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Background: The lesion size is a risk factor for keloid recurrence after postoperative radiotherapy. However, it remains unclear whether the major axis diameter is the most appropriate parameter to evaluate lesion size, because keloids are often irregular in shape. Additionally, no previous study has investigated computed tomography (CT) densitometry parameters of keloids as potential predictors for recurrence after postoperative radiotherapy. Materials and Methods: The size and CT densitometry parameters were measured for 74 lesions with CT images of sufficient quality for evaluation. The association between recurrence and size or CT densitometry parameters was analyzed for 64 lesions that could be followed up for 6 months or more. Results: The major axis diameter × minor axis diameter × thickness showed the strongest correlation with volume (ρ = 0.96, P <.0001). The median follow‐up period was 71 months, and 17 lesions recurred. The major axis diameter × minor axis diameter × thickness ≥2.5 cm3 (hazard ratio = 5.9, P =.0052) and volume ≥1.2 ml (hazard ratio = 4.3, P =.029) were significantly associated with keloid recurrence under multivariate analyses, while the major axis diameter alone were not. The mean and maximum CT values, and the kurtosis and skewness of density histogram were not significantly different between recurrent and non‐recurrent lesions. Conclusion: The major axis diameter × minor axis diameter × thickness may be a better parameter than the major axis diameter alone. CT densitometry analyses may not help to predict keloid recurrence after postoperative electron beam radiotherapy. [ABSTRACT FROM AUTHOR]