Quality assurance of craniospinal irradiation in helical tomotherapy using a dose reconstruction tool based on leaf...

The delivery quality assurance (DQA) of craniospinal irradiation (CSI) due to the target length results in no ideal verification devices. Delivery Analysis (DA) could calculate the dose distribution based on the measured multi leaf open time in helical tomotherapy (HT). This study aimed to evaluate the efficacy of DA for DQA of CSI in HT.

32 CSI plans were classified into two groups based on γ analysis of the PTV-cranial and PTV-spine plans using a 2D ionization chamber matrix (MatriXX). Plans with γ passing rates ≥ 95% at 3%/2 mm were classified as the passed group, while those < 95% were classified as the failed group. Receiver operating characteristic (ROC) curves identified optimal passing rate threshold for DA in HT. Logistic regression analyzed risk factors for DQA failure, and failed plans were reoptimized according to the adjusted parameter.

For PTV-cranial plans, 30 passed and two failed; for PTV-spine plans, 21 passed and 11 failed. ROC analysis revealed areas under the curve of 0.858 (PTV-cranial, threshold: 89.0%) and 0.714 (PTV-spine, threshold: 86.0%). Logistic regression identified planned modulation factor (MF-plan; p = 0.046; p = 0.023) and actual modulation factor (MF-actual; p = 0.027; p = 0.008) as independent risk factors for DQA failure in both MatriXX and DA. Additionally, beam on time (p = 0.043), gantry period (p = 0.007) and maximum leaf open time (p = 0.007) were identified as independent risk factors for DA. Reoptimization of failed plans with MF-plan = 2.6 significantly improved passing rates in DA (73.70% ± 13.30% vs. 88.20% ± 12.30%; p = 0.010) and MatriXX (91.20% ± 2.60% vs. 96.10% ± 1.40%; p < 0.001).

Delivery Analysis could be a feasible tool for DQA of CSI in HT. Increasing the MF-plan is recommended to enhance the passing rate.