Radiobiological comparison between Cobalt‐60 and Iridium‐192 high‐dose‐rate brachytherapy sources: Part I—cervical cancer

Purpose This study aimed to compare the biological effective doses (BEDs) to clinical target volume (CTV) and organs at risk (OARs) for cervical cancer patients treated with high‐dose‐rate (HDR) Iridium‐192 (192Ir) or Cobalt‐60 (60Co) brachytherapy (BT) boost and to determine if the radiobiological differences between the two isotopes are clinically relevant. Methods Considering all radiosensitivity parameters and their reported variations, the BEDs to CTV and OARs during HDR 60Co/192Ir BT boost were evaluated at the voxel level. The anatomical differences between individuals were also taken into account by retrospectively considering 25 cervical cancer patients. The intrafraction repair, proliferation, hypoxia‐induced radiosensitivity heterogeneity, relative biological effectiveness (RBE), and source aging dose‐rate variation were also taken into account. The comparisons in CTV were performed based on equivalent uniform BED (EUBED). Results Considering nominal parameters with no RBE correction, the CTV EUBEDs were almost similar with a median ratio of ∼1.00 (p