Early response assessment by PET scan in chemoradiotherapy for nasopharyngeal carcinoma

Abstract

AIM: Change in uptake on PET scan after induction chemotherapy (IC) and during radiotherapy (RT) may reflect early tumor response to chemoradiotherapy and allow selection of poor responder for intensified treatment METHODS: Patients with T3/T4N0-3M0 nasopharyngeal carcinoma (NPC) were treated with IC followed by concurrent chemoradiotherapy (CRT). IC was either PF (cisplatin 100mg/sqm D1 and 5FU 1G/sqm D1-5) or GP (gemcitabine 1G/sqm D1, D8 and cisplatin 100mg/sqm D1), every 3 weeks for 3 cycles. CRT was cisplatin 100mg/sqm given on D1, D22, D43 of RT. At baseline, each patient was evaluated with F18-FDG PET/CT scan and MRI. PET/CT was repeated after IC and at 30Gy of RT. The gross tumor volume in NP (GTVNP) was localized according to baseine MRI and received 70Gy in 35 fractions. The biological tumor volume (BTVNP) was delineated on PET scan. Complete response on PET scan (CRPET) was defined as SUVmax <2.5 or SUVmean 1.25 of liver background. For patients with incomplete response, the residual BTVNP received an additional 6Gy in 3 fractions. RESULTS: 18 patients were treated from 9/2011 to 4/2013. The stage distribution was: T3 in 10 and T4 in 8 patients; stage III in 8 and stage IV in 10 patients. IC was GP in 6 patients and PF in 12 patients. Median follow up after completion of RT was 8 months (4-21 months). Table 1 summarized the changes in uptake on PET during chemoradiotherapy. Six patients achieved CRPET after IC and another patient achieved CRPET after 30Gy RT. Compared with baseline, the mean drop in SUVmax after IC and at 30Gy were 56.2% an 61.4%, respectively. Two patients had persistent disease in NP after chemoradiotherapy and additional boost. Both had incomplete response after induction chemotherapy and at 30Gy. The decrease in SUVmax after IC and after 30Gy was lower than the group’s average (30% and 46%; 33% and 44%). Another patient who achieved CRPET developed distant failure with local control. CONCLUSIONS: Early response with CRPET is noted after IC. PET at 30Gy is not of additional value. Further study is required to correlate early response with outcome. RT boost to residual BTV is feasible.