Optimizing Radiotherapy for Keloids: A Meta-Analysis Systematic Review Comparing Recurrence Rates Between Different Radiation Modalities

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Dear Editor,
We read the article by Mankowski et al1 entitled “Optimizing Radiotherapy for Keloids: A Meta-Analysis Systematic Review Comparing Recurrence Rates Between Different Radiation Modalities” with great interest. The authors performed a meta-analysis comparing recurrence rates between different radiation modalities for the treatment of keloids.
The occurrence rate of each treatment complication from radiotherapy management of keloids is shown in Figure 8. The point which captures our attention is that they use different definitions of recurrence. Ragoowansi et al2 indicated that there were no reported cases of serious radiation toxicity exceeding World Health Organization grade 3 or above, and the author said there were only mild side effects such as hyperpigmentation. The number of cases was not specified in the article. The author does not identify whether he counted the figure of complication from the study as 0 or if he had contacted to the author individually to find out the number. Therefore, clarifying the definition of complication seems necessary.
The electron external beam radiation therapy 2 treatments commonly use 6 to 9 MeV electrons because the maximum absorbed dose is reached at about 1.5 cm and 2 cm in water, respectively. The study of van de Kar et al,3 however, used low energy of 0.25 MeV electrons. Zmax usually occurs at a quarter of the depth of energy. Thus, Zmax of 0.25 MeV electrons is 0.0625 cm, which is quite shallow. Because of the specific morphologic character of keloids, the energy of electrons should reach the proliferating core collagen with hypercellular whorling nodules. The high recurrence rate in the study by van de Kar et al3 can be explained by the fact that 0.25 MeV electrons cannot reach the proliferating center of the keloid collagen structure.
A recent systemic review indicated that the short-time interval of less than 7 hours between keloid excision and irradiation results in a lower recurrence rate compared with longer time intervals of more than 24 hours.4 In consideration of this recent tendency, we suggest that the time to recurrence be divided into 3 parts: less than 7 hours, from 7 to 24 hours, and 24 hours or more.
Furthermore, we are a bit confused by the statistical method used in calculating the overall recurrence rates shown in Figures 2, 3, and 4.1 For instance, according to Figure 2, the overall recurrence rate after the use of brachytherapy is 0.15. However, when the same parameter is calculated using the values mentioned in Figure 2, the overall recurrence rate is 0.173.
∑ (Each study's recurrence rate * its given weight) for each study
There is a significant difference between your reported value and our calculated value. In fact, your reported value underestimates the overall recurrence rate, which might jeopardize the validity of the research. These discrepancy and underestimation are true for Figures 3 and 4 as well. Of course, we do understand that the formula we used to calculate the overall recurrence rate is not suitable. Hence, it would be better to elaborate on the methodology used to calculate the overall recurrence rates.
Lastly, the authors described the recurrence rate of study by Speranza et al5 as 47%, which is different from the recurrence rate of 45.8% stated in their article. Even if we round up 45.8% to 46%, it is still lower than the figure that the author described. Therefore, we believe that this may be a typing error.
In terms of future prospective research, we believe a further multicenter study is warranted. However, we congratulate the authors on their successful validation of various radiation modalities using meta-analysis.

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