Vienna, Austria

ESTRO 2023

Session Item

May 13
16:45 - 17:45
Business Suite 1-2
Technical improvements in radiotherapy practice
Rianne de Jong, The Netherlands
Poster Discussion
Using CBCT-based adaptive radiotherapy to implement a no-simulation treatment pathway for palliation
Xenia Ray, USA


Using CBCT-based adaptive radiotherapy to implement a no-simulation treatment pathway for palliation

Xenia Ray1, Andrew Bruggeman1, Kevin Moore1

1UC San Diego, Radiation Medicine and Applied Sciences, San Diego, USA

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Purpose or Objective

Patients receiving palliative single fraction radiation typically require multiple visits to the clinic for consult, simulation, and treatment. In most cases, treatment will not occur until several days following consultation.  They are in pain and the plans are simple, thus these extended wait times are suboptimal and waste clinical resources, particularly CT sim time. The purpose of this project was to leverage the daily adaptive radiotherapy platform of the Varian Ethos to implement an expedited, no-simulation, same day consult and treatment workflow for single-fraction palliation.

Material and Methods

The patient’s most recent diagnostic CT scan is used to create an initial plan in the Ethos treatment planning system (TPS) by the covering Ethos physicist. The physician contours the GTV on this image after the patient consultation. A PTV is auto-generated using a specified symmetric margin (e.g. 5mm). The initial plan is optimized using only two constraints: PTV D95%>100% and PTV D0.03cc<107%. By default, the Ethos TPS will optimize four plans using different beam arrangements: 9-field IMRT, 12-field IMRT, 2 arc VMAT, and 3 arc VMAT.  When needed, a custom beam arrangement can be imported for optimization. The plan is reviewed and approved by the physician.  When the patient is brought to the treatment room, a kilovoltage cone-beam CT image is acquired. Targets and organs-at-risk from the original plan are auto-segmented on the new image and edited as necessary. The plan is reoptimized to account for changes in body positioning and target volume and then delivered. 


We successfully treated 10 patients requiring palliative care with 800 cGy in a single fraction using this workflow. Disease sites included: sternum, rib, spine, sacrum, iliac crest, and a retroperitoneal mass. Diagnostic scans for initial planning were on average from 47 days (range: 11-157 days) prior to treatment. Default Ethos beam arrangements were used for 6/10 cases, the remaining targets benefited from custom beam arrangements (e.g. partial arcs entering anteriorly for the sternum). The auto-segmented GTV was edited for 8/10 cases (volumes changed 13.3cc±26.6cc). In all cases, the adapted plan was selected for treatment. All adapted plans were normalized for PTV D95%=100%, PTV D0.03cc ranged from 104-113%. If the initial plan had been delivered without adaptation, PTV D95% would have decreased to 65.1%±33.9%. Average total time for the on-couch adaptive process was 11.0±3.4 minutes. Average total in-room times were 19.1±2.9 minutes. Average total in-clinic time for patients (from consult check-in to end of treatment) was 3.2 hours.


Prior to the implementation of this workflow, palliative patients required separate appointments over multiple days for consult, simulation CT, and treatment. This new workflow reduces on-site time to a few hours and frees clinical resources. Adapting the dose ensures excellent target coverage despite changes in target volume between the diagnostic scan and treatment.