Andrea Wittig

Boron analysis and boron imaging in biological materials for Boron Neutron Capture Therapy (BNCT)

Boron Neutron Capture Therapy (BNCT) is based on the ability of the stable isotope 10B to capture neutrons, which leads to a nuclear reaction producing an alpha- and a 7Li-particle, both having a high biological effectiveness and a very short range in tissue, being limited to approximately one cell diameter. This opens the possibility for a highly selective cancer therapy. BNCT strongly depends on the selective uptake of 10B in tumor cells and on its distribution inside the cells. The chemical properties of boron and the need to discriminate different isotopes make the investigation of the concentration and distribution of 10B a challenging task. The most advanced techniques to measure and image boron are described, both invasive and non-invasive. The most promising approach for further investigation will be the complementary use of the different techniques to obtain the information that is mandatory for the future of this innovative treatment modality.

Uptake of two 10B-compounds in liver metastases of colorectal adenocarcinoma for extracorporeal irradiation with boron neutron capture therapy (EORTC Trial 11001).

Disseminated metastases of colorectal cancer in liver are incurable. The trial EORTC 11001 investigates whether autotransplantation after extracorporeal irradiation of the liver by boron neutron capture therapy (BNCT) might become a curative treatment option because of selective uptake of the compounds sodium mercaptoundecahydro‐closo‐dodecaborate (BSH) or L‐para‐boronophenylalanine (BPA). BSH (50 mg/kg bw) or BPA (100 mg/kg bw) were infused into patients who subsequently underwent resection of hepatic metastases. Blood and tissue samples were analyzed forthe 10B‐concentration with prompt gamma ray spectroscopy (PGRS). Three patients received BSH and 3 received BPA. Adverse effects from the boron carriers did not occur. For BSH, the highest 10B‐concentration was observed in liver (31.5 ± 2.7 μg/g) followed by blood (24.8 ± 4.7 μg/g) and tumor (23.2 ± 2.1 μg/g) with a mean 10B‐concentration ratio metastasis/liver of 0.72 ± 0.07. For BPA, the highest 10B‐concentration was measured in metastases (12.1 ± 2.2 μg/g) followed by liver (8.5 ± 0.5 μg/g) and blood (5.8 ± 0.8 μg/g). As BPA is transported actively into cells, viable, metabolically active cells accumulate exclusively this compound. Consequently, a model is proposed to adjust the values measured by PGRS for the proportion of viable cells to express the relevant 10B‐concentration in the tumor cells, revealing a 10B‐concentration ratio metastasis/liver of 6.8 ± 1.7. In conclusion, BSH is not suitable as 10B‐carrier in liver metastases as the 10B‐concentration in liver was higher compared to metastasis. BPA accumulates in hepatic metastases to an extent that allows for extracorporeal irradiation of the liver with BNCT.

Local tumor control probability modeling of primary and secondary lung tumors in stereotactic body radiotherapy

BACKGROUND AND PURPOSE To evaluate whether local tumor control probability (TCP) in stereotactic body radiotherapy (SBRT) varies between lung metastases of different primary cancer sites and between primary non-small cell lung cancer (NSCLC) and secondary lung tumors. MATERIALS AND METHODS A retrospective multi-institutional (n=22) database of 399 patients with stage I NSCLC and 397 patients with 525 lung metastases was analyzed. Irradiation doses were converted to biologically effective doses (BED). Logistic regression was used for local tumor control probability (TCP) modeling and the second-order bias corrected Akaike Information Criterion was used for model comparison. RESULTS After median follow-up of 19 months and 16 months (n.s.), local tumor control was observed in 87.7% and 86.7% of the primary and secondary lung tumors (n.s.), respectively. A strong dose-response relationship was observed in the primary NSCLC and metastatic cohort but dose-response relationships were not significantly different: the TCD90 (dose to achieve 90% TCP; BED of maximum planning target volume dose) estimates were 176 Gy (151-223) and 160 Gy (123-237) (n.s.), respectively. The dose-response relationship was not influenced by the primary cancer site within the metastatic cohort. CONCLUSIONS Dose-response relationships for local tumor control in SBRT were not different between lung metastases of various primary cancer sites and between primary NSCLC and lung metastases.

Tissue uptake of BSH in patients with glioblastoma in the EORTC 11961 phase I BNCT trial.

Purpose: The uptake of the boron compound Na2B12H10-SH (BSH) in tumor and normal tissues was investigated in the frame of the EORTC phase I trial ‘Postoperative treatment of glioblastoma with BNCT at the Petten Irradiation Facility’ (protocol 11961).Methods and Materials: The boron concentration in blood, tumor, normal brain, dura, muscle, skin and bone was detected using inductively coupled plasma-atomic emission spectroscopy in 13 evaluable patients. In a first group of 10 patients 100 mg BSH/kg bodyweight (BW) were administered; a second group of 3 patients received 22.9 mg BSH/kg BW. The toxicity due to BSH was evaluated.Results: The average boron concentration in the tumor was 19.9±9.1 ppm (1 standard deviation (SD)) in the high dose group and 9.8±3.3 ppm in the low dose group, the tumor/blood ratios were 0.6±0.2 and 0.9±0.2, respectively. The highest boron uptake has been detected in the dura, very low uptake was found in the bone, the cerebro-spinal fluid and especially in the brain (brain/blood ratio 0.2±0.02 and 0.4±0.2). No toxicity was detected except flush-like symptoms in 2 cases during a BSH infusion at a much higher speed than prescribed.Conclusion: BSH proved to be safe for clinical application at a dose of 100 mg BSH/kg infused and at a dose rate of 1 mg/kg/min. The study underlines the importance of a further investigation of BSH uptake in order to obtain enough data for significant statistical analysis. The boron concentration in blood seems to be a quite reliable parameter to predict the boron concentration in other tissues.

Support Vector Machine-Based Prediction of Local Tumor Control After Stereotactic Body Radiation Therapy for Early-Stage Non-Small Cell Lung Cancer

BACKGROUND Several prognostic factors for local tumor control probability (TCP) after stereotactic body radiation therapy (SBRT) for early stage non-small cell lung cancer (NSCLC) have been described, but no attempts have been undertaken to explore whether a nonlinear combination of potential factors might synergistically improve the prediction of local control. METHODS AND MATERIALS We investigated a support vector machine (SVM) for predicting TCP in a cohort of 399 patients treated at 13 German and Austrian institutions. Among 7 potential input features for the SVM we selected those most important on the basis of forward feature selection, thereby evaluating classifier performance by using 10-fold cross-validation and computing the area under the ROC curve (AUC). The final SVM classifier was built by repeating the feature selection 10 times with different splitting of the data for cross-validation and finally choosing only those features that were selected at least 5 out of 10 times. It was compared with a multivariate logistic model that was built by forward feature selection. RESULTS Local failure occurred in 12% of patients. Biologically effective dose (BED) at the isocenter (BED(ISO)) was the strongest predictor of TCP in the logistic model and also the most frequently selected input feature for the SVM. A bivariate logistic function of BED(ISO) and the pulmonary function indicator forced expiratory volume in 1 second (FEV1) yielded the best description of the data but resulted in a significantly smaller AUC than the final SVM classifier with the input features BED(ISO), age, baseline Karnofsky index, and FEV1 (0.696 ± 0.040 vs 0.789 ± 0.001, P<.03). The final SVM resulted in sensitivity and specificity of 67.0% ± 0.5% and 78.7% ± 0.3%, respectively. CONCLUSIONS These results confirm that machine learning techniques like SVMs can be successfully applied to predict treatment outcome after SBRT. Improvements over traditional TCP modeling are expected through a nonlinear combination of multiple features, eventually helping in the task of personalized treatment planning.

EORTC trial 11001: distribution of two 10B‐compounds in patients with squamous cell carcinoma of head and neck, a translational research/phase 1 trial

Boron neutron capture therapy (BNCT) provides highly targeted delivery of radiation through the limited spatial distribution of its effects. This translational research/phase I clinical trial investigates whether BNCT might be developed as a treatment option for squamous cell carcinoma of head and neck (SCCHN) relying upon preferential uptake of the two compounds, sodium mercaptoundecahydro‐closo‐dodecaborate (BSH) or L‐para‐boronophenylalanine (BPA) in the tumour. Before planned tumour resection, three patients received BSH and three patients received BPA. The 10B‐concentration in tissues and blood was measured with prompt gamma ray spectroscopy. Adverse effects from compounds did not occur. After BPA infusion the 10B‐concentration ratio of tumour/blood was 4.0 ± 1.7. 10B‐concentration ratios of tumour/normal tissue were 1.3 ± 0.5 for skin, 2.1 ± 1.2 for muscle and 1.4 ± 0.01 for mucosa. After BSH infusion the 10B‐concentration ratio of tumour/blood was 1.2 ± 0.4. 10B‐concentration ratios of tumour/normal tissue were 3.6 ± 0.6 for muscle, 2.5 ± 1.0 for lymph nodes, 1.4 ± 0.5 for skin and 1.0 ± 0.3 for mucosa. BPA and BSH deliver 10B to SCCHN to an extent that might allow effective BNCT treatment. Mucosa and skin are the most relevant organs at risk.

Laser postionization secondary neutral mass spectrometry in tissue: a powerful tool for elemental and molecular imaging in the development of targeted drugs.

The exact intracellular localization and distribution of molecules and elements becomes increasingly important for the development of targeted therapies and contrast agents. We show that laser postionization secondary neutral mass spectrometry (laser-SNMS) is well suited to localize particular elements and small molecules with subcellular spatial resolution applying the technique exemplary to Boron Neutron Capture Therapy (BNCT). We showed in a murine sarcoma that the drugs used for clinical BNCT, namely l-para-boronophenylalanine (700 mg/kg body weight i.p.) and sodium mercaptoundecahydro-closo-dodecaborate (200 mg/kg body weight i.p.), transport the therapeutic agent 10B into the cytoplasm and into the nucleus itself, the most sensitive area of the cell. Sodium mercaptoundecahydro-closo-dodecaborate distributes 10B homogeneously and l-para-boronophenylalanine heterogeneously. When combining laser-SNMS with prompt γ-ray analysis as a screening technique, strategies for BNCT can be elaborated to develop new drugs or to improve the use of existing drugs on scientifically based evidence. The study shows the power of laser-SNMS in the early stages of drug development, also outside BNCT. [Mol Cancer Ther 2008;7(7):1763–71]

Effect of temperature during irradiation on the level of micronuclei in human peripheral blood lymphocytes exposed to X-rays and neutrons.

Objectives: It has been reported that the level of cytogenetic damage in human peripheral blood lymphocytes (PBL) is higher following irradiation at 37°C than at 0–4°C. The mechanisms of this cytogenetic temperature effect are not fully known. The aim of our study was to check whether the effect was related to the indirect or direct action of radiation. Materials and methods: PBL were kept at 37°C and 0°C for 20 min and exposed to 2 Gy of X-rays. In some experiments PBL were isolated and 0.5 M dimethyl sulfoxide (DMSO) was added for 5 min before exposure. PBL were also irradiated at 37°C and 0°C with 1 Gy of 6 MeV neutrons. Micronuclei were scored as the endpoint. Following exposure to X-rays the level of initial DNA damage was also measured by the alkaline and neutral comet assay. Results: The frequency of micronuclei in cells exposed at 37°C to X-rays or neutrons was higher than that after exposure at 0°C. No effect of temperature was seen when PBL were exposed to X-rays in the presence of DMSO. No effect of temperature was observed on the level of DNA damage measured with the alkaline or neutral comet assay. Conclusions: The results of experiments with DMSO indicate that the temperature effect is due to the indirect action of radiation, i.e., via reactive oxygen species. However, this is not supported by the results with neutrons and the comet assay. Possible reasons for the discrepancies are discussed.

Electron Irradiation of Conjunctival Lymphoma—Monte Carlo Simulation of the Minute Dose Distribution and Technique Optimization

PURPOSE External beam radiotherapy is the only conservative curative approach for Stage I non-Hodgkin lymphomas of the conjunctiva. The target volume is geometrically complex because it includes the eyeball and lid conjunctiva. Furthermore, the target volume is adjacent to radiosensitive structures, including the lens, lacrimal glands, cornea, retina, and papilla. The radiotherapy planning and optimization requires accurate calculation of the dose in these anatomical structures that are much smaller than the structures traditionally considered in radiotherapy. Neither conventional treatment planning systems nor dosimetric measurements can reliably determine the dose distribution in these small irradiated volumes. METHODS AND MATERIALS The Monte Carlo simulations of a Varian Clinac 2100 C/D and human eye were performed using the penelope and penEasyLinac codes. Dose distributions and dose volume histograms were calculated for the bulbar conjunctiva, cornea, lens, retina, papilla, lacrimal gland, and anterior and posterior hemispheres. RESULTS The simulated results allow choosing the most adequate treatment setup configuration, which is an electron beam energy of 6 MeV with additional bolus and collimation by a cerrobend block with a central cylindrical hole of 3.0 cm diameter and central cylindrical rod of 1.0 cm diameter. CONCLUSIONS Monte Carlo simulation is a useful method to calculate the minute dose distribution in ocular tissue and to optimize the electron irradiation technique in highly critical structures. Using a voxelized eye phantom based on patient computed tomography images, the dose distribution can be estimated with a standard statistical uncertainty of less than 2.4% in 3 min using a computing cluster with 30 cores, which makes this planning technique clinically relevant.

Early clinical trial concept for boron neutron capture therapy: A critical assessment of the EORTC trial 11001

BNCT causes selective damage to tumor cells by neutron capture reactions releasing high LET-particles where (10)B-atoms are present. Neither the (10)B-compound nor thermal neutrons alone have any therapeutic effect. Therefore, the development of BNCT to a treatment modality needs strategies, which differ from the standard phase I-III clinical trials. An innovative trial design was developed including translational research and a phase I aspect. The trial investigates as surrogate endpoint BSH and BPA uptake in different tumor entities.