三维适形调强放射治疗减少放疗后口干症

Reduction of Xerostomia in Patients With head and neck Cancer Receiving Intensity Modulated or Three Dimensional Conformal Radiation Therapy

头颈部恶性肿瘤放射治疗后口干症的发生率很高，腮腺受到40Gy以上的照射将导致持久性口干。近10年来计算机技术使三维适形放疗和调强放射治疗新技术得到发展，新技术提高了靶区剂量，同时明显减少肿瘤周围正常组织包括腮腺的放射剂量，从而减少了口干症的发生率。新技术采用放射位置固定、CT／MRI扫描、三维放疗计划、评估、优化和验证，并通过三维剂量、DVH、肿瘤和腮腺容积剂量评价达到保护腮腺功能的目的。我们在2001年对20例头颈部癌放疗患者分成常规放疗组和3DCRT组行放射治疗，常规放疗组肿瘤剂量55．6～68．6Gy（平均58．8Gy），3DCRT组肿瘤剂量53．5～68．5Gy（平均58．3Gy），记录患者的口干症评分和全唾液量。结果证明3DCRT对口腔放疗患者健侧腮腺能达到比较好的保护，腮腺放射剂量常规组和3DCRT组分别为51．8Gy和24．7Gy，放疗后6个月，常规组Ⅰ～Ⅳ级口干症的发生率分别为25％，25％，37．5％和12．5％，3DCRT组Ⅰ、Ⅱ级口干症的发生率为8．3％和8．3％，口干症级别和发生率比常规放疗组明显降低。调强放疗对腮腺的保护比3DCRT更好，口干症的发生率达到很低水平。Lee等报告IMRT治疗67例鼻咽癌患者，肿瘤剂量65～70Gy，放射治疗后3个月，口干Ⅰ级28％，Ⅱ级64％，无口干8％；至放射治疗后24个月，口干Ⅰ级32％，Ⅱ级仅2％，而无口干达66％。可以相信，三维适形调强放射治疗新技术的日益成熟，将使头颈部恶性肿瘤放疗后的口干症发生率降到很低的水平。

The rate of xerostomia is high in patients with head and neck cancer after conventional radiation therapy. The radiation dose of more than 40Gy on parotid glands will cause post radiation xerostomia permanently. New computer-aided radiation techniques, intensity modulated radiation therapy（IMRT） or three dimensional conformal radiation therapy （3DCRT）, have been developing since last ten years. IMRT and 3DCRT can be defined as an attempt to shape the high-dose volume of the radiation treatment to the tumor while minimizing the dose to surrounding normal tissues including parotid glands. 3DCRT techniques are to spare parotid glands in the treatment of head and neck cancer to reduce the rate of xerostomia. New radiation technique includes using immobilization of the patients, CT/MRI scan, 3D radiation treatment planning, treatment plan evaluation, optimization and documentation. Analysis of 3D dose distributions and dose volume histograms （DVH） was used to evaluate the dose and volume of tumor and parotid glands to protect the function of parotids in the patients during 3D radiation treatment planning. Twenty patients with head and neck cancer were divided into conventional radiation group and new radiation technique group （3DCRT） to observe the effect on reduction of rate of postradiation xerostomia in our hospital on 2001.Tumor dose of 55.6～68.6Gy （average 58.8Gy） was given to conventional radiation group and 53.5～68.5Gy （average 58.3Gy） to new radiation technique group. Whole saliva flaw rates and subjective xerostomia scores were assessed in patients during radiation course and follow-up. The doses of parotid glands in patients of conventional radiation group and 3DCRT group were 51.8Gy and 24.7Gy, respectively. The rates of xerostomia Ⅰ, Ⅱ, Ⅲ and Ⅳ six months after radiotherapy in conventional radiation group were 25%, 25%, 37.5% and 12.5%, respectively. The rates of xerostomia Ⅰ and Ⅱ six months after radiotherapy in patients 3DCRT group were 8.3% and 8.3%, respectively. It was showed that 3D-RTPS can reduce the rate of postradiation xerostomia in patients with head and neck cancer obviously. Intensity modulated radiation therapy （IMRT） to spare parotid glands in head and neck cancer is more than 3DCRT. So the rates of xerostomia after IMRT can be reduced to minimum lever. Lee et al reported that the results of IMRT for 67 nasopharyngeal patients with tumor dose 65～70Gy. The rates of xerostomia Ⅰ and Ⅱ 3 months after radiotherapy in patients were 28% and 64%, respectively. The rates of xerostomia Ⅰ and Ⅱ 24 months after radiotherapy in patients were 32% and 2%, respectively. It is believed that the progress of IMRT and 3DCRT techniques will make the rates of postradiation xerostomia to reduce to lower lever in patients with head and neck cancer.