Uptake of 4-borono-2-[18F]fluoro-L-phenylalanine in sporadic and neurofibromatosis 2-related schwannoma and meningioma studied with PET

A bis-boron boramino acid PET tracer for brain tumor diagnosis

PURPOSE

Boramino acids are a class of amino acid biomimics that replace the carboxylate group with trifluoroborate and can achieve the 18F-labeled positron emission tomography (PET) and boron neutron capture therapy (BNCT) with identical chemical structure.

METHODS

This study reports a trifluoroborate-derived boronophenylalanine (BBPA), a derived boronophenylalanine (BPA) for BNCT, as a promising PET tracer for tumor imaging.

RESULTS

Competition inhibition assays in cancer cells suggested the cell accumulation of [18F]BBPA is through large neutral amino acid transporter type-1 (LAT-1). Of note, [18F]BBPA is a pan-cancer probe that shows notable tumor uptake in B16-F10 tumor-bearing mice. In the patients with gliomas and metastatic brain tumors, [18F]BBPA-PET shows good tumor uptake and notable tumor-to-normal brain ratio (T/N ratio, 18.7 ± 5.5, n = 11), higher than common amino acid PET tracers. The [18F]BBPA-PET quantitative parameters exhibited no difference in diverse contrast-enhanced status (P = 0.115-0.687) suggesting the [18F]BBPA uptake was independent from MRI contrast-enhancement.

CONCLUSION

This study outlines a clinical trial with [18F]BBPA to achieve higher tumor-specific accumulation for PET, provides a potential technique for brain tumor diagnosis, and might facilitate the BNCT of brain tumors.

Comparison of the synthesis and biological properties of no-carrier-added and carrier-added 4-borono-2-[18F]fluorophenylalanine ([18F]FBPA)

PURPOSE

Boron neutron capture therapy (BNCT), an attractive strategy for cancer treatment, can kill tumor cells and avoid injury to surrounding healthy cells. 4-Borono-2-[¹⁸F]fluorophenylalanine ([¹⁸F]FBPA) positron emission tomography (PET) is a reliable tool for patient screening. Due to the relatively low radiochemical yield when employing the electrophilic route, this study was able to develop a new method to produce no-carrier-added (NCA) [¹⁸F]FBPA and compare the biological characteristics with carrier-added (CA) characteristics.

PROCEDURES

By starting from 4-bromo-2-nitrobenzaldehyde, NCA [¹⁸F]FBPA was prepared using radiofluorination, alkylation, borylation, and hydrolysis. Cellular uptake analyses, microPET imaging, and biodistribution analyses were conducted to characterize the biological properties of NCA and CA [¹⁸F]FBPA.

RESULTS

The radiochemical yield of NCA [¹⁸F]FBPA was 20 % ± 6 % (decay corrected) with a radiochemical purity of >98 % and molar activity of 56 ± 15 GBq/μmol in a 100-min synthesis. The in vitro accumulation was significantly higher for NCA [¹⁸F]FBPA than for CA [¹⁸F]FBPA in both SAS and CT-26 cells. However, no apparent differences in tumor uptake were observed between NCA and CA [¹⁸F]FBPA-injected tumor-bearing mice.

CONCLUSIONS

We successfully prepared NCA [¹⁸F]FBPA through nucleophilic substitution and achieved improved radiochemical yield and purity. We also demonstrated the effects of the amount of nonradioactive FBPA on in vitro cellular uptake and in vivo imaging studies.

Improved Stability and Practicality for Synthesis of 4-Borono-2-[18F]fluoro-l-phenylalanine by Combination of [18O]O2 Single-Use and [18F]CH3COOF Labeling Agents

Purpose

4-Borono-2-[¹⁸F]fluoro-l-phenylalanine ([¹⁸F]FBPA) synthesized with [¹⁸F]F₂, produced using the ¹⁸O(p, n)¹⁸F reaction, has been reported for increasing radioactivity. However, a dedicated system and complex procedure is required to reuse the costly [¹⁸O]O₂ gas; also, the use of [¹⁸F]F₂ as a labeling agent reduces the labeling rate and radiochemical purity. We developed a stable and practical method for [¹⁸F]FBPA synthesis by combining [¹⁸F]F₂, produced using a [¹⁸O]O₂ single-use system, and a [¹⁸F]CH₃COOF labeling agent.

