| Nasopharyngeal carcinoma is a common malignant tumor in China, and radiotherapy is the most important therapy method of nasopharyngeal carcinoma. Using radiotherapy alone for early nasopharyngeal carcinoma will obtain good efficacy, and the five-year survival ratio can reach more than 70%. However, the conventional radiotherapy may induce acute and chronic radiation reaction seriously. With the development of equipment, radiation physics and radiation biology, the radiotherapy technology of nasopharyngeal cancer has obtained tremendous progress. The application of new technologies could greatly improve the treatment efficacy of nasopharyngeal carcinoma. Current treatment technologies include the conventional radiotherapy, three-dimensional conformal radiotherapy, intensity modulated conformal radiotherapy, brachytherapy and stereotactic radiotherapy; and the study on dose segmentation model which included conventional fraction, hyperfraction, late accelerated hyperfractionated and continuous accelerated irradiation is hot research recently. In this study, we expected to compare with the dose distribution between Conventional Radiotherapy (CRT) and Intensity Modulated Radiotherapy (IMRT) in early stage nasopharyngeal carcinoma, then clarify the advantages and disadvantages of the two treatment methods from the perspective of clinical dosimetry.1. The effect on the target dosimetry distribution between the two plansWe selected the imaging data of ten early stage nasopharyngeal carcinoma patients, then used conventional radiotherapy and intensity modulated radiotherapy approach to design the therapy plans for each case separately. We selected twelve indexes for evaluation, and the statistical analysis of the experiment data showed that: the majority indicators of the distribution of target volume dose showed a significant difference between the two design methods (P<0.05); there were only two indicators (GTV's Dmean and PTV60's Dmin) didn't show significant differences (P>0.05). So we can conclud that the intensity modulated radiotherapy can satisfy the target dose requirements better in our study, and may improve the dose of target.2. The effect on the target volume's coverage ratio of isodose line, the index of conformality and the index of dose heterogeneity between the two plansThe statistical analysis of the experiment data showed that: the target volume's coverage ratio of isodose curve and index of conformality (1.04 vs 1.00) showed significant differences (P<0.05); but the index of dose heterogeneity between the two plans in this experiment, didn't show a statistical difference (1.05 vs 1.14, P=0.072). So we can conclud that the target volume coverage ratio of isodose line and conformal degrees of target volume in intensity modulated radiotherapy are better than conventional radiotherapy.3. The effect on the peripheral organ of target between the two plansThe statistical analysis of the experiment data showed that: the absorbed dose of two eye crystals showed significant differences between the two designed methods (1.97Gy vs 3.10Gy, P=0.013), but the absorbed dose of optic chiasm (39.76Gy vs 44.23Gy, P=0.180) and spinal cord (39.99Gy vs 39.75Gy, P=0.169) had no significant statistical difference (P>0.05); the absorbed dose of optic nerve (40.55Gy vs 36.33Gy, P=0.012), temporomandibular joint (68.58Gy vs 35.50Gy, P=0.000) and parotid (68.81Gy vs 31.20Gy, P=0.000) had obvious statistical significances (P<0.05); but the absorbed dose of brain stem showed that: the D1 had no statistical difference (44.38Gy vs 45.27Gy, P=0.172), but the D5 had significant difference (46.23Gy vs 44.18Gy, P=0.041). So we concluded that the intensity modulated radiotherapy can guarantee to achieve high target volume's dose, meanwhile, reduce the peripheral organ absorbed dose, thus improve tumor's local control probability and reduce the probability of complications of the normal organ. |
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