Anatomy of the fetal membranes using optical coherence tomography: part 1.

INTRODUCTION: In vitro studies on the structure of human fetal membranes have involved light or electron microscopy with fixation, dehydration, and staining. Recently, optical coherence tomography (OCT), an imaging technology, has provided high-resolution cross-sectional images of living biological tissues, with a penetration of 2-3 mm. We evaluated the use of this technology to examine the histologic features of human fetal membranes immediately after delivery. METHODS: Samples of fetal membranes of ten patients undergoing cesarean deliveries (four uncomplicated pregnancies, four with preeclampsia, and two with chorioamnionitis) and eight patients undergoing vaginal deliveries (six uncomplicated pregnancies and two with chorioamnionitis) were collected immediately after delivery. Samples were stretched across customized disks, rinsed, and analyzed using a time-domain OCT imaging system. Following OCT scanning, the samples were placed in formalin for histologic study. The OCT images were compared to histologic images of common human fetal membrane features. RESULTS: We were able to delineate the layers of the fetal membranes using bench-top time-domain OCT. The system was able to image histologic features of the fetal membranes, such as microscopic chorionic pseudocysts, ghost villi, meconium stained membranes, and chorioamnionitis. The OCT images corresponded with the histologic findings. DISCUSSION: This feasibility study demonstrates the potential of OCT technology for real-time assessment of human fetal membranes and may provide clinically useful information at delivery.

Time-dependent changes in CT-based dosimetry of I-125 prostate brachytherapy.

To determine the effect of time between prostate brachytherapy and evaluation CT scan on calculated target coverage. CT scans from 11 consecutive, unselected patients with stage T1 or T2 prostatic carcinoma who had transperineal I-125 implants at MSKCC in 1996 were analyzed for target coverage at 0, 2, and 6 months after implantation. The outer margins of the prostate were outlined on each CT section by a single investigator. In each CT plane, the prescription isodose (150 Gy) was overlaid on the target contour from the postimplant CT to calculate the integral Dose-Volume Histogram. The postimplant target volume on the day of the implant ranged from 93% to 160% of the preimplant volume (average: 117%). In all patients, the target size returned to the preimplant size or smaller within 2 months of the procedure and was relatively stable between 2 to 6 months. Immediately following the implant, an average of 84% of the target (range: 73-98%) was covered by the 150 Gy isodose line. Consistent with changes in the target volume over time, the target coverage increased from an average of 84% to 90% between 0 to 2 months and did not change substantially between 2 and 6 months. There was minimal source loss from the target area after the implant. It was concluded that temporary, postimplant swelling will increase the target volume, making target coverage inferior to what would be calculated if a dosimetry scan was taken sometime later, after the acute swelling has subsided. Until the clinical significance of the effect of postimplant volume changes is better defined, we are continuing to obtain evaluation scans on the day of the implant.

CT-based dosimetry for transperineal I-125 prostate brachytherapy.

PURPOSE: To demonstrate CT-based target coverage achieved by an experienced brachytherapy team, with a documented history of clinical efficacy. These results may serve as a point of reference by which other implant teams could evaluate their technical results. METHODS AND MATERIALS: Two to 4 h after implantation, a CT scan of the pelvis was obtained, taking 3-mm thick images at 3 mm scan intervals. The outer margins of the rectum and prostate were outlined on each CT section by a single investigator (KW). CT scans from 20 consecutive, unselected patients with stage T1 or T2 prostatic carcinoma who had transperineal I-125 implants at MSKCC in 1995 were analyzed. The prescribed minimum peripheral prostate dose was 140 Gy, based on a preimplant CT scan of the prostate. Target volumes were determined based on planar reconstruction of the prostate. RESULTS: An average of 84% of the target (range: 76-92%) was covered by the 140 Gy isodose line. An average of 90% of the target (range: 81-96%) was covered by the 120 Gy isodose line. The average minimum target dose was 57 Gy (range: 40-70 Gy). There was a loose correlation between the minimum dose and the degree of target coverage (r = 0.33). CONCLUSIONS: Based on CT scanning on the day of the implant, coverage of 80% or more of the target volume by the prescription dose is probably adequate. Accurate evaluation is a complex problem that is made imprecise by difficulty in target identification and by volume changes after the implant.

Modeling analysis of platinum-195m for targeting individual blood-borne cells in adjuvant radioimmunotherapy.

UNLABELLED: The inability to eradicate a population of single, isolated, blood-borne tumor cells with the radionuclides currently in use may limit the efficacy of adjuvant radioimmunotherapy. We have examined the possibility of sterilizing single blood-borne cells using surface-bound emitters of Auger and conversion electrons. METHODS: The number of cell-surface decays required for 99% sterilization was found by using the linear-quadratic model of cell survival (alpha = 0.3 Gy-1, alpha/beta = 10 Gy) to transform absorbed dose to survival probability. The absorbed dose to the center of the cell was calculated by evaluating the point dose kernel at the cell radius of 6 microns and multiplying it by the number of surface decays. A two-compartment model of whole-body pharmacokinetics was used to obtain the red marrow dose corresponding to a given number of cell-surface decays. RESULTS: Platinum-195m (T 1/2 = 4 days) proves to be a particularly effective radionuclide. The 195mPt protocol requires 1.2 GBq of injected activity and is calculated to give an average red-marrow dose of 1.23 Gy, well within marrow tolerance. CONCLUSION: Analysis of the targeting efficiency as a function of cell radius reveals that 195mPt is expected to sterilize cells with radii up to 8 microns without delivering more than 2.5 Gy to red marrow. It also emits photons that are appropriate for external imaging and has been used to study the biodistribution of cisplatin in humans. High-specific activity 195mPt may be obtained by decay of cyclotron-produced 195mIr (T 1/2 = 3.8 hr).