Abstract
ObjectiveTo analyze the pattern of failure in relation to pre-treatment [18F] FDG-PET/CT uptake in head and neck squamous cell carcinoma (HNSCC) patients treated with definitive radio-chemotherapy (RT-CHT).Methods and MaterialsFrom 2012 to 2016, 87 HNSCC patients treated with definitive RT-CHT, with intensity modulated radiation therapy with simultaneous integrated boost (IMRT-SIB), underwent pre-treatment [18F] FDG-PET/CT (PETpre), and MRI/CT for radiotherapy (RT) planning purposes. Patients with local recurrence, received [18F] FDG-PET/CT, (PETrec) at the time of the discovery of recurrence. In these patients, the biological target volume (BTV), BTVpre and BTVrec were segmented on PET images by means of an adaptive thresholding algorithm. The overlapping volume between BTVpre and BTVrec (BTVpre&rec) was generated and the dose coverage of BTVrec and BTVpre&rec was checked on the planning CT using the D99 and D95 dose metrics. The recurrent volume was defined as: ‘‘In-Field (IF)’’, ‘‘Extending Outside the Field (EOF)’’ or ‘‘Out-of-Field (OF)’’ if D95 was respectively equal or higher than 95%, D95 was between 95% and 20% or the D95 was less than 20% of prescribed dose.ResultsWe found 10/87 patients (11.5%) who had recurrence at primary site. Mean BTVpre was 13.1 cc (4.6-37.4 cc), while the mean BTVrec was 4.3 cc (1.1-12.7 cc). Two recurrences resulted 100% inside BTVpre, 4 recurrences were mostly inside (61%-91%) and 4 recurrences were marginal to BTVpre (33-1%). At dosimetric analysis, six recurrences (60%) were IF, 3 (30%) EOF and one (10%) OF. The mean D99 of the overlapping volumes BTVpre&rec was 68.1Gy (66.5-69.2 Gy), considering a prescription dose of 70 Gy to the planning target volume (PTV). ConclusionOur study shows that the recurrence may originate from the volume with the highest FDG-signal. Results support the hypothesis that an intensification of the dose on these volumes could be helpful to prevent local relapse.
Target volume definition and dosimetric issues in radiotherapy treatment of head and neck disease with FDG-PET/CT: A monocentric experience