Abstract
The optimization of radiotherapy should mean maximizing the probability of destroying the tumor tissue and minimizing the probability of harming the normal tissue.
If the patient involved both the superficial-and deep-seated tumor is treated with a single-field of high energy X-ray beams (10 MV X-rays or more), the superficial-seated tumor will be received a smaller dose due to the build-up effect. And if the patient is irradiated with two opposed fields, the doses of all the normal and tumor tissue between the two fields will be just the same.
As treatment planning for these patients, we studied to use two opposed fields with different dose-ratio and different MV's of high energy X-rays.
Thirty isodose charts were drawn. Type and energy of radiation :
Linac 6MV and 12MV X-rays. Source-surface distance : 100cm
Field size : 15x15cm2
Field separation : 20cm
Dose-ratio : 1 : 1, 1.5 : 1, 2 : 1, 2.5 : 1, 3 : 1 Phantom : Mix Dp. 30x30x20cm3
It is hoped that the charts will be useful both for references in treatment planning and practice.
