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Background To introduce and compare multiple biological effectiveness guided (BG) proton plan optimization strategies minimizing variable relative biological effectiveness (RBE) induced dose burden in organs at risk (OAR) while maintaining plan quality with a constant RBE. Methods Dose-optimized (DOSEopt) proton pencil beam scanning reference treatment plans were generated for ten cranial patients with prescription doses ≥ 54 Gy(RBE) and ≥ 1 OAR close to the clinical target volume (CTV). For each patient, four additional BG plans were created. BG objectives minimized either proton track-ends, dose-averaged linear energy transfer (LET d ), energy depositions from high-LET protons or variable RBE-weighted dose (D RBE ) in adjacent serially structured OARs. Plan quality (RBE = 1.1) was assessed by CTV dose coverage and robustness (2 mm setup, 3.5% density), dose homogeneity and conformity in the planning target volumes and adherence to OAR tolerance doses. LET d , D RBE (Wedenberg model, α/β CTV  = 10 Gy, α/β OAR  = 2 Gy) and resulting normal tissue complication probabilities (NTCPs) for blindness and brainstem necrosis were derived. Differences between DOSEopt and BG optimized plans were assessed and statistically tested (Wilcoxon signed rank, α = 0.05). Results All plans were clinically acceptable. DOSEopt and BG optimized plans were comparable in target volume coverage, homogeneity and conformity. For recalculated D RBE in all patients, all BG plans significantly reduced near-maximum D RBE to critical OARs with differences up to 8.2 Gy(RBE) ( p  < 0.05). Direct D RBE optimization primarily reduced absorbed dose in OARs (average ΔD mean  = 2.0 Gy; average ΔLET d,mean  = 0.1 keV/µm), while the other strategies reduced LET d (average ΔD mean  < 0.3 Gy; average ΔLET d,mean  = 0.5 keV/µm). LET-optimizing strategies were more robust against range and setup uncertaintes for high-dose CTVs than D RBE optimization. All BG strategies reduced NTCP for brainstem necrosis and blindness on average by 47% with average and maximum reductions of 5.4 and 18.4 percentage points, respectively. Conclusions All BG strategies reduced variable RBE-induced NTCPs to OARs. Reducing LET d in high-dose voxels may be favourable due to its adherence to current dose reporting and maintenance of clinical plan quality and the availability of reported LET d and dose levels from clinical toxicity reports after cranial proton therapy. These optimization strategies beyond dose may be a first step towards safely translating variable RBE optimization in the clinics.

Protons are conventionally regarded as a low-linear energy transfer (low-LET) radiation modality with a relative biological effectiveness (RBE) of 1.1, suggesting direct mechanistic similarity to X-rays in the underpinning biological effects. However, exposure to spread-out Bragg peak (SOBP) protons reveals instructive deviations from this assumption. Indeed, proton beams have a maximum LET of ~5 keV/µm but display reduced reliance on classical non-homologous end joining (c-NHEJ) as well as an increased dependence on homologous recombination (HR) and alternative end joining (alt-EJ). These features are well described in cells exposed to high-LET radiation and typically manifest between 100 and 150 keV/µm. We hypothesized that this apparent discrepancy reflects biological consequences of proton-beam properties that remain uncharacterized. In the present study, we outline exploratory experiments aiming at uncovering such mechanisms. We begin by investigating for both entrance and SOBP protons the dose-dependent engagement of HR we recently showed for X-rays. Consistent with our previous findings with X-rays, HR engagement after exposure to both types of proton beams declined with dose, from ~80% at 0.2 Gy to less than 20% at higher doses. RAD51/γH2AX foci ratios, reflecting HR engagement, were modestly higher following proton irradiation, in line with increased HR utilization. G2-checkpoint activation, previously linked to HR, was also stronger after exposure to protons, as was DNA end resection. Moreover, the formation of structural chromosomal abnormalities (SCAs) was higher for SOBP than entrance protons and X-rays. Collectively, our results suggest quasi-high-LET characteristics for proton beams and raise the question as to the physical proton properties that underpin them. We discuss that the commonly employed definition of LET may be insufficient for this purpose.

