This prospective, open-label, Phase I/II, clinical trial is feasibility study to evaluate MR-guided radiotherapy with the Alberta linac-MR P3 system in adult patients with cancer that are treated with external beam radiotherapy in four graduated stages (described below), progressing from palliative participants with simple techniques to curative participants with complex techniques, with progression to each stage determined by an internal SAFE review committee. Conventional treatment margins and doses will be utilized, with the MR being utilized in place of CT based imaging. The intent is to replicate current CT based treatments on the Alberta linac-MR P3 system using MR guided imaging, planning and treatment delivery. MR imaging will be utilized for simulation, planning and image guidance. Dosimetry will be done as per standard of care. MRI contrast may be used, as applicable. Adverse events will be collected weekly during RT, and participants will complete one questionnaire at the end of their RT treatment. Follow-up will consist of adverse event assessment at 1, 3, 6, and 12 months following completion of RT, and may be assessed annually via chart review for up to 5 years. Survival status will be assessed at 12 months following completion of RT, and then annually for up to 5 years.

In stage 1, 10 to 28 participants with incurable malignancies that require palliative radiotherapy with parallel-opposed pair beam arrangements will be enrolled. These will be patients with bone or brain metastases from their malignancies that require either a single fraction or multiple fractions of radiotherapy. The treatment will be a simple opposed pair beam arrangement to a dose of a single 8 Gy or to a dose of 20 Gy over a course of 5 fractions. Once some initial treatments are completed, and at the discretion of an internal SAFE review committee, additional treatment sites will be permitted (i.e. lung, abdomen, etc.) that are also utilizing a simple opposed pair beam arrangement with the above doses.

In stage 2, 10 to 28 participants with malignancies (curative or palliative treatments) that require multi-field arrangement for their external beam radiotherapy will be enrolled. Initially, 4 field techniques (anterior, posterior, right lateral, left lateral) will be utilized to treat central tumors using fractionation schemes that are currently considered standard of care. Patients with pelvic malignancies (i.e. rectal cancers, cervical cancers, endometrial cancers) or other malignancies requiring simple four field techniques will be identified for this stage. As well, breast patients requiring a simple tangential opposed pair beam arrangement or 3 - 4 field technique (to include the supraclavicular nodal regions) will be enrolled, with preference for standard hypofractionation schedules, if possible.

In stage 3, 10 to 28 participants with malignancies (primarily curable, but incurable malignancies may also be considered) that require more complicated multi-field 3DCRT treatments (not requiring IMRT) for their external beam radiotherapy (i.e. lung, brain, etc.) will be enrolled. This will include the use of field-in-field techniques such as step-and-shoot techniques to allow for modulation of the radiation beam during treatment.

In stage 4, 10 to 28 participants with malignancies (primarily curable, but incurable malignancies may also be considered) that require more complicated multi-field IMRT treatments for their external beam radiotherapy (i.e. prostate, head and neck, lung, brain, etc.) will be enrolled.