Retrospective Evaluation on Dosimetric Comparison and Secondary Cancer Risks for Three Treatment Planning System on Nasopharyngeal Carcinoma Irradiation

• Main Authors: Shih-Hsun Kuo, 郭仕勳
• Other Authors: E-Fong Kao
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/43402914997254374199

碩士 === 高雄醫學大學 === 醫學影像暨放射科學系碩士在職專班 === 105 === Objectives: This study aimed to investigate the secondary cancer risk of normal tissues induced by different treatment plans adopted for nasopharyngeal carcinoma (NPC). This study also examined the results of different doses administered to normal tissues in the treatment plans targeting various levels of NPC tumor invasion. Materials and methods: The research participants comprised 37 NPC patients who received radiation therapy during the period between 2010 and 2016. Three indices: conformity index (CI), homogeneity index (HI), and organ-specific dose, were used to assess the advantages and disadvantages of three treatment plans and the influence of different levels of tumor invasion in the treatment plans. Results: The organ at risk (OAR) doses were compared when the CI of the TomoTherapy® Treatment Planning System was 1.03±0.01, and the HI was 0.05±0.01. The maximum dose (Dmax) for spinal cord was 2813.0±458.4 cGy, and that for brain stem was 3891.6±444.7 cGy, and that for oral cavity was 6635.9±460.3 cGy, which were the optimal doses in the three treatment plans. The OAR doses were also compared regarding various tumor sizes. The maximum dose administered to the right optic nerve of patient T4 was 3598.9±1505.1 cGy, and that for left optic nerve was 3164.8±1452.7 cGy, and that for chiasma was 3841.8±1526.1 cGy, which were the highest. Regarding the OAR doses for neck lymph node metastasis, the maximum dose administered to the thyroid gland of the patient N3 was 6795.5±524.9 cGy, which was the highest. In the secondary cancer risk analysis, the difference between the three treatment plans for the thyroid cancer risk was significant (p = 0.013 < 0.05). The tumor size difference for the thyroid cancer risk was also nonsignificant (p = 0.113 > 0.05). Moreover, the degree of neck lymph node metastasis exhibited significant difference regarding the thyroid cancer risk (p = 0.011< 0.05). Despite the nonsignificant difference of the degree of neck lymph node metastasis, the average thyroid dose for N3 was higher than that for other degrees of neck lymph node metastasis. Because the T4 tumor was close to the brainstem, a small part of brainstem volume was not covered, in order to increase the coverage of the target volume in the tumor treatment; therefore, 50.0% of the patients received a maximum dose over 50 Gy. There were 97.3% of the patients with various degrees of neck lymph node metastasis, the maximum dose administered to thyroid was higher than 45 Gy but lower than 80 Gy. This may be because radiation oncologists performed preventive radiation therapy when delineating the planning target volume of the neck lymph nodes. Conclusion: Currently, cancer patients receiving radiation therapy have an increasingly high survival rate. Therefore, determining how to increase the coverage of the planning target area and reasonably reduce the dose administered to the non-target area, as well as how to reduce the incidence rate of secondary cancer and the deterministic effect, are worth investigating.