Theoretical models for supercritical fluid extraction.

For the proper design of supercritical fluid extraction processes, it is essential to have a sound knowledge of the mass transfer mechanism of the extraction process and the appropriate mathematical representation. In this paper, the advances and applications of kinetic models for describing supercritical fluid extraction from various solid matrices have been presented. The theoretical models overviewed here include the hot ball diffusion, broken and intact cell, shrinking core and some relatively simple models. Mathematical representations of these models have been in detail interpreted as well as their assumptions, parameter identifications and application examples. Extraction process of the analyte solute from the solid matrix by means of supercritical fluid includes the dissolution of the analyte from the solid, the analyte diffusion in the matrix and its transport to the bulk supercritical fluid. Mechanisms involved in a mass transfer model are discussed in terms of external mass transfer resistance, internal mass transfer resistance, solute-solid interactions and axial dispersion. The correlations of the external mass transfer coefficient and axial dispersion coefficient with certain dimensionless numbers are also discussed. Among these models, the broken and intact cell model seems to be the most relevant mathematical model as it is able to provide realistic description of the plant material structure for better understanding the mass-transfer kinetics and thus it has been widely employed for modeling supercritical fluid extraction of natural matters.

[Dosimetric comparison between helical tomotherapy and step-and-shoot intensity modulated radiation therapy for endometrial carcinoma].

BACKGROUND AND OBJECTIVE: Helical tomotherapy (HT) has shown its dosimetric advantages in the radiotherapy for many cancers. To date, no published studies have performed a dosimetric evaluation of whole pelvic radiotherapy (WPRT) using HT for postoperative endometrial cancer. This study was to compare the dosimetric characteristics of HT and step-and-shoot intensity modulated radiation therapy (SaS-IMRT) for endometrial cancer patients undergoing postoperative WPRT, and to explore whether whole pelvic HT for postoperative endometrial cancer has the advantage of dosimetry. METHODS: Ten patients with endometrial cancer undergoing postoperative WPRT were enrolled in this study. SaS-IMRT and HT Plans were developed for each patient. The dose distributions of the targets, organs at risk and normal tissue were analyzed and compared. RESULTS: The mean PTV100 were 95.6% and 95.8% (P=0.72) for the SaS-IMRT and HT plans, respectively. The mean homogeneity indexes were 1.10 and 1. 07 (P=0.00). The mean conformity indexes were both 0.87. The mean doses to rectum and bladder for HT were decreased by 1.3 Gy and 3.0 Gy compared with SaS-IMRT, respectively, while the mean dose to pelvic bones was increased by 1.1 Gy. The volumes of small intestine and colon, pelvic bones receiving moderate and low dose also increased. The V5, V10 and V20 of normal tissue were increased by 13.0%, 18.0%, and 5.0% (P=0.00). The mean dose to normal tissue was increased by 2.5 Gy (P=0.00). CONCLUSIONS: Compared with SaS-IMRT, HT resulted in more homogeneous PTV dose distribution, better sparing of rectum and bladder. The volumes of small intestine and colon, pelvic bones and normal tissue receiving moderate and low dose for HT increased. The clinical significance of the dosimetric differences needs further investigations.

Interstitial permanent implantation of 125I seeds as salvage therapy for re-recurrent rectal carcinoma.

PURPOSE: To assess the feasibility, efficacy, and morbidity of (125)I seeds interstitial permanent implant as salvage therapy for re-recurrent rectal cancer. METHODS AND MATERIALS: From September 2003 to October 2007, (125)I seeds implant procedures were performed under CT or ultrasound guidance for thirteen patients with locally re-recurrent rectal carcinoma. The minimal peripheral doses (MPD) of (125)I seeds implanted ranged from 120 to 160 Gy, with a median MPD of 140 Gy to total decay. Three patients also received two to four cycles of chemotherapy after seed implantation. RESULTS: After a median follow-up of 10 months (range 3-45), the pain-free interval was 0-14 months with a median of 7 months (95% CI: 3-11 months). The response rate of pain relief was 46.2% (6/13). Local control was 3-14 months with a median of 7 months (95% CI: 3.5-10.5 months). The 1- and 2-year local control rates were 14.4% and 0%, respectively. Three (23.1%) patients died of local recurrence; seven (53.8%) patients died of local recurrence and metastases; one (7.7%) patient died of metastases. Two (15.4%) patients survived to follow-up. At the time of analysis, the median survival was 10 months (95% CI: 3.9-16.1 months). The 1- and 2-year actuarial overall survival rates were 46.2% and 11.5%, respectively. Two (15.4%) patients experienced a grade 4 toxic event. Seed migration to the pelvic wall was observed in one (7.7%) patient. There was no associated neuropathy. CONCLUSION: (125)I seed implantation is feasible, effective, and safe as a salvage or palliative treatment for patients with re-recurrent rectal cancer.