AbstractID: 7718 Title: Optimized Interstitial PDT Prostate Treatment Planning with the Cimmino
Algorithm
Interstitial photodynamic therapy (PDT) for the prostate is performed with linear light sources of various lengths inserted to various
depths within the matrix of parallel catheters perpendicular to a base plate. A phase I trial of Motexafin Lutetium (Mlu)-mediated
PDT (λ730 nm) is on-going at the University of Pennsylvania. This protocol uses equal source strengths (150 mW/cm) and equalspaced loading (1-cm). Clinical experience with brachytherapy and animal PDT studies suggest a need to limit dose to the urethra and
rectum while meeting the prescription to the entire prostate gland. It is thus desirable to optimize the distributions of source strength
and source location in the treatment plan. As a first step, we use the Cimmino algorithm to optimize the weights of light catheters
already chosen and inserted into a clinical patient. Uniform optical properties are assumed. The goal is to see whether the urethra and
rectum can be spared with minimal effect on PTV treatment by manipulating light exposure times of the sources. Maximum and
minimum allowed doses to 889 points in four volumes (prostate, urethra, rectum, and background) are used to determine the weights
of 12 linear light sources. Importance weights are chosen for organ volumes, and normalized. The weight of a voxel is its organ
weight divided by the number of voxels in the organ. Dose constraints that allow sparing of the urethra and rectum are shown to exist.
Evidence is presented that the combined selection of positions, lengths, and weights of interstitial light sources drastically improves
outcome.