Pretreatment central quality control for craniospinal irradiation in non-metastatic medulloblastoma

Abstract

Purpose Several studies have demonstrated the negative impact of radiotherapy protocol deviations on tumor control in medulloblastoma. In the SIOP PNET5 MB trial, a pretreatment radiotherapy quality control (RT-QC) program was introduced. A first analysis for patients enrolled in Germany, Switzerland and Austria with focus on types of deviations in the initial plan proposals and review criteria for modern radiation technologies was performed. Methods and patients Sixty-nine craniospinal irradiation (CSI) plans were available for detailed analyses. RT-QC was performed according to protocol definitions on dose uniformity. Because of the lack of definitions for high-precision 3D conformal radiotherapy within the protocol, additional criteria for RT-QC on delineation and coverage of clinical target volume (CTV) and planning target volume (PTV) were defined and evaluated. Results Target volume (CTV/PTV) deviations occurred in 49.3% of initial CSI plan proposals (33.3% minor, 15.9% major). Dose uniformity deviations were less frequent (43.5%). Modification of the RT plan was recommended in 43.5% of CSI plans. Unacceptable RT plans were predominantly related to incorrect target delineation rather than dose uniformity. Unacceptable plans were negatively correlated to the number of enrolled patients per institution with a cutoff of 5 patients (p = 0.001). Conclusion This prospective pretreatment individual case review study revealed a high rate of deviations and emphasizes the strong need of pretreatment RT-QC in clinical trials for medulloblastoma. Furthermore, the experiences point out the necessity of new RT-QC criteria for high-precision CSI techniques.

Types of deviation and review criteria in pretreatment central quality control of tumor bed boost in medulloblastoma—an analysis of the German Radiotherapy Quality Control Panel in the SIOP PNET5 MB trial

“…In contrast to our experiences in RT-QC of CSI plans and the published results for atypical and malignant meningioma, we did not see any difference in the need for plan modifications when comparing low-recruiting and high-recruiting centers (≤ 4 patients 42.3% vs. ≥ 5 patients 35.9%) [8,13]. However, the majority of unacceptable plans (88%) occurred in patients who were among the first 3 patients of each institution.…”

“…RT-QC was organized on a national basis. Data on patients enrolled in Germany, Switzerland, and Austria, including details on treatment schedule, treatment techniques, workflow of RT-QC, results of RT-QC of CSI plans, and the German radiotherapy control panel, have been published elsewhere [13]. In the first years of trial recruitment, transfer and central review of Digital Imaging and Communications in Medicine (DICOM)-RT data with Magnetic Resonance Imaging (MRI) fusion could not be ensured in all participating countries.…”

“…For target delineation, RT-QC criteria were adapted from the SIOP Ependymoma II protocol (ClinicalTrials.gov identifier: NCT02265770) for evaluation (Table 1). Furthermore, deviations were rated for clinical relevance and scored as "acceptable" or "unacceptable" as described elsewhere [13].…”

“…Therefore, we have proposed appropriate definitions helping to better display relevant findings in a structured way in the future (Table 3). According to our proposal for CSI, modification of the PTV should be recommended if the reference CTV is not covered [13]. Moreover, a cutoff for too large PTVs needs to be defined depending on the location of the RT volume and, accordingly, to the expected increase in the risk K of late toxicity (e.g., 0.5 cm inside the posterior fossa).…”

“…Regarding dose uniformity, we found appropriate dose coverage in most of the cases. Therefore, we propose using stricter dose uniformity constraints (V95% ≥ 98%), as is recommended by the ICRU report 83 for intensity-modulated RT techniques (IMRT) and as proposed for CSI when using high-precision techniques [13,23]. The same constraints shall also be used for proton plans, respecting the recommendations of the ICRU 78 report [24].…”