Recurrent Cox Analysis And Design Optimization Of Radiotherapy

Purpose: To retrospectively analyze the clinical features and prognosticfactors in the re-treatment of recurrent nasopharyngeal carcinoma.Materials and methods: Eighty-six patients with recurrent nasopharyngealcarcinoma from January2005to December2011were included in theretrospective analysis. In these patients,30were only locally recurrent,2wereonly regionally recurrent,49were locoregionally recurrent,3were locallyrecurrent with distant metastasis, and only2patients had locoregionallyrecurrent with distant metastasis.Results: Median time for local recurrence was42.5months, and that forregional recurrence was45months. According to2010American JointCommittee on Union for International Cancer Control staging system (AJC/UICC2010), the populations for rT1, rT2, rT3, rT4and uncertain in84locally recurrent patients were8,28,23,23and2, respectively. The populationsfor rN1, rN2, rN3a, rN3b and uncertain in53regionally recurrent patients were32,11,8,1and1, respectively. The most common places of local recurrencewere nasopharynx (86.0%), parapharyngeal space (53.5%), cranial base (44.2%)and sphenoid sinus (22.1%). II, III and IV regions were the most common placesof regional recurrence. During the secondary therapy,25(29.1%) patientsreceived only radiotherapy (12with3D-CRT and IMRT, and13with Co60),5(5.8%) patients received only chemotherapy,48(55.8%) patients received withchemoradiotherapy,6(7.0%) patients were treated with surgery andchemoradiotherapy, and2(2.3%) patients didn’t received treatment. The medianfollow-up time was13months. The overall survival, progression-free survival,local region control of one-and two-year were65.7%and55.7%,82.8%and75.1%, and84.1%and76.1%, respectively. The result of univariate analysisshowed that gender, the age of first treatment, re-stage of recurrence, T-stage ofrecurrence, N-stage of recurrence, treatment method, radiotherapy modality,interval time from the end of first course of radiotherapy to recurrence atdiagnosis, dose of nasopharynx and fractional modality had statisticalsignificance for prognosis. The result of multivariate analysis showed thatgender, radiotherapy modality, re-stage of recurrence, dose of nasopharynx andfractional modality influenced the prognosis of recurrent NPC.Conclusion: The local and/or regional recurrence of nasopharyngeal carcinoma occurs within3years after the first treatment. The most common places of localrecurrence are nasopharynx, parapharyngeal space, cranial base and sphenoidsinus. II, III and IV regions are the most common places of regional recurrence.Radiotherapy is still the important re-treatment for the recurrent nasopharyngealcarcinoma, and also can prolong survival time for some patients. The gender,radiotherapy modality, dose of nasopharynx and fractional modality areindependent prognostic factors for recurrent NPC. Objective: To compare the dosimetric character on the target area and organat risk (OAR) for recurrent nasopharyngeal carcinoma withvolumetric-modulated arc therapy (VMAT) and intensity-modulated radiationtherapy (IMRT).Materials and methods:1. The dosimetric comparition between VMAT and IMRT for simple localrecurrent NPC.29patients diagnosed with simple local recurrent NPC wereincluded in this study. The target area received two dose levels usingsimultaneous integrated boosts (SIB) technique, PGTV2.26Gy/F and PCTV2Gy/F in30fractions. For a fair comparison, VMAT and IMRT treatment planswere respectively designed for every patient with the same dosimetricconstraints．Dosimetric comparisons between VMAT and IMRT plans were analyzed to evaluate (1) target coverage, homogeneity index (HI) andconformity index (CI),(2) sparing of OARs, and (3) monitor units (MUs).2. The dosimetric comparition on OARs between VMAT and IMRT forlocalregional recurrent NPC.45patients diagnosed with localreginonal recurrentNPC were included in the study. The target area received two dose levels usingsimultaneous integrated boosts (SIB) technique, PGTV2.2Gy/F and PCTV1.8Gy/F in30fractions. For a fair comparison, two-arc360°VMAT,300°VMATand IMRT treatment planning were respectively designed for every patient withthe same dosmetry constraints, to compare the OAR of the three plannings withthe confirming consistency of the CI and HI. Dosimetric comparisons wereanalyzed to evaluate (1) sparing of OARs and (2) delivery time and MUs.Results:1. For simple local recurrent NPC patients, VMAT is higher than IMRT inaverage dose of planning clinical target volume (PCTV), dose received by2%(D2) and98%(D98) of the PCTV(P<0.05); VMAT is better than IMRT (P<0.05)in the target CI and lower than IMRT (P<0.05) in HI. Compared with IMRT,VMAT had a better sparing affect on right temporal lobe D1(P<0.05), worse onbrainstem, left temporomandibular joint Dmax and left temporal lobe Dmax(P<0.05). However, there is no statistical significance in spinal cord Dmax, opticnerve Dmax, crystal Dmax, and parotid gland D50(P>0.05). Moreover, the totalMUs of VMAT has reduced by an average of33.2%(P<0.05).2. For localregional recurrent NPC patients,VMAT had a better sparing effect than IMRT on spinal cord Dmax and Dmean, spinal cord+0.5cm Dmaxand Dmean, left eye Dmin, right eye Dmin, left crystal Dmin, right optic nerveDmax Dmin Dmean, left temporomandibular joint D1cc, right parotid glandDmean and D50and throat Dmin and Dmean (P<0.05). IMRT was superior toVMAT on brain stem Dmax and D1, mandible Dmin and right temporal lobeDmin (P<0.05). But there were no statistical significance on left eye Dmean,right eye Dmean, left crystal Dmean, right crystal Dmean, right crystalDmin,hypophysis Dmean, left optic nerve Dmax and Dmean, righttemporomandibular joint Dmax and D1cc, left temporal lobe Dmin, left andright temporal lobe D1, right parotid gland Dmin and D50. The MUs anddelivery time per fraction for two-arc360°VMAT,300°VMAT had reduced58.0％,62.8%and55.6％and61.4%,compared with IMRT.Conclusion:1. VMAT provides a better average dose of planning clinical target,conformity and homogeneity, and fewer MUs than IMRT for simple localrecurrent nasopharyngeal carcinoma patients. However, VMAT is similar toIMRT on normal tissue sparing.2. Under the conforming condition of the dose distribution of target area,VMAT not only obviously reduces the MUs and delivery time, but alsoeffectively spares spinal cord, crystal, eyes, optic nerve, temporomandibularjoint, parotid gland and throat for locoregional rNPC patients. But, VMAT isworse than IMRT on minority normal organs such as brain stem, mandible and temporal lobe.