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, 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 metabolic target volume (MTV), MTVpre and MTVrec were segmented on PET images by means of an adaptive thresholding algorithm. The overlapping volume between MTVpre and MTVrec (MTVpre&rec) was generated and the dose coverage of MTVrec and MTVpre&rec was checked on the planning CT using the D99 and D95 dose metrics. The recurrent volume was defined as: ‘‘In-Field (IF)’’, “Marginal recurrence” 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 MTVpre was 12.2 cc (4.6–28.9 cc), while the mean MTVrec was 4.3 cc (1.1–12.7 cc). Two recurrences resulted 100% inside MTVpre, 4 recurrences were mostly inside (61–91%) and 4 recurrences were marginal to MTVpre (1–33%). At dosimetric analysis, five recurrences (50%) were IF, 4 (40%) marginal and one (10%) OF. The mean D99 of the overlapping volumes MTVpre&rec was 68.1 Gy (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. Tumor relapse in the high-dose volume support the hypothesis that an intensification of the dose on these volumes could be further assessed to prevent local relapse.
Highlights
Head and neck cancers (HNCs) represent the 6th most common cancer in the world and 5% of malignancies worldwide [1]
The D99 of MTVpre&rec was calculated to state if there were dose “cold spots” within this sub-volume from which recurrence could originate, The D99 and the D95 within MTVrec were calculated to assess the dose coverage of the volume of relapse during RT
We analyzed 87 out of 126 consecutive patients with squamous HNC treated by intensity modulated radiation therapy (IMRT), who met the selection criteria
Summary
Head and neck cancers (HNCs) represent the 6th most common cancer in the world and 5% of malignancies worldwide [1]. Chao et al observed that almost 50% of failures after definitive RT were infield and occurred within the 95% isodose coverage region, despite an adequate target definition and coverage [5].In addition to CT and MRI, [18F] FDG-PET/CT can be used to assess metabolic tumor function and anatomic localization for staging, RT planning, and restaging during follow-up in HNC [6,7,8]. Some authors found that the majority of HNC failures map to the pre-treatment PET abnormality [9,10,11] These studies suggest the presence of radioresistant tumor sub-volumes within the primary target, that could be detected by [18F] FDG-PET/CT. In such cases, metabolic imaging could drive tailored treatment intensification by dose painting
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