Accuracy of the Treatment Plan Dose Preview Functionality of a Newly Commercially-Available, CBCT-Based, Online Adaptive Radiotherapy Treatment System

Abstract

The treatment planning module of a recently introduced, CBCT-based, online adaptive radiotherapy system includes a dose preview functionality to provide clinicians feedback regarding the set and priority of desired dose objectives. Informed clinical decision making requires that this prediction is accurate and not dependent on the specific technique and optimization solution selected for treatment. This work evaluates the accuracy of this dose preview functionality with respect to different IMRT and VMAT treatment configurations. A software emulator of the online adaptive radiotherapy system was used to retrospectively create alternative treatment plans for 10 cervical cancer and 10 rectal cancer patients. The dose preview functionality was used to predict the value of dosimetric variables optimized and calculated for five different treatment configurations, including a 7-, 9-, and 12-field IMRT plan, as well as a 2- and 3-arc VMAT plan. The dosimetric variables evaluated were the volume of the PTV receiving 95% of the 45 Gy prescription dose (PTV V95%) and the maximum dose (Dmax) to the bladder, bowel, and femoral heads. The accuracy of the dose preview functionality was comparable for all treatment field configurations. Across all configurations for the rectal patients, the average magnitude of the dose preview error was 1.0% (σ = 0.7%) for the PTV V95%, and 0.6 Gy (σ = 0.5 Gy), 0.9 Gy (σ = 1.4 Gy), and 1.7 Gy (σ = 1.4 Gy) for the bladder, bowel, and femoral head Dmax, respectively. For the cervical patients, the values were 0.7% (σ = 0.3%) for the PTV V95%, and 0.9 Gy (σ = 0.6 Gy), 1.2 Gy (σ = 1.1 Gy), and 2.6 Gy (σ = 2.5 Gy) for the bladder, bowel, and femoral head Dmax, respectively. Initial experience suggests that the dose preview functionality of the online adaptive radiotherapy system is accurate for both IMRT and VMAT plans to within a couple percent and a couple Gray. While the dose of the actual treatment plan should be known to greater accuracy, this may be sufficient for the purpose of informing clinicians as to the appropriateness of dose objectives prior to optimization of the actual treatment plan.