AbstractID: 8952 Title: Dosimetry of GliaSite brain implants with two balloons
A technique for the treatment of recurrent Glioblastoma Multiforme is to implant a balloon into the resection cavity during
surgery. The balloon is later filled with a liquid I-125 solution to treat the residual disease at its surface. If the resection cavity is too
large for a single balloon, the neurosurgeon may decide to insert two balloons to fill
the cavity. In this work we describe the
dosimetry of such a two-balloon implant. Here two prescription points are required, in contrast to the single point used for one
balloon. We present a prescription method as well as equations to calculate the required activities for each balloon, and describe an inhouse computer code which calculates two-dimensional isodose distributions. We apply the calculation to the case of a patient with
15 and 30 cm3 balloons. For a prescribed minimum dose of 60 Gy at 1 cm, the dose at 1 cm around the balloons ranges from 60 to 111
Gy. Also, the maximum surface dose is approximately double that of a single-balloon implant. To allow the physician to observe the
spatial distribution of these non-uniformities relative to the critical structures, we have modeled the balloons in a 3D treatment
planning computer and show isodose lines superimposed on the MRI. This allows manipulation of the activities to obtain an
acceptable dose distribution. Although the dosimetry of a GliaSite treatment with two balloons is worse than for a single balloon, it
can be accomplished using the methods described in this work.