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

Abstract

Purpose This study aimed to compare the biological effective doses (BED) to clinical target volume (CTV) and organs at risk (OARs) for cervical cancer patients treated with high-dose-rate (HDR) ¹⁹²Ir or 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 (p60Co with respect to ¹⁹²Ir. For OARs, the median values of D_2cc (in EQD2₃) for ⁶⁰Co were lower than that of ¹⁹²Ir up to 9.2% and 11.3% (p60Co and ¹⁹²Ir sources, this numerical study suggests that a dose escalation to ∼4% is feasible and safe while sparing well the surrounding normal tissues. This 4% dose escalation should be benchmarked with clinical evidences (such as the results of clinical trials) before it can be used in clinical practice. This article is protected by copyright. All rights reserved