Fast delivery of IMRT to metastatic disease without planning CT simulation.

Purpose
Radiotherapy (RT) is an effective treatment for metastatic disease. Fast treatment is desirable for patients requiring pain control and result 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 extension could be different during RT-delivery. We developed a palliative workflow 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.

Material/methods
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
Results
All TPa met clinical acceptance criteria. Minor adaption of CTV, which was defined as contour adaptation 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 TPa versus TPd,, while achieving similar target coverage as TPref (Figure 2). Doses delivered to OARs by the TPA 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.

Conclusion
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.