ESTRO 2024 - Abstract Book

S3170

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

References:

Billas et al (2021). Phys. Med. Biol. 66 (2021) 165006

Francescon et al (2008). Med. Phys. 35 (2): 504–513

Duchaine et al (2020). Phys. Med. Biol. 67 (2022) 045007

23

Digital Poster

Receiver operating characteristic curve analysis for stereotactic body radiotherapy plans

Łukasz Szczurek

International Oncology Center Affidea Poznań, Medical Physics, Poznań, Poland

Purpose/Objective:

Stereotactic body radiotherapy (SBRT) is defined as highly precise radiotherapy in a single or in a few fractions, thus dosimetric errors during treatment delivery may have greater impact on the overall accuracy of the dose delivered to the planning target volume (PTV) and organs at risk (OAR) than conventional radiotherapy fractionation schemes. The sensitivity for the gamma index method was analyzed to correctly identify the pre-treatment volumetric modulated arc therapy (VMAT) plans with high dose errors and to quantify the incidence of false negatives (FN) and true positive (TP).

Material/Methods:

Pre-treatment verifications were performed for 20 SBRT plans by acquiring the planar dose distribution with a I’mRT MatriXX detector. Additionally a point dose measurements using diode SRS and Phantom Ruby were analyzed. Percentage gamma passing rates (%GP) with different acceptance criteria: 3%/3 mm, 2%/2 mm were obtained with OmniPro software. Dosimetric errors (%DE) were calculated from treatment planning system Monaco and point dose measurements. Sensitivity between %GP and %DE was investigated using receiver operating characteristic (ROC) curve. The number of FN cases and TP cases were calculated. FN had dosimetric errors >3% among those patients with %GP >95%. All the cases TP had errors >3% and %GP <95%. The average area under the curves (AUC) of ROC was compared to investigate the ability of 3%/3 mm and 2%/2 mm criterion to identify accurately the plan with dose errors >3%.

Results: