What question did this study set out to answer?

This research aims to compare the effectiveness of deformable image registration and conventional adaptive radiotherapy in addressing anatomical changes during radiation treatment for oral cavity cancer.

February 26, 2026Open Access

Evaluation of deformable image registration vs offline adaptive replanning in post-op oral cavity cancer treated with volumetric modulated Arc therapy

Key Points

This research aims to compare the effectiveness of deformable image registration and conventional adaptive radiotherapy in addressing anatomical changes during radiation treatment for oral cavity cancer.
Enrolled post-operative OCSCC patients undergoing adjuvant RT with significant skin contour changes.
Used cone beam computed tomography for imaging and imported data into Velocity® for synthetic CT generation.
Created separate treatment plans based on re-simulation and synthetic CT anatomy.
Evaluated geometric and dosimetric differences between both treatment planning approaches.
DIR showed geometric accuracy for most structures except spinal cord (DSC = 0.75).
Significant volume reduction was found on sCT compared to pCT for most structures, with an increase in the larynx.
Initial plan projection onto sCT showed significant loss in coverage for low-risk PTV (V95% p = 0.001).
Non-significant dose reductions to critical organs, with notable increases in doses for mandible and spinal cord.
Overall, dART improved organ at risk sparing but compromised target coverage parameters.

Abstract

Anatomical changes during adjuvant radiotherapy (RT) for post-operative oral cavity squamous cell carcinoma (OCSCC) have greater dosimetric effects with highly conformal techniques, thereby necessitating plan adaptation. We compared conventional adaptive RT (cART) with deformable image registration (DIR)-based ART (dART). Post-operative OCSCC patients receiving adjuvant RT with a ≥ 5 mm change in skin contour on cone beam computed tomography (CBCT) were enrolled. After re-simulation, planning CT (pCT) and extended CBCT were imported into Velocity® to generate a synthetic CT (sCT) using DIR. Separate plans were created on the re-simulation CT (rCT) and sCT. The initial plan he was also projected onto the sCT anatomy and compared with the original plan on the pCT. Geometric (volume, Dice similarity coefficient DSC, mean distance to agreement MDA) and dosimetric (mean dose, dose-volume histogram DVH) differences were evaluated between rCT- and sCT-based plans. Twenty-five patients were prospectively enrolled. Based on DSC and MDA, DIR showed acceptable geometric accuracy for all structures except the spinal cord (DSC = 0.75). Compared to pCT, most structures had significant volume reduction on sCT, except the low-risk planning target volume (PTVLR) (p = 0.14) and the larynx (increased, p = 0.04). Projection of the initial plan onto sCT revealed significant loss in PTVLR coverage (V95% p = 0.001; D98% p = 0.01) and a non-significant loss for the high-risk PTV (PTVHR). Organs at risk (OARs) doses increased non-significantly, except for the mandible (p = 0.007). Comparison of rCT and sCT volumes showed a 3.7% increases in PTVHR (p = 0.009) and 5.7% in PTVLR (p = 0.049), with non-significant OAR volume increases (2.4%–6.3%) except for the larynx (decreased). DVH comparison showed non-significant dose reductions to the parotids (0.6%), the mandible (0.5%), and the larynx (5.8%), but slight increases for the spinal cord (2.6%) and its planning organ at risk volume (PRV) (3.7%). Target coverage was significantly lower with sCT-based plans (PTVHR V95% by 3.2%, D98% by 3.8%, PTVLR V95% by 4.1% and D98% by 4.3%). dART improved OAR sparing but was compromised in a few target coverage parameters. Further enhancement of DIR accuracy is needed. Currently, DIR is primarily used in ART for dose accumulation to assess the need for plan adaptation.

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