| problem to improve the efficacy of radiotherapy. The intensity-modulated radiation therapy(IMRT) has been widely applied in the treatment of head and neck cancer by the dosimetric advantage, especially the simultaneous integrated boost- intensity modulated radiotherapy(SIB-IMRT), the technology can realize the dosimetric requirement of the target volumes and surrounding normal tissues and organs, patients often use a plan throughout the treatment course. However, in clinic, we find that a series of factors, including the primary tumor and metastasis lymph nodes shrinkage, especially larger tumor size or big normal tissues involving the scope of the target volumes, leads to change in the patient anatomy structure during the treatment course. Based on the above changes, all NPC patients rolled into the research received weekly CT scans, and investigate the volumetric and dosimetric changes of target volumes and organs at risk(OARs), which provides some replanning data as a reference for the clinician. Objective: On the hand, the location of nasopharyngeal tumor is deeper and easily prone to lymph node metastasis, it is difficult to achieve complete surgical resection; on the other hand, the pathological classification of most of nasopharyngeal carcinoma(NPC) is poorly differentiated squamous cell carcinoma, and is more sensitive to radiation ray, which determines the radiotherapy as the first choice and main treatment. Nasopharyngeal anatomy structure is complex and adjacent to many important normal tissues and organs, their receiving dose has a close relationship with the patient's quality of life, thus increasing the irradiation dose to target volumes and reducing dose to surrounding normal tissue is the keyMaterials and Methods: About 20 loco-regional advanced NPC patients were enrolled in this study. Patients receiving IMRT and concurrent chemotherapy for nasopharyngeal carcinoma had repeated helical computer tomography scans, which were acquired at the 1st weeks(5th fraction), 2nd weeks(10th fraction), 3rd weeks(15th fraction), 4th weeks(20th fraction), and 5th weeks(25th fraction) during treatments. The new target volumes and OARs were delineated on weekly repeated CT scans by resident physician. Then the original plans radiation beams configurations were copied on new repeated CT scans, and generated a “hybrid plan”(HPLAN) by calculation. The dose distribution on the HPLAN is the actual receiving dose if patients perform by PLAN0 during treatment. And record weight loss from beginning to end of radiotherapy. The weekly volume and dose of the target volumes and the OARs were measured and analyzed.gland volume increased 4.04 ? 3 comparing with CT0 images, and the difference was statistically significant(P = 0.002) at the end of the 1st week. The volume reduced 3.38 ? 3 at the 2nd week comparing with the 1st week. The volumes of 3rd, 4th, 5th week were gradually shrinking. The difference on the 5th week was no statistically significant comparing with the 4th week. The volume of right parotid gland increased 3.66 ? 3 at the end of the week 1. The volume reduced 2.24 ? 3 at the 2nd week comparing with the 1st week. The volumes of 3rd, 4th, 5th week were gradually shrinking. The actual dose and D50% to the both sides of the parotid gland is gradually increased. D50% of 5 cases exceed 35 Gy in 20 cases, including 1 case was bilateral parotid glands, 2 cases were left parotid gland and 2 cases were right parotid gland. The maximum actual dose of brainstem and spinal cord of 6-17 patients per week exceeded the limitation of RTOG during the treatment period. Result: The greatest absolute reduction in the volume of the gross tumor volume(GTV), clinical tumor volume1(CTV1) and clinical tumor volume2(CTV2) occurred between original CT(CT0) and week 1(Table 2). This reduction was statistically significant(P<0.001, <0.001 and 0.003, respectively). The volumes of 2nd, 3rd, 4th, 5th week were gradually shrinking, and the shrinkage rate gradually decreases. Corresponding the minimum dose to planning tumor volume(PTV), PTV1 and PTV2 on HPLAN1 was statistically significant(P <0.001, <0.001,and <0.001,repectively) comparing with PLAN0. The volume of left parotidConclusion: For NPC patients treated with the SIB- IMRT combined chemotherapy, in 6-7 weeks of treatment, with the treatment of target area and endanger the organ volume and the corresponding dose have obvious change; it is necessary to reset and remaking planning during radiotherapy, which not only can make up for the target volumes inadequate dosage but also decrease the high dose to the organs at risk. |
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