Reirradiation and Niraparib in Patients With Recurrent Glioblastoma

The goal of this clinical trial is to investigate a drug called niraparib in patients with glioblastoma that was previously treated but has returned (called recurrent glioblastoma, or rGBM). Through this study, investigators would like to find out the best dose of niraparib to give to treat the disease when given together with radiotherapy (known in this study as reirradiation, or re-RT). Patients receive 10 doses of reirradiation over approximately 2 weeks. At the same time, niraparib capsules are taken orally at home, every day. Niraparib treatment continues until the patient is required to stop either because the treatment stops working or because of side-effects. Participants will come into clinic weekly for blood tests and clinical examinations in the first month of treatment. After this, the assessments will be done monthly. Once the patient has finished niraparib treatment, the patient will enter follow-up and be seen once a year to see if there are any late side-effects from trial treatment, how the disease is doing, and if further treatments have been received for it. This follow-up continues until the end of the trial.