AbstractID: 7981 Title: The Linear Quadratic Model and Fractionated Stereotactic
Radiotherapy
Stereotactic radiosurgey performed using the Gamma Knife or linear accelerator has
become the preferred treatment modality for certain intra-cranial lesions. As in
conventional radiotherapy, multiple-fraction stereotactic treatment regime is sometimes
desired for certain tumors because of its radiobiological advantage. As a practical matter
fractionated stereotactic radiotherapy typically involves few fractions with large fraction
sizes. The purpose of this study is to determine the fraction size that could be used when
stereotactic treatments are delivered in two or more fractions. The linear quadratic model
is used to calculate the dose per fraction for a multiple-fraction regimen which is
biologically equivalent to a given single-fraction treatment. The results are summarized
in lookup tables. These tables could be used as a guide by practicing clinicians in
planning fractionated treatment. For the typical doses prescribed in Gamma Knife or
accelerator based stereotactic treatments, the model is not sensitive to the choice of the
ratio, α/β, of the linear quadratic model. A simple rule of thumb is found that for a twoand three- fraction treatments the dose per fraction is roughly 2/3 and 1/2 of the single
fraction treatment dose, respectively.