Rapid Access Palliative Radiation Workflow Using MRI-Guided Single-Session Simulation, Online Adaptation, and Treatment

Abstract

In the palliative setting, priority is placed on streamlining the process of radiation delivery to avoid unnecessary treatment delay and expedite symptom relief. We hypothesized that using magnetic resonance imaging (MRI) guidance, adaptive planning software, and pre-existing diagnostic computed tomography (CT) imaging, we could deliver palliative radiation without the need for a separate CT simulation scan, thus decreasing the time and steps required to start palliative treatment. For patients necessitating urgent palliative radiotherapy, a simple “pre-plan” was created on diagnostic CT imaging prior to patient transport to the treatment machine. For dose calculation purposes, the electron density of the CT was deformed to MRI in the pre-plan or was overridden to water density. In the treatment vault, the patient was imaged in treatment position with volumetric MRI. The pre-plan was then rapidly adapted online to the MRI, updating the target definition, re-defining fields, and re-balancing beam weights. Once the online-adapted plan was finalized and approved, the patient was treated. Eighteen patients with metastatic cancer were treated from October 2015 to November 2016 with urgent palliative radiation for indications such as pain, obstruction, and bleeding. Dose/fractionation regimens included 8 Gy in 1 fraction (8 pts), 25 Gy in 5 fractions (4 pts), and 30 Gy in 10 fractions (6 pts). Median planning target volume (PTV) size was 187cc. Online adaptive MRI-guided radiotherapy enabled plan changes to be made rapidly. Conformal 3D adaptive plans were delivered as quickly as more conventional AP/PA beam arrangements with a median delivery time of 122s. MRI-guided adaptive radiotherapy was planned and delivered in one-hour appointments for each patient, compared with a mean time from CT simulation to delivery of first treatment of 30 hours (95% CI, 24-35) for a similar sample of urgent palliative cases planned and treated with more traditional radiotherapy workflow. Clinical outcomes were similar to historical and sampled controls, with improvement in pain in 11 of 14 patients, relief of obstructive symptoms in 3 of 3 patients, and hemostasis in 1 of 1 patient treated with MRI-guided adaptive radiotherapy. Integrated treatment planning using available MRI-guided online adaptive radiotherapy allows a rapid-access treatment workflow obviating the need for a separate CT simulation. Conformal pre-plans can be created without time pressure and, if necessary, adapted to anatomy at treatment. This streamlined palliative radiation workflow makes efficient use of both staff and patient time and expedites palliative treatment with similarly successful clinical results.