Comparison of three high-resolution digitizers for radiochromic film dosimetry

A recently introduced radiographic film scanner from Howtek is evaluated and compared to two other commercially available densitometry systems for its use in radiochromic (RC) film dosimetry in the clinical dose range 0-100 Gy. It has a high-intensity red LED light-source centered at 662 nm (near the major absorption peak for RC film), and is coupled to a CCD linear array detector. This new densitometry system is directly compared to two high-resolution film scanners commonly employed in RC film dosimetry, namely the Lumiscan 75 digitizer (He-Ne laser light source) and the Vidar VXR-16 digitizer (fluorescent light source). A spot densitometer (Nuclear Associates Radiochromic Densitometer) with a filtered 671 nm laser-diode light source is also included as a reference for comparison. The response of the spot densitometer and three high-resolution digitizers is characterized by the dose required to reach a net optical density of 1 (DNOD1), and is 16.0, 37.3, and 46.4 Gy for the Nuclear Associates Radiochromic Densitometer, Howtek MultiRAD 460 and Lumiscan 75 digitizer, respectively. The Vidar VXR-16 does not reach a net optical density of 1. The minimum usable dose at which a 2% level of uncertainty can be achieved (MUD2%) on the three digitizers are 2.6, 6.0, and 38.5 Gy for the Howtek MultiRAD 460, Lumiscan 75, and Vidar VXR-16, respectively. The Howtek MultiRAD 460 shows the greatest sensitivity, lowest MUD2% and best signal-to-noise ratio in the clinical dose range 0-100 Gy. Furthermore, it has no apparent interference (moiré) artifacts that severely limit the low optical density region of the He-Ne laser digitizer. For high-resolution radiochromic dosimetry in the clinical dose range 0-100 Gy, the high-intensity red LED light-source digitizer proves to be the superior modality.

The use of an inexpensive red acetate filter to improve the sensitivity of GAFChromic dosimetry

The sensitivity of GAFChromic dosimetry using a conventional broad band light source densitometer has significantly been improved twofold using an inexpensive red acetate filter overlay during the densitometric measurements. This thin sheet of red acetate enhances the dosimetric analysis of radiochromic blue image distributions recorded on GAFChromic films. The combination provides higher sensitivity in the optical density measurements than the more expensive He-Ne laser-scanning densitometers.

A rapid colour stabilization technique for radiochromic film dosimetry

Various forms of GAFChromic film have been used for several years as radiographic media for measuring dose distributions of brachytherapy sources and small radiation fields. Upon irradiation the film changes colour and darkens with time post-irradiation. The darkening is most rapid in the first 24 h, and it has been suggested that for accurate dosimetry a waiting period of 24 h should occur before any optical density (OD) measurements are taken. A more rapid colour stabilization (RCS) procedure has been developed and is evaluated. The procedure consists of heating the film post-irradiation for a period of 2 h at 45 degrees C. The RCS procedure is compared with a control group and the dose response is tested for linearity, stability and reproducibility using two densitometers with light sources at different wavelengths (632.8 nm and 671 nm). The rise in net optical density (NOD) for the period 3-168 h is less than 3% for the RCS group as compared with 12% for the controls. In the first 24 h, the increase in NOD for the RCS samples is less than 0.5%, as opposed to 6% for the control group.

Predicting optical densitometer response as a function of light source characteristics for radiochromic film dosimetry

Various forms of GAFChromic (GC) film have been used for several years as radiographic media for measuring dose distributions of brachytherapy sources and small radiation fields. In order to optimize the measurement sensitivity and thus improve precision, we describe a method to calculate the dose response curves (net optical density at a give wavelength or spectrum versus absorbed dose) for different densitometer light sources using measured GC film absorption spectra. Comparison with measurements on the latest version of GC film (model MD-55-2) using four types of densitometers [He-Ne laser, broadband (white light) densitometer, and two LED (red-light) filtered densitometers] confirm the accuracy of this predictive model. The linearity and sensitivity of the dose response curves are found to be highly dependent on the light source spectrum. Initial slope is a function of the average weighted absorbance. Early saturation and decreased linearity of the dose response curves are ascribed to the nonuniform transmission of the light source through the GC film. We found that an LED (red-light) source with a narrow bandpass filter centered at 671 nm near the major absorption peak achieves nearly the maximum possible sensitivity (almost four times more sensitive than He-Ne laser, 632.8 nm) and may be suitable for in vivo dosimetry.

Changing the technique of background subtraction alters calculated renal function on pediatric mercaptoacetyltriglycine renography

PURPOSE

Although many operative decisions are based on apparent changes in function detected by serial diuretic renography, the reliability of relative renal function data has been questioned. We investigated the effect of background subtraction on calculated renal function.

