Experimental measurement and theoretical analyses of the freezing-thawing processes around a probe.

Both the experimental and the analytical studies of the freezing/thawing process around a cryosurgical cylinder probes in a simulative biological tissue are presented in this paper. The enthalpy method and the finite element scheme are applied to solve the multidimensional phase change problems in cryosurgery. A very good agreement is found between the computed solutions and the experimental results. The influences of different cooling-warming schemes of the probe on the ice ball development, the temperature variation, the axial and the radial temperature gradients inside the tissues, and the requirement of cooling power are analyzed

Kinetic method for the quantitative resolution of structural isomers based on the catalytic properties of beta-cyclodextrin.

This paper describes a new approach for the quantitative resolution of mixtures of structural isomers. The method is based on the observation that rate constants for the cyclodextrin-catalyzed hydrolysis of selected structural isomers are significantly different. By using cure-fitting methods, it is possible to use these differences in rate constants to resolve kinetic responses for mixtures into the responses for the individual components. The new approach is evaluated for the ortho-, meta-, and para-isomers of nitrophenyl acetate. At pH 10, with beta-cyclodextrin as catalyst, ratios of rate constants for the three isomers differ by ratios of 1:6.7:1.6 in the order mentioned above. Results are reported for both two- and three-component mixtures. For two-component mixtures of the ortho- and para-isomers which have rate constants differing by only 1.6-fold, linear least-squares slope and intercept of determined vs prepared concentrations for the ortho-isomer were 1.00 +/- 0.02 and 2 +/- 2.2 mumol/L for three runs on each of five samples in the concentration range from 22 to 176 mumol/L. The pooled standard deviation for these 15 runs was 3.7 mumol/L, corresponding to a relative standard deviation of 3.7% for the average concentration. Similar results were obtained for other two- and three-component mixtures.

Downstaging of advanced rectal cancer following combined preoperative chemotherapy and high dose radiation.

PURPOSE: To assess the potential downstaging of advanced rectal cancer with combined preoperative chemoradiation. METHODS AND MATERIALS: Thirty-one patients with fixed rectal cancers (stage > or = cT3) were treated with concomitant preoperative chemotherapy and high-dose radiation in an effort to improve resectability. Three (10%) patients had partially fixed low rectal cancers, 24 (77%) patients had fixed tumors, and 4 (13%) had advanced fixation with pelvic sidewall invasion. Radiation was delivered to the whole pelvis using shaped anterior and posterior and lateral fields to 45 Gy followed by a boost to the tumor. Median total radiation dose was 55.8 Gy. Chemotherapy consisted of low dose continuous infusion of 5-FU (200-300 mg/m2/day) for the duration of radiation treatment. All 31 patients underwent surgical resection of tumor 6-8 weeks following treatment. Median follow up is 24 months (range 9-60). RESULTS: Twenty-three (74%) of the tumors were clinically downstaged following preoperative treatment. Of 24 fixed cancers, 11 (46%) became mobile, 6 (25%) became partially fixed, and 7 remained fixed. Of the four tumors with advanced fixation, two (50%) became mobile and two (50%) no longer had tumor extension to the pelvic sidewall. Two of the three initially partially fixed cancers became mobile and one remained partially fixed. Following surgery, the pathologic postradiation T-stages were as follows: T0: 10%, T1: 0%, T2: 32%, T3: 42%, and T4:16%. Seven patients (23%) were also node-positive (T0-2: 2, T3: 4, T4: 1), and two patients (6%) had liver metastases at surgery. Preoperative chemoradiation was well tolerated. There was no significant hematological toxicity. Acute grade 3 gastrointestinal toxicity was seen in six patients requiring a short hospitalization for dehydration and/or abdominal discomfort. No patient developed grade 4 toxicity. Five patients (16%) developed local recurrence of disease (T0-2: 0/13, T3: 1/13, and T4: 4/5). The actuarial 3-year survival is 68%. CONCLUSIONS: Concomitant preoperative chemoradiation using low dose continuous infusional 5-FU for advanced rectal cancer is relatively safe with acceptable morbidity. This approach is associated with considerable clinical and pathologic downstaging of cancer. Tumor resectability is improved with potential for improved local control of disease and survival.

Analytical applications of catalytic properties of modified cyclodextrins.

This paper describes the evaluation of the catalytic properties of modified cyclodextrins for analytical applications. The beta-dimethylcyclodextrin was modified by adding one and two imidazolyl groups at carbon three positions. The modifications produced enhancements of catalytic activity for the hydrolysis of p-nitrophenyl acetate at neutral pH by factors of 1000 or more relative to the unmodified cyclodextrins. The catalytic properties of the monosubstituted cyclodextrin were evaluated for the quantification of p-nitrophenyl acetate in the concentration range of 10-90 mumol/L. Results obtained by equilibrium, initial-rate, and error-compensating predictive kinetic methods were compared. The equilibrium and predictive kinetic options yielded virtually identical results, with linear changes with concentration throughout the range studied and severalfold larger than the initial-rate option and dependencies on temperature, pH, and catalyst concentration that are 5-10-fold smaller than the initial-rate option.