@article{oai:repo.qst.go.jp:00058698,
 author = {Matsubara, Hiroaki and Karasawa, Kumiko and Matsufuji, Naruhiro and Tsuji, Hiroshi and Yamamoto, Naoyoshi and Nakajima, Mio and Karube, Masataka and Takahashi, Wataru and 唐澤 久美子 and 松藤 成弘 and 辻 比呂志 and 山本 直敬 and 中嶋 美緒 and 軽部 雅崇 and 高橋 渉},
 issue = {5},
 journal = {Medical physics},
 month = {Feb},
 note = {We appreciate the interest of Carrara et al.1 in our recent article
 on the assessment method in digital images of skin erythema
 caused by radiotherapy.2 Matsubara et al. presented a linear
 relationship between skin blood flow and skin dose, while
 Carrara et al. suggest that their clinical data do not reproduce
 it even though their sample number of patients treated is ten
 times larger than that of Matsubara et al. We would like to
 suggest that the disagreement between the data by Carrara
 et al. and Matsubara et al. is qualitatively reasonable because
 it arises from neglecting the recovery process of damaged
 skin as is explained below.
 Skin erythema is physiologically caused by expansion of
 capillaries due to increased blood flow, which is a part of the
 biological skin repair response. As long as the skin erythema
 is an acute toxicity, the skin recovers and the symptom usually
 disappears in several months. This indicates that skin blood
 flowincreases owing to the repair process just after irradiation,
 but decreases owing to the recovery process from the damaged
 skin a few tens of days later.
 Matsubara et al. treated six patients who had the carbon
 beam therapy with a total prescription dose of 50 Gy (RBE).2
 It should be noted that the prescription dose was delivered by
 a single fraction from four ports, indicating that the treatment
 was completed in one day. On the other hand, Carrara et al.
 treated 61 patients who had the 6/15 MV photon therapy with
 a total prescription dose of 50 Gy but with a 2 Gy fraction,
 indicating that the treatment was completed in 25 days. The
 recovery process for skin erythema is assumed to work during
 the treatment. This would result in the reduction of skin blood
 flow per accumulated skin dose, causing nonlinearity between
 skin blood flow and skin dose. The disagreement between the
 data by Carrara et al. and Matsubara et al. can be qualitatively
 understood by taking the recovery process into account. That
 is why Matsubara et al. selected only the cases of a single
 fraction in order to avoid the recovery effect.
 As Carrara et al. suggest, however, we agree that the
 linearity observed by Matsubara et al. is not based on physical
 evidence. What Matsubara et al. discussed was just that the
 gross trend of the obtained data could be expressed by the
 linear relationship with moderate accuracy, where several
 variations due to individuality of patient or time dependence
 of skin erythema were assumed to be negligible as discussed
 in Ref. 2. There is no known numerical relationship between
 accumulated skin dose and time dependence of skin erythema.
 The new data suggested by Carrara et al., therefore, are
 assumed to be important for further investigation of skin
 erythema.},
 title = {Response to "Comment on 'Objective assessment in digital images of skin erythema},
 volume = {43},
 year = {2017}
}