Constraints, Cumulative Doses, and Toxicity Outcomes in Glioma Reirradiation: A Systematic Review and Radiobiological Comparison From the Reirradiation Collaborative Group (ReCOG).
Finbar Slevin, Xuguang Scott Chen, Benjamin S Rosen et al.
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In 30 seconds
This systematic review examined organ-at-risk constraints, planned cumulative doses and toxicity outcomes in adults receiving reirradiation for recurrent glioma. It included 27 studies, most involving glioblastoma. Constraints and reported cumulative doses varied substantially; none of the studies used tissue recovery factors. Serious optic pathway, eye or brainstem toxicity was not reported, while radionecrosis was infrequent but sometimes severe. The review found no clear relationship between cumulative constraints or planned cumulative doses and radionecrosis, and concluded that the evidence does not support definitive organ-at-risk constraints.
Key findings
- Of 24 studies reporting constraints, 17 used flat constraints and 11 used cumulative constraints; none used tissue recovery factors.
- No serious optic pathway, eye or brainstem toxicities were reported; radionecrosis was infrequent, with some severe cases.
- No clear pattern linked cumulative constraints or planned cumulative doses with radionecrosis.
- Candidate cumulative maximum or near-maximum EQD2Gy limits were 75-80Gy for optic pathways and 85-100Gy for brainstem, associated with <5% risk of severe toxicity.
Why it matters
Reirradiation decisions require balancing tumour treatment against potential injury to previously irradiated normal tissues. This review shows that published constraints and dose reporting are inconsistent, and that available data do not establish reliable dose-toxicity relationships. Its candidate limits may help frame discussion, but the evidence gaps—particularly for larger-volume normal brain exposure—underscore the need for cautious interpretation and more standardised reporting.
What to keep in mind
The included studies were heterogeneous, and data on larger-volume normal brain constraints and toxicity outcomes from centres using cumulative constraints with tissue recovery factors were lacking.