Optimized interstitial PDT prostate treatment planning with the Cimmino feasibility algorithm

Abstract

The primary aim of this study was to determine whether optimized photodynamic therapy (PDT) treatment planning (seeking optimized positions, lengths, and strengths of the light sources to satisfy a given dose prescription) can improve dose coverage to the prostate and the sparing of critical organs relative to what can be achieved by the standard PDT plan. The Cimmino algorithm and search procedures based on that algorithm were tested for this purpose. A phase I motexafin lutetium (MLu)-mediated photodynamic therapy protocol is ongoing at the University of Pennsylvania. PDT for the prostate is performed with cylindrical diffusing fibers of various lengths inserted perpendicular to a base plate to obtain longitudinal coverage by a matrix of parallel catheters. The standard plan for the protocol uses sources of equal strength with equal spaced (1-cm) loading. Uniform optical properties were assumed. Our algorithms produce plans that cover the prostate and spare the urethra and rectum with less discrepancy from the dose prescription than the standard plan. The Cimmino feasibility algorithm is fast enough that changes to the treatment plan may be made in the operating room before and during PDT to optimize light delivery.

Treatment planning using tailored and standard cylindrical light diffusers for photodynamic therapy of the prostate

“…Other groups have previously proposed using the Cimmino feasibility algorithm (Censor et al 1988) to optimize the diffuser outputs (Altschuler et al 2005, Johansson et al 2007. However, De Pierro and Iusem (1985) have shown that, for the inconsistent case, the Cimmino algorithm minimizes (2.8) rather than (2.5), making the comparison of different diffuser positions in the outer loops inconsistent.…”

“…The cost function (2.5) expresses the weighted sum of all square deviations from the prescribed dose range, and it is similar to equation (4) in (Altschuler et al 2005):…”

“…This property was verified extensively under multiple conditions for the inner loop algorithm (defined below). For better comparison with the work from Altschuler et al (2005), we have calculated f Altschuler (s) when reporting the optimal costs in figure 2.…”

“…Computer-based optimization can improve planning efficiency and potentially find better solutions, yet only a few groups have investigated such strategies. Altschuler et al (2005) developed an optimization strategy that employs cylindrical diffusers, while the algorithm of Johansson et al (2007) assumes cut end fibres. These groups have implemented similar optimization strategies, where a search over diffuser positions is combined with a Cimmino linear feasibility algorithm (Censor et al 1988) to find the output powers (or irradiation times) for the diffusers.…”

The role of photodynamic therapy (PDT) physics

“…98 A kernelbased algorithm was developed to calculate light fluence rate distribution in the optically heterogeneous prostate gland, 109 which, coupled with an optimization engine allows optimization of light source powers to achieve a uniform light fluence distribution. 110,98 This area of research will evolve into a totally computerized delivery, monitoring, and dosimetry system for real-time feedback control.…”