Methods

The produced [¹⁸F]F₂ was optimized, and then [¹⁸F]FBPA was synthesized. For passivation of the target box, 0.5% F₂ was pre-irradiated in argon. Gaseous products were discarded; the target box was filled with [¹⁸O]O₂ gas, and then irradiated (first irradiation). Then, the [¹⁸O]O₂ gas was discarded, 0.05–0.08% F₂ in argon was fed into the target box, and it was again irradiated (second irradiation). The [¹⁸F]F₂ obtained after this was passed through a CH₃COONa column, converting it into the [¹⁸F]CH₃COOF labeling agent, which was then used for [¹⁸F]FBPA synthesis.

Results

The mean amount of as-obtained [¹⁸F]F₂ was 55.0 ± 3.3 GBq and that of as-obtained [¹⁸F]CH₃COOF was 21.6 ± 1.4 GBq after the bombardment. The radioactivity and the radiochemical yield based on [¹⁸F]F₂ of [¹⁸F]FBPA were 4.72 ± 0.34 GBq and 12.2 ± 0.1%, respectively. The radiochemical purity and molar activity were 99.3 ± 0.1% and 231 ± 22 GBq/mmol, respectively.

Conclusion

We developed a method for [¹⁸F]FBPA production, which is more stable and practical compared with the method using [¹⁸O]O₂ gas-recycling and [¹⁸F]F₂ labeling agent.

Theranostics in Boron Neutron Capture Therapy

Boron neutron capture therapy (BNCT) has the potential to specifically destroy tumor cells without damaging the tissues infiltrated by the tumor. BNCT is a binary treatment method based on the combination of two agents that have no effect when applied individually: ¹⁰B and thermal neutrons. Exclusively, the combination of both produces an effect, whose extent depends on the amount of ¹⁰B in the tumor but also on the organs at risk. It is not yet possible to determine the ¹⁰B concentration in a specific tissue using non-invasive methods. At present, it is only possible to measure the ¹⁰B concentration in blood and to estimate the boron concentration in tissues based on the assumption that there is a fixed uptake of ¹⁰B from the blood into tissues. On this imprecise assumption, BNCT can hardly be developed further. A therapeutic approach, combining the boron carrier for therapeutic purposes with an imaging tool, might allow us to determine the ¹⁰B concentration in a specific tissue using a non-invasive method. This review provides an overview of the current clinical protocols and preclinical experiments and results on how innovative drug development for boron delivery systems can also incorporate concurrent imaging. The last section focuses on the importance of proteomics for further optimization of BNCT, a highly precise and personalized therapeutic approach.

Boron Neutron Capture Therapy and Photodynamic Therapy for High-Grade Meningiomas

Meningiomas are the most common type of intracranial brain tumors in adults. The majority of meningiomas are benign with a low risk of recurrence after resection. However, meningiomas defined as grades II or III, according to the 2016 World Health Organization (WHO) classification, termed high-grade meningiomas, frequently recur, even after gross total resection with or without adjuvant radiotherapy. Boron neutron capture therapy (BNCT) and photodynamic therapy (PDT) are novel treatment modalities for malignant brain tumors, represented by glioblastomas. Although BNCT is based on a nuclear reaction and PDT uses a photochemical reaction, both of these therapies result in cellular damage to only the tumor cells. The aim of this literature review is to investigate the possibility and efficacy of BNCT and PDT as novel treatment modalities for high-grade meningiomas. The present review was conducted by searching PubMed and Scopus databases. The search was conducted in December 2019. Early clinical studies of BNCT have demonstrated activity for high-grade meningiomas, and a phase II clinical trial is in progress in Japan. As for PDT, studies have investigated the effect of PDT in malignant meningioma cell lines to establish PDT as a treatment for malignant meningiomas. Further laboratory research combined with proper controlled trials investigating the effects of these therapies is warranted.

4-Borono-2-18F-fluoro-L-phenylalanine PET for boron neutron capture therapy-oriented diagnosis: overview of a quarter century of research

