Development of a Comprehensive Dosimetric Framework for Radiotherapy Quality Assurance in Nigerian Cancer Treatment Centres

Nigeria's radiotherapy infrastructure has expanded significantly in recent years with new linear accelerator installations in Lagos, Abuja, Ibadan, and Enugu, yet comprehensive dosimetric quality assurance frameworks adapted to the resource and clinical context of Nigerian cancer treatment centres remain underdeveloped. Dosimetric errors in radiotherapy can cause severe under-dosing of tumours or dangerous over-dosing of normal tissue, with life-threatening consequences for patients. This study develops a comprehensive dosimetric framework for radiotherapy quality assurance covering beam characterisation, treatment planning system validation, and in-vivo dosimetry for Nigerian radiotherapy centres. The framework integrates ionisation chamber reference dosimetry following the IAEA TRS-398 code of practice, multi-dimensional water phantom commissioning measurements, independent Monte Carlo dose verification using GEANT4, and radiochromic film patient-specific quality assurance. The framework is implemented and validated at two linac-equipped centres in Lagos State and one in Abuja. Discrepancies between calculated and measured dose exceeding 3 percent are identified in 12 percent of tested treatment plans due to inadequate heterogeneity correction in the clinical TPS. An uncertainty budget for the complete dosimetric chain achieves combined standard uncertainty of 1.8 percent at the 95 percent confidence level. The framework is proposed for adoption as the Nigerian standard for radiotherapy QA by the Nuclear and Radiological Regulatory Authority. Keywords: radiotherapy dosimetry, quality assurance, linear accelerator, Nigeria, Monte Carlo