Clinical Implementation of Single Visit Palliative Adaptive Radiotherapy without Prior CT Simulation

Abstract

<h3>Purpose/Objective(s)</h3> Standard workflows of radiotherapy for metastatic disease palliation often involve multiple clinic visits and (long) waiting times. Fast palliation completed during a single clinic visit can be achieved by omitting a treatment planning CT scan and using available diagnostic imaging for treatment planning. The use of a diagnostic CT can be challenging due to differences in patient positioning and location of target and organs at risk (OAR), but adaptive treatment platforms provide possible solutions. We integrated a fast palliative workflow using diagnostic imaging for pre-planning, with subsequent on couch contour and plan adaption based on a synthetic CT derived from cone-beam CT imaging (CBCT), and report our clinical and dosimetric experiences. <h3>Materials/Methods</h3> An ethics-approved protocol for fast palliation (FAST-METS) was implemented in November 2021. Patients referred for palliative radiotherapy of painful bony metastatic disease of any primary site, available recent diagnostic imaging (<4 weeks) with visualization of both the metastasis and OAR were eligible. The workflow was as follows: 1) a radiation oncologist consulted the patient by telephone; 2) pre-planning on the diagnostic CT, using standard planning templates; 3) in-clinic consult at day of treatment, with obtaining informed consent for questionnaires; and 4) CBCT scan with on-couch adaptation of the target, OAR and treatment plan on the Linac. Different strategies were explored for beam setup including 6-12 fields IMRT and VMAT, in order to optimize dose calculation and beam-on times. Treatment times were collected from DICOM data and patient questionnaires. <h3>Results</h3> Data of the first eight patients are presented. The treated metastases were located in the lumbar (2) or thoracic (3) spine and pelvis (3). In all patients, the on-couch re-optimized plan was used for treatment, with a PTV_V95% coverage of ≥95%. In three patients, target and OAR volumes were adapted on-couch by the radiation oncologist. All patients completed their consult and treatment within 2 hours. Plan re-optimization time was <2 min. for IMRT (N=5), and 5-7 min. for VMAT plans (N=3). However, a 12-field IMRT setup was less preferable in three patients due to longer beam-on time compared to VMAT, and was addressed by using a 6-field IMRT setup. All 8 patients indicated satisfaction with the FAST-METS procedure. <h3>Conclusion</h3> A fast workflow for a single visit palliative IMRT delivery without dedicated planning CT scan was implemented for patients with bone metastases. All patients completed consultation and treatment within 2 hours on average, and indicated satisfaction with the procedure.