ESTRO 2021 Abstract Book

S1465

ESTRO 2021

When there were no interruptions during and between tasks the overall time for treatment planning was typically 40-60 minutes from import of planning images through contouring, plan creation and plan sign off (similar to the lead time for virtual simulation). Within this time, automated plan generation took no more than 5 minutes. Treatment preparation tasks typically took 15-20 minutes. This compares favorably to previous cases planned via a standard IMRT workflow which took up to 3 hours for treatment planning and checking tasks and 1 hour for treatment preparation tasks. Dose distributions were clinically approved and noted to achieve a more uniform dose distribution to the intended target, compared with the traditional parallel-opposed or single applied field techniques that tend to produce hotspots outside the target and offer poor dose fall-off. Treatments were all delivered in standard 20-minute appointment slots. Conclusion Whilst there will still be occasions when single fields are an optimal solution, we found that using the ETHOS workflow in IGRT mode allowed the creation of good-quality IMRT plans in time frames comparable to those using virtual simulation techniques. This could allow for optimal choice of planning technique for each case rather than choosing the fastest technique for clinical need. Our aim is to develop the workflow further for it to become our default choice for urgent plans with a contoured target volume. PO-1743 Patient positioning and intrafraction movement control protocol using an IGRT and SGRT system in SRS M. Pinto Monedero 1 , R. Rodríguez Romero 1 , P. Sánchez Rubio 1 , J. Martínez Ortega 1 , A. López Corella 1 , M. Torres López 1 , J. Ciudad Roca 1 , A.M. Lloret Gudiña 1 1 Hospital Universitario Puerta de Hierro Majadahonda, Medical Physics Department, Madrid, Spain Purpose or Objective Surface guided radiotherapy (SGRT) monitors patient position through its surface during treatment, complementing image guidance. Stereotactic radiotherapy treatments (SRS) requires submilimetric accuracy and precision. The purpose of this work is to describe a protocol for patient positioning and intra-fraction movement control in SRS treatments using a SGRT system complementing radiographic image, which has allowed to achieve an accuracy and precision in treatments comparable to the system previous existing in the center (<0.3mm, 0.3 °) Materials and Methods SRS technique was previously performed using a Novalis linac (Brainlab, Germany) and IGRT ExacTrac system with 6D robotic couch (Brainlab), which allowed image control using orthogonal X-ray images, for any combination of couch and gantry rotation. Closed masks were used for radiosurgery (Brainlab) and accuracy <0.3 mm, 0.3 ° was achieved. SRS technique has been implemented using a TrueBeam HD120MLC with a 6D robotic couch (Varian Medical Systems, USA) and an AlignRT surface guidance system (VisionRT, UK). AlignRT monitors the patient's surface throughout the treatment by comparing it, with six degrees of freedom, with the reference surface from the CT simulation. Also, a CBCT can be performed with the table at 0 °, but not when couch is rotated. The masks used for immobilization of the patient are open Encompass SRS Fibreplast (Q-Fix, USA). Results SRS workflow is summarized in Figure 1. After positioning the patient at the isocenter, AlignRT monitors the patient surface. Initial deviations from the reference surface> 0.5mm, 0.5 ° are corrected by acquiring a treatment capture. A CBCT is performed with couch rotation 0 °, then image registration, and the corrections are applied with 6 degrees of freedom. If AlignRT showed discrepancies greater than tolerance (0.3mm, 0.3 °), the CBCT would be repeated; otherwise, a reference capture is acquired, and fields with couch rotation 0 ° are treated. For each beam with different couch rotation, an AP portal image is taken to correct deviations in longitudinal, lateral and rotation until they are within tolerance. If the deviations were vertical, roll or pitch, the CBCT would be repeated with couch rotation 0 °. If all deviations are within tolerance, a new reference capture is acquired and beams treated. If during treatment any threshold is exceeded and there is suspicion of patient movement, the CBCT would be repeated with couch rotation at 0 °. If the occlusion of one of the cameras (POD) is responsible for the discrepancies, support of the medical physicist is required to assess a temporary opening of the tolerance or an increase in the maximum allowed deviation time.