Using the radioluminescence light of solid state probes coupled to long and flexible fibers for dosimetry in radiotherapy offers many advantages in terms of probe size, robustness and cost efficiency. However, especially in hadron fields, radioluminophores exhibit quenching effects dependent on the linear energy transfer. This work describes the discovery of a spectral shift in the radioluminescence light of beryllium oxide in dependence on the residual range at therapeutic proton energies. A spectrally resolving measurement setup has been developed and tested in scanned proton fields. It is shown that such a system can not only quantitatively reconstruct the dose, but might also give information on the residual proton range at the point of measurement.

Objectives Radiotherapy (RT) for pediatric ependymoma remains challenging due to the young age of the patients and the close proximity of the tumour to critical structures. In Germany, Austria and Switzerland, a Radiotherapy Quality Assurance (RTQA) program was implemented within the SIOP Ependymoma II trial to ensure patient safety and protocol compliance. Methods Pre-trial site approvals and prospective plan reviews for patients in stratum 1 and 2 were performed. Plans were submitted by the treating centres to the reference centres Essen and Leipzig, who evaluated the plans regarding compliance to the study protocol and the German RTQA guideline. Results were categorized as per protocol, acceptable variation, justified unacceptable variation or unacceptable variation, respectively. Unacceptable variations required plan modification and re-review. Results Between May 2019 and December 2021, 33 patients (median age 5.1 years) from 8 institutions were reviewed. Thirty patients in stratum 1 received conformal RT. Within stratum 2, 3 patients received an additional stereotactic boost. The majority (n=31) of the patients were treated with protons. Of the 33 conformal RT plans, 4 (12%) were reviewed as per protocol, 14 (42%) as acceptable variation, 4 (12%) as justified unacceptable variation and 11 (33%) as unacceptable variation. Six of the unacceptable plans were re-submitted after modification. Four of them were approved after re-submission (acceptable variation=1, justified unacceptable variation=3), whereas 2 plans still had unacceptable variations. Reasons for rejecting plans were target volume delineation (44%), uniformity of target volume (33%) and dose to organs at risk (22%). All stereotactic boost plans were accepted (acceptable variation=1, justified unacceptable variation=2). Conclusion The high rate of rejected initial RT plans underlines the importance of a rigorous RTQA program. Improving the quality of RT plans potentially impacts favourably on outcome and long term side effects although requiring a high effort.

Objective. Due to the radiosensitizing effect of biocompatible noble metal nanoparticles (NPs), their administration is considered to potentially increase tumor control in radiotherapy. The underlying physical, chemical and biological mechanisms of the NPs’ radiosensitivity especially when interacting with proton radiation is not conclusive. In the following work, the energy deposition of protons in matter containing platinum nanoparticles (PtNPs) is experimentally investigated. Approach. Surfactant-free monomodal PtNPs with a mean diameter of (40 ± 10) nm and a concentration of 300 μg ml −1 , demonstrably leading to a substantial production of reactive oxygen species (ROS), were homogeneously dispersed into cubic gelatin samples serving as tissue-like phantoms. Gelatin samples without PtNPs were used as control. The samples’ dimensions and contrast of the PtNPs were verified in a clinical computed tomography scanner. Fields from a clinical proton machine were used for depth dose and stopping power measurements downstream of both samples types. These experiments were performed with a variety of detectors at a pencil beam scanning beam line as well as a passive beam line with proton energies from about 56–200 MeV. Main results. The samples’ water equivalent ratios in terms of proton stopping as well as the mean proton energy deposition downstream of the samples with ROS-producing PtNPs compared to the samples without PtNPs showed no differences within the experimental uncertainties of about 2%. Significance. This study serves as experimental proof that the radiosensitizing effect of biocompatible PtNPs is not due to a macroscopically increased proton energy deposition, but is more likely caused by a catalytic effect of the PtNPs. Thus, these experiments provide a contribution to the highly discussed radiobiological question of the proton therapy efficiency with noble metal NPs and facilitate initial evidence that the dose calculation in treatment planning is straightforward and not affected by the presence of sensitizing PtNPs.