AbstractID: 8606 Title: Optimization of Compensator Design for Proton Therapy
Construction of treatment plans for Proton therapy using passive
diffusion through a compensating bolus to create a conformal dose
distribution to a target volume is possible through the use of broad
beam algorithms, such as those implemented in CMS/FOCUS. However,
comparison of the broad beam dose calculations to dose distributions
constructed using a pencil beam approach show significant differences
at the distal range of the target volume. In a pencil beam approach,
the lateral scattering of the individual pencil beams is considered in
detail, presenting a significant spread of the pencil beam as it
propagates through the patient volume. Such calculations indicate an
under-dose to the distal end of the target compared to the broad beam
calculation results. This under-dose is significant near regions of
high curvature in the target volume, increasing with depth in the
patient volume. To compensate for the error in the broad beam
calculation, it is necessary to perform a pencil beam calculation to
create an optimal dose plan. However, such dose calculations can be
computationally expensive and require multiple iterations to optimize.
A hybrid routine is being developed to iteratively correct the
distal target dose calculation using the pencil beam algorithm along
the distal surface of the treatment prescription. The results of the
pencil dose calculation are used to modify the compensating bolus to
achieve the prescribed dose distribution. Results of this approach will
be presented along with suggestions to correct for the lateral
scattering of the proton beam deep in the patient.