S1886
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
compared with the IMRT9 and VMAT plans generated using the same planning directive. Statistical significance between delivery techniques was determined using repeated measures analysis of variance (p<0.05, with Bonferroni correction). Results: For both the PTV and OAR dose metrics presented in Table 1 and Figure 1, statistical significance was observed between both IMRT techniques and VMAT, but not between IMRT9 and IMRT12. At least one clinically unacceptable PTV metric was observed for 10 out of 24 VMAT plans (specifically PTV high risk V100%<93% and PTV low risk D99%<50 Gy). There was one IMRT9 plan where D99% of PTV low risk was unacceptable. For the OARs, all techniques achieved clinically acceptable dose sparing. However, the VMAT plans yielded a notable increase in dose for both the brainstem and spinal cord. Mean ± std planning times for each technique were 3.1±0.3 minutes for IMRT9, 3.6±0.3 minutes for IMRT12 and 14.1±0.9 minutes for VMAT.
below 0.8% (D90%, D95%, D98%). For truncated CBCTs, mean and maximum dose differences remained <1.23%, and coverage deviations were <2.6%. Conclusion: The Virtual CT–based automated workflow in RayStation markedly improved dose evaluation efficiency and accuracy. It enables near real-time verification while the patient is still in the clinic, reducing delays and improving clinical decision- making. Next steps include implementation for offline adaptive replanning and dose tracking in routine clinical practice. Keywords: Automated workflow, Virtual CT, Dose recalculation HyperSight-ARCHER study: a comparison of target coverage and organ-at-risk sparing for IMRT and VMAT plans in head and neck cancer using Ethos Peter R Martin 1 , R Lee Macdonald 1,2 , Cheryl Anderson 1 , Lucy Ward 1 , Marc LeBlanc 1 , Kenny Zhan 1 , Jennifer DeGiobbi 1 , Natasha McMaster 1,3 , Murali Rajaraman 1,3 , Lara Best 1,3 , Derek Wilke 1,3 , Amanda Cherpak 1,2 1 Radiation Oncology, QE2 Cancer Centre, Halifax, Canada. 2 Physics and Atmospheric Science, Dalhousie University, Halifax, Canada. 3 Radiation Oncology, Dalhousie University, Halifax, Canada Digital Poster Highlight 2461 Purpose/Objective: The Ethos radiotherapy system with the HyperSight imaging solution (Varian Medical Systems) has demonstrated improved target coverage and organ-at- risk (OAR) sparing for head and neck (H&N) radiotherapy patients through adaptive planning at treatment fraction 21 using 12-field intensity- modulated radiation therapy (IMRT12).1 However, this system can also generate 9-field IMRT (IMRT9) and 2- arc volumetric modulated arc therapy (VMAT) plans from each planning directive. It was the purpose of this work to compare target coverage, OAR sparing and plan calculation time for these treatment delivery techniques in the context of adaptive radiotherapy using HyperSight imaging in Ethos Treatment Management (ETM). Material/Methods: Twenty-four H&N radiotherapy patients (prescribed 70 Gy in 35 fractions) were imaged on Ethos with HyperSight (iCBCT Acuros reconstruction) prior to the start of treatment, as part of the HyperSight-ARCHER study2 (ClinicalTrials.gov ID: NCT05666193). Structures were contoured on all images, with targets contoured by radiation oncologists. Clinically acceptable IMRT12 plans were created in ETM (version 2.0), and target coverage, OAR sparing, and plan calculation time were
Conclusion: VMAT plans showed significantly lower target coverage compared to IMRT9 and IMRT12. However, clinically
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