Methodology for adaptive and robust FDG-PET escalated dose painting by numbers in head and neck tumors

Abstract

Objective. To develop a methodology for using FDG PET/CT in adaptive dose painting by numbers (DPBN) in head and neck squamous cell carcinoma (HNSCC) patients. Issues related to noise in PET and treatment robustness against geometric errors are addressed.

Methods. Five patients with locally advanced HNSCC scheduled for chemo-radiotherapy were imaged with FDG-PET/CT at baseline and 2–3 times during radiotherapy (RT). The GTV_PET was segmented with a gradient-based method. A double median filter reduces the impact of noise in the PET uptake-to-dose conversion. Filtered FDG uptake values were linearly converted into a voxel-by-voxel prescription from 70 (median uptake) to 86 Gy (highest uptake). A PTV_PET was obtained by applying a dilation of 2.5 mm to the entire prescription. Seven iso-uptake thresholds led to seven sub-levels compatible with the Tomotherapy HiArt^® Treatment Planning System. Planning aimed to deliver a median dose of 56 Gy and 70 Gy in 35 fractions on the elective and therapeutic PTVs, respectively. Plan quality was assessed with quality volume histogram (QVH). At each time point, plans were generated with a total of 3–4 plans for each patient. Deformable image registration was used for automatic contour propagation and dose summation of the 3 or 4 treatment plans (MIMvista^®).

Results. GTV_PET segmentations were performed successfully until week 2 of RT but failed in two patients at week 3. QVH analysis showed high conformity for all plans (mean V_{Q = 0.95} 93%; mean V_{Q = 1.05} 3.9%; mean QF 2.2%). Good OAR sparing was achieved while keeping high plan quality.

Conclusion. Our results show that adaptive FDG-PET-based escalated dose painting in patients with locally advanced HNSCC is feasible while respecting strict dose constraints to organs at risk. Clinical studies must be conducted to evaluate toxicities and tumor response of such a strategy.

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Erratum

Acknowledgments

S. Differding is supported by a Télévie Grant from the Belgian ‘Fonds National pour la Recherche Scientifique F.R.S.-FNRS’ (Grant number 7.4601.13F). John A. Lee is a Research Associate with the F.R.S.-FNRS. This work was supported by a grant from the Belgian Foundation against Cancer (SCIE2012-203).

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

Supplementary material available online

Supplementary Figure 1 and Table I–IV, available online at http://www.informahealthcare.com/doi/abs/10.3109/0284186X.2015.1046997.