4-¹⁰B-Borono-2-¹⁸F-fluoro-L-phenylalanine (¹⁸F-FBPA) was developed for monitoring the pharmacokinetics of 4-¹⁰B-borono-L-phenylalanine (¹⁰B-BPA) used in boron neutron capture therapy (BNCT) with positron emission tomography (PET). The tumor-imaging potential of ¹⁸F-FBPA was demonstrated in various animal models. Accumulation of ¹⁸F-FBPA was higher in melanomas than in non-melanoma tumors in animal models and cell cultures. ¹⁸F-FBPA was incorporated into tumors mediated mainly by L-type amino acid transporters in in vitro and in vivo models. Tumoral distribution of ¹⁸F-FBPA was primarily related to the activity of DNA synthesis. ¹⁸F-FBPA is metabolically stable but is incorporated into melanogenesis non-enzymatically. These in vitro and in vivo characteristics of ¹⁸F-FBPA corresponded well to those of ¹⁰B-BPA. Nuclear magnetic resonance and other studies using non-radioactive ¹⁹F-^10/11B-FBPA also contributed to characterization. The validity and reliability of ^18/19F-FBPA as an in vivo probe of ¹⁰B-BPA were confirmed by comparison of the pharmacokinetics of ¹⁸F-FBPA and ¹⁰B-BPA and direct measurement of both ¹⁸F and ¹⁰B in tumors with various doses of both probes administered by different routes and methods. Clinically, based on the kinetic parameters of dynamic ¹⁸F-FBPA PET, the estimated ¹⁰B-concentrations in tumors with continuous ¹⁰B-BPA infusion were similar to those measured directly in surgical specimens. The significance of ¹⁸F-FBPA PET was verified for the estimation of ¹⁰B-concentration and planning of BNCT. Later ¹⁸F-FBPA PET has been involved in ¹⁰B-BPA BNCT of patients with intractable tumors such as malignant brain tumors, head and neck tumors, and melanoma. Usually a static PET scan is used for screening patients for BNCT, prediction of the distribution and accumulation of ¹⁰B-BPA, and evaluation of treatment after BNCT. In some clinical trials, a tumor-to-normal tissue ratio of ¹⁸F-FBPA > 2.5 was an inclusion criterion for BNCT. Apart from BNCT, ¹⁸F-FBPA was demonstrated to be a useful PET probe for tumor diagnosis in nuclear medicine: better tumor-to-normal brain contrast compared with ¹¹C-methionine, differentiation of recurrent and radiation necrosis after radiotherapy, and melanoma-preferential uptake. Further progress in ¹⁸F-FBPA studies is expected for more elaborate evaluation of ¹⁰B-concentrations in tumors and normal tissues for successful ¹⁰B-BPA BNCT and for radiosynthesis of ¹⁸F-FBPA to enable higher ¹⁸F-activity amounts and higher molar activities.

Evaluation of the most commonly used (semi-)quantitative parameters of 18F-FDG PET/CT to detect malignant transformation of neurofibromas in neurofibromatosis type 1

In patients with neurofibromatosis type 1, transformation of neurofibromas into a malignant peripheral nerve sheath tumor (MPNST) is a severe complication of the disease. Fluorine-18-fluorodeoxyglucose PET/computed tomography (PET/CT) is a viable option for detecting malignant tumors in neurofibromatosis type 1 patients. The aim of this review was to assess the diagnostic performance of the most frequently used parameters of PET/CT in detecting MPNST. An extensive computer search was performed using the Cochrane Library, Pubmed, and Medline/Embase databases. Two reviewers independently extracted data of relevant studies and assessed the methodological quality (QUADAS-2). The diagnostic performance of PET/CT parameters in individual studies was determined by calculating a diagnostic odds ratio (DOR) using the absolute numbers of true-positive, true-negative, false-positive, and false-negative test results. A total of eight studies were included, of which three evaluated the standardized uptake value as a diagnostic parameter, two assessed the tumor-to-liver (T/L) ratio, and three articles described both parameters. The cut-off values for maximum standardized uptake value (SUVmax) ranged from 3.2 to 4.5; for the T/L ratio, the cut-off values were between 1.0 and 4.3. The sensitivity and specificity ranged from 90 to 100% and from 80 to 100%, respectively (SUVmax). T/L ratios were associated with 92-100% sensitivity and 72-94% specificity. The corresponding DORs ranged from 57 to 145 (SUVmax) and 35 to 655 (T/L ratio). Both the SUV and the T/L ratio are associated with high sensitivity combined with acceptable specificity in detecting MPNST. There is a tendency toward higher DORs using the T/L ratio, but the number of studies is limited.

Reliable radiosynthesis of 4-[10B]borono-2-[18F]fluoro-L-phenylalanine with quality assurance for boron neutron capture therapy-oriented diagnosis

Objective

The aim of this study was to establish a reliable and routine method for the preparation of 4-[¹⁰B]borono-2-[¹⁸F]fluoro-l-phenylalanine (l-[¹⁸F]FBPA) for boron neutron capture therapy-oriented diagnosis using positron emission tomography.

