Physical and biological approaches to the improvement of dosimetry and delivery of brachytherapy treatments

Abstract

The linear quadratic model has been successfully used to describe the biological effects of radiation on normal tissue and tumors. In the first part of this study a generalized extrapolated response dose equation has been developed based on the linear quadratic model to account for the variation of dose rate, including incomplete repair of sublethal damage during and between fractions of irradiation. In addition, this equation can deal with treatment times that are not identical for different fractions. This equation has been applied to pulsed brachytherapytreatments. The therapeutic advantage over low dose rate brachytherapy has been studied. It is seen that a therapeutic advantage of greater than unity is possible. This equation has also been used to suggest pulsing schemes that would maximize the therapeutic advantage while complying with the requirement of the Nuclear Regulatory Commission without increasing hospital personnel hours. The second aspect studied relates to permanent implantation of the prostate. The ultrasound guided technique of implantation has improved the ease of effective radioactive source placement. The prostate base dose coverage, the issue of differences in prostate volume as imaged using ultrasound and CT, techniques to perform CT-based post-implant dosimetry, and finally various treatment strategies have been proposed, evaluated, and discussed.