A Study on Design and Application of Tissue Compensator for 6MV X-rays / 대한치료방사선과학회지

A radiation beam incident on an irregular or sloping surface produces the non-uniformity of absorbed dose. The use of a tissue compensator can partially correct this dose inhomogeneity. The tissue compensator is designed based on the patient's three dimensional contour. After required compensator thickness was determined according to tissue deficit at 25 cmx 25 cm field size, 10 cm depth for 6MV x-rays, tissue deficit was mapped by isoheight technique using laser beam system. Compensator was constructed along the designed model using 0.5 mm lead sheet or 5 mm acryl plate. Dosimetric verification were performed by film dosimetry using humanoid phantom. Dosimetric measurements were normalized to central axis full phantom readings for both compensated and non-compensated field. Without compensation, the percent differences in absorbed dose ranged as high as 12.1% along transverse axis, 16.8% along vertical axis. With the tissue compensators in place, the difference was reduced to 0~4.3% Therefore, it can be concluded that the compensator system constructed by isoheihnt technique can produce good dose distribution with acceptable inhomogeneity, and such compensator system can be electively applied to clinical radiotherapy.

Radiotherapy Results of pineal Tumors / 대한치료방사선과학회지

A retrospective analysis was performed on 23 patients with pineal region tumors treated with radiation from 1979 through 1985 at the Department of Therapeutic Radiology, Seoul National University Hospital, Histologic confirmation was done in only one case by surgical removal, and in the remaining 22 patients, the diagnosis was based on clinical and radiological findings. The radiation volume was the primary tumor site in 1 case, whole brain in 14 cases, and the whole craniospinal axis in 8 cases. The overall 5 year survival was 71.5%. The 5 year survival was 69. 3% for whole brain treated group and 73.3% for craniospinal axis treated group. The survival for the two groups did not differ significantly. In two cases sites of recurrence were detected. One in supratentorial area, and the other in the lung. The results from this retrospective analysis and the review of other reports indicate that routine use of prophlatic spinal irradiation is not warranted in pineal region tumor, and the craniospinal irradiation is recommended in cases with high risk for subarachnoid seeding such as positive CSF cytology, surgical removal or biopsy.

Application of Generalized Batho Method to Arbitrary Shape of Heterogeneous Tissues / 대한치료방사선과학회지

The generalized Batho method, proposed by Webb and Fox, which is a method of calculation of dose correction factor for the multilayer of heterogeneous tissue, is complex even for a few kind of tissues. The method was modified for the purpose of getting a simple method that divide the multilayer of heterogeneous tissues into some groups of adjacent-tissue pairs. This new method could reduce the number of exponential terms and the time for calculating the dose correction factors by manual and computer calculation.