3080 - Considerations of Plan Adaptation and CBCT-Based Accumulated Dose In the Prediction of Patient-Reported Xerostomia Post Radiotherapy for Oropharyngeal Cancer Patients

12:30pm - 01:45pm ET

Poster Hall - Exhibit Hall A

Screen: 19

POSTER

Presenter(s)

Androniki Mitrou, MS - The University of Texas MD Anderson Cancer Center, Houston, TX

A. Mitrou^1,2, B. McDonald³, A. Sahli⁴, C. E. Barbon⁴, T. T. Tang², J. P. Long⁵, T. Y. Lim⁶, A. J. Schaefer⁷, P. Balter⁶, A. C. Moreno³, C. D. Fuller³, and K. K. Brock^2,6; ¹The University of Texas MD Anderson Cancer Center UTHealth Houston Graduate School of Biomedical Sciences, Houston, TX, ²Department of Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, ³Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, ⁴The Department of Head and Neck Surgery, The University of Texas MD Anderson Cancer Center, Houston, TX, ⁵Department of Biostatistics, The University of Texas MD Anderson Cancer Center, Houston, TX, ⁶Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, ⁷Rice University, Houston, TX

Purpose/Objective(s):

Test improvements in modeling patient-reported xerostomia with accumulated, versus planned, dose as predictor

Materials/Methods:

Radiotherapy (RT) planning and delivery data, including CBCTs, as well as MD Anderson Symptom Inventory (MDASI) patient-reported outcome measure scores of dry mouth at baseline and 3-6 months post-RT were identified for 183 patients undergoing curative VMAT for oropharyngeal cancer between 2018-2024. Any plan adaptations were noted. CBCTs were expanded to full field-of-view, leveraging deformable image registration. Deformable dose accumulation was performed using the corrected CBCTs and average dose to the contralateral parotid gland was extracted and compared to planned average dose. Statistical analysis was performed on the logistic regression models created for patient-reported xerostomia (MDASI dry mouth > 6) using accumulated and planned dose.

Results:

Accumulated mean dose to the contralateral parotid gland was higher than planned (10.19 ±7.620 Gy, 9.76 ± 7.35 Gy). 23% of the patients analyzed to date were re-planned at least once (range: 1-3). All the adapted patients had a 3-6 month MDASI score lower than 6, i.e. did not report severe xerostomia. For single plan patients, the median MDASI score was 4 (range: 0-10). All resulting logistic regression models for both planned and accumulated dose achieved excellent calibration (intercept ~ 0, slope ~ 1). While gains were modest, accumulated dose models improved in area under receiver operating curve (AUC), precision-recall AUC (PR AUC), Brier score, and McFadden coefficient of determination (R²). Single plan patient and adapted patient cohorts were considered separately and including adaptive cases strengthened trend tests (Cochran–Armitage p (two-sided), see Table 1).

Conclusion:

With plan adaptation increasing in management of head and neck cancer patients, mixed cohorts emphasize the utility of accumulated dose to predict patient-reported xerostomia from contralateral parotid mean dose.

Table 1: Planned and accumulated dose logistic regression model statistics for non-adapted and total (mixed) cohorts

Metric	Non-adapted (Planned)	Non-adapted (Accum)	Non-adapted (Difference: Accum- Planned)	Total (Planned)	Total (Accum)	Total (Difference: Accum- Planned)
AUC	0.662	0.678	0.016	0.748	0.765	0.017
PR AUC	0.602	0.614	0.012	0.594	0.607	0.013
Brier	0.227	0.227	0.000	0.189	0.188	-0.001
McFadden R²	0.053	0.055	0.002	0.128	0.131	0.003
Cochran–Armitage p	0.496	0.427	-0.069	0.2617	0.219	-0.043