Model-based assessment of combination therapies - ranking of radiosensitizing agents in oncology.

BACKGROUND: To increase the chances of finding efficacious anticancer drugs, improve development times and reduce costs, it is of interest to rank test compounds based on their potential for human use as early as possible in the drug development process. In this paper, we present a method for ranking radiosensitizers using preclinical data. METHODS: We used data from three xenograft mice studies to calibrate a model that accounts for radiation treatment combined with radiosensitizers. A nonlinear mixed effects approach was utilized where between-subject variability and inter-study variability were considered. Using the calibrated model, we ranked three different Ataxia telangiectasia-mutated inhibitors in terms of anticancer activity. The ranking was based on the Tumor Static Exposure (TSE) concept and primarily illustrated through TSE-curves. RESULTS: The model described data well and the predicted number of eradicated tumors was in good agreement with experimental data. The efficacy of the radiosensitizers was evaluated for the median individual and the 95% population percentile. Simulations predicted that a total dose of 220 Gy (5 radiation sessions a week for 6 weeks) was required for 95% of tumors to be eradicated when radiation was given alone. When radiation was combined with doses that achieved at least 8 [Formula: see text] of each radiosensitizer in mouse blood, it was predicted that the radiation dose could be decreased to 50, 65, and 100 Gy, respectively, while maintaining 95% eradication. CONCLUSIONS: A simulation-based method for calculating TSE-curves was developed, which provides more accurate predictions of tumor eradication than earlier, analytically derived, TSE-curves. The tool we present can potentially be used for radiosensitizer selection before proceeding to subsequent phases of the drug discovery and development process.

Impact of the Spectral Composition of Kilovoltage X-rays on High-Z Nanoparticle-Assisted Dose Enhancement.

Nanoparticles (NPs) with a high atomic number (Z) are promising radiosensitizers for cancer therapy. However, the dependence of their efficacy on irradiation conditions is still unclear. In the present work, 11 different metal and metal oxide NPs (from Cu (ZCu = 29) to Bi2O3 (ZBi = 83)) were studied in terms of their ability to enhance the absorbed dose in combination with 237 X-ray spectra generated at a 30-300 kVp voltage using various filtration systems and anode materials. Among the studied high-Z NP materials, gold was the absolute leader by a dose enhancement factor (DEF; up to 2.51), while HfO2 and Ta2O5 were the most versatile because of the largest high-DEF region in coordinates U (voltage) and Eeff (effective energy). Several impacts of the X-ray spectral composition have been noted, as follows: (1) there are radiation sources that correspond to extremely low DEFs for all of the studied NPs, (2) NPs with a lower Z in some cases can equal or overcome by the DEF value the high-Z NPs, and (3) the change in the X-ray spectrum caused by a beam passing through the matter can significantly affect the DEF. All of these findings indicate the important role of carefully planning radiation exposure in the presence of high-Z NPs.

Gold Nanoparticle Enhanced Proton Therapy: Monte Carlo Modeling of Reactive Species' Distributions Around a Gold Nanoparticle and the Effects of Nanoparticle Proximity and Clustering.

Gold nanoparticles (GNPs) are promising radiosensitizers with the potential to enhance radiotherapy. Experiments have shown GNP enhancement of proton therapy and indicated that chemical damage by reactive species plays a major role. Simulations of the distribution and yield of reactive species from 10 ps to 1 µs produced by a single GNP, two GNPs in proximity and a GNP cluster irradiated with a proton beam were performed using the Geant4 Monte Carlo toolkit. It was found that the reactive species distribution at 1 µs extended a few hundred nm from a GNP and that the largest enhancement occurred over 50 nm from the nanoparticle. Additionally, the yield for two GNPs in proximity and a GNP cluster was reduced by up to 17% and 60% respectively from increased absorption. The extended range of action from the diffusion of the reactive species may enable simulations to model GNP enhanced proton therapy. The high levels of absorption for a large GNP cluster suggest that smaller clusters and diffuse GNP distributions maximize the total radiolysis yield within a cell. However, this must be balanced against the high local yields near a cluster particularly if the cluster is located adjacent to a biological target.

