Development of intensity modulated radiation therapy (IMRT) based on radiobiology

建立了我院IMRT的质量保证方法。测得的剂量分布与计算的剂量分布相差2-4%。我们测量了头颈癌患者的屈伸和干涉器官运动和设置误差。根据测量的系统误差和随机误差，我们的IMRT系统的规划目标体积（PTV）裕度为5mm。单次IMRT需要15-20分钟，这可能会导致剂量率效应或功能期间的亚致死损伤修复。比较IMRT和常规放射治疗下SCCVII肿瘤和CHO细胞的细胞存活曲线。在10 Gy以下，细胞存活曲线无明显差异。采用同步集成增强（SIB）方法的IMRT治疗恶性胶质瘤。IMRT向总肿瘤体积（GTV）输送70 Gy/28分/每天2.5 Gy，向周围水肿（临床靶体积环（CTV-a））输送56 Gy/28分/每天2.0 Gy。虽然这种治疗在生理和临床上都是可行的，但局部控制并没有得到改善。分析保留腮腺的IMRT治疗头颈癌患者局部复发的规律。对侧腮腺和同侧腮腺的平均剂量分别为24.0 Gy和30.3 Gy，在33例患者中，19例患者（58%）仅表现为0.1级口干。因此，保留腮腺的IMRT可以减少口干症的发生率。然而，在PTV边缘有一些复发。IMRT中PTV的划定应足够谨慎。

A method of quality assurance in IMRT at our hospital was established. The measured dose distribution in phantoms were consistent with the calculated dose distribution within a difference of 2-4%. We measured the intrafraction and interfraction organ motions and set-up errors for patients with head and neck cancer. Based on the measured systematic and random errors, a planning target volume (PTV) margin of 5 mm was appropriate for our IMRT system.It took 15-20 min for a single fraction of IMRT, which may cause a dose-rate effect or sublethal damage repair during a farction. Cell survival curves of SCCVII tumors and CHO cells irradiated with IMRT and conventional beams were compared. Below the range of 10 Gy, no significant difference in cell survival curves were detected.IMRT using the simultaneous integrated boost (SIB) method was designed for treating malignant gliomas. IMRT delivered 70 Gy/28 fractions/daily 2.5 Gy to the gross tumor volume (GTV) and 56 Gy/28 fractions/daily 2.0 Gy to the surrounding edema defined as the clinical target volume annulus (CTV-a). Although this treatment was feasible both physically and clinically, the local control was not improved.The patterns of local-regional recurrence in patients with head and neck cancer treated by parotid-sparing IMRT were analyzed. The mean doses to the contra- and ipsi-lateral parotid glands were 24.0 Gy and 30.3 Gy, respectively Among the 33 patients, 19 patients (58%) showed only grade-0,1 xerostomia. Thus, parotid-sparing IMRT could reduce the incidence of xerostomia. However, some recurrences were noted at the margin of PTV. PTV delineation in IMRT should be cautious enough.