  Most commercially available treatment planning systems for brachytherapy
operate based on physical dose and do not incorporate fractionation or
tissue-specific response. The purpose of this study is to investigate the
potential for hypofractionation in HDR brachytherapy, thereby reducing the
number of implants required. A new treatment planning algorithm was built in
order to optimize based on tissue and fractionation specific parameters.
Different fractionation schemes were considered for 6 patients, and plans were
created using the new algorithm. A baseline fractionation scheme consisting of
5 fractions was compared to hypofractionated plans of 1 to 4 fractions. The
effectiveness of each plan was evaluated using radiobiological criteria taken
from GEC-ESTRO guidelines. The results of this study indicate that an
optimization algorithm based on biological parameters has similar functionality
to traditional planning methods with the additional ability to account for
fractionation effects. Using this algorithm, it was shown that plans consisting
of 3 and 4 fractions have comparable target coverage with equivalent normal
tissue exposure. In some specific cases, further fractionation may present
acceptable target coverage as well.