Nanoscale dose deposition in cell structures under X-ray irradiation treatment assisted with nanoparticles: An analytical approach to the relative biological effectiveness.

In this study, an analytical model for the assessment of the modification of cell culture survival under ionizing radiation assisted with nanoparticles (NPs) is presented. The model starts from the radial dose deposition around a single NP, which is used to describe the dose deposition in a cell structure with embedded NPs and, in turn, to evaluate the number of lesions formed by ionizing radiation. The model is applied to the calculation of relative biological effectiveness values for cells exposed to 0.5mg/g of uniformly dispersed NPs with a radius of 10nm made of Fe, I, Gd, Hf, Pt and Au and irradiated with X-rays of energies 20keV higher than the element K-shell binding energy.

Cost-Effectiveness Analysis of Afatinib versus Gefitinib for First-Line Treatment of Advanced EGFR-Mutated Advanced Non-Small Cell Lung Cancers.

INTRODUCTION: The irreversible ErbB family blocker afatinib and the reversible EGFR tyrosine kinase inhibitor gefitinib were compared in the multicenter, international, randomized, head-to-head phase 2b LUX-Lung 7 trial for first-line treatment of advanced EGFR mutation-positive NSCLCs. Afatinib and gefitinib costs and patients' outcomes in France were assessed. METHODS: A partitioned survival model was designed to assess the cost-effectiveness of afatinib versus gefitinib for EGFR mutation-positive NSCLCs. Outcomes and safety were taken primarily from the LUX-Lung 7 trial. Resource use and utilities were derived from that trial, an expert-panel questionnaire, and published literature, limiting expenditures to direct costs. Incremental cost-effectiveness ratios (ICERs) were calculated over a 10-year time horizon for the entire population, and EGFR exon 19 deletion or exon 21 L858R mutation (L858R) subgroups. Deterministic and probabilistic sensitivity analyses were conducted. RESULTS: For all EGFR mutation-positive NSCLCs, the afatinib-versus-gefitinib ICER of was €45,211 per quality-adjusted life-year (QALY) (0.170 QALY gain for an incremental cost of €7697). ICERs for EGFR exon 19 deletion and L858R populations were €38,970 and €52,518, respectively. Afatinib had 100% probability to be cost-effective at a willingness-to-pay threshold of €70,000/QALY for patients with common EGFR mutations. CONCLUSION: First-line afatinib appears cost-effective compared with gefitinib for patients with EGFR mutation-positive NSCLCs.

Roadmap to Clinical Use of Gold Nanoparticles for Radiation Sensitization.

The past decade has seen a dramatic increase in interest in the use of gold nanoparticles (GNPs) as radiation sensitizers for radiation therapy. This interest was initially driven by their strong absorption of ionizing radiation and the resulting ability to increase dose deposited within target volumes even at relatively low concentrations. These early observations are supported by extensive experimental validation, showing GNPs' efficacy at sensitizing tumors in both in vitro and in vivo systems to a range of types of ionizing radiation, including kilovoltage and megavoltage X rays as well as charged particles. Despite this experimental validation, there has been limited translation of GNP-mediated radiation sensitization to a clinical setting. One of the key challenges in this area is the wide range of experimental systems that have been investigated, spanning a range of particle sizes, shapes, and preparations. As a result, mechanisms of uptake and radiation sensitization have remained difficult to clearly identify. This has proven a significant impediment to the identification of optimal GNP formulations which strike a balance among their radiation sensitizing properties, their specificity to the tumors, their biocompatibility, and their imageability in vivo. This white paper reviews the current state of knowledge in each of the areas concerning the use of GNPs as radiosensitizers, and outlines the steps which will be required to advance GNP-enhanced radiation therapy from their current pre-clinical setting to clinical trials and eventual routine usage.

