AbstractID: 7069 Title: Intensity Modulated Electron Radiation Therapy (IMeRT) Algorithms
for Arc Therapy Planning
ABSTRACT:
In the 1980’s techniques for electron arc chest wall therapy were developed and successfully
applied using special purpose tertiary collimators. Building on this work, we discuss automated
optimization techniques for electron arc modulation aimed at implementation with a multi-leaf
collimation system. The basic idea is to choose reference points within a tumor volume, and
optimize leaf-widths and monitor unit weights along the arc to achieve a homogeneous dose
which spares organs at risk. The optimization proceeds one transverse plane at a time, starting
with the central plane. Leaf-widths along the arc are optimized with a gradient descent method,
one arc segment at a time. Weights are determined through a constrained least squares fit for the
central plane. The algorithm uses accurate 3D electron dose calculations during the optimization.
These dose calculations are based on Hogstrom’s pencil beam technique. Besides the choice of
reference points and prescribed dose in the tumor volume, the only other main input is patient
CT data. The optimization and dose calculation package are implemented within a clinical
software planning system, and is called IMeRT. We believe the procedure will be efficient
enough that the algorithm can be used routinely in a clinical setting. We present examples which
implement the algorithm on historical data sets, and compare these results to conventional
treatment planning. These results show that a good delivered dose can be achieved, making dose
planning for electron arcs with multi-leaves or other collimators quite practical.
AbstractID: 7069 Title: Intensity Modulated Electron Radiation Therapy (IMeRT) Algorithms
for Arc Therapy Planning