Cumulative lung dose-volume predictors of radiation pneumonitis in thoracic reirradiation: A systematic scoping review.

BACKGROUND

Reirradiation (reRT) is increasingly used for locoregional recurrences of lung cancer. Radiation pneumonitis (RP) remains a major dose-limiting toxicity, yet cumulative lung dose constraints are not well established.

METHODS

A systematic scoping review was conducted following PRISMA guidelines. Studies published between January 2010 and December 2024 were included if they reported an association between at least one lung dose-volume parameter and RP occurrence or severity after thoracic reRT. Only studies with explicit dose-toxicity data were retained. Evidence strength was assessed using GRADE. Clinical risk factors were also extracted when reported.

RESULTS

Nineteen retrospective studies were included: stereotactic body radiation therapy (SBRT) after conventional radiation therapy (RT) (n = 4), SBRT after SBRT (n = 7), and conventional RT after conventional RT (n = 8). EQD2 (α/β = 3-4) was applied in 84% of studies, and 3D dose summation in 79%. Deformable registration was used in 47%, rigid in 32%, and not specified in 21%. V5Gy, V20Gy, and mean lung dose were the most frequently associated parameters with RP, each supported by 3-5 small studies. The certainty of evidence for these parameters was consistently low. Evidence for V10Gy, V30Gy, V40Gy, VS5-20 Gy, and cardiac dose metrics was graded as very low. Among clinical factors, reRT type (in-field vs. out-of-field), tumor location (central vs. peripheral), interval between treatments, and baseline pulmonary status showed inconsistent associations.

CONCLUSION

Cumulative low-dose lung metrics may influence RP risk after thoracic reRT, although current evidence is limited by heterogeneity and low certainty, and prospective multicenter studies are needed to define validated cumulative constraints.