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.

PURPOSE: In Germany, Austria, and Switzerland, pretreatment radiotherapy quality control (RT-QC) for tumor bed boost (TB) in non-metastatic medulloblastoma (MB) was not mandatory but was recommended for patients enrolled in the SIOP PNET5 MB trial between 2014 and 2018. This individual case review (ICR) analysis aimed to evaluate types of deviations in the initial plan proposals and develop uniform review criteria for TB boost. PATIENTS AND METHODS: A total of 78 patients were registered in this trial, of whom a subgroup of 65 patients were available for evaluation of the TB treatment plans. Dose uniformity was evaluated according to the definitions of the protocol. Additional RT-QC criteria for standardized review of target contours were elaborated and data evaluated accordingly. RESULTS: Of 65 initial TB plan proposals, 27 (41.5%) revealed deviations of target volume delineation. Deviations according to the dose uniformity criteria were present in 14 (21.5%) TB plans. In 25 (38.5%) cases a modification of the RT plan was recommended. Rejection of the TB plans was rather related to unacceptable target volume delineation than to insufficient dose uniformity. CONCLUSION: In this analysis of pretreatment RT-QC, protocol deviations were present in a high proportion of initial TB plan proposals. These findings emphasize the importance of pretreatment RT-QC in clinical trials for MB. Based on these data, a proposal for RT-QC criteria for tumor bed boost in non-metastatic MB was developed.

Pretreatment central quality control for craniospinal irradiation in non-metastatic medulloblastoma : First experiences of the German radiotherapy quality control panel in the SIOP PNET5 MB trial.

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.

A realistic phantom of the human head for PET-MRI.

BACKGROUND: The combination of positron emission tomography (PET) and magnetic resonance imaging (MRI) (PET-MRI) is a unique hybrid imaging modality mainly used in oncology and neurology. The MRI-based attenuation correction (MRAC) is crucial for correct quantification of PET data. A suitable phantom to validate quantitative results in PET-MRI is currently missing. In particular, the correction of attenuation due to bone is usually not verified by commonly available phantoms. The aim of this work was, thus, the development of such a phantom and to explore whether such a phantom might be used to validate MRACs. METHOD: Various materials were investigated for their attenuation and MR properties. For the substitution of bone, water-saturated gypsum plaster was used. The attenuation of 511 keV annihilation photons was regulated by addition of iodine. Adipose tissue was imitated by silicone and brain tissue by agarose gel, respectively. The practicability with respect to the comparison of MRACs was checked as follows: A small flask inserted into the phantom and a large spherical phantom (serving as a reference with negligible error in MRAC) were filled with the very same activity concentration. The activity concentration was measured and compared using clinical protocols on PET-MRI and different built-in and offline MRACs. The same measurements were carried out using PET-CT for comparison. RESULTS: The phantom imitates the human head in sufficient detail. All tissue types including bone were detected as such so that the phantom-based comparison of the quantification accuracy of PET-MRI was possible. Quantitatively, the activity concentration in the brain, which was determined using different MRACs, showed a deviation of about 5% on average and a maximum deviation of 11% compared to the spherical phantom. For PET-CT, the deviation was 5%. CONCLUSIONS: The comparatively small error in quantification indicates that it is possible to construct a brain PET-MRI phantom that leads to MR-based attenuation-corrected images with reasonable accuracy.