Irinotecan-ChemoSeed in Surgically Resectable Glioblastoma

Part 1 (dose escalation, safety, and preliminary efficacy) Part 1 is a non-randomised, single-arm design in 12 participants with recurrent GBM suitable for maximal safe surgical resection. Part 1 will evaluate safety, determine the MTD of irinotecan-ChemoSeed and the RP2D (corresponding to coverage of as much of the resection cavity as possible, up to the MTD) and evaluate efficacy. All Part 1 participants will be administered irinotecan- ChemoSeed concurrent to Standard of Care (SoC) treatment. Part 1 dose- escalation will start at 72 mg of IRN Part 2, in 135 participants with newly diagnosed GBM suitable for maximal safe surgical resection, will assess the efficacy of irinotecan-ChemoSeed. The actual number of irinotecan-ChemoSeeds administered into the resected tumour margin of the tumour cavity after surgical resection will be at the discretion of the neurosurgical consultant up to the MTD, to cover as much of the resection cavity as possible. Participants will be randomised in a 2:1 ratio: * Arm 1: Irinotecan-ChemoSeed +SoC: Irinotecan-Chemoseeds administered into the resection margin following maximal safe surgical resection, with fractionated RT, concomitant and maintenance TMZ (based on Stupp protocol) starting 4 to 6 weeks after surgery per institution standard practice. * Arm 2: SoC treatment only: maximal safe surgical resection with fractionated RT, concomitant and maintenance TMZ (based on Stupp protocol) starting 4 to 6 weeks after surgery per institution standard practice.