Tumor vascular signals in renal masses: detection with Doppler US

The vascularity of 49 renal masses (26 malignant and 23 benign lesions) was investigated with duplex Doppler ultrasound. Doppler signals obtained at the margins of renal masses were defined as "tumor signals" when the Doppler-shifted frequency of the lesion exceeded the frequency shift in the ipsilateral main renal artery. These exceeded 2.5 kHz with a 3-MHz insonating frequency. Among the 26 renal masses that subsequently proved to be malignant, tumor signals were obtained in 15 of 18 (83%) untreated renal cell carcinomas, in three of four Wilms tumors, and in two patients with metastases to the kidney, but not in the one patient with lymphoma. None of the 23 benign renal masses demonstrated tumor signals. Tumor vascularity in malignant lesions gives rise to abnormal, high-velocity, Doppler-shifted signals that can help in the differential diagnosis of renal masses.     

Custom step wedge blocking using dynamic multileaf collimation for parametrial pelvic boost irradiation following brachytherapy for carcinoma of the cervix

Carcinoma of the cervix is typically treated with a combination of intracavitary brachytherapy and external beam radiation. The external beam dose is delivered with whole pelvis fields followed by split fields that protect midline organs at risk (bladder and rectum) while treating the parametria. Three approaches have been developed to shield midline structures: a simple rectangular block, a block customized to a single brachytherapy isodose line, and a step wedge filter constructed to conform to multiple brachytherapy isodose lines. A customized step wedge filter has the potential to produce a more homogeneous dose distribution but has not achieved widespread use due to labor intensive construction. We have developed a simple, novel method to produce a custom midline step wedge using dynamic multileaf collimation (dMLC). A comparison of film measurements in a phantom with the dose calculated by a commercial treatment planning system demonstrated agreement within 3% or 3 mm. The technique requires delivery times comparable to conventional techniques.     

Validation of target volume and position in respiratory gated CT planning and treatment

The capability of a commercial respiratory gating system based on video tracking of reflective markers to reduce motion-induced CT planning and treatment errors was evaluated. Spherical plastic shells (2.8-82 cm3), simulating the gross target volume (GTV), were placed in a water-filled body phantom that was moved sinusoidally along the longitudinal axis of the CT scanner and the accelerator for +/- 1 cm at 15-30 cycle/min. During gated CT imaging, the x-ray exposure was initiated by the gating system shortly before the end of expiration (so that the imaging time would be centered at the end of expiration); it was terminated by the scanner after completion of each slice. In nongated CT images, the target appeared distorted and often broken up. GTVs volume errors ranged 16%-110% in axial scans, and 7%-36% in spiral scans. In gated CT images, the spheres appeared 3 and 5 mm longer than their actual diameters (volume errors 2%-16%), at the respective respiration rates of 15 and 20 cycles/min. At 30 cycles/min the target appeared 1 cm longer, and volume error ranged 25%-53%. During treatment, gating kept the beam on for a duration equal to the CT acquisition time of 1 s/slice. The difference in positional errors between gated CT and portal films was 1 mm, regardless the size of residual motion errors. Because of the potential of suboptimal placement of the gating window between CT imaging and treatment, an extra 1.5-2.5 mm safety margin can be added regardless of the size of residual motion error. For respiratory rates > or = 30 cycles/min, the effectiveness of gating is limited by large residual motion in the 1 s CT acquisition time.     

Dosimetric effect of respiration-gated beam on IMRT delivery

Intensity modulated radiation therapy (IMRT) with a dynamic multileaf collimator (DMLC) requires synchronization of DMLC leaf motion with dose delivery. A delay in DMLC communication is known to cause leaf lag and lead to dosimetric errors. The errors may be exacerbated by gated operation. The purpose of this study was to investigate the effect of leaf lag on the accuracy of doses delivered in gated IMRT. We first determined the effective leaf delay time by measuring the dose in a stationary phantom delivered by wedge-shaped fields. The wedge fields were generated by a DMLC at various dose rates. The so determined delay varied from 88.3 to 90.5 ms. The dosimetric effect of this delay on gated IMRT was studied by delivering wedge-shaped and clinical IMRT fields to moving and stationary phantoms at dose rates ranging from 100 to 600 MU/min, with and without gating. Respiratory motion was simulated by a linear sinusoidal motion of the phantom. An ionization chamber and films were employed for absolute dose and 2-D dose distribution measurements. Discrepancies between gated and nongated delivery to the stationary phantom were observed in both absolute dose and 2-D dose distribution measurements. These discrepancies increased monotonically with dose rate and frequency of beam interruptions, and could reach 3.7% of the total dose delivered to a 0.6 cm3 ion chamber. Isodose lines could be shifted by as much as 3 mm. The results are consistent with the explanation that beam hold-offs in gated delivery allowed the lagging leaves to catch up with the delivered monitor units each time that the beam was interrupted. Low dose rates, slow leaf speeds and low frequencies of beam interruptions reduce the effect of this delay-and-catch-up cycle. For gated IMRT it is therefore important to find a good balance between the conflicting requirements of rapid dose delivery and delivery accuracy.     

