Radiation protection in practice: Assessment of shielding block efficacy in external beam radiotherapy at a leading cancer centre in sub-Saharan Africa

Background: Radiotherapy aims to provide either curative treatment or palliation, with radiation transmission through shielding blocks ideally not exceeding 5% of the incident dose. Aim: This study assessed the attenuation efficacy of Cerrobend shielding blocks, determining the thickness required for achieving 95% attenuation and evaluating the adequacy of currently used blocks. Methods: An experimental study was conducted using a 1·25 MeV cobalt-60 teletherapy machine. Radiation intensities transmitted through Cerrobend blocks of varying thicknesses (1-5 cm) were measured with a calibrated ionization chamber and electrometer. Measurements were performed with a fixed field size of 10 cm × 10 cm at a 100-cm source-to-chamber distance, minimizing scatter. Baseline and transmitted intensities were recorded, with each measurement repeated five times for precision. Results: The percentage transmission, linear attenuation coefficients and thickness required for 5% transmission were calculated using regression analysis. Radiation intensity decreased exponentially with increasing Cerrobend block thickness, from 15·01 nC (0 cm) to 0·939 nC (5 cm thickness). Regression analysis showed a strong negative linear relationship (y = -0·5386x + 2·6705; R2 = 0·992). The thickness required for maximum transmission of 5% was determined to be 6 cm, while the routinely used 5 cm blocks at the study site allowed 8% transmission, exceeding the recommended threshold. Minimal environmental variations ensured measurement consistency. Conclusion: The study demonstrated that 6 cm Cerrobend blocks were necessary to achieve the recommended 95% attenuation, whereas the 5 cm blocks in use resulted in suboptimal shielding. This highlights the need to revise shielding practices to improve radiation protection and patient safety in resource-constrained radiotherapy settings.