Methods

To produce l-[¹⁸F]FBPA by electrophilic fluorination of 4-[¹⁰B]borono-l-phenylalanine (l-BPA) with [¹⁸F]acetylhypofluorite ([¹⁸F]AcOF) via [¹⁸F]F₂ derived from the ²⁰Ne(d,α)¹⁸F nuclear reaction, several preparation parameters and characteristics of l-[¹⁸F]FBPA were investigated, including: pre-irradiation for [¹⁸F]F₂ production, the carrier F₂ content in the Ne target, l-BPA-to-F₂ ratios, separation with high-performance liquid chromatography (HPLC) using 10 different eluents, enantiomeric purity, and residual trifluoroacetic acid used as the reaction solvent by gas chromatography-mass spectrometry.

Results

The activity yields and molar activities of l-[¹⁸F]FBPA (n = 38) were 1200 ± 160 MBq and 46–113 GBq/mmol, respectively, after deuteron-irradiation for 2 h. Two 5 min pre-irradiations prior to [¹⁸F]F₂ production for ¹⁸F-labeling were preferable. For l-[¹⁸F]FBPA synthesis, 0.15–0.2% of carrier F₂ in Ne and l-BPA-to-F₂ ratios > 2 were preferable. HPLC separations with five of the 10 eluents provided injectable l-[¹⁸F]FBPA without any further formulation processing, which resulted in a synthesis time of 32 min. Among the five eluents, 1 mM phosphate-buffered saline was the eluent of choice. The l-[¹⁸F]FBPA injection was sterile and pyrogen-free, and contained very small amounts of D-enantiomer (< 0.1% of l-[¹⁸F]FBPA), l-BPA (< 1% of l-FBPA), and trifluoroacetic acid (< 0.5 ppm).

Conclusions

l-[¹⁸F]FBPA injection was reliably prepared by the electrophilic fluorination of l-BPA with [¹⁸F]AcOF followed by HPLC separation with 1 mM phosphate-buffered saline.

Non-invasive estimation of 10 B-4-borono-L-phenylalanine-derived boron concentration in tumors by PET using 4-borono-2-18 F-fluoro-phenylalanine

In boron neutron capture therapy (BNCT), 10 B-4-borono-L-phenylalanine (BPA) is commonly used as a 10 B carrier. PET using 4-borono-2-18 F-fluoro-phenylalanine (18 F-FBPA PET) has been performed to estimate boron concentration and predict the therapeutic effects of BNCT; however, the association between tumor uptake of 18 F-FBPA and boron concentration in tumors remains unclear. The present study investigated the transport mechanism of 18 F-FBPA and BPA, and evaluated the utility of 18 F-FBPA PET in predicting boron concentration in tumors. The transporter assay revealed that 2-aminobicyclo-(2.2.1)-heptane-2-carboxylic acid, an inhibitor of the L-type amino acid transporter, significantly inhibited 18 F-FBPA and 14 C-4-borono-L-phenylalanine (14 C-BPA) uptake in FaDu and LN-229 human cancer cells. 18 F-FBPA uptake strongly correlated with 14 C-BPA uptake in 7 human tumor cell lines (r = .93; P < .01). PET experiments demonstrated that tumor uptake of 18 F-FBPA was independent of the administration method, and uptake of 18 F-FBPA by bolus injection correlated well with BPA uptake by continuous intravenous infusion. The results of this study revealed that evaluating tumor uptake of 18 F-FBPA by PET was useful for estimating 10 B concentration in tumors.

Carbon-11 and Fluorine-18 Labeled Amino Acid Tracers for Positron Emission Tomography Imaging of Tumors

Tumor cells have an increased nutritional demand for amino acids (AAs) to satisfy their rapid proliferation. Positron-emitting nuclide labeled AAs are interesting probes and are of great importance for imaging tumors using positron emission tomography (PET). Carbon-11 and fluorine-18 labeled AAs include the [1-¹¹C] AAs, labeling alpha-C- AAs, the branched-chain of AAs and N-substituted carbon-11 labeled AAs. These tracers target protein synthesis or amino acid (AA) transport, and their uptake mechanism mainly involves AA transport. AA PET tracers have been widely used in clinical settings to image brain tumors, neuroendocrine tumors, prostate cancer, breast cancer, non-small cell lung cancer (NSCLC) and hepatocellular carcinoma. This review focuses on the fundamental concepts and the uptake mechanism of AAs, AA PET tracers and their clinical applications.

Influence of fluorine substituents on the properties of phenylboronic compounds

Rapid development of research on the chemistry of boronic acids is connected with their applications in organic synthesis, analytical chemistry, materials’ chemistry, biology and medicine. In many applications Lewis acidity of boron atoms plays an important role. Special group of arylboronic acids are fluoro-substituted compounds, in which the electron withdrawing character of fluorine atoms influences their properties. The present paper deals with fluoro-substituted boronic acids and their derivatives: esters, benzoxaboroles and boroxines. Properties of these compounds, i.e. acidity, hydrolytic stability, structures in crystals and in solution as well as spectroscopic properties are discussed. In the next part examples of important applications are given.

