ESTRO 2026 - Abstract Book PART II

S2935

RTT- RTT operational practice and workflow innovations

ESTRO 2026

and demonstrations for the team.6) Development of a structured decision tree to support decision making Results: A new policy with specific work instructions and troubleshooting sections, was created to aid RTTs in their decision-making during treatment delivery in an attempt to optimise this process.(Figure 1)

completion of contouring tasks in prostate radiotherapy workflows, delivering modest but operationally meaningful efficiency gains. While variability limits impact in complex gynaecological cases, observed improvements align with NHS productivity goals. These findings provide NHS-specific evidence to inform departmental optimisation and future implementation strategies. Keywords: AI, efficiency Digital Poster 3251 Optimising Prostate SABR: An Image-Guided Decision Tree for Auto Beam Hold Jack Hutchinson 1 , Sarah Dowley 1 , Katie Dooher 1 , Una Cooper 1 , Laura Barry 2,3 , Ita Marie Dunne 1 , Ece Tek 1 , Eimear O'Neill 1 , Michelle Coonan 1 , Erica Bennett 2,3 , Ciara Lyons 1 1 UPMC Hillman Cancer Centre UPMC Whitfield, UPMC, Waterford, Ireland. 2 UPMC Hillman Cancer Centre,

UPMC, Waterford, Ireland. 3 Bons Secours Radiotherapy, Bons Secours, Cork, Ireland

Purpose/Objective: Intrafraction motion is challenging when delivering prostate stereotactic ablative radiotherapy (SABR) as internal organ motion can displace the Planning Target Volume (PTV) and there is potential to deliver additional dose to critical organs at risk (OARs) (1, 2). To mitigate this, Varian™ have developed Automatic Beam Hold (ABH) that detects intrafraction motion of the PTV by monitoring the position of pre-implanted fiducial markers. The beam is paused if the fiducials drift outside a pre-defined tolerance region. Although this is automated, Radiation Therapists (RTTs) need to make clinical decisions if fiducials drift out of tolerance as prolonged treatment delivery times increase the risk of intrafraction motion (3). The aim of this project was to introduce, audit, and optimise ABH when used with triggered imaging for prostate SABR patients. A new Image-Guided Radiotherapy (IGRT) protocol was required with an audit strategy to test and develop a decision tree to support radiation therapists when using ABH . Material/Methods: Prostate SABR was initiated at our centre in March 2025 using a prescribed dose of 36.25Gy in 5# (PACE B and C constraints. A core implementation multi- disciplinary team was formed and, following a review of current evidence, the following steps were undertaken: 1) Failure Mode Effects Analysis risk assessment completed2) User Testing of software on motion phantom3) Guidance sought from centres utilising ABH4) Policy created, with specific work instructions and troubleshooting section5) Training

Figure 1: Prostate SABR Decision Tree Conclusion:

Minimising intrafraction motion of the prostate and OARs to ensure treatment accuracy is essential. However, this is multifactorial and a clear workflow aids RTT decisions and standardises the procedure. With ongoing audit of this process, the aim is to safely reduce the imaging interval, IGRT dose, and optimise using ABH actively or passively. References: 1. McNeice, J.M. et al. (2023) 'Prostate stereotactic body radiotherapy: Quantifying intra-fraction motion and calculating margins using the new BIR geometric uncertainties in daily online IGRT recommendations', BJR, 96(1146). doing 10.1259/bjr.202208522. Ng, M et al (2014) 'Fiducial markers and Spacers in prostate

radiotherapy: Current applications'. BJU International, 113 (S2),pp. 13-20. doing:

10.111/bju.126243. Van As, N. et al. (2023) '5-Year Outcomes from PACE B: An International Phase III RCT Comparing Stereotactic Body Radiotherapy vs. Conventionally Fractionated or Moderately Hypo

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