To evaluate the clinical outcome in patients affected by locally advanced oropharyngeal cancer undergoing intensity modulated radiation therapy, by means of Helical Tomotherapy (HT), with dose escalation to FDG-PET/CT positive tumor sub-volumes using the Simultaneous Integrated Boost (SIB).
We analyzed 38 patients treated between 2005 and 2013 for squamocellular oropharyngeal stage III-IVB disease in our Institution. HT was delivered with the SIB technique (HT-SIB) in 30 fractions at different dose levels concomitantly: 69 Gy (2.3 Gy/day) to the gross tumor PET-positive volume (GTV-PET), 66 Gy (2.2 Gy/day) to the clinical target volume for tumor and metastatic nodal station, 54 Gy (1.8 Gy/day) to the clinical negative neck region. Thirty-one patients received concurrent chemotherapy (cisplatin 75-100 mg/m²/21 days for 23 patients, cisplatin 30-40 mg/m²/week for 6 patients and cetuximab for 2 patients). The 2.5-year Overall Cancer specific (OS), Local Tumor disease-free (LTDF), Local Node disease-free (LNDF) and distant metastasis-free (DMFS) survivals were calculated. Correlations between PET volumetric parameters and 2.5-year OS, LTDF, LNDF and DMFS were assessed. The PET/CT metabolic parameters of primary tumor included GTV-PET, metabolic tumor volume (MTV), MTV thresholds 40%, 50%, 60% (MTV-T-40%, MTV-T-50%, MTV-T-60%) and mean standardized uptake value (SUVmean). The median follow-up was 28 months (range: 3-109 months).
All patients completed the treatment as scheduled. The 2.5-year OS, LTDF, LNDF and DMFS were 88%, 83%, 88% and 77%, respectively. Multivariate Cox regression analyses revealed that GTV-PET and GTV-T-PET are predictors for OS with a best-cut-off value equal to 30.9 cc (p=0.022) and 22.4 cc (p=0.029) respectively, while MTV-T-40%, MTV-T-60% and SUVmean are predictors for OS with a best-cut-off value equal to 21.3 (p<0.0001), 13.3 (p<0.0001) and 9.2 (p=0.01), respectively. Temporary treatment interruption due to acute toxicity, mainly mucosae, was observed in 8 patients.
The use of HT-SIB with dose escalation to FDG-PET/CT positive tumor sub-volumes, even with concurrent chemotherapy, allows very promising 2.5-year loco-regional disease control rates. Moreover, the results of the present study suggest that PET/CT metabolic volumetric parameters have a predictive value for the outcome of the patients affected by locally advanced squamocellular oropharingeal cancer undergoing HT-SIB. Thus FDG-PET/CT may constitute the basis for more personalized treatme