Attenuation of intracavitary applicators in 192Ir-HDR brachytherapy

Unlike the penetrating monoenergetic 662 keV gamma rays emitted by 137Cs LDR sources, the spectrum of 192Ir used in HDR brachytherapy contains low-energy components. Since these are selectively absorbed by the high-atomic number materials of which intracavitary applicators are made, the traditional neglect of applicator attenuation can lead to appreciable dose errors. We investigated the attenuation effects of a uterine applicator, and of a set of commonly used vaginal cylinders. The uterine applicator consists of a stainless steel source guide tube with a wall thickness of 0.5 mm and a density of 8.02 g/cm3, whereas the vaginal cylinders consist of the same stainless steel tube plus concentric polysulfone cylinders with a radius of 1 or 2 cm and a density of 1.40 g/cm3. Monte Carlo simulations were performed to compute dose distributions for a bare 192Ir-HDR source, and for the same source located within the applicators. Relative measurements of applicator attenuation using ion-chambers (0.125 cm3) confirmed the Monte Carlo results within 0.5%. We found that the neglect of the applicator attenuation overestimates the dose along the transverse plane by up to 3.5%. At oblique angles, the longer photon path within applicators worsens the error. We defined attenuation-corrected radial dose and anisotropy functions, and applied them to a treatment having multiple dwell positions inside a vaginal cylinder.     

Daily,limited access to methamphetamine self-administration during pregnancy leads to increased methamphetamine sensitivity in adult offspring

Methamphetamine use by women, even throughout pregnancy, is common. But there is limited knowledge about the effects in prenatally methamphetamine-exposed children. This study investigated how prenatal methamphetamine exposure in rats, via maternal i.v. self-administration, affected the sensitivity of adult offspring to methamphetamine in comparison with controls. The offspring were generated from dams either self-administering methamphetamine daily under limited-access conditions prior to and throughout pregnancy, or their respective saline-yoked control dams. Spontaneous and methamphetamine-induced locomotor activity was assessed in male and female offspring of both exposure groups after a range of methamphetamine doses. In a separate group of offspring, acquisition of i.v. methamphetamine self-administration, responding under fixed and progressive ratio schedules of methamphetamine reinforcement, and reinstatement of extinguished drug-seeking behavior were assessed. Methamphetamine dose-dependently increased locomotor activity in both exposure groups. However, methamphetamine-exposed males showed significantly enhanced locomotor activity compared with controls at 1 mg/kg, and methamphetamine-exposed females showed significantly enhanced locomotor activity compared with controls at 3.2 mg/kg. Methamphetamine-exposed offspring of both sexes acquired methamphetamine self-administration faster and showed overall higher levels of methamphetamine-induced reinstatement compared with controls. Taken together, these results indicate that prenatal methamphetamine exposure to relatively low levels alters methamphetamine sensitivity in male and female adult offspring.     

CHANGING TRENDS OF LEPROSY IN ARMED FORCES

A total of 651 cases of leprosy were hospitalised from Jan 1987 to Dec 1992. Each patient underwent haemogram, total and differential white cell count, urinalysis, liver function tests, skin slit smear for AFB and skin biopsy. Nerve conduction studies, electomyographic studies and nerve/nerve sheath biopsies were undertaken as and when indicated. These patients were managed with multidrug therapy. Paucibacillary (PB) leprosy accounted for 476 (73.1%) cases which comprised of indeterminate leprosy 90 (13.8%), tuberculoid leprosy 14 (2.2%), borderline tuberculoid leprosy 310 (47.6%) and neuritic leprosy 62 (9.5%). The remaining 175 patients (26.9%) were multibacillary (MB) which included borderline leprosy 9 (1.4%), borderline lepromatous leprosy 129 (19.8%) and lepromatous leprosy 37 (5.7%) patients. There were total 153 patients in 1987. This number declined to 44 in 1992. PB declined from 113 in 1987 to 39 in 1992 and MB cases from 40 to 5.KEY WORDS: Leprosy