Boron neutron capture therapy and 18F-labelled borophenylalanine positron emission tomography: a critical and clinical overview of the literature

Positron emission tomography (PET) is considered one of the most useful tool for molecular imaging both in clinical and preclinical research for in vivo assessing of biochemical and pharmacological processes. Boron neutron capture therapy (BNCT) is a biologically-targeted radiotherapy that can selectively hit the tumour cells, saving the surrounding normal tissue. Boron 10 ((10)B) is the isotope widely used for this purpose, and acts as killer for tumor cells, releasing highly reactive α and (7)Li-particles when it absorbs a thermal neutron. The basic requirements for a successful BNCT treatment are firstly that the boron-containing compound/material has to be delivered to the neoplastic tissue, and secondly the amount of boron atoms concentrated inside/around the cancer cells must be sufficient for an optimal therapeutic response. The irradiation of tissue or organ with therapeutic doses of thermal neutrons can lead to a selective, complete ablation of the malignant lesion. Specific carriers have been developed for BNCT: para-borophenylalanine (BPA), represents one of them and the most employed in clinical trials to preferentially deliver boron to the malignancy. For the in vivo examination of pharmacokinetic, accumulation and metabolism characteristics of L-B-BPA, a positron-labeled boronophenylalanine analogue, L-(18)F-(10)BPA was proposed and its pharmaco-properties were non-invasively evaluated by PET imaging. Herein, we summarize BNCT principles and applications, boron carrier and boron imaging with PET, PET-guided BNCT and other studied and employed tracers for PET in order to optimizeBNCT.

Fluorine-18-labeled boronophenylalanine positron emission tomography for oral cancers: Qualitative and quantitative analyses of malignant tumors and normal structures in oral and maxillofacial regions

The present study aimed to demonstrate the features of fluorine-18-labeled boronophenylalanine positron emission tomography ((18)F-BPA-PET) to reveal oral cancer, as well as normal structures in the oral and maxillofacial regions. We analyzed (18)F-BPA-PET findings from 8 patients with histologically confirmed recurrent and/or advanced oral cancer scheduled for boron neutron capture therapy. The capacity of (18)F-BPA-PET to delineate tumor and normal structures was assessed qualitatively and quantitatively. Tumors were easily identified as high uptake areas in all cases. Although the eyes, which were depicted as a low uptake area, and tongue musculature were readily identified, major vessels were not noted in any of the cases. Areas corresponding to the surface of the dorsum tongue to middle pharynx were expressed as high uptake areas in all of the cases. Quantitatively, tumors were expressed as the highest uptake area in 6 of the 8 cases, while the dorsum tongue had the highest uptake area in the remaining 2 cases. (18)F-BPA-PET is useful in demonstrating the presence of a tumor. Thus, it is crucial to note the presence of a high uptake area corresponding to the dorsum area of the tongue when diagnosing a tumor using this technique.

Intractable sciatica due to intraneural nodular fasciitis detected by positron emission tomography

STUDY DESIGN

Case report.

OBJECTIVE

To describe a patient with nodular fasciitis in the sciatic nerve, detected by positron emission tomography (PET).

SUMMARY OF BACKGROUND DATA

Severe sciatic pain is commonly caused by lumbar disc herniation, lumbar spinal stenosis, or neoplastic lesion. These lesions are usually diagnosed by plain radiograph, myelography, computed tomography, and magnetic resonance imaging.Nodular fasciitis is a benign connective tissue tumor usually presenting as a firm, rapidly-growing lesion, occasionally arising in the forearm. Only 5 cases of intraneural nodular fasciitis have been reported in the published data, and although some have demonstrated mild neuropathy, none have shown nodular fasciitis with intractable sciatica.

METHODS

A 37-year old woman experienced severe sciatica after hitting her left buttock hard on the edge of a bathtub. Physical examination demonstrated intense radiating pain from the left buttock to the lateral calf. There was weakness in the sciatic nerve innervated musculature. She was diagnosed with piriformis syndrome in a local hospital. However, the symptoms remained unchanged after surgery, releasing the piriformis. Conventional imaging of the sciatica including plain radiograph, computed tomography, and magnetic resonance imaging of the spine showed a return of abnormal findings.

RESULTS

PET detected an abnormal lesion in the sciatic nerve in the posterior compartment of the patient's left thigh, indicating an intraneural tumor in the sciatic nerve. Subtotal resection was achieved and histologