2110 - Clinical Experience with a CT-Free CBCT-Guided Online Adaptive Workflow for Palliative Radiotherapy

02:30pm - 04:00pm PT

Hall F

Screen: 2

POSTER

Presenter(s)

Ashaya Jaglal, MS - Amsterdam UMC, Amsterdam, Noord-Holland

A. T. Jaglal^1,2, K. J. Nelissen^1,2, A. R. W. van Vlaenderen^1,2, A. L. de la Fuente^1,2, W. F. A. R. Verbakel^1,3, F. L. Schneiders^1,2, P. S. N. van Rossum^1,2, J. Wiersma^1,2, S. Senan^1,2, E. Versteijne^1,2, and J. Visser^4,5; ¹Amsterdam UMC location Vrije Universiteit Amsterdam, Department of Radiation Oncology, Amsterdam, Netherlands, ²Cancer Center Amsterdam, Amsterdam, Netherlands, ³Varian, a Siemens Healthineers Company, Palo Alto, CA, ⁴Cancer Center Amsterdam, Cancer Therapy, Treatment and quality of life, Amsterdam, Netherlands, ⁵Radiation Oncology, Amsterdam UMC location University of Amsterdam, Meibergdreef 9, Amsterdam, Netherlands

Purpose/Objective(s):

Online adaptive radiotherapy (oART) for palliative treatments was implemented at our department in 2022 through the FAST-METS study, using the diagnostic CT for initial planning. Introduction of upgraded software and hardware have enabled a CT-free workflow using on-couch contouring, dose calculation, and optimization on the CBCT. This study presents the first clinical experiences with this CT-free, CBCT-guided oART workflow for palliative radiotherapy.

Materials/Methods:

In this study, we evaluated two different clinical CT-free oART workflows. In both workflows a cylindrical water phantom (40×80 cm, diameter × length) was used to meet software constraints requiring an initial plan with a predefined template and beam setup before CBCT-based adaptation. Workflow 1 incorporated pre-treatment imaging (diagnostic CT or MRI) for initial clinical target volume (CTV) contouring. The CTV was transferred to the phantom and rigidly mapped to the CBCT on-couch and serving as an intermediate step to Workflow 2, where the CTV was directly contoured on-couch on the CBCT. Both workflows utilized a standardized planning template for all treatment sites with a generic lateral 7-field or 9-field IMRT beam setup, depending on the target site. Organs-at-risk (OARs) were delineated using AI-based auto-contouring. Clinical dose coverage goals (V95%) for both CTV and planning target volume (PTV) were assessed for each patient, along with workflow efficiency, including the time spent in different stages of the treatment.

Results:

Thirteen patients were included, with treated locations in the cervical (n=1), thoracic (n=5), lumbar (n=2), and pelvic (n=5) regions. For ten patients, diagnostic CT-based contours (n=9) or MRI-based contours (n=1) were transferred to the phantom (Workflow 1). Three patients received treatment without initial contouring (Workflow 2). Both oART workflows successfully achieved the defined clinical goals, with PTV V95% = 98.6%, and CTV V95% = 100%. The overall treatment time was similar to that with the previous FAST-METS workflow, with a median treatment time of 31 minutes (range: 24—43) from patient entry to exit. Detailed times for the treatment stages are summarized in Table 1.

Conclusion:

This study demonstrates the clinical feasibility of fully CT-free workflows for palliative radiotherapy utilizing on-couch CBCT-based contouring and dose calculation. A CT-free workflow enabled efficient treatment delivery, requiring only a single departmental visit, and a median in-room time of 31 minutes. The use of a standardized planning template and CBCT-guided adaptation facilitated rapid and safe patient care, making this workflow attractive for emergency cases.

Abstract 2110 - Table 1: Median and range of treatment stage times


Treatment stage	Median [range] (minutes:seconds)
Setup	6:54 [4:41 —12:24]
Contouring	5:07 [3:31 —18:50]
Calculation	1:57 [1:39 —2:44]
Plan evaluation	3:29 [2:44 —4:30]
Treatment delivery and patient exit	8:18 [5:23 —10:03]