ESTRO 2021 Abstract Book

S1315

ESTRO 2021

(www.myvarian.com/montecarlo).

The dosimetric accuracies of the HA plans and PRIMO simulations were evaluated using EBT3 radiochromic film (RCF) dosimetry. Film pieces of 4 cm x 4 cm (same film batch) were sandwiched in the RW3 phantom at the planned positions of the targets. Delivery of each HA plan was repeated three times on different days. RCF dosimetry was performed using the Radiochromic.com v 3.3.6 web application. 2D global gamma analysis (Eclipse vs. film and PRIMO vs. film) was focused in the region around each target defined by the 20% dose threshold. Local dose differences at the center of each target (DD%) were also

evaluated.

Results 1. 2D global (G) gamma passing rates (GPRs) for comparisons of Eclipse and PRIMO dose calculations vs RCF dosimetry are shown in Tables 1 and 2, respectively. 2. Eclipse-EBT3 GRPs were > 95% for 3%(G)/1 mm, while PRIMO-EBT3 GRPs were > 95% for majority of cases for 5%(G)/1 mm. 3. Peak dose differences (%DD) were within 3.5% for Eclipse-EBT3 comparison. %DD differences up to 8% were observed for PRIMO-EBT3 comparison. 4. PRIMO dose statistical uncertainty (U) was within 2% (k=2), while the estimated U for our RCF dosimetry method was 4% (k=2).

Conclusion Excellent dosimetric agreement with film dosimetry was found for the phantom-based HA plans calculated by Eclipse, including targets down to 5 mm-diameter (0.07 cm 3 ). This study validates the use the PRIMO software for independent verification of the HA plans using a 5%(G)/1 mm criteria. PO-1592 Performance of the Mobius 3D software for cranial SRS patient-specific QA J. Calvo-Ortega 1 , M. Hermida-López 2 , C. Laosa-Bello 1 , S. Moragues-Femenia 1 , J. Caslas-Farran 1 1 hospital Quirónsalud Barcelona, Radiation Oncology, Barcelona, Spain; 2 hospital Vall D'hebron, Servei De Física I Protecció Radiològica, Barcelona, Spain Purpose or Objective To assess the performance of the Mobius 3D (M3D, v. 3.1) software for independent verification of SRS plans. Materials and Methods Fifteen SRS plans designed with the Eclipse HyperArc technique were included. Plans consisted of 4-5 non- coplanar VMAT arcs treating solitary lesions (3 cases) and multiple brain metastases (12 cases, 2 to 35 targets