Anatomic And Dosimetric Changes During The Treatment Of Neo-adjuvant Chemotherapy Followed By Concurrent Chemoradiation For Locoregionally Advanced Nasopharyngeal Carcinoma

Objective: To investigate how the anatomic and dosimetric of the target area and the surrounding normal tissue changes during the therapy by using neo-adjuvant chemotherapy followed by IMRT with concurrent chemotherapy for local-advanced nasopharyngeal carcinoma(NPC) patients.Then clear the role of neoadjuvant chemotherapy in adaptive radiationMethods: From May 2014 to September 2014, 15 patients with NPC treated with neo-adjuvant chemotherapy followed by radiotherapy with concurrent chemotherapy(CCRT) were included.CT scans were performed before treatment,after 2 cycles of neo-adjuvant chemotherapy,in the period of IMRT(the radiation dose of 40Gy) and in the treatment ended. All target volumes and normal structures were manually outlined on the CT images. The plans were based on the each CT images. The hybrid plan2′ were generated by applying the beam configurations of the original plan1 which was based on the first scanned CT images to the CT2 which were scanned after 2 cycles of neo-adjuvant chemotherapy.The hybrid plan3′ and plan4′ were generated by applying the beam configurations of the plan2 which was based on the second scanned CT image to the CT3 and CT4 which were scanned in the period of IMRT(the radiation dose of 40Gy) and in the treatment ended.The anatomic and dosimetric changes were assessed by comparing the plan1 with plan2′ and the plan2 with plan3′ and plan4′,respectively.Results: Significant volumetric changes of target volumes were observed during the treatment. The volumes of primary gross target volume(GTVnx) 、 the involved lymph nodes(GTVnd) and the parotid glands reduced significantly. There were no lack of the GTVnx, GTVnd and CTV-2 of tumor target dose in the process of treatment.The dose of CTVnd decreased during the treatment.But it didn’t reach the clinical criteria of insufficient dosimetry.The Dmean(mean dose) and the D50(50% dose of the organ volume of the organ volume) increased during the neo-adjuvant chemotherapy treatment for the parotid glands of which the shortest diameter were greater than 3cm(N≥3cm). The dose did not raised obviously for the bilateral parotid glands of N <3cm.And the dose of the parotid glands increased obviously in the process of radiotherapy with concurrent chemotherapy.The increased dose followed down after replanning.Conclusions: Neo-adjuvant chemotherapy followed by CCRT could cause the anatomic and dosimetric change of the target area and the surrounding normal tissue. And making the radiaton therapy treatment when the neo-adjuvant chemotherapy was finished can benefit the parotid glands. Especially for the larger neck metastasis lymph nodes of patients with nasopharyngeal carcinoma, the benefit gained from parotid glands would be more significant. Then the dose of the parotid glands changing obviously in the process of radiotherapy with concurrent chemotherapy,it can benefit from replanning on the dose of 40 Gy.