The skin erythema grade of a patient who had conservative surgery for breast cancer and received 2 Gy/Fr, 5 Fr/w, and 50 Gy/25 Fr (±10Gy/5 Fr boost) to the breast was temporally observed using a spectrophotometer (CM-2500d ,Konica Minolta, Japan). The data obtained with the L*a*b* color system were changed into hue, saturation, and brightness. In addition, nonlinear regression could be used if the data were log transformed. Therefore, this result was applied to the GLQ model. In addition, because normal tissue does not improve beyond the state prior to irradiation, constants are set so that the limiting value of S [ t ] can be set to 1.0 ( Fig. 8 ). Figure 9 reproduces the changes in color that were calculated using the abovementioned GLQ model to a virtual breast in 3 dimensions ( it exhibits a reddish character during irradiation ).Left figure shows corresponding color factors change (Hue, Saturation, and Brightness) during and after irradiation.
It appears that the skin reaction due to radiotherapy to a breast becomes stronger in patients with larger breasts. Because there are many large-breasted patients, the grades of skin reactions due to radiotherapy to a breast have been reported for a Western country. According to this report, the skin reaction to radiation becomes stronger as the breast size increases (Dundas KL, Atyeo J, Cox J. What is a large breast? Measuring and categorizing breast size for tangential breast radiation therapy. Australian Radiology. 2007;51(6):589-593).
In our research, when the sizes of the patients' breasts were divided into 3 groups on the basis of treatment depth of irradiation, skin reactions became stronger as the treatment depth increased. That is, skin reactions become stronger as breast size increases. The results for the hue, saturation, and brightness, which were applied to the GLQ model, are shown in Fig. 10. Figure 11 shows a projection of this relationship onto a 3D virtual breast reproduced on the basis of breast size (the breast exhibits a reddish character during irradiation). Because the value of the standard before irradiation is not in agreement with a regression curve, small sized breast patients in my study seems to have originally little bit bright skin color. Moreover, the model reproduces correctly that a skin reaction becomes stronger with time as breast size increases.
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Recently, high-precision radiotherapy has become possible. Stereotactic radiotherapy, which is irradiation by a large dose with a small number of fractions, has been used for small size lung cancer. For example, it is possible to irradiate with a total dose of 48 Gy in 4 days using 12 Gy/Fr. If the LQ model or the LQT model is used, irradiation can be completed without causing accelerated re-population during that time. According to these models, if irradiation of 4 Fr/4 days and 4 Fr/4 weeks is compared, the biological effectiveness will not change. In contrast, if the GLQ model is used, a difference in the probability of survival when treatment consists of 50 Gy/5 Fr during 4 days or 28 days can be shown ( Fig. 12 ) (In this figure, the first day of irradiation was set to day 0. The ratio of apoptosis to division-associated cell death was assumed to be 5:95).
Transition assessed by CT when radiotherapy (50 Gy/5 Fr/4 days) was delivered to a cancer in the left lung apex (squamous cell carcinoma) is shown in Fig. 13.
Simulation of radiotherapy and the subsequent patient's progress was performed using the GLQ model. α/β of squamous cell carcinoma was set to 10, the volume doubling time was assumed to be 112.5 days (calculated on the basis of the article in Chest 1974;65:3-8), and the half-life was assumed to be 74.5 days. The simulation is shown in Fig. 14. If it is assumed that cancer cells exist in a 3-dimensional space at random according to a Gaussian distribution, each point in this figure represents a clonogenic cell. The growth rate was assumed to be 10%, and the interphase death (apoptosis) was assumed to be 5%. The effect of irradiation appears after a period of time and is followed by cell death. When a tumor was irradiated with 50 Gy/5 Fr at a frequency of 1 time each week in Fig. 12, the tumor showed the dynamic state that changed with time in the right figure (B) of Fig. 14. In accordance with the irradiation period, the tumor is red in Fig. 14. The irradiation effect appears slowly if the irradiation period is extended, and there is a consequent decline in the local control rate.
Simulation of a tumor that showed histological shrinkage can also be presented. Although the α/β value of prostatic cancer is considered to be small, in this simulation, we used α = 0.22, β = 0.039, and α/β = 5.64 on the basis of values calculated from the dose-survival curve of cultured cells of prostatic cancer (DU145). Simulation of the dose-effect relationship when radiotherapy of 74 Gy/37 Fr (2 Gy/Fr, 5 Fr/w) was delivered to this prostatic cancer was performed using a Voronoi diagram (Fig. 15).