| Objectives: Three-dimensional conformal radiation therapy , which possess the characters of "three high and one low" (high-precision, high-dose, high-efficacy, low-damage), is currently the most widely used method of radiotherapy. In this study, radiotherapy plans was developed in specialized computer software simulation system; and the radiation dose of the surrounding normal tissues was calculated. The aim of the study is to evaluate the protection efficiency of individualized bite block system in three-dimensional conformal radiation therapy.Methods: A total of twenty-seven patients who suffered from oral and maxillofacial cancer and had undergone three-dimensional conformal radiotherapy were elected in the study. According to the target organ to be protected and the thickness of individualized bite block system, the subjects were grouped as follows: Group 1, cancers of tongue and floor of mouth, with mandible as protection organ, according to the thickness of the system were divided into not used group, 5mm group, 10mm group, 15mm group; Group 2, gingival cancers, with tongue as protection organ, were divided into groups not to use, 5mm group, 10mm group, 15mm group; Group 3, lip and cheek cancers: with the jaw (mainly mandible) as protection organ, were divided into groups not to use, 5mm group, 10mm group, 15mm group; Group 4, cancer of maxilla and palate, with jaw as protection organ, were divided into open group (mouth opening 25mm) and closed groups; Group5, patients in whom the total dose of radiation was not less than 6000cy(1Gy=100cy) were research object, and divided into groups not to use, 5mm group, 10mm group, 15mm group. CT scan imaging was obtained, and then the tumor volume, clinical target volume, internal target volume, planning target volume, treatment volume, irradiated volume, and the border of the protection of organs were illustrated by the physicist and physician using three-dimensional conformal radiotherapy design system and supporting software, and at last radiation therapy planning completed. In group 1, group 2, group 3 and group 4, the radiation dose of the protected the organs was calculated respectively. In group 5, V50 (the percentage of volume in which the radiation dosage surpass 50Gy) of the protected mandible was calculated. Data recorded and then analyzed by the statistical software.Results:1 Tongue cancer and carcinoma of floor of mouth group: Among the three groups P=0.046, according toα=0.05 level, there were differences between the groups. Calculate the data between the 5mm, 10mm, 15mm groups and the control group to find the dose ratio of after used and pre-used the individualized bite block system. Dependability check had been used between the thickness and the dose-ratio. First, draw the scatter plot between the two, and there are relevant changes. Associated validation results obtained correlation coefficient was -0.966, P<0.0001, according toα= 0.05 level of statistical significance that the thickness and the dose ratio have a negative correlation. So with the thickness of the system increased, the dose became smaller.2 Gingival cancer group: When the individualized bite block system adopted, the data showed that the dose in tongue was less than that in no using situation. And with the system thickness increases the dose reduced. However, there were no statistical differences because of the too small number.3 Lip cancer and carcinoma of cheek group: The data showed that the individualized bite block system (5, 10,15mm) could reduce the dose of the protect organs. Inter-group results, P=0.002, according toα=0.05 level, and there was a significance difference between the groups. The scatter plot showed negative correlation between the thickness and the dose-related. The correlation between the two tests, correlation coefficient was -0.985, P<0.0001, according toα=0.05 level, a statistical significance showed that the individualized bite block system and the dose ratio had a negative correlation. So when the thickness increased, the dose decreased.4 Maxillary and palate tumor group: The individualized bite block system had let patients keep mouse opened at the time of radiation, and the radiation dose in target organs was significantly lower than that of mouth closed. A significant difference was showed in the paired rank test, P=0.018, according toα=0.05 level.5 Dose-volume group: In patients in whom the total dose of radiation was not less than 6000cy, V50 significantly lower when three different thickness bite system was used than that of not used. Among the three groups P=0.046, according toα=0.05 level, there was a significant difference among the groups. The scatter plot showed that the thickness and the dose volume had a negative correlation. The correlation coefficient was -0.733, P<0.0001, according toα=0.05 level, a statistical significance difference showed that the individualized bite block system thickness and dose-volume ratio had a negative correlation. The thickness increased the volume ratio of the dose decreased.Conclusions:1 The study had evidenced that the individualized bite block system could reduce the dose of normal tissue adjacent to the target area by measuring the radiation dose and dose-volume. There was a negative correlation between the thickness and dose. That meant the more thick of the individualized bite block system, the lower dose of the normal tissue adjacent to the target.2 The 10-15mm thickness of the individualized bite block system could effectively reduce the radiation received by normal tissue dose, and the thickness is in the range of patients'acceptances.3 The materials used for the individualized bite block system was methyl methacrylate, which used wildly and easily in dental clinical. The methyl methacrylate was similar to the soft tissue in means of rays penetrating. So methyl methacrylate could be used as an ideal material for manufacture of the individualized bite block system. |
PDF Full Text Request