ESTRO 2023 - Abstract Book

S2052

Digital Posters

ESTRO 2023

A 1.5T Elekta Unity® MRI-Linac and a 1.5T Philips Ingenia® MRI simulator have been recently installed at our Institution. A protocol to integrate MR simulation in the radiotherapy process has been defined. MR is obtained in treatment position with Philips Ingenia® for patients undergoing radical or adjuvant radiotherapy for primary and secondary HN and brain tumors, on both MRI-Linac or other Linacs (Accuray Radixact® or Cyberknife®). The MR acquisition protocol has been adjusted for the best tradeoff between acquisition time and image quality. Tolerability of the procedure has been evaluated. Results On Philips Ingenia, images were acquired before treatment and periodically (every 7-10 days) during treatment. The standard MR acquisition protocol includes plain 3d TSE T1, 3d TSE T2 and DWI for HN tumors, and 3d TSE T1, 3d TSE T2, T2 flair and T2 DTI for brain tumors. The flex coils are used for all the sequences but for T2 DTI where the standard brain tumor coil was used. For patients treated with Elekta Unity®, 3d TSE T2 images were used for both delineation of targets and OAR and for treatment planning. For patients treated with conventional Linacs, MR images were used as secondary reference. From August 25th 2022 to October 24th 2022, 30 patients were scanned on Philips Ingenia: 14 with HN tumor and 12 with brain tumor. 2 patients had prostate and gynecological cancer. Of these, 8 were subsequently treated on Unity® (5 HN and 3 brain). Despite an increase in acquisition time in respect to CT, the procedure was well tolerated by all patients and no imaging interruption of the single exam has been required. During the normo-fractionated treatment (30 to 33 fraction) a median number of 4 MRI/patient (range 1-6). Some of the exams were used for re-planning Conclusion MRI simulation in treatment position is valuable for treatment planning both with MRI-Linac and conventional Linacs and could be effectively integrated in the workflow of radiation oncology Centers. Acquisition of MR simulation images is well tolerated by cancer patients. A prospective trial is already open to assess the clinical benefits of this workflow and to standardize and optimize the use of the different sequences, for clinical and research purposes.

PO-2282 SABR Prostate: A review of specialised techniques for motion management

J. mitchell 1 , D. McLaren 2 , W. Nailon 3

1 Edinburgh Cancer Centre , Radiotherapy, ECC , Western General Hospital , Edinburgh , United Kingdom; 2 Edinburgh Cancer Centre, NHS Lothian , Clinical Oncology , Edinburgh Cancer Centre , Edinburgh , United Kingdom; 3 Edinburgh Cancer Centre, NHS Lothian , Radiotherapy Physics, Edinburgh Cancer Centre , Edinburgh , United Kingdom

Purpose or Objective Background and Purpose

The widespread adoption of hypo-fractionated stereotactic ablative radiotherapy (SABR) for treating prostate cancer has led to an increase in the use of specialised techniques for monitoring inter- and intra-fraction motion. The aim of this study was to critically review two such systems and to present initial findings on their use within a SABR prostate clinical trial reporting on measured displacements, and the impact this has on dose to the bladder and rectum, and acute patient reported toxicity (PROMs).

Materials and Methods Materials and Methods

18 patients recruited to the PRINToUT clinical trial (UK-NCT04081428), Using breath analysis to PRedIct Normal TissUe and Tumour response during prostate cancer SBRT, study (IRAS 240335) were included in this critical review. 9 patients underwent transperineal implantation of the RayPilot® transmitter and 9 patients were fitted with the urinary catheter system RayPilot Hypocath. Real time positional information was recorded at 1 second intervals in x,y and z directions throughout treatment for both systems with a manual intervention necessary to halt beam delivery should motion exceed 2mm. All patients were treated with 36.25 Gy to the prostate gland in 5 fractions over 7 days. Gold markers were implanted for positional verification and cone beam computed tomography scans were acquired before and after each fraction of treatment. Acute RTOG PROMs were collected at baseline, end of treatment, 6 weeks, and 12 weeks post treatment.

Results Results

The largest motion detected, in both groups, is in the ant/post direction (-1.71cm- 0.11cm) The average dose received by the bladder and rectum is smaller in those patients fitted with the HC device, with these patients also shown to have a more consistent bladder volume overall when compared to those fitted with the RP device. This does not relate to acute toxicity as G2 GU toxicity is reported at wk 12 and G3 GI toxicity is reported at wk 6 in the HC group. Further findings noted : 1. No system recorded greater than 2 mm motion in any direction during treatment delivery time (Fig 1) .

2. From the positional information of each system (Fig1) the (NEW) average delivered dose was 2.1. Bladder

2.1.1. Raypilot group 427.5cGy- 1575.5 cGy 2.1.2. Hypocath Group 520.01cGy- 1312.63 cGy

2.2. Rectum