Quantitative evaluation of acute mucosal reaction to interstitial brachytherapy using color histograms

Purpose Color histograms of tongue photographs were used to make a quantitative evaluation of acute mucosal reaction to high-dose-rate fractionated interstitial brachytherapy. Methods and materials Six patients with oral cavity cancer were analyzed with two methods (color histogram and vinyl plate). Using a photograph of the tongue, we calculated the histogram of each pixel of 1 mm2 of the tongue surface. The results were compared with the physicianʹs inspection and the radiation dose. Results The histogram showed a difference between the reactive area (erythema and pseudomembranous mucositis [PM]) and the nonreactive area. The relationship between inspection and the histogram showed a good correlation, although the histogram tended to change earlier than the subjective judgment. The peak time was 12–13 days after delivery of the final fraction of brachytherapy. The minimum dose required to cause PM was 3.3–3.6 Gy per fraction (total: 29.7–32.4 Gy). Conclusions Our new method of using color histograms for quantitative evaluation is helpful in the analysis of the relationship between mucosal reaction and radiation dose. The minimum dose causing PM was considered to be about 30 Gy per nine fractions.