[Effect of underdilated stent on the occurrence of hepatic encephalopathy after transjugular intrahepatic portosystemic shunt creation]

Objective: To evaluate whether underdilated stent could reduce the occurrence of hepatic encephalopathy (HE) after transjugular intrahepatic portosystemic shunt (TIPS) creation. Methods: A total of 197 patients with decompensated liver cirrhosis, who had underwent TIPS creation at Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, were analyzed retrospectively, including 110 males and 87 females with age 25-79 (54±11) years old. Uncovered and covered stents with 8 mm diameter were implanted in all subjects, and then dilated by balloon catheters with 6 mm or 8 mm diameter. The patients were divided into two groups, including underdilated group (6 mm, n=105) and control group (8 mm, n=92).Kaplan-Meier curves were used to illustrate cumulative rate of HE, and the differences were assessed with the log-rank test. Multivariate analyses with a Cox regression model were conducted to explore the risk factors for HE. Results: During a median follow-up period of 29 (12-54) months, 16 (15.2%) patients developed HE in the underdilated group and 27 (29.3%) patients in the control group. There was a significant difference in the cumulative rate of HE (P=0.014), but no statistical differences were found in terms of variceal rebleeding, shunt dysfunction and survival between the two groups (P=0.608, P=0.659, P=0.968). In multivariated analysis, group assignment (underdilated vs. control, HR=0.291, 95%CI 0.125-0.674, P=0.004) was identified as an independent risk factor for HE after TIPS creation. Conclusion: Underdilated TIPS could reduced the risk of HE compared with completely dilated TIPS, with comparable risk of variceal rebleeding, shunt dysfunction and mortality. And it is worthy of applying this technique to a large sample of patients in clinical practice.

Small-bowel displacement system for the sparing of Small bowel in three-dimensional conformal radiotherapy for cervical cancer

AIMS

The efficacy of the small-bowel displacement system (SBDS) in three-dimensional conformal radiotherapy (3-D CRT) planning for sparing the volume of small bowel is presented for cervical cancer.

MATERIALS AND METHODS

Ten consecutive patients, who received pelvic radiation therapy for uterine cervical cancer with the SBDS from January to March 2003, were included in this study. The SBDS consists of a customised Styrofoam compression device, which can displace the small bowel out of the radiation fields, and an individualised immobilisation board. With oral contrast before scanning, computed tomography was taken in the prone position with and without the SBDS. 3-D conformal planning was carried out, and dose distribution was compared in the target volumes and in the organs-at-risk with and without the SBDS.

RESULTS

In all patients, the SBDS significantly reduced the small-bowel volume within radiation fields. The median small-bowel volume with SBDS was reduced by 56.4% compared with the small-bowel volume without SBDS (from 491 to 214 cm3; P = 0.004). Among the 10 patients, the highest small-bowel volume reduction was 70.2% (from 544 to 62 cm3). At the prescription dose, the median volume of small bowel irradiated was reduced significantly with SBDS (9.8% vs 1.2%; P = 0.005). Differences in the dose-volume histogram for the rectum and the bladder between the 3-D CRT plans with and without SBDS were not statistically significant (P > 0.1). All patients completed radiotherapy without a break in treatment.

CONCLUSION

The SBDS is a novel method that can be used to displace the small bowel away from the 3-D CRT fields effectively, and reduce radiation therapy morbidity.

Physical properties of new collimator cone system for stereotactic radiation therapy developed in samsung medical center

PURPOSE

A new collimator cone system has been developed at the Samsung Medical Center that overcomes some of the limitations of present commercially supplied collimator cones. The physical properties of the newly developed cone system are described in this report.

METHODS AND MATERIALS

The new cones have relatively larger aperture sizes (3.0-7.0 cm in diameter) and are 16 cm in length. Each new cone is fabricated with cerrobend alloy melted and poured into a stainless steel housing that is permanently fixed to a mounting plate. The mounting plate of the new cone is designed to insert into the wedge mount slot of the gantry head. The mechanical accuracy of the central axis of the cone pointing to the isocenter was tested using film, a steel ball positioned at the isocenter by the mechanical isocenter device. For the evaluation of beam flatness and penumbra, off-axis ratios at 5 cm depth were measured by film dosimetry using polystyrene phantom.

RESULTS

The average error of the mechanical isocenter was 0.27 mm (+/- 0.16 mm). The beam flatness was excellent in the central region of the beam, and the average penumbra width was 3.35 mm (+/- 0.25 mm). The new cone design has more clearance between the patient's head and the gantry, and can more easily be removed from the gantry head because it slides in and out of the wedge slot. This facilitates changing cone sizes during one treatment session, and makes the process of double exposure port films easier.

CONCLUSIONS

A new collimator cone system for stereotactic radiation therapy has been developed. The mechanical accuracy and physical properties are satisfactory for clinical use, and the new design permits a wider range of clinical applications for stereotactic radiation therapy.

A glass compensator filter to improve breast image quality in radiation therapy simulation

PURPOSE

To improve the image quality of simulation films in tangential radiotherapy for breast cancer, we have designed a new compensator filter for the variation of breast contour using high-density-glass material.

METHODS AND MATERIALS

The measurements and analyses of the body contour were done using CT scans, taken in the treatment position, of 20 breast cancer patients. The maximum tissue deficit that needed to be compensated for was 8 cm, and the authors fabricated the compensator system using high-density-glass material to maintain transparency. The glass compensator can be attached to the accessory mount of the simulator head and its position can be easily adjusted according to breast shape and position. The image qualities of simulation films taken with and without the glass compensator in tangential breast radiotherapy field were compared and the film densitometry was performed using the humanoid phantom.

RESULTS

Using this compensator system, the overall image quality improved, resulting in enhanced contrast and resolution of the breast simulation image. The delineator wires for the beam margins were also well depicted, and the surgical clips within the breast tissue can be easily demonstrated. The film densitometry resulted in much less saturation over the breast tissue when using the glass compensator.

CONCLUSION

Using the glass compensator system, the geographical miss may be reduced with the virtue of the improved image quality.

Design and development of new collimator cones for fractionated stereotactic radiation therapy in Samsung Medical Center

PURPOSE

In stereotactic radiotherapy using X-Knife system, the commercially supplied collimator cone system had a few mechanical limitations. The authors have developed new collimator cones to overcome these limitations and named them "SMC type" collimator cones.

METHODS

We made use of cadmium-free cerrobend alloy within the stainless steel cylinder housing. We made nine cones of relatively larger sizes (3.0 cm to 7.0 cm in diameter) and of shorter length with bigger clearance from the isocenter than the commercial cones. The cone housing and the collimator cones were designed to insert into the wedge mount of the gantry head to enable double-exposure linac-gram taking.

RESULTS

The mechanical accuracy of pointing to the isocenter was tested by ball test and cone rotation test, and the dosimetric measurements were performed, all of which were with satisfactory results. A new innovative quality assurance procedure using linac-grams on the patients at the actual treatment setup was attempted after taking 10 sets of AP and lateral linac-grams and the overall mechanical isocenter accuracy was excellent (average error = 0.4 +/- 0.2 mm).

CONCLUSIONS

We have developed the SMC type collimator cone system mainly for fractionated stereotactic radiation therapy use with our innovative ideas. The new cones' mechanical accuracy and physical properties were satisfactory for clinical use, and the verification of the isocenter accuracy on the actual treatment setup has become possible.