ESTRO 2024 - Abstract Book

S65 ESTRO 2024 1 Hospital Sant Joan de Reus, Medical Physics, Reus, Spain. 2 Hospital Clinic de Barcelona, Radiation Oncology, Barcelona, Spain Invited Speaker

Abstract:

The accurate modeling of Multi-Leaf Collimators (MLC) within Treatment Planning Systems (TPSs) is crucial for the precision of IMRT/VMAT dose calculations. Despite its importance, there is a lack of standardized procedures for commissioning MLC models in TPSs as per international protocols and guidelines. This absence leads to varied methods being employed, resulting in significant variability in the clinically used MLC parameters and substantial uncertainties in TPS dose calculations for IMRT/VMAT plans. This presentation introduces a novel methodology and formalism aimed at standardizing MLC models in TPSs. This approach utilizes a combination of synchronous (SG) and asynchronous sweeping gap (aSG) tests, alongside average doses measured with a Farmer-type ion chamber, to accurately determine the MLC parameters for TPS configuration. It also highlights the necessary trade-offs, revealing current limitations in MLC models and suggesting directions for their future enhancement. This methodology has garnered endorsement from authoritative bodies, including AAPM (Medical Physics Practice Guidelines 5.b) and NCS (NCS 39), underscoring its significance and reliability. We will explore practical applications of this methodology across various MLCs from leading manufacturers like Varian (Millennium 120, HD120, Halcyon) and Elekta (Agility, MLCi2, Unity), and different TPSs (Eclipse, RayStation, Monaco, Pinnacle, Elements). The presentation will draw upon findings from several key publications, demonstrating the wide reaching implications and benefits of this standardized approach in improving the accuracy and reliability of IMRT/VMAT dose calculations. • Commissioning of the tongue-and-groove modelling in treatment planning systems: from static fields to VMAT treatments. Phys Med Biol. 2017; 62(16):6688-6707. • A new method for modelling the tongue-and-groove in treatment planning systems. Phys Med Biol. 2018; 63(24):245005. • On the need for tuning the dosimetric leaf gap for stereotactic treatment plans in the Eclipse treatment planning system. J Appl Clin Med Phys. 2019; 20(7):68-77. • A novel procedure for determining the optimal MLC configuration parameters in treatment planning systems based on measurements with a Farmer chamber. Phys Med Biol. 2020; 65(15):155006. • Dosimetric leaf gap and leaf trailing effect in a double-stacked multileaf collimator. Med Phys. 2021; 48(7):3413 3424. • Investigation on the impact of the leaf trailing effect using the Halcyon integrated platform system. Med Phys. 2022; 49(9):6161-6170. • Challenges in modeling the Agility multileaf collimator in treatment planning systems and current needs for improvement. Med Phys. 2022; 49(12):7404-7416. • Universal evaluation of MLC models in treatment planning systems based on a common set of dynamic tests. Radiother Oncol. 2023;186:109775. • Improving the modelling of a multi-leaf collimator with tilted leaf sides used in radiotherapy. Phys Imaging Radiat Oncol. 2024;29:100543. • Multileaf collimator characterization and modeling for a 1.5 T MR-linac using static synchronous and asynchronous sweeping gaps. Phys Med Biol. Published online February 27, 2024.

3429

Modulating innate immunity by DNA damage response inhibition

Kevin J Harrington