Permanently Implanted Research Articles

Source localization following permanent transperineal prostate interstitial brachytherapy using magnetic resonance imaging

Dosimetric evaluation of completed brachytherapy implant procedures is crucial in developing proper technique and has prognostic implications. Accurate definition of the prostate gland and localization of the implanted radioactive sources are critical to attain meaningful dosimetric data. Methods using radiographs and CT accurately localize sources, but poorly delineate the prostate gland. MRI has been recognized as a superior imaging modality in delineating the prostate gland, but poor in localizing sources due to lack of source visibility. The purpose of this study was to optimize the visualization of sources using MRI and compare to CT derived source localization. Multiple MRI scanning techniques were attempted until an acceptable sequence to visualize both the prostate gland and the implanted sources was found. The exams were performed using a pelvic coil only in approximately 15 min. The CT and MRI scans of 20 consecutive patients who had received TRUS-guided permanent transperineal interstitial prostate 125Iodine or 103Palladium brachytherapy were evaluated using an in-house dosimetry system. To eliminate anatomical dependence, the MRI-derived DVHs for the entire calculation volume were then compared to those derived from the CT scans. The differences in isodose volumes, of the calculation volumes, for all implants at all dose levels were not statistically significant at the 95% confidence level. Calculation volume isodose volumes derived from MR images were statistically similar to those derived from CT images at the prescription dose for both 125Iodine (p < 0.01) and 103Palladium (p < 0.026). This study presents the first evidence that MRI may be reliably used to identify permanently implanted 125Iodine and 103Palladium sources. Given the advantage of target definition characteristics of MRI, substantially more accurate dosimetric analysis of prostate implants is now possible. The cost of the optimized and abbreviated MR scanning sequence used in this study is comparable to a pelvic CT scan. Postimplant MRI allows more accurate volumetric and anatomically relevant evaluation of permanent prostate implants, which may provide useful clinical correlation.

Evaluation of the function of microdialysis probes permanently implanted into the rat CNS and coupled to an on-line HPLC system of analysis

The aim of the microdialysis technique is to reflect as closely as possible the status and fluctuations of substances contained in the extracellular space. Most often, microdialysis is performed with repetitively implanted probes. We have recently devised an experimental set-up which allows microdialysis to be performed in the spinal cord of unrestrained rats through chronically permanently implanted probes. In the present study, we have compared the in vitro recovery of a non-biogenic amine (DHBA) and of 5-HT, and the in vivo recovery of the former. Thus, we could extrapolate the in vivo recovery of endogenous 5-HT released. Moreover, we have found that the recovery does not vary irrespective of whether the animal is at rest or performing sustained physical exercise, and that it also remains stable with time, from 8 to 36 days after permanent implantation of the probe. We conclude that this simple method can be applied to standard experiments of microdialysis, and thus allow one to measure the actual rate of recovery for a given probe. Moreover, it permits control of the stability of dialysis parameters with time for long-term permanently implanted probes.

Effect of tumour shrinkage on the biological effectiveness of permanent brachytherapy implants

A tumour shrinkage factor is incorporated into previously derived linear-quadratic (LQ) formulae which allowed radiobiological assessment of the efficacy of permanently implanted radionuclides. The new formulations relate the biologically effective dose (BED) to radionuclide half-life, recovery half-life, tumour radiosensitivity, potential doubling time and linear shrinkage rate. Specific attention has been given to the following radionuclides: gold-198 (half-life, 2.7 days), palladium-103 (half-life, 17 days), ytterbium-169 (half-life, 32 days) and iodine-125 (half-life, 60 days). For each nuclide the log cell kill resulting from typically prescribed doses was calculated for a range of tumour clonogen doubling times at various radiosensitivities and linear shrinkage rates. It is shown that even relatively modest shrinkage rates are capable of enhancing the clinical potential of the longer-lived nuclides. However, even though the effect of tumour shrinkage is minimal in the case of gold-198, for fast growing and/or insensitive tumours there are fewer radiobiological uncertainties associated with the use of this nuclide. The revised equations may also have applications in certain types of biologically targeted radiotherapy.

Tissue and microdialysate changes after repeated and permanent probe implantation in the striatum of freely moving rats

Neurochemical and morphological effects of repeated microdialysis or permanent microdialysis probe implantations in striatum were studied. The extracellular levels of dopamine did not change between a first and a second probe insertion separated by 2 weeks or at a third dialysis session 2 days later. The 3,4-dihydroxyphenylacetic acid and homovanillic acid levels were similar at the first and second microdialysis session, but decreased at the third. Probes implanted permanently for 2 weeks clogged, and the recovery varied markedly after insertion of new probes. Tyrosine hydroxylase-stained dopamine fibers appeared unaffected after all dialysis sessions, although some swollen fibers were observed surrounding the probes. No change in the glial fibrillary acidic protein staining was seen immediately after the first dialysis session, although 2 weeks later gliosis was observed. After the second and third dialysis a diffuse gliosis was observed, while a glial barrier was seen surrounding the permanently implanted probes. Immediately after the first dialysis session enlarged laminin-stained blood vessels were seen, whereas repeated probe implantation also increased the blood vessel density. Thus, chronic in vivo microdialysis with permanently implanted probes is limited by severe technical problems and marked tissue changes. On the other hand, repeated probe insertion in the same brain site appears to be acceptable for performing chronic microdialysis studies in the same subject, provided neurochemical and morphological changes are taken into consideration.