Purpose Survival in recurrent ependymoma (EPN) depends mainly on the extent of resection achieved. When complete resection is not feasible, chemotherapy is often used to extend progression-free and overall survival. However, no consistent effect of chemotherapy on survival has been found in patients with recurrent EPN. Methods Systemic chemotherapeutic treatment of 138 patients enrolled in the German HIT-REZ-studies was analyzed. Survival depending on the use of chemotherapy, disease-stabilization rates (RR), duration of response (DOR) and time to progression (TTP) were estimated. Results Median age at first recurrence was 7.6 years (IQR: 4.0–13.6). At first recurrence, median PFS and OS were 15.3 (CI 13.3–20.0) and 36.9 months (CI 29.7–53.4), respectively. The Hazard Ratio for the use of chemotherapy in local recurrences in a time-dependent Cox-regression analysis was 0.99 (CI 0.74–1.33). Evaluable responses for 140 applied chemotherapies were analyzed, of which sirolimus showed the best RR (50%) and longest median TTP [11.51 (CI 3.98; 14.0) months] in nine patients, with the strongest impact found when sirolimus was used as a monotherapy. Seven patients with progression-free survival > 12 months after subtotal/no-resection facilitated by chemotherapy were found. No definitive survival advantage for any drug in a specific molecularly defined EPN type was found. Conclusion No survival advantage for the general use of chemotherapy in recurrent EPN was found. In cases with incomplete resection, chemotherapy was able to extend survival in individual cases. Sirolimus showed the best RR, DOR and TTP out of all drugs analyzed and may warrant further investigation.

Background: Proton beam therapy (PBT) is a valuable alternative to photon radiotherapy of CNS tumors in children and adolescents. While most recent studies deal with the outcome or long-term side effects of PBT, the aim of this study was to investigate the feasibility of PBT with a particular focus on the acute toxicity of a simultaneous radiochemotherapy (sPBCT). Patients and methods: We enrolled 199 children [median age 7.4 years (range, 0.9–17.9)], who received altogether 200 courses of PBT/sPBCT at initial diagnosis (n = 121) or at relapse (n = 79) with sPBCT in 52 (26%) courses. Data collection to PBT/sPBCT was based on the medical records and the KiProReg (Registry study of Standard Proton Therapy in Children at West German Proton Therapy Center) with a primarily descriptive-statistical and logistic regression analysis. Results: During PBT/sPBCT a total of n = 704 adverse events (AEs, mean 3.4 per course) were observed. Eighty-seven of them were graded as high-grade adverse events (HGAEs, Common Terminology Criteria for Adverse Eventº ≥3 (CTCAE)) which occurred in 67 (33.5%) PBT/sPBCT courses. HGAEs were in particular hematotoxicity (n = 43; 64.1%) and infections (n = 18; 26.8%). A significantly higher rate of HGAEs was documented in patients treated with sPBCT (n = 33/52; 63.5%) compared to those with PBT only (n = 34/148; 23.0%) (p = 0.001). In children with sPBCT, 15 (28.8%) patients could not receive the recommended dose or schedule of the planned chemotherapy (CTx) due to HGAEs, with the rate of planned CTx courses performed being significantly lower in patients receiving intensive intravenous CTx (p < 0.001). Interruptions of PBT and of simultaneous CTx were both significantly associated with the occurrence of infections [Odds ratios 3.002 (95% CI 1.005–8.971, p = 0.049) and 3.905 (95% CI 1.005–15.174, p = 0.049)]. Total discontinuation of treatment did not occur. Conclusions: Concurrent CTx during proton therapy is associated with a significant increased risk for HGAE occurrence and therapy interruptions requiring individual dose and schedule adjustments dependent on CTx intensity, very experienced interdisciplinary teams as well as intensive care and in-/out-patient oncology facilities on site.

Homogeneous and common objective disease assessments and standardised response criteria are important for better international clinical trials for CNS germ cell tumours. Currently, European protocols differ from those of North America (the USA and Canada) in terms of criteria to assess radiological disease response. An international working group of the European Society for Paediatric Oncology Brain Tumour Group and North American Children's Oncology Group was therefore established to review existing literature and current practices, identify major challenges regarding imaging assessment, and develop consensus recommendations for imaging response assessment for patients with CNS germ cell tumours. New clinical imaging standards were defined for the most common sites of CNS germ cell tumour and for the definition of locoregional extension. These new standards will allow the evaluation of response to therapy in patients with CNS germ cell tumours to be more consistent, and facilitate direct comparison of treatment outcomes across international studies.

Purpose The management of soft tissue sarcoma (STS) at reference centers with specialized multidisciplinary tumor boards (MTB) improves patient survival. The German Cancer Society (DKG) certifies sarcoma centers in German-speaking countries, promoting high standards of care. This study investigated the variability in treatment recommendations for localized STS across different German-speaking tertiary sarcoma centers. Methods In this cross-sectional case-based survey study, 5 anonymized patient cases with imaging data of localized STS were presented to MTBs of 21 German-speaking tertiary referral hospitals. Centers provided recommendations on treatment sequence and modalities, along with the consensus level within their MTB. Agreement percentages were calculated, and consensus levels were rated on a scale of 1 to 10. Results Five patient cases were discussed resulting in 105 recommendations. Agreement percentages for case 1 to 5 were 14.3%, 61.9%, 33.3%, 52.4% and 9.3%, with a median agreement percentage of 33.3%. Grouping pre- and postoperative therapies as \"perioperative\" and including recommendations with and without regional hyperthermia raised the median agreement to 47.6%. The mean consensus level within each center across all 5 cases was 9.5. Conclusion This first case-based analysis of inter-center agreement for STS management in German-speaking countries reveals low inter-center agreement but high intra-center consensus. Our study includes nearly all tertiary sarcoma centers in German-speaking countries, affirming its strong external validity. These findings suggest potential and clinically very relevant differences in treatment standards among sarcoma centers. Enhanced case-based exchanges and collaborative efforts are needed to reduce discrepancies and standardize the management of STS patients.

ZusammenfassungHintergrundDie Radiotherapie (RT) ist integraler Bestandteil der Behandlung vieler Tumoren in der Nachbarschaft empfindlicher Organe und Strukturen, zu denen insbesondere auch Kopf-Hals- und Schädelbasistumoren zählen. Aufgrund der mit einer Strahlentherapie verbundenen Risiken von Nebenwirkungen wird die Nutzung hochkonformaler RT-Techniken favorisiert. Für viele Indikationen ist daher die Protonentherapie (PT) bereits Teil des modernen Behandlungsstandards.Ziel der ArbeitÜbersicht über heutige Indikationen für PT mit Schwerpunkt auf Tumoren im Kopf-Hals-Bereich und der Schädelbasis. Zusammenfassung und Diskussion relevanter Ergebnisse und aktueller Entwicklungen.Material und MethodenBewertung relevanter Studien und Zusammenschau aktueller Fragestellungen der PT für Tumoren im Kopf-Hals- und Schädelbasisbereich.ErgebnisseDie Untersuchungen zur PT weisen insgesamt vielversprechende Ergebnisse auf. Neben den dosimetrischen Untersuchungen deuten auch klinische Studien auf Vorteile der PT hin, besonders hinsichtlich der Reduzierung von Nebenwirkungen.DiskussionGegenwärtig wird besonders die Nutzung des „model-based approach“ diskutiert. Hierdurch sollen anhand der „normal tissue complication probability“ (NTCP) die Patienten identifiziert werden, die besonders von einer PT profitieren. Weiterhin wird die PT für die Re-RT diskutiert.

Alt-EJ is an error-prone DNA double-strand break (DSBs) repair pathway coming to the fore when first-line repair pathways, c-NHEJ and HR, are defective or fail. It is thought to benefit from DNA end-resection—a process whereby 3′ single-stranded DNA-tails are generated—initiated by the CtIP/MRE11-RAD50-NBS1 (MRN) complex and extended by EXO1 or the BLM/DNA2 complex. The connection between alt-EJ and resection remains incompletely characterized. Alt-EJ depends on the cell cycle phase, is at maximum in G2-phase, substantially reduced in G1-phase and almost undetectable in quiescent, G0-phase cells. The mechanism underpinning this regulation remains uncharacterized. Here, we compare alt-EJ in G1- and G0-phase cells exposed to ionizing radiation (IR) and identify CtIP-dependent resection as the key regulator. Low levels of CtIP in G1-phase cells allow modest resection and alt-EJ, as compared to G2-phase cells. Strikingly, CtIP is undetectable in G0-phase cells owing to APC/C-mediated degradation. The suppression of CtIP degradation with bortezomib or CDH1-depletion rescues CtIP and alt-EJ in G0-phase cells. CtIP activation in G0-phase cells also requires CDK-dependent phosphorylation by any available CDK but is restricted to CDK4/6 at the early stages of the normal cell cycle. We suggest that suppression of mutagenic alt-EJ in G0-phase is a mechanism by which cells of higher eukaryotes maintain genomic stability in a large fraction of non-cycling cells in their organisms.

PurposeNeuroblastoma (NB) is the most common extracranial solid malignancy during childhood. Despite a multimodal treatment approach, the prognosis of patients with metastatic NB is not satisfactory. Although radiotherapy (RT) has become an integral part of treatment of the primary tumor, the role of RT in osteomedullary lesions is not well defined. A retrospective analysis was conducted to evaluate the impact of RT for metastatic sites in children with high-risk NB.MethodsAll patients with stage 4 NB from the prospective, multicenter NB trials NB97 and NB2004 who received RT to metastatic sites during frontline treatment were included in this retrospective analysis.ResultsA total of 18 children were irradiated with a median dose of 36 Gray (Gy; range 20–45 Gy) to one or more (range 1–3) osteomedullary metastases with or without concomitant RT to the primary tumor site. The median follow-up time was 149 months (range 55–220) in survivors. At 5 years, local relapse-free survival (LRFS) at irradiated metastatic sites and metastases-free survival (MFS) at distant, non-irradiated site rates were 51.4 and 39.9%, respectively. The estimated overall survival (OS) rate at 5 years was 49.4%. No high-grade acute or late toxicity and no secondary malignancy was reported.ConclusionRT to metastases is feasible for patients with stage 4 NB. However, an impact of RT to residual metastatic sites on outcome was not found. Studies with larger cohorts or prospective trials would be desirable in order to elucidate the role of RT for metastases.