Personalized Monitoring of Dosimetric Variations In Nasopharyngeal Carcinoma Using Modified CUSUM Control Charts
Abstract
Purpose
During radiotherapy for nasopharyngeal carcinoma, patients frequently experience anatomical variations, leading to discrepancies between the delivered and planned doses. Adaptive radiotherapy (ART) can compensate for these deviations; however, its optimal timing remains unclear. This study explores the use of a modified cumulative sum (CUSUM) chart for personalized monitoring of these variations to guide ART decisions.
Methods
We retrospectively analyzed data from 24 NPC patients treated with the Radixact X7 Tomotherapy System. Daily MVCT scans acquired prior to irradiation were reviewed using the PreciseART tool. Initial structures were propagated onto each MVCT image using image registration. The planned dose was mapped onto each daily MVCT image based on rigid registration performed at the time of treatment. Spearman's rank correlation coefficient was employed to analyze the correlation between ΔV and ΔD. Wilcoxon signed-rank tests were used to compare parameter differences between different treatment fractions. In the modified CUSUM chart, the parameter value from the first treatment MVCT scan was employed as the target value (T). The upper and lower control limits (UCL and LCL) are defined as 7%*T for the target volume and 15%*T for the OARs. The modified cumulative sum (CUSUM) charts were used to track dosimetric variations in target volumes and organs at risk (OARs) throughout treatment.
Results
The results demonstrated a weak correlation between ΔV and ΔD, with Spearman coefficients ranging from -0.47 to 0.32. While the GTVnd and parotid glands exhibited relatively consistent trends of increasing dose, variations in other structures were highly patient- and organ-dependent. Notably, most dosimetric breaches of the CUSUM control limits first occurred between fractions 5 and 10.
Conclusion
For ART decision-making, greater emphasis should be placed on ΔD than on ΔV. CUSUM charts are valuable for monitoring dose metric variations during treatment and may guide adaptive radiotherapy in individual patients.