Pitfalls in IMRT treatment planning with the CadPlan-Helios system

The CadPlan-Helios treatment planning system for intensity-modulated radiation therapy (IMRT) includes some physical parameters that are specified by the planner, and thus can be subjectively interpreted. The choice of the value of these parameters strongly depends on the practical experience of the planner. This paper presents some extremes of the optimization constraints, to illustrate some traps of IMRT planning. The examples used in this paper are not directly related to clinical situations and some problems were deliberately exaggerated. Treatment fields were defined as recommended by Memorial Sloan-Kettering Cancer Center procedures for prostate IMRT. Prostate plans were arranged using a 5-field technique and 20-MV photon beam. The target and critical structures were defined and contoured for CadPlan-Helios. All computer calculations were performed for the same field arrangement. The following optimization parameters and factors are presented and analyzed in examples to visualize the importance of each parameter: dose-volume constraints and priority factors, scatter distance, maximum number of iterations and termination tolerance. The presented analysis strongly suggests that all constraints and parameters should be recorded in individual planning charts because without their nominal values, any reanalysis or dose recalculation may be difficult.