Comparing gold nano-particle enhanced radiotherapy with protons, megavoltage photons and kilovoltage photons: a Monte Carlo simulation.

Gold nanoparticles (GNPs) have shown potential to be used as a radiosensitizer for radiation therapy. Despite extensive research activity to study GNP radiosensitization using photon beams, only a few studies have been carried out using proton beams. In this work Monte Carlo simulations were used to assess the dose enhancement of GNPs for proton therapy. The enhancement effect was compared between a clinical proton spectrum, a clinical 6 MV photon spectrum, and a kilovoltage photon source similar to those used in many radiobiology lab settings. We showed that the mechanism by which GNPs can lead to dose enhancements in radiation therapy differs when comparing photon and proton radiation. The GNP dose enhancement using protons can be up to 14 and is independent of proton energy, while the dose enhancement is highly dependent on the photon energy used. For the same amount of energy absorbed in the GNP, interactions with protons, kVp photons and MV photons produce similar doses within several nanometers of the GNP surface, and differences are below 15% for the first 10 nm. However, secondary electrons produced by kilovoltage photons have the longest range in water as compared to protons and MV photons, e.g. they cause a dose enhancement 20 times higher than the one caused by protons 10 µm away from the GNP surface. We conclude that GNPs have the potential to enhance radiation therapy depending on the type of radiation source. Proton therapy can be enhanced significantly only if the GNPs are in close proximity to the biological target.

Monte Carlo study of radiation dose enhancement by gadolinium in megavoltage and high dose rate radiotherapy.

MRI is often used in tumor localization for radiotherapy treatment planning, with gadolinium (Gd)-containing materials often introduced as a contrast agent. Motexafin gadolinium is a novel radiosensitizer currently being studied in clinical trials. The nanoparticle technologies can target tumors with high concentration of high-Z materials. This Monte Carlo study is the first detailed quantitative investigation of high-Z material Gd-induced dose enhancement in megavoltage external beam photon therapy. BEAMnrc, a radiotherapy Monte Carlo simulation package, was used to calculate dose enhancement as a function of Gd concentration. Published phase space files for the TrueBeam flattening filter free (FFF) and conventional flattened 6MV photon beams were used. High dose rate (HDR) brachytherapy with Ir-192 source was also investigated as a reference. The energy spectra difference caused a dose enhancement difference between the two beams. Since the Ir-192 photons have lower energy yet, the photoelectric effect in the presence of Gd leads to even higher dose enhancement in HDR. At depth of 1.8 cm, the percent mean dose enhancement for the FFF beam was 0.38±0.12, 1.39±0.21, 2.51±0.34, 3.59±0.26, and 4.59±0.34 for Gd concentrations of 1, 5, 10, 15, and 20 mg/mL, respectively. The corresponding values for the flattened beam were 0.09±0.14, 0.50±0.28, 1.19±0.29, 1.68±0.39, and 2.34±0.24. For Ir-192 with direct contact, the enhanced were 0.50±0.14, 2.79±0.17, 5.49±0.12, 8.19±0.14, and 10.80±0.13. Gd-containing materials used in MRI as contrast agents can also potentially serve as radiosensitizers in radiotherapy. This study demonstrates that Gd can be used to enhance radiation dose in target volumes not only in HDR brachytherapy, but also in 6 MV FFF external beam radiotherapy, but higher than the currently used clinical concentration (>5 mg/mL) would be needed.

Assessment of the radiation-equivalent of chemotherapy contributions in 1-phase radio-chemotherapy treatment of muscle-invasive bladder cancer.

