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. 2019 Nov 1;14(1):189.
doi: 10.1186/s13014-019-1400-3.

Adaptive radiotherapy for head and neck cancer reduces the requirement for rescans during treatment due to spinal cord dose

Louise Belshaw  1 , Christina E Agnew  1 , Denise M Irvine  1 , Keith P Rooney  2 , Conor K McGarry  3   4
Affiliations

Adaptive radiotherapy for head and neck cancer reduces the requirement for rescans during treatment due to spinal cord dose

Louise Belshaw et al. Radiat Oncol. .

Abstract

Background: Patients treated with radiotherapy for head and neck (H&N) cancer often experience anatomical changes. The potential compromises to Planning Target Volume (PTV) coverage or Organ at Risk (OAR) sparing has prompted the use of adaptive radiotherapy (ART) for these patients. However, implementation of ART is time and resource intensive. This study seeks to define a clinical trigger for H&N re-plans based on spinal cord safety using kV Cone-Beam Computed Tomography (CBCT) verification imaging, in order to best balance clinical benefit with additional workload.

Methods: Thirty-one H&N patients treated with Volumetric Modulated Arc Therapy (VMAT) who had a rescan CT (rCT) during treatment were included in this study. Contour volume changes between the planning CT (pCT) and rCT were determined. The original treatment plan was calculated on the pCT, CBCT prior to the rCT, pCT deformed to the anatomy of the CBCT (dCT), and rCT (considered the gold standard). The dose to 0.1 cc (D0.1cc) spinal cord was evaluated from the Dose Volume Histograms (DVHs).

Results: The median dose increase to D0.1cc between the pCT and rCT was 0.7 Gy (inter-quartile range 0.2-1.9 Gy, p < 0.05). No correlation was found between contour volume changes and the spinal cord dose increase. Three patients exhibited an increase of 7.0-7.2 Gy to D0.1cc, resulting in a re-plan; these patients were correctly identified using calculations on the CBCT/dCT.

Conclusions: An adaptive re-plan can be triggered using spinal cord doses calculated on the CBCT/dCT. Implementing this trigger can reduce patient appointments and radiation dose by eliminating up to 90% of additional un-necessary CT scans, reducing the workload for radiographers, physicists, dosimetrists, and clinicians.

Keywords: Adaptive radiotherapy; Deformable image registration; Head and neck; Image guided radiotherapy; Radiation dose; Radiotherapy; Spinal cord.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
The percentage change in body contour volume between the pCT and rCT with the fraction of treatment for re-scan. There is a larger reduction in body contour volume as treatment progresses
Fig. 2
Fig. 2
Spinal cord dose increases for the patients in this study. a shows the frequency distribution of the differences in spinal cord D0.1cc doses between pCT and rCT. The majority of patients experience a small change in spinal cord dose. The distribution is skewed by a small number of patients showing a large increase in D0.1cc. b shows the changing doses for each patient between the pCT and the rCT. The pCT dose is in grey with a solid outline and the rCT dose shown as a stacked light grey bar with a dashed outline. For the patients whose D0.1cc to spinal cord was reduced at the rCT with respect to the pCT, the decrease is shown as a dark outline over the initial pCT dose
Fig. 3
Fig. 3
Bland-Altmann charts illustrating the difference between the D0.1cc to spinal cord for each patient as calculated on (a) the CBCT and (b) the dCT, compared to the gold standard of calculating on the rCT. The solid line indicates the mean difference and the dashed lines the 95% confidence intervals. On each panel, the data points representing patients triggered for a re-plan using the CBCT and dCT have been highlighted with a circle and compared to those triggered on the rCT, which are highlighted with a square
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