Clinical Results of Titanium Retinal Tacks With Pneumatic Insertion

We used titanium retinal tacks inserted with a pneumatic instrument for retinal fixation in 11 operative procedures in ten eyes with complicated retinal detachments. Titanium was selected for permanent implantation because of its documented biologic tolerance. No intraoperative or postoperative complications related to the tacks were encountered. Three tacks, one 0.7 mm in length and two 1.6 mm in length, became dislodged postoperatively; 50 permanently implanted tacks, each 1.6 mm in length, remained in place after a mean follow-up of five months. Retinal reattachment at the end of the follow-up period was achieved in eight eyes and useful visual function was obtained in three eyes. Titanium retinal tacks are useful when immediate retinal fixation is required either temporarily or permanently to prevent retraction and detachment of the retina until adjunctive diathermy, cryopexy, or photocoagulation becomes effective.

Interstitial therapy suing non-absorbable (Ir192 nylon ribbon) and absrobable (I125 "Vicryl") suturing techniques.

Permanent and removable interstitial implantation techniques using absorbable and unabsorbable sutures are described. Most of these techniques can be performed in the clinic easily and quickly with basic instruments: needle holder, needle book, and hemoclips. Specifically, Ir192 (74-4 day half life, 300-610 keV, and 6.0 cm. hvl in tissue) nylon ribbon and I125 (60 day half life, 27-35 keV, and 2.0 cm. hvl in tissue) Vicryl sutures are described. A major advantage of the I125 over the Ir192 see (other than the fact that it can be permanently implanted and needs less radiation protection) is that the patient does not remain highly radioactive for as long a period due to hte extremely low I125 energy and may be allowed to leave the hospital. Both nuclides have the advantage of a long shelf life, making their use practical and economically feasible.

Permanently implanted transvenous pacemakers. Electrical measurements of function.

Three patients with complete heart block had a high resistance to electrical stimulation of the endocardium through transvenous pacemaker systems. One patient died; one needed reoperation for implantation of epicardial electrodes; and the third required a generator of higher current. The present enthusiasm for permanent transvenous implantation of pacemakers must be tempered somewhat by the knowledge that high endocardial resistance to pacing represents another cause of failure. Simple and rapid methods of determining the current necessary to stimulate the endocardium are available and should be used prior to permanent implantation of the generator. If a substantial margin of safety does not exist, one should consider substituting a pulse generator with greater output or an epicardial electrode system.

A study of estrogen-sensitive hypothalamic centers using a technic for rapid application and removal of estradiol.

SummaryThe effect of estrogen-tipped steel tubes has previously been studied with permanent implant methods. An improved technique makes it possible to place and remove 27-gauge estrogen-tipped tubes through a short 22-gauge “guide barrel” permanently implanted in the calvarium. The “guide barrel” is implanted and the animal allowed to recover from the effects of surgery prior to placement of the estrogen tube. Three experiments are described demonstrating the value of this technique: (i) Castrated female rats with estrogen tubes placed in the preoptic-suprachiasmatic region of the anterior hypothalamus exhibited behavioral lordosis and mating in less time than that previously described for rats with permanent tube implants. (ii) Estrogen tubes placed in the estrogen-sensitive center of the posterior hypothalamus of intact, normally cycling female rats for 7 days suppressed the return of normal vaginal cycles for 16-37 days after the tubes were removed. In previous reports with permanently implanted tubes...

Current Status of the Treatment of Complete Heart Block

Medical management of complete heart block affords but a temporary control neither stable nor dependable and its failure is too frequently unheralded and fatal. Electric pacing by interim transvenous stimulation provides immediate, stable, and dependable control. Indications for transvenous pacing or pacemaker implantation should include not only Stokes-Adams disease, but heart block with signs and symptoms of diminished cardiac output and with heart rates under 40 per minute as well. Patients with complete heart block are protected best by pacing with a transvenous intracardiac dipolar electrode preparatory to and during anesthesia for surgery. A series of 40 patients is presented. There was a total of 56 catheterizations. There were nine emergencies requiring immediate transvenous pacing. In this group, there were five deaths due to extensive intercurrent disease. This stresses the importance of the use of the dipolar electrode in patients too ill for permanent implantation, because despite their desperate medical condition, four of these patients were supported sufficiently so that subsequent permanent implantation was done without a fatality. Permanent asynchronous implantable pacemakers, though requiring battery change, are relatively simple to insert and are preferable to externally worn units. Of the 31 patients who have had permanently implanted pacemakers, there was one postoperative death. The four others died months later of unrelated disease, and the remaining patients, despite corrective episodes of pacemaker failure are all well, free of symptoms of heart block, and rehabilitated to activity normal for their age. Those patients who returned because of permanent pacemaker system failure and were paced transvenously, and those patients with intermittent regular sinus rhythm exhibited competitive pacing mechanisms. Electric or sino-atrial impulses appearing during any phase of the cardiac cycle did not precipitate ventricular fibrillation.