Influence Of Induction Chemotherapy To The Target Volume And Dosimetry Of Intensity Modulated Radiation Therapy For Locally Advanced Nasopharyngeal Carcinoma And Analysis Of The Dosimetric Characteristics Of Replanning After Induction Chemotherapy

Objective: Discussthe influence of induction chemotherapyto the target volume and dosimetry of intensity modulated radiation therapy(IMRT) for locally advanced nasopharyngeal carcinoma(NPC) and analysis of the dosimetric characteristics of replanning after induction chemotherapyto explore the influence to dosimetry with the target regionchanges in the process of therapy and the feasibility of replanning, thus to provide clinical data for appropriateradiotherapy plan.Methods: Scan with enhanced CTbefore and after induction chemotherapy to get scanning images.Transmit theseimages to planning system.Delineate target regions respectivelyaccording to the scans and MRI image data by the same physicianunder the guidance of two or three high qualification specialists. And set prescription dose under the same conditions. The two radiotherapy plans of one patient should be designed by the same physicist on the same terms at the same time, defined as the Plan1 and Plan2, while Plan2 for the actual treatment. Then copy the target structures after induction chemotherapy to match the first section of the Plan,generating the third paragraph,defined as a Plan1-2. Plan1-2 is the the actual target Plan with Plan1 on target region after induction chemotherapy.Compare the two target volumes with eache other, and dosimetry parameters of target regions and organs at risk of the three plans respectively. And observe its curative effect in the near future and adverse reaction.Results: 1.Before and after induction chemotherapy, GTVnx of primary focus and GTVnd of neck lymph nodes reduced significantly(P<0.05). 2.Before and after induction chemotherapy, isodose volumesof 72.6 Gy and 62.7 Gy(V72.6 Gy, V62.7 Gy) reducedsignificantly(P<0.05). 3.Beforeand after induction chemotherapy, the first period of plan: actual minimum dose of PGTV had a tendency to reduce(P=0.055),actual mean dose of all target regionsreduced significantly(P<0.05);Although the actual mean dose of brain stem and maximum dose of temporal lobes decreasedsignificantly(P<0.05), the mean dose and maximum dose of spinal cord were significantly increased(P<0.05);CI reduced significantly, and HI increased(P<0.05). 4.Replanning after induction chemotherapy:actual mean dose of target regions and actual minimum dose of GTV, PGTV increased significantly(P<0.05), the actual maximum dose of CTV1 and PTV1 has also increased(P=0.095);Actual mean dose of temporal lobe decreased significantly(P<0.05), and maximum dose and mean dose of spinal cord decreasedsignificantly(P<0.05);CI increased significantly,and HI decreased(P<0.05). 5.Compare Plan2 with induction chemotherapy before: mean dose of PGTVincreased(P<0.05), and the maximumdose of CTV1 and PTV1 has a increasing trend(P=0.095);The mean dose of temporal lobes and parotid glands reduced significantly(P<0.05);CI and HI has no significant differences(P>0.05). 6.Complete response rate was 93.3%3 months after radiotherapy.Conclusion: 1.Tumors reduced obviously after chemotherapy, the dosimetric distribution of first paragraph IMRT plan became worse. 2.Replanning after induction chemotherapy has more advantages on dosimetry, and it`s feasible.