-4 exhibited a sensitivity of 8 pg/ml and a dynamic range up to 1000 pg/ml. Human sIL-4R was detected by two monoclonal antibodies directed against different epitopes. This ELISA was inhibited by recombinant IL-4 suggesting the measurement of predominantly free sIL-4R. Complexes between soluble IL-4R and IL-4 were detected by a monoclonal anti-sIL-4R antibody in combination with an anti-IL-4 antibody. When supernatants of activated T cells were analyzed, the majority of the IL-4 was in free form. The amount of complexed IL-4 was low as indicated by the fact that most of total IL-4 could be detected as free IL-4. Although values obtained for complexed IL-4 correlated with the difference between total and free IL-4, precise values could not be determined, presumably due to the dynamic nature of the complex between the two proteins. We suggest that the ability to quantitate total and free IL-4 in combination with sIL-4R may provide a new insight of the role that IL-4 plays in different pathophysiological conditions.

Doses and population irradiation factors for Canadian radiation technologists (1978 to 1988).

Individual and collective radiation doses received by Canadian radiation technologists (RTs) working in diagnostic radiology, nuclear medicine and radiotherapy are summarized for the period 1978 to 1988. The data were obtained directly from the National Dose Registry, Department of National Health and Welfare. Over the 11-year study period the mean annual dose equivalent fluctuated around 0.2, 1.8 and 1.1 mSv for RTs working in diagnostic radiology, nuclear medicine and radiotherapy respectively. Over the same period the occupational collective dose equivalent decreased in diagnostic radiology (by 44%) and radiotherapy (by 35%) and increased in nuclear medicine (by 45%). Approximately 10,000 RTs are monitored each year, with an estimated total occupational collective dose equivalent of about 3.6 person-sieverts. Analysis of dose distribution data showed that only 1.3% of all monitored RTs received an annual whole-body dose equivalent greater than the current legal limit for members of the public (5 mSv). Approximately half of the RTs working in nuclear medicine and radiotherapy received an annual dose equivalent in excess of 0.5 mSv; only 7.3% of their diagnostic radiology counterparts exceeded this level. Demographic data showed a high preponderance of young women in all three RT classifications, and an analysis of the radiation risks to this occupational group revealed increases of up to 12% above the risk associated with a "standard" adult working population exposed to the same collective dose equivalent.

Occupational doses to medical radiation technologists in Manitoba (1978-1988).

In Canada, occupational exposure to medical technologists accounts for about 8 per cent of all occupational exposure. In this paper, occupational doses to Manitoban radiation technologists (RTs) in diagnostic radiology, nuclear medicine and radiotherapy are presented for the period 1978-1988. Particular attention is paid to the distribution of dose among this population. The importance of age and sex demographics on radiation detriment is also estimated.

Radiation doses due to breast imaging in Manitoba: 1978-1988.

The number of mammographic examinations performed annually in the province of Manitoba, Canada, and their associated radiation doses (total collective breast dose and average glandular dose [AGD] per view) are reported for the period 1978-1988. These data indicate that the total number of examinations performed annually increased by a factor of five during the 11-year study. The total annual collective breast dose, meanwhile, increased at a much slower rate, from 40 person-Gy in 1978 to 97 person-Gy in 1988; this difference is attributable to the gradual replacement of xeroradiography by screen-film mammography and to changes in technique. In the late 1980s, the AGD due to xeroradiography for a craniocaudal view was 3.3 mGy, a factor of 2.4 greater than the corresponding dose associated with dedicated screen-film units.

Occupational doses in radiation oncology in Manitoba--1980 to 1986.

The province of Manitoba (population of 1.0 million) has two radiotherapy centers employing a number of people, of whom about 60 are exposed to radiation during the course of their work. The individual and collective radiation doses to these workers, as recorded by thermoluminescent dosimeter plaques, were reviewed for the period 1980 to 1986. Whole-body doses to radiotherapy technologists responsible for operating the treatment machines and brachytherapy afterloading procedures ranged from 0.5 to 2.5 mSv y-1, whereas the corresponding doses to nursing staff working on a hospital brachytherapy ward were about 1.0 mSv y-1. The collective occupational dose from radiotherapy in Manitoba was approximately 70 person-mSv. Trends show individual operator and collective doses to be increasing at a higher rate than the number of patients undergoing radiotherapy. Occupational exposure in radiotherapy in this province was found to be comparable to that encountered in nuclear medicine in Manitoba and greater than that in diagnostic radiology.

Radiation doses in extracorporeal shock wave lithotripsy.

Patients undergoing lithotripsy on the Siemens Lithostar system are exposed to radiation in three modes: film radiography, electronic radiography and fluoroscopy. Radiation exposure techniques (kVp, field size, number of exposures and projection) were recorded for the first 125 patients undergoing treatment on a recently installed Lithostar unit at a Winnipeg hospital. These data were then used in conjunction with phantom-based radiation dose measurements to calculate entrance skin dose and total energy imparted for each patient. Values of 142 mGy and 53 mJ, respectively, were found. In the case of energy imparted, 20% of the total arose from film radiography, 30% from electronic radiography and the remaining 50% from fluoroscopy. The estimated effective dose-equivalent, HE, to the average patient undergoing lithotripsy was 0.75 mSv. This corresponds to an estimated radiation risk for the induction of fatal cancers and genetic defects (in the first two generations of offspring) of between 5 and 11 per million.

Development of a tissue-equivalent phantom for diaphanography.

A phantom is proposed for quality control and calibration of instruments used for transillumination of the breast for early detection of cancer. A container is filled with a material having optical properties very similar to those of breast tissue, and internal objects are viewed by transmitted light. The phantom can be used to optimize operating conditions for the visualization of small or deep-seated lesions.

A multirange ELISA for the measurement of plasma renin in humans and primates.

A sensitive solid phase enzyme-linked immunosorbent assay (ELISA) has been developed using two anti-human renin monoclonal antibodies, which were shown to bind both human as well as primate renin at two different epitopic sites. One monoclonal antibody (3-36-16) was used to coat each well of a 96 well microtitre plate in which renin, contained in 5 to 20 ul of plasma, was allowed to react. Plates were then incubated with the gamma globulin (gamma G) fraction of a rabbit anti-human renin serum followed by development with sheetp anti-rabbit gamma G conjugated to alkaline phosphatase. Quantification was carried out by the addition of the alkaline phosphatase substrate, p-nitrophenylphosphate, which produced a colorimetric reaction. The sensitivity of the assay is 25 pg ml-1. The method recognises both active and inactive renin from plasma, kidney, amniotic fluid and chorionic cells. Plasma renin can be measured within 6 hours when values are greater then 150 pg ml-1 or within 24 hours when plasma values are less than 150 pg ml-1. The ELISA has already been used to measure total immunoreactive renin in plasma obtained from patients with several forms of hypertension. The values ranged from 25 pg ml-1 in patients with primary aldosteronism to as large as 60 ng ml-1 in a patient with a renin-secreting tumour.(ABSTRACT TRUNCATED AT 250 WORDS)