PURPOSE: To estimate the radiation equivalent of the chemotherapy contribution to observed complete response rates in published results of 1-phase radio-chemotherapy of muscle-invasive bladder cancer. METHODS AND MATERIALS: A standard logistic dose-response curve was fitted to data from radiation therapy-alone trials and then used as the platform from which to quantify the chemotherapy contribution in 1-phase radio-chemotherapy trials. Two possible mechanisms of chemotherapy effect were assumed (1) a fixed radiation-independent contribution to local control; or (2) a fixed degree of chemotherapy-induced radiosensitization. A combination of both mechanisms was also considered. RESULTS: The respective best-fit values of the independent chemotherapy-induced complete response (CCR) and radiosensitization (s) coefficients were 0.40 (95% confidence interval -0.07 to 0.87) and 1.30 (95% confidence interval 0.86-1.70). Independent chemotherapy effect was slightly favored by the analysis, and the derived CCR value was consistent with reports of pathologic complete response rates seen in neoadjuvant chemotherapy-alone treatments of muscle-invasive bladder cancer. The radiation equivalent of the CCR was 36.3 Gy. CONCLUSION: Although the data points in the analyzed radio-chemotherapy studies are widely dispersed (largely on account of the diverse range of chemotherapy schedules used), it is nonetheless possible to fit plausible-looking response curves. The methodology used here is based on a standard technique for analyzing dose-response in radiation therapy-alone studies and is capable of application to other mixed-modality treatment combinations involving radiation therapy.

Investigation of the diffusion abnormality index as a new imaging biomarker for early assessment of brain tumor response to radiation therapy.

BACKGROUND: Diffusion MRI, although having the potential to be a biomarker for early assessment of tumor response to therapy, could be confounded by edema and necrosis in or near the brain tumors. This study aimed to develop and investigate the ability of the diffusion abnormality index (DAI) to be a new imaging biomarker for early assessment of brain metastasis response to radiation therapy (RT). METHODS: Patients with either radiosensitive or radioresistant brain metastases that were treated by whole brain RT alone or combined with bortezomib as a radiation sensitizer had diffusion-weighted (DW) MRI pre-RT and 2 weeks (2W) after starting RT. A patient-specific diffusion abnormality probability function (DAProF) was created to account for abnormal low and high apparent diffusion coefficients differently, reflecting respective high cellularity and edema/necrosis. The DAI of a lesion was then calculated by the integral of DAProF-weighted tumor apparent diffusion coefficient histogram. The changes in DAI from pre-RT to 2W were evaluated for differentiating the responsive, stable, and progressive tumors and compared with the changes in gross tumor volume and conventional diffusion metrics during the same time interval. RESULTS: In lesions treated with whole brain RT, the DAI performed the best among all metrics in predicting the posttreatment response of brain metastases to RT. In lesions treated with whole brain RT + bortezomib, although DAI was the best predictor, the performance of all metrics worsened compared with the first group. CONCLUSIONS: The ability of DAI for early assessment of brain metastasis response to RT depends upon treatment regimes.

Opportunities and challenges in the era of molecularly targeted agents and radiation therapy.

The first annual workshop for preclinical and clinical development of radiosensitizers took place at the National Cancer Institute on August 8-9, 2012. Radiotherapy is one of the most commonly applied and effective oncologic treatments for solid tumors. It is well recognized that improved clinical efficacy of radiotherapy would make a substantive impact in clinical practice and patient outcomes. Advances in genomic technologies and high-throughput drug discovery platforms have brought a revolution in cancer treatment by providing molecularly targeted agents for various cancers. Development of predictive biomarkers directed toward specific subsets of cancers has ushered in a new era of personalized therapeutics. The field of radiation oncology stands to gain substantial benefit from these advances given the concerted effort to integrate this progress into radiation therapy. This workshop brought together expert clinicians and scientists working in various disease sites to identify the exciting opportunities and expected challenges in the development of molecularly targeted agents in combination with radiation therapy.

Pemetrexed for the first-line treatment of locally advanced or metastatic non-small cell lung cancer.

