Session Item

Radiotherapy (RT) is an effective treatment for metastatic disease. Fast treatment is desirable for patients requiring pain control and results in shorter interruptions of any systemic treatments. However, significant delays can arise if a dedicated planning CT-scan (pCT) has to be scheduled before target contouring and treatment planning is performed. Most patients have a recent diagnostic CT-scan or PET-CT scan available but patient positioning and tumor expansion could be different during RT-delivery. We developed a workflow for palliative patients that involved performing pre-planning on available diagnostic CTs (dCT), and subsequently used plan adaption to account for any changes in target anatomy changes using a cone-beam CT-scan (CBCT) prior to RT-delivery. This retrospective study assessed the feasibility of this workflow.

Fifteen patients were selected from the hospital database based on the following criteria: palliative treatment of metastatic disease to the spine or ribs (1x8Gy), time between a dCT and pCT of <6 weeks and CTV and OARs visible on dCT. Images from the selected patients were analyzed in the Ethos platform (Varian Medical Systems), where the full treatment workflow from treatment planning (TP) up until TP adaption on-couch was emulated. The workflow involved the following steps; 1) contouring of target and OARs on dCT by radiation oncologist (RO), with use of clinical PTV margins (5mm); 2) treatment planning on dCT (TP_ref) according to departmental guidelines (CTV_V95%≥98%, PTV_V95%≥95%) by a researcher, reviewed by a medical physicist; 3) a RO reviewed the CBCT made during treatment, and manually adapted contours if tumor progression was visible. The RO also reviewed dosimetry of TP_ref on the daily contours (TP_d), followed by a final adapted plan of the day (TP_a) based on the on-couch anatomy on a CBCT. Treatment quality was analyzed by comparing target coverage (PTV_V95% and CTV_V95%) and OAR dose between the TP_ref , TP_d and TP_a. 

All TP_a met clinical acceptance criteria. Minor adaption of CTV, which was defined as contour adaptation in <4 slices, was needed in 7 out of 15 patients, while major CTV adaption (edits in >4 slices) were needed in 4 patients, and 4 patients required no CTV adaptions. Figure 1 shows an improvement in target coverage in the TP_a versus TP_d,, while achieving similar target coverage as TP_ref (Figure 2). Doses delivered to OARs by the TP_A were all within clinical acceptance criteria, and differences seen were due to changes in target volume arising from tumor progression between the dCT and treatment.

This study found that online adaption of palliative treatment plans that were initially generated using dCTs, was feasible using on-couch CBCT scans on the Ethos platform. We will now implement this workflow in our clinic, with expected benefits in both departmental logistics and patient experience.