ESTRO 2024 - Abstract Book

S3376

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

[iii] Maeve Masterson (2022). A review of micro silica beads in radiation dosimetry applications. Radiation Physics and Chemistry

2983

Digital Poster

Patient specific QA of CyberKnife SRS plans using radiochromic films in Vestibular Schwannoma

Marta Kruszyna-Mochalska 1,2 , Barbara Bajon 1 , Agnieszka Skrobała 1,2 , Dorota Borowicz 3 , Kinga Graczyk 1 , Piotr Romański 1 1 Greater Poland Cancer Centre, 1. Department of Medical Physics, Poznań, Poland. 2 University of Medical Sciences, 2. Department of Electroradiology, Poznań, Poland. 3 International Oncology Center Affidea, 1. Department of Medical Physics, Poznań, Poland

Purpose/Objective:

Vestibular Schwannoma (VS) is a benign nervous tumor located in the brain with the auditory nerve. Depending on Koos classification of VS radiosurgery (SRS) or stereotactic radiotherapy (SRT) techniques (1 fx 12 Gy or 3 fx 6 Gy) are used as a treatment method, which allows the planned dose to be delivered to the treated area while protecting the organs at risk (OARs): the cochlea and brainstem. Small fields (typical collimator size for CyberKnife 5-10mm), high gradients, and proximity the planning target volume (PTV) to OARs are challenging for Patient Specific Quality Assurance (PSQA).

The main aim was to develop a pretreatment PSQA for CyberKnife, verify plan delivery in chosen planes representing both PTV and the area of OARs by radiochromic films and consider using this verification method in clinical practice.

Material/Methods:

A group of 7 treatment plans for a vestibular schwannoma using CyberKnife (Accuray, USA) were included. PSQA was done with a 2D-array OCTAVIUS detector 1600SRS (PTW, Freiburg) in the coronal plane and additionally with radiochromic films. Due to dose levels, EBT-XD (for average planned dose >10 Gy in PTV) and EBT3 (for average planned dose <10 Gy in OARs) Gafchromic films (Ashland, USA) were used to perform patient specific QA and placed in the chosen planes (coronal for planes representing PTV and axial for OARs) and depths, in the solid phantom. The detectors were calibrated at known doses with a 6 MV FFF beam using a solid phantom and Semiflex chamber (PTW, Freiburg) to prepare the detectors. The films were scanned using the Epson Perfection v850 Pro scanner (Seiko Epson Corporation, Japan) with the following parameters: 72 dpi, red-green-blue (RGB) mode, no color or sharpness correction, and consistent orientation and then analyzed in the PTW-Verisoft (Freiburg) using the following gamma test parameters: L2%/2mm, TH 10%, gamma passing rates (GPR) >90%.