Modified Reduced-volume Intensity-modulated Radiation Therapy In Non-metastatic Nasopharyngeal Carcinoma

Background and purposeDelineation of clinical target volume(CTV)is one of the most critical steps in successful treatment of nasopharyngeal carcinoma(NPC)using intensity-modulated radiation therapy(IMRT).The optimal selection and definition for CTV in IMRT for NPC especially at the primary site has not yet been determined.On the basis of previous studies,the current study utilized de-intensification technique that omitted the contouring of CTV1 and narrowed the margin of CTV2 from 10 mm to 8mm,namely “modified reduced-volume IMRT”,aimed to evaluate the efficacy and feasibility of this renew technique.Patients and materialsTo evaluate the feasibility of ‘‘modified reduced-volume IMRT”,40 pathologically confirmed non-metastatic NPC cases with different T classifications(10 in each)were enrolled in pre-experiment.After optimization of radiotherapy plan,the dose volume histogram(DVH)was used to evaluate the feasibility of our modification.The results confirmed that this technique met the dosimetry requirements of the Radiation Therapy Oncology Group(RTOG).Subsequently,this de-intensification technique was applied in non-metastatic NPC patients treated in our attending group from November 2014 to December 2017.Survival outcomes focused on local recurrence-free survival(LRFS),and local failure pattern were analyzed.For patients with local recurrence,magnetic resonance imaging(MRI)images at time of local failures were transferred to the pretreatment planning computed tomography(CT)for delineation of the recurrent gross tumor volume(r GTV).The dose of radiation received by r GTV during definitive radiotherapy was calculated and analyzed with DVH.Failures were classified as: “in field” if95% of r GTV was within the 95% isodose,“marginal” if 20%～95% of r GTV was within the 95% isodose,or “outside” if less than 20% of r GTV was inside the 95% isodose. ResultsPreliminary dosimetric evaluation of “modified reduced-volume IMRT”showed that the 60 Gy isodose curve generated naturally by this technique could well wrap the target area of CTV1 and satisfy its dosimetry requirements.Subsequent observation series,which included a total of 471 patients and had a median follow-up time of 46.2 months(range,3.7-70.8months),reported that4-year estimated LRFS,regional recurrence-free survival(RRFS),distant metastasis-free survival(DMFS)and overall survival(OS)were 96.6%,97.7%,87.7% and 92.4%,respectively.Thirteen patients developed local relapse at time of last following up,most of them were T3-4 disease at primary diagnosis.The results of local recurrence pattern analysis of 11 cases with complete data showed that all recurrent lesions occurred within 95% isodose lines were considered in-field failures,and there was no local recurrence caused by insufficient dose to the primary tumor.Multivariate analyses showed that T classification remained as the single adverse prognostic factor for local control(P=0.038).ConclusionsOur de-intensification technique “modified reduced-volume IMRT” was feasible and did not compromise therapeutic efficacy,well-designed multicenter prospective trials are needed for further research.