Objective Functional Scores Research Articles

Optimizer convergence and local minima errors and their clinical importance

Two of the errors common in the inverse treatment planning optimization have been investigated. The first error is the optimizer convergence error, which appears because of non-perfect convergence to the global or local solution, usually caused by a non-zero stopping criterion. The second error is the local minima error, which occurs when the objective function is not convex and/or the feasible solution space is not convex. The magnitude of the errors, their relative importance in comparison to other errors as well as their clinical significance in terms of tumour control probability (TCP) and normal tissue complication probability (NTCP) were investigated. Two inherently different optimizers, a stochastic simulated annealing and deterministic gradient method were compared on a clinical example. It was found that for typical optimization the optimizer convergence errors are rather small, especially compared to other convergence errors, e.g., convergence errors due to inaccuracy of the current dose calculation algorithms. This indicates that stopping criteria could often be relaxed leading into optimization speed-ups. The local minima errors were also found to be relatively small and typically in the range of the dose calculation convergence errors. Even for the cases where significantly higher objective function scores were obtained the local minima errors were not significantly higher. Clinical evaluation of the optimizer convergence error showed good correlation between the convergence of the clinical TCP or NTCP measures and convergence of the physical dose distribution. On the other hand, the local minima errors resulted in significantly different TCP or NTCP values (up to a factor of 2) indicating clinical importance of the local minima produced by physical optimization.

Squeaky Wheel Optimization

We describe a general approach to optimization which we term `Squeaky Wheel' Optimization (SWO). In SWO, a greedy algorithm is used to construct a solution which is then analyzed to find the trouble spots, i.e., those elements, that, if improved, are likely to improve the objective function score. The results of the analysis are used to generate new priorities that determine the order in which the greedy algorithm constructs the next solution. This Construct/Analyze/Prioritize cycle continues until some limit is reached, or an acceptable solution is found. SWO can be viewed as operating on two search spaces: solutions and prioritizations. Successive solutions are only indirectly related, via the re-prioritization that results from analyzing the prior solution. Similarly, successive prioritizations are generated by constructing and analyzing solutions. This `coupled search' has some interesting properties, which we discuss. We report encouraging experimental results on two domains, scheduling problems that arise in fiber-optic cable manufacturing, and graph coloring problems. The fact that these domains are very different supports our claim that SWO is a general technique for optimization.

FUNCTIONAL OUTCOME OF COMBINED MENISCAL REPAIR AND ACL RECONSTRUCTION.

1304 Operative repair of meniscal injuries identified at the time of ACL reconstruction is becoming more common. The goal of this prospective study was to compare functional outcome for patients who undergo meniscal repair in conjunction with ACL reconstruction (ACL+M) and those with isolated ACL injury(ACL-I). There were 19 patients in the ACL+M group and 55 in the ACL-I group. Both groups were allowed immediate motion and weight bearing as tolerated and followed the same rehabilitation protocol. Outcomes were measured by KT-2000 laxity testing, isokinetic strength testing of quadriceps and hamstrings at 60 and 180 degrees/sec., four hopping tests, and the modified Noyes knee rating questionnaire. Analysis of Variance failed to reveal statistically significant differences between the two groups for the hopping tests, KT scores, and, isokinetic extension strength. A statistically significant difference was found between between groups for flexion strength but not when compared to body weight (p=0.04). The isolated difference in flexion strength was not reflected in subjective or objective functional scores. Based upon this study we conclude that training protocols need not be modified after ACL reconstruction whether or not concomitant meniscal repair is performed.

Inclusion body myositis: treatment with intravenous immunoglobulin.

We report the results of nine patients with inclusion body myositis treated with intravenous immunoglobulin in an open-label uncontrolled study. None of our patients improved on objective manual muscle testing or functional disability scores. One patient developed mild neutropenia, complicating the intravenous immunoglobulin treatment. Our results do not exclude the possibility that intravenous immunoglobulin could be beneficial in some patients by slowing the rate of deterioration or perhaps stabilizing the disease. However, given the lack of objective improvement and high cost of treatment, we would not recommend intravenous immunoglobulin in the treatment of inclusion body myositis unless a blinded, controlled trial demonstrates clear benefit.