Cobalt-60 Nuclear Source Decay and Gamma Photon Dose Delivery in Radiosurgery: A Radiobiological Comparison of Single- and Multi-Session Irradiation for meningioma
DOI:
https://doi.org/10.31185/wjps.1067Keywords:
Gamma Knife, Cobalt 60, MeningiomaAbstract
Gamma Knife radiosurgery (GKRS) using Cobalt-60 sources has found wide application in the treatment of intracranial meningiomas because it is used to deliver highly conformal dose distributions with steep gradients. This study was aimed at performing a radiobiological comparison of single-session and multi-session meningioma cases by including dose rate decay, sublethal damage repair, and analytical modeling of probabilistic outcomes.
Methods: One hundred intracranial meningioma cases were studied (single-session, 50 cases; multi-session, 50 cases) in this prospective study at Ghazi Alharriri Gamma Knife Center, Medical Complex, Baghdad, Iraq, between January 2025 and March 2026. Dosimetric parameters and beam-on time were extracted, and radiobiological calculations were made in accordance with the linear-quadratic model. BED, EQD2, dose-rate-corrected BED, and Lea-Catcheside repair factor (G) were calculated. Tumor control probability (TCP) as well as normal tissue complication probability (NTCP) were estimated using logistic and Lyman-Kutcher-Burman models, respectively. The statistical comparisons were performed with independent t-tests.
Results: Multi-session treatments demonstrated significantly lower effective dose rates and higher beam-on times (p < 0.01), reflecting time-dependent Cobalt-60 decay effects. Single-session radiosurgery yielded higher BED and EQD2 (p < 0.0001); however, TCP remained comparable between groups (p = 0.312), indicating a dose–response plateau. NTCP was significantly reduced in the multi-session group (p = 0.021). A strong inverse correlation was observed between dose rate and repair factor (r = −0.62, p < 0.001), while beam-on time was negatively correlated with NTCP (r = −0.41, p = 0.01).
Conclusion: Time-dependent dose delivery significantly influences radiobiological response in GKSRS. Multi-session treatment achieves equivalent tumor control with improved normal tissue sparing, supporting its role as a physics-optimized strategy for meningioma management.
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