MATERIALS AND METHODS

We reviewed 23 pediatric mercaptoacetyltriglycine renograms. Regions of interest for background subtraction were redrawn and relative renal function values were recalculated.

RESULTS

In patients with left hydronephrosis left differential renal function was consistently underestimated by 7.3% compared to the superior and 4.7% compared to the average background subtraction technique. In patients with right hydronephrosis, when considering lower pole background activity only, right differential renal function was consistently overestimated by 15.8% compared to the superior and 2.4% compared to the average background subtraction technique. In patients younger than 1 year at the time of study these differences were exaggerated.

CONCLUSIONS

Because of overlapping hepatic background activity, the position of regions of interest for background subtraction may greatly influence calculated renal function. We recommend that the preferred method of calculating background subtraction to minimize error be based on a region of interest surrounding the whole kidney. This method is especially pertinent in patients with right hydronephrosis and in those younger than 1 year. Reported relative renal function data should be interpreted with caution.

Comparison of dose response of radiochromic film measured with He-Ne laser, broadband, and filtered light densitometers

Dose response curves for GAFChromic MD-55-2 film were measured using three different densitometer systems: a He-Ne laser densitometer, a broadband (white light) densitometer, and a filtered red light densitometer. These were found to differ significantly; the dose needed to achieve a net optical density of 1 (DNOD1) was greater than 100 Gy for the white light densitometer, 56 Gy for the He-Ne densitometer, and only 14.8 Gy for the filtered red light densitometer. This represents approximately a fourfold increase in response for the filtered red light versus the He-Ne laser densitometer, which is a significant improvement. For some patient prescriptions this enables us to achieve an accuracy and precision sufficient to verify daily dose to within 5%.

Exogenous endothelin-1 causes renal vasodilation in the fetal lamb

PURPOSE

Endothelin-1 is known to be a potent vasoconstrictor. We investigated the effects and mechanisms of action of endothelin-1 and its receptors in regulating renal vascular tone in the fetal lamb.

MATERIALS AND METHODS

We observed the in vivo effects of endothelin-1, an endothelin-b receptor agonist (4-alanine-endothelin-1), endothelin-a receptor antagonists (BQ-610 and BQ-123), and the inhibition of prostaglandin and nitric oxide synthesis on the response of the renal circulation to endothelin-1 in a chronic preparation in third trimester fetal lambs.

RESULTS

After injection of 250 ng./kg. endothelin-1 into the descending aorta proximal to the renal arteries in 8 fetal animals, renal blood flow increased (4.4 +/- 0.7 ml. per minute per kg., p < 0.001 versus vehicle), as did mean arterial blood pressure (3.0 +/- 0.3 mm. Hg,p < 0.001 versus vehicle). Calculated renal vascular resistance decreased (-1.1 +/- 0.2 mm. Hg per minute per kg./ml., p < 0.001 versus vehicle). After injection of 1,725 ng./kg. 4-alanine-endothelin-1 in 5 animals renal blood flow increased (3.8 +/- 0.4 ml. per minute per kg., p < 0.05 versus vehicle) and mean arterial blood pressure was unchanged (1.6 +/- 1.7 mm. Hg). Calculated renal vascular resistance decreased (-0.8 +/- 0.2 mm. Hg per minute per kg./ml., p < 0.05 versus vehicle). After injection of 0.5 mg./kg. BQ-610 in 6 animals renal blood flow increased (2.3 +/- 0.7 ml. per minute per kg., p < 0.05) and mean arterial blood pressure decreased (-2.7 +/- 0.3 mm. Hg, p < 0.05 versus vehicle). Calculated renal vascular resistance decreased but this difference was not statistically significant (-0.7 +/- 0.3 mm. Hg per minute per kg./ml., p < 0.07). A dose of 1 mg./kg. BQ-123 in 2 animals decreased renal vascular resistance markedly. Infusion of a prostaglandin synthesis inhibitor (1 mg./kg. per minute meclofenamic acid) did not alter the decrease in renal vascular resistance after endothelin-1 (-0.7 +/- 0.4 mm. Hg per minute per kg./ml). In contrast, during infusion of a nitric oxide synthesis inhibitor (1.5 mg./kg. per minute N-omega-nitro-L-arginine) endothelin-1 increased renal vascular resistance (1.2 +/- 0.2 mm. Hg per minute per kg./ml., p < 0.001).

CONCLUSIONS

Endothelin-1 is a vasodilator in the fetal renal circulation, which acts primarily via endothelin-b receptors. Ongoing activity of endothelin-a receptors contributes to renal vascular tone in fetal lambs. The vasodilatory effects of endothelin-1 in the fetal lamb renal circulation are mediated via the nitric oxide system and not via prostanoids.

Contradictory renal function measured with mercaptoacetyltriglycine diuretic renography in unilateral hydronephrosis

PURPOSE

We studied apparently supranormal renal function in hydronephrotic kidneys, as measured by 99mtechnetium mercaptoacetyltriglycine renography.

MATERIALS AND METHODS

We retrospectively reviewed the clinical history, ultrasonography and renography of 29 children.

RESULTS

Of the 29 children 7 had greater than 50% relative function in the hydronephrotic kidney. This finding was independent of patient age, gender, degree of hydronephrosis or obstructive pattern. Of these 7 cases 6 occurred on the right side (p < 0.05 versus a large registry).

CONCLUSIONS

In most cases supranormal renal function is caused by a technical problem, likely the inadequate background subtraction of mercaptoacetyltriglycine in the liver.

Renal preservation despite 35 days of partial bladder obstruction in the fetal lamb

To determine whether the increase in renal blood flow and preservation of renal function that we demonstrated after 10 days of chronic partial bladder obstruction in the third trimester fetal lamb also occur after earlier longer obstruction, we modified our preparation and studied the effects of 35 days of obstruction begun during the second trimester. Partial bladder obstruction was created in 10 fetal lambs at 90 days of gestation (term equals 147 days). At repeat surgical intervention 28 days later vascular catheters and a left renal artery flow transducer were placed, and catheters were externalized. We then studied renal blood flow and function at gestational ages 120 days and 125 days after 30 days and 35 days of obstruction, respectively. Tissue was obtained for histology at the time of sacrifice. Eight control fetal lambs without obstruction were studied in a similar way. Bilateral hydroureteronephrosis was noted in all fetal lambs after partial obstruction, whereas the kidneys and bladders of the control animals had a normal appearance. Renal blood flow was higher in the obstructed fetal lambs than in controls (20.2 +/- 4.9 versus 10.2 +/- 0.9 ml. per minute per kg., p < 0.05 after 30 days and 17.1 +/- 2.7 versus 9.7 +/- 0.9 per minute per kg., p < 0.05 after 35 days). There was no evidence of decreased renal function by any parameter and, in fact, glomerular filtration rate and urine volume were increased after 30 days of obstruction (1.59 +/- 0.32 versus 0.69 +/- 0.07 ml. per minute per kg., p < 0.05 and 15.7 +/- 4.3 versus 5.2 +/- 0.8 ml. per hour per kg., p < 0.05, respectively). Histological studies demonstrated normal architecture of the kidneys but thinned cortex. We conclude that the physiological responses of the fetus are such that partial lower urinary tract obstruction in our preparation results in a prolonged increase in renal blood flow and preservation of renal function.

Newborn penile glans amputation during circumcision and successful reattachment

Circumcision, the most common operation in male patients in the United States, is performed by a variety of health care professionals. Although not technically difficult, it results in a large number of reported and unreported complications annually. We report the successful reattachment of a distal penile glans, which was amputated when the Sheldon clamp was used for newborn circumcision. The literature is reviewed, and prevention and treatment of this type of circumcision injury are described.

Toxoplasmosis of the bladder: case report and review of the literature

Toxoplasma gondii is an intracellular parasite that is responsible for an asymptomatic or minimally symptomatic lymphadenopathy syndrome, which in the immunocompromised host can be life threatening. Toxoplasmosis commonly affects the central nervous system. Genitourinary involvement is uncommon with reported cases limited to Toxoplasma orchitis and the nephrotic syndrome. To our knowledge we report the first case of toxoplasmosis of the bladder as an intravesical mass without central nervous system or other organ involvement in a young man with the acquired immunodeficiency syndrome.

Munchausen's syndrome: manifestation as renal colic

Over a four-year period, 3 patients with manifestations of renal colic were identified to have Munchausen's syndrome. A review of these cases and the literature is undertaken to provide urologists with a greater understanding of the origin and treatment of this syndrome.

Laparoscopic pyelocaliceal diverticula ablation

Pyelocaliceal diverticula are cystic urine collections within the renal parenchyma communicating with the collecting system. They occur in 0.2% to 0.5% of the population and often contain calculi. Flank pain is the most common complaint, and most lesions are diagnosed by intravenous urography. In the past, treatment has required open renal surgery, with potential loss of renal function, or prolonged percutaneous procedures. We propose surgical treatment of caliceal diverticula by laparoscopic unroofing and fulguration. The benefits include renal preservation as well as decreased morbidity and an earlier return to work for the patient.