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. 2024 Jan 23;19(1):13.
doi: 10.1186/s13014-024-02406-9.

Cone beam CT-based adaptive intensity modulated proton therapy assessment using automated planning for head-and-neck cancer

Yihang Xu  1   2 , William Jin  1 , Michael Butkus  1 , Mariluz De Ornelas  1 , Jonathan Cyriac  1 , Matthew T Studenski  1 , Kyle Padgett  1 , Garrett Simpson  1 , Stuart Samuels  1 , Michael Samuels  3 , Nesrin Dogan  4
Affiliations

Cone beam CT-based adaptive intensity modulated proton therapy assessment using automated planning for head-and-neck cancer

Yihang Xu et al. Radiat Oncol. .

Abstract

Background: To assess the feasibility of CBCT-based adaptive intensity modulated proton therapy (IMPT) using automated planning for treatment of head and neck (HN) cancers.

Methods: Twenty HN cancer patients who received radiotherapy and had pretreatment CBCTs were included in this study. Initial IMPT plans were created using automated planning software for all patients. Synthetic CTs (sCT) were then created by deforming the planning CT (pCT) to the pretreatment CBCTs. To assess dose calculation accuracy on sCTs, repeat CTs (rCTs) were deformed to the pretreatment CBCT obtained on the same day to create deformed rCT (rCTdef), serving as gold standard. The dose recalculated on sCT and on rCTdef were compared by using Gamma analysis. The accuracy of DIR generated contours was also assessed. To explore the potential benefits of adaptive IMPT, two sets of plans were created for each patient, a non-adapted IMPT plan and an adapted IMPT plan calculated on weekly sCT images. The weekly doses for non-adaptive and adaptive IMPT plans were accumulated on the pCT, and the accumulated dosimetric parameters of two sets were compared.

Results: Gamma analysis of the dose recalculated on sCT and rCTdef resulted in a passing rate of 97.9% ± 1.7% using 3 mm/3% criteria. With the physician-corrected contours on the sCT, the dose deviation range of using sCT to estimate mean dose for the most organ at risk (OARs) can be reduced to (- 2.37%, 2.19%) as compared to rCTdef, while for V95 of primary or secondary CTVs, the deviation can be controlled within (- 1.09%, 0.29%). Comparison of the accumulated doses from the adaptive planning against the non-adaptive plans reduced mean dose to constrictors (- 1.42 Gy ± 2.79 Gy) and larynx (- 2.58 Gy ± 3.09 Gy). The reductions result in statistically significant reductions in the normal tissue complication probability (NTCP) of larynx edema by 7.52% ± 13.59%. 4.5% of primary CTVs, 4.1% of secondary CTVs, and 26.8% tertiary CTVs didn't meet the V95 > 95% constraint on non-adapted IMPT plans. All adaptive plans were able to meet the coverage constraint.

Conclusion: sCTs can be a useful tool for accurate proton dose calculation. Adaptive IMPT resulted in better CTV coverage, OAR sparing and lower NTCP for some OARs as compared with non-adaptive IMPT.

Keywords: Adaptive; CBCT; Head and neck cancer; IMPT.

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Conflict of interest statement

The authors declare there are no competing interests.

Figures

Fig. 1
Fig. 1
Workflow for the validation of CBCT-based proton dose calculation on the sCT
Fig. 2
Fig. 2
An example case with different CT images. a pCT; b rCT; c CBCT; d rCTdef with gold standard contours; e sCT with DIR-propagated contours
Fig. 3
Fig. 3
Box plot of dice similarity coefficient (DSC) for CTV and OARs. The dashed line is positioned at the recommended tolerance by AAPM report TG-132 (DSC > 0.8) [38]
Fig. 4
Fig. 4
Box plots of the difference in dose-volume indices between rCTdef and pCT, sCT with physician-corrected contours, and sCT with uncorrected contours. The blue box represents the difference between rCTdef and pCT, the red box represents the difference between rCTdef and sCT with uncorrected contours, and the green box represents the difference between rCTdef and sCT with physician-corrected contours
Fig. 5
Fig. 5
Dose-volume indices (V95) of planned dose (black diamond), non-adapted fractional dose (red dots), and adapted fractional dose (green dots) for the CTVs. A reference line is placed at V95 = 95%. Note that some patients only had a CTV_primary
Fig. 6
Fig. 6
Dose-volume indices of planned dose (black diamond), non-adapted fractional dose (red dots), and adapted fractional dose (green dots) for constrictor, larynx, and bilateral parotid. A reference line is placed at constraint level for each OAR. Note that the figure does not present the dose-volume indices for some patients when the dose was too low (< 1 Gy) or when the parotid or larynx was the primary target
Fig. 7
Fig. 7
Box plots of NTCP difference between the adapt and non-adapt cohorts
Fig. 8
Fig. 8
Dose difference map for patient 3 (a and b) and patient 8 (c and d). The left column shows the difference between planned and non-adapted dose and the right column shows the difference between the planned and adapted dose
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