ESTRO 2024 - Abstract Book

S4951

Physics - Quality assurance and auditing

ESTRO 2024

Creating similarly robust plans for different radiotherapy delivery systems

Jose A Baeza-Ortega 1 , Mo Hussein 2 , Catharine H Clark 2,3,4 , Peter B Greer 5,1 , Joerg Lehmann 5,1,6

1 The University of Newcastle, School of Information and Physical Sciences, Newcastle, Australia. 2 National Physical Laboratory, Metrology for Medical Physics, Teddington, United Kingdom. 3 Radiotherapy Physics, UCLH NHS Foundation Trust, London, United Kingdom. 4 Department of Medical Physics and Biomedical Engineering, University College London, London, United Kingdom. 5 Calvary Mater Newcastle, Department of Radiation Oncology, Newcastle, Australia. 6 University of Sydney, Institute of Medical Physics, Sydney, Australia

Purpose/Objective:

Purpose

Complex radiotherapy treatment plans are more vulnerable to mechanical errors during delivery [1], especially in anatomical locations where critical organs are close to the target. Delivery errors, in the order of machine mechanical tolerances, have shown the potential to have a relevant clinical impact in dose distributions, particularly when combined [2].

For studies comparing the performance of quality assurance processes on multiple types of radiotherapy delivery systems (e.g., in different facilities) it can be desirable to create dosimetrically equivalent treatment plans for each of the systems. These plans should produce similar dose distributions and be similarly robust towards outside influences, such as slight changes in the treatment delivery due to mechanical deviations of components of the delivery system (e.g., MLC positions).

This work has explored the creation of dosimetrically equivalent treatment plans for different linear accelerators to compare the impact of within-tolerance mechanical delivery errors on those plans.

Material/Methods:

The study used a feature available in a commercial treatment planning system which is intended to create plans in a contingency situation, enabling a patient to be treated on another treatment machine if the original machine were unavailable (Raystation Fallback planning, Raysearch Laboratories, Sweden). Fallback plans were created for three common treatment machines: Elekta Versa Agility (Elekta AB, Sweden), Varian TrueBeam HD and TrueBeam Millenium (Varian Medical Systems, USA). Three different head-and-neck VMAT plans were explored, two with simultaneous integrated boost from the Head Neck-PET-CT collection of The Cancer Imaging Archive [3], which were both planned for a TrueBeam HD, and a credentialing plan from the ART DECO study [4], planned for an Elekta Agility. The fallback planning process resulted in nine treatment plans: three originals and six fallback plans (i.e. two for each original plan). Close-to-tolerance delivery errors were introduced to the nine plans using an in-house tool developed in Matlab (The MathWorks Inc., USA). These included MLC position errors, collimator angle errors, machine output errors, and combinations of those.