This paper presents a summary of the evidence review group (ERG) report into the clinical effectiveness and cost-effectiveness of pemetrexed for the first-line treatment of locally advanced or metastatic non-small cell lung cancer (NSCLC), in accordance with the licensed indication, based upon the evidence submission from Eli Lilly Ltd to the National Institute for Health and Clinical Excellence (NICE) as part of the single technology appraisal process. The majority of the efficacy evidence described in the manufacturer's submission is derived from a phase III open-label randomised controlled trial (RCT) known as the JMDB trial. The trial achieved its primary objective to demonstrate non-inferiority of pemetrexed/cisplatin to gemcitabine/cisplatin for overall survival in all patients with NSCLC. Because no other studies were found comparing pemetrexed/cisplatin with any other relevant comparator, additional efficacy evidence was presented from two phase III RCTs comparing gemcitabine/cisplatin with gemcitabine/carboplatin and docetaxel/cisplatin. The manufacturer's submission reported from its indirect comparisons' analysis that median overall survival and progression-free survival and tumour response rates were more favourable for pemetrexed/cisplatin than for any other comparator. The manufacturer did not identify any published cost-effectiveness analyses of pemetrexed for the first-line treatment of patients with NSCLC. Therefore economic evidence was derived solely from a de novo economic model developed by the manufacturer. A Markov model was developed to evaluate the cost-effectiveness of pemetrexed/cisplatin compared to gemcitabine/cisplatin, docetaxel/cisplatin and gemcitabine/carboplatin. The clinical data used in the economic evaluation were primarily generated from the JMDB trial, with additional data from the two further trials used in the indirect comparisons analysis. The ERG identified a series of problems with this economic model. As a result, three different versions of the model were submitted to NICE and considered by the ERG. The ICERs estimated by this final version of the model ranged from 8056 pounds to 33,065 pounds per QALY, depending on the comparator, the population and the application of a continuation rule. The ERG considered that the model required extensive modification and redesign, and should be subjected to thorough validation against the JMDB trial results. A full quality audit was also required as it was likely that further model inconsistencies may be present that had not yet been identified. The manufacturer subsequently included evidence in the form of three cost effectiveness analyses (two models and an 'in-trial' analysis), stating that a thorough validation process had been followed according to the NICE request. The very short time available to the ERG to consider the new evidence precluded a comprehensive assessment. Instead, the ERG chose to present a simple exploratory analysis combining its own survival projections with key cost estimates obtained from the JMDB trial individual patient data. Compared to gemcitabine, this resulted in ICERs ranging from 17,162 pounds to 30,142 pounds per QALY, depending on the patient population, the maximum number of cycles of chemotherapy and whether a cycle based efficacy adjustment was applied or not. The guidance issued by NICE in September 2009 states that pemetrexed in combination with cisplatin is recommended as an option for the first-line treatment of patients with locally advanced or metastatic NSCLC only if the histology of the tumour has been confirmed as adenocarcinoma or large-cell carcinoma.

Topotecan for the treatment of recurrent and stage IVB carcinoma of the cervix.

This paper presents a summary of the evidence review group (ERG) report into the clinical effectiveness and cost-effectiveness of topotecan in combination with cisplatin for the treatment of recurrent and stage IVB carcinoma of the cervix, in accordance with the licensed indication, based upon the evidence submission from the manufacturer to the National Institute for Health and Clinical Excellence (NICE) as part of the single technology appraisal (STA) process. The outcomes measured were overall survival, progression-free survival, response rates, adverse effects of treatment, health-related quality of life (HRQoL) and quality-adjusted life-years (QALYs) gained. The manufacturer stated that topotecan plus cisplatin is the only combination regimen to date to have demonstrated a statistically significant survival advantage compared to cisplatin monotherapy in the licensed population. The clinical evidence came from three clinical trials comparing topotecan plus cisplatin with cisplatin monotherapy (GOG-0179), topotecan plus cisplatin with paclitaxel plus cisplatin (GOG-0169), and four cisplatin-based combination therapies: topotecan plus cisplatin, paclitaxel plus cisplatin, gemcitabine plus cisplatin, and vinorelbine plus cisplatin (GOG-0204). Results from GOG-0179 showed greater median overall survival with topotecan plus cisplatin than with cisplatin monotherapy: 9.4 months versus 6.5 months. Similar results were also reported for median progression-free survival. Response rates also showed an advantage with topotecan plus cisplatin compared with cisplatin monotherapy. The response rates in patients receiving cisplatin monotherapy were very low, but the potential reasons for this were not discussed in the manufacturer's submission. Patients receiving topotecan plus cisplatin experienced a greater number of adverse events and the ERG was concerned with some of the assumptions related to HRQoL. In the base-case direct comparison, the incremental cost-effectiveness ratio (ICER) of topotecan plus cisplatin versus cisplatin monotherapy was 17,974 pounds per QALY in the main licensed population, 10,928 pounds per QALY in the cisplatin-naive population (including stage IVB patients) and 32,463 pounds per QALY in sustained cisplatin-free interval patients. In response to the point for clarification raised by the ERG, the manufacturer submitted a revised indirect comparison incorporating HRQoL and a longer time horizon. Where the hazard ratio derived from GOG-0169 was employed, paclitaxel plus cisplatin was dominated by topotecan plus cisplatin, but, where the hazard ratio from GOG-0204 was adopted, paclitaxel plus cisplatin was found to have an ICER of 13,260 pounds per QALY versus topotecan plus cisplatin. At present there is a paucity of evidence available on the clinical effects of topotecan plus cisplatin and the effects of palliative treatment in general for women with advanced and recurrent carcinoma of the cervix. Further trials, or the implementation of registries, are required to establish the efficacy and safety of topotecan plus cisplatin. The guidance issued by NICE on 28 October 2009 as a result of the STA states that topotecan in combination with cisplatin is recommended as a treatment option for women with recurrent or stage IVB cervical cancer, only if they have not previously received cisplatin. Women who have previously received cisplatin and are currently being treated with topotecan in combination with cisplatin for the treatment of cervical cancer should have the option to continue therapy until they and their clinicians consider it appropriate to stop.

Cost utility of docetaxel as induction chemotherapy followed by chemoradiation in locally advanced squamous cell carcinoma of the head and neck.

BACKGROUND: Trial TAX 324 showed that induction chemotherapy with docetaxel plus cisplatin and 5-fluorouracil (TPF) compared with cisplatin and 5-fluorouracil (PF) followed by chemoradiation increases survival and time to progression in squamous cell carcinoma of head and neck (SCCHN). METHODS: A Markov model was developed to estimate the cost-effectiveness of induction chemotherapy with docetaxel in the United Kingdom from the payer perspective. Health states were based on the WHO criteria for objective response to cancer treatments. Efficacy and safety data were obtained from the trial. Resource utilization, costs, and utility data were primarily derived from the literature. RESULTS: A patient on TPF gained 4.1 quality adjusted life years (QALYs) versus 2.0 QALYs for PF patient. Corresponding lifetime costs were pound 32,440 and pound 28,718. The cost per QALY gained for TPF versus PF was pound 1782. CONCLUSIONS: TPF is cost-effective as induction chemotherapy in locally advanced SCCHN compared with PF. Local treatment patterns may impact findings for other countries.

Progress in the use of gadolinium for NCT.

The evaluation of possible improvement in the use of Gd in cancer therapy, in reference to gadolinium in cancer therapy (GdNCT), has been analysed. At first the problem of the gadolinium compounds toxicity was reviewed identifying the Motexafin Gadolinium as the best. Afterwards, the spectrum of IC and Auger electrons was calculated using a special method. Afterwards, this electron source has been used as input of the PENELOPE code and the energy deposit in DNA was well defined. Taking into account that the electron yield and energy distribution are related to the neutron beam spectrum and intensity, the shaping assembly architecture was optimised through computational investigations. Finally the study of GdNCT was performed from two different points of view: macrodosimetry using MCNPX, with calculation of absorbed doses both in tumour and healthy tissues, and microdosimetry using PENELOPE, with the determination of electron RBE through the energy deposit. The equivalent doses were determined combining these two kinds of data, introducing specific figures of merit to be used in treatment planning system (TPS). According to these results, the GdNCT appears to be a fairly possible tumour therapy.

In vitro neutron irradiation of glioma and endothelial cultured cells.

To fully develop its potential boron neutron capture therapy (BNCT) requires the combination of a suitable thermal/epithermal neutron flux together with a selective intake of (10)B-boron nuclei in the target tissue. The latter condition is the most critical to be realized as none of the boron carriers used for experimental or clinical purposes proved at the moment an optimal selectivity for cancer cells compared to normal cells. In addition to complex physical factors, the assessment of the intracellular concentration of boron represent a crucial parameter to predict the dose delivered to the cancer cells during the treatment. Nowadays the dosimetry calculation and then the prediction of the treatment effectiveness are made using Monte Carlo simulations, but some of the model assumption are still uncertain: the radiobiological dose efficacy and the probability of tumour cell survival are crucial parameters that needs a more reliable experimental approach. The aim of this work was to evaluate the differential ability of two cell lines to selectively concentrate the boron-10 administered as di-hydroxyboryl-phenylalanine (BPA)-fructose adduct, and the effect of the differential boron intake on the damage produced by the irradiation with thermal neutrons; the two cell lines were selected to be representative one of normal tissues involved in the active/passive transport of boron carriers, and one of the tumour. Recent in vitro studies demonstrated how BPA is taken by proliferating cells, however the mechanism of BPA uptake and the parameters driving the kinetics of influx and the elimination of BPA are still not clarified. In these preliminary studies we analysed the survival of F98 and human umbilical vein endothelial cells (HUVEC) cells line after irradiation, using different thermal fluencies at the same level of density population and boron concentration in the growing medium prior the irradiation. This is first study performed on endothelium model obtained by a primary human cell line (HUVEC). The perspective application of this work is to develop a model able to foresee the effects produced by different combination of boron influx with a thermal neutron fluencies, applying a standardized radiobiological methodology, and in particular to continue the investigation of the radiobiological effects on the endothelium model as the main tissue involved in the transport of boronated molecules.

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.

Monte Carlo modelling of the influence of boron microdistribution on BNCT microdosimetry.

The ion transport Monte Carlo code SRIM has been used to calculate single event lineal energy spectra for the products of the boron-neutron capture reaction in a water-based medium. The event spectra have been benchmarked against spectra measured with a boron-loaded tissue-equivalent proportional counter (TEPC). Agreement is excellent and supports the use of Monte Carlo methods in understanding the influence of boron delivery on the effectiveness of boron-neutron capture therapy (BNCT).

A detailed Monte Carlo accounting of radiation transport in the brain during BNCT.

The collision type central to BNCT is (10)B(n, alpha)(7)Li, however, other types of nuclear reactions also take place in the patient. In addition to the major elements (H, C, N, O), minor elements such as Na, Mg, P, S, Cl, K, Ca and Fe present in body tissues also interact in neutron collisions. Detailed accounting of the above not only provides a better understanding of radiation transport in the human body during BNCT, but such knowledge affects the design of the facility, as well as treatment planning, imaging and verification for a given BNCT agent. Of the methods of investigation currently available, only Monte Carlo simulation could provide the detailed accounting and breakdown of the quantities required. We report Monte Carlo simulation of an anthropomorphic voxel phantom, the VIP-Man and show how these quantities change with different (10)B concentrations in the tumour, the blood and the remaining tissues. The (10)B biodistribution has been chosen to be the variable of interest, since it is not accurately known, is frequently approximated and is a crucial quantity upon which dose calculations are based.