Significance Of Functional Parameters In Prognosis Of Nasopharyngeal Carcinoma Treated With ¹⁸F-FDG PET-CT Guided High-dose Simultaneous Modulated Accelerated Biological Radiation Therapy

Objective:Whether high-dose irradiation prescribed to¹⁸F-FDG PET-CT metabolic active region of nasopharyngeal cancer（NPC）could bring survival benefits is a controversial issue.This study reported the treatment results for 87 NPC patients treated by ¹⁸F-FDG PET-CT guided high-dose simultaneous modulated accelerated biological radiotherapy（SMABRT）with long-term follow-up.The prognostic value of functional parameters had been analyzed.Methods:87 patients with nasopharyngeal carcinoma underwent¹⁸F-FDG PET-CT guided simultaneous modulated accelerated biological radiation therapy（SMABRT）from 2007 to 2011 in Hunan Cancer Hosipital were retrospectively analyzed.Patients were simulated with¹⁸F-FDG PET-CT and visually delineated the high metabolic activity area of nasopharyngeal tumor as GTVnx.pet.The nasopharyngeal tumor based on CT or MRI was contoured as GTVnx,and the abnormal nodes as GTVnd.The high risk and low risk regions had also been delineated as CTV1 and CTV2 according to hospital protocol.The median radiation doses for GTVnx.pet,GTVnx,GTVnd,PTV1 and PTV2 were 78Gy、74.6Gy、72Gy、60Gy and 54-56Gy respectively and was delivered in 32to 33 fractions.The functional parameters of ¹⁸F-FDG PET-CT such as maximum standard uptake value（SUVmax）,mean SUV（SUVmean）,metabolic tumor volume（MTV）and total lesion glycolysis（TLG）were measured and calculated for the primary nasopharyngeal tumors and neck nodes respectively.Their prognostic value had been analyzed based on the long-term follow up outcome.Results:1.The median follow-up time was 64.8 months（3 to 90 months）,the 5-year overall survival（OS）,local recurrence-free survival（LRFS）,local regional recurrence-free survival（LRRFS）,distant metastasis-free survival（DMFS）and disease-free survival（DFS）were 80.2%,93.9%,91.4%,85.6%and 77.6%respectively.There were 3 cases of nasopharyngeal and 2 cases of neck nodes recurrence alone,1 case of both nasopharynx and neck recurrence,13 cases of distant metastasis,and1 case of both nasopharyngeal recurrence and distant metastasis.4 in 5 of nasopharyngeal recurrent site were within GTVnx.pet,only 1 case was within the more than 77Gy prescription dose region;2.There were no adverse effects of grade 3 or above in late radiotherapy in 80 patients who underwent late radiotherapy adverse reactions;3.Multivariate analysis showed that GTVnx.pet dose was independent prognostic factor for5-year LRRFS.MTV-P≥11cm³,SUVmax-N≥7 and MTV-N≥14cm³ were independent prognostic factors for 5-year DMFS.Conclusion:1.¹⁸F-FDG PET-CT guided high-dose SMABRT had achieved very high local and regional control rates,and the distant metastasis was the main reason of failure.2.¹⁸F-FDG PET-CT guided high-dose SMABRT was safe when the metabolic active area dose was above 77Gy.Its late radiotherapy adverse reactions did not increase significantly.3.GTVnx.pet dose is an independent prognostic factor for LRRFS.MTV of nasopharyngeal tumor,SUVmax and MTV of neck metastatic nodes are independent prognostic factors for DMFS.