The Impact Of Neoadjuvant Chemotherapy In Local-advanced Nasopharyngeal Carcinoma With Adaptive Radiation Therapy

Objective: This study was to investigate how the shrinking gross tumor volumes after neoadjuvant chemotherapy of local-advanced nasopharyngeal carcinoma(NPC) patients impacted the dose distribution during the intensity modulated radiation therapy(IMRT), and find out the meaning of the neoadjuvant chemotherapy in adaptive radiotherapy( ART).Methods: From May 2014 to September 2014, 15 patients with NPC(nasopharyngeal carcinoma) treated with TP(Paclitaxel and cisplatin) were included. Computed tomography(CT) scans were performed before treatment(CT1) and 2 weeks after 2 cycles of neo-adjuvant chemotherapy(CT2). The target volume such as GTVnx, GTVnd, CTV1, CTV2, CTVnd and organs at risk(OARs) were contoured based on the CT images. Plan1 and plan2 were based on CT1 and CT2, respectively. Plan1′was generated by applying the beam configurations of plan1 to the anatomy of CT2. The anatomic and dosimetric changes were measured by comparing the plan1, plan1′and plan2 respectively.Results: Significant volumetric changes of target volumes(GTVnx and GTVnd) were observed after 2 cycles of neo-adjuvant chemotherapy. The volumes of GTVnx before and after chemotherapy were 58.92±33.59cm3 vs 32.47±19.14 cm3(p=0.000), the volumes of GTVnd were 31.71±21.97cm3 vs 13.76±11.07cm3(p=0.000). Comparing with plan1, dose of CTVnd(including Dmean, D95, V93 of CTVnd) shrank in plan 1′,while there weren’t significant difference in GTVnx, GTVnd and CTV2; on the contrary, the Dmean and D50 of parotid(N≥3cm)increased(p<0.05). In contrast with plan1′, plan2 showed increased doses of GTVnd(including Deam and V93 of GTVnd), CTVnd(including D95 and V93 of CTVnd) and decreased doses of CTV2( including Dmean and V93 of CTV2), spinal cord(including Dmax and D1 cc of cord), parotid(patients who had metastatic cervical lymph nodes which were greater than 3cm in diameter, N≥3cm) in replanning(p<0.05). Analysis of the dosimetric changes of brain stem of 6 locally advanced patients, found that the Dmax of brain stem reduced from 60.58±2.91 Gy to 56.01±2.01Gy(p=0.001),and D1 cc reduced from 52.64±2.03 Gy to 49.72±1.34Gy(p=0.038). The dosimetric changes of temporal lobe, lens, optic nerve, optic chiasma and mandible were not significantly different.Conclusions: Neoadjuvant chemotherapy by TP could reduce the anatomic and dosimetric changes, which would lessen the deviation of actual and planned does distribution in the progress of IMRT, and the frequency of replanning, thus benefit the implementation of ART. For patients who had lymph nodes metastases(N≥3cm), neoadjuvant chemotherapy helped protecting parotid glands; while, neoadjuvant chemotherapy could also reduce the damage of brain stem to patients whose primary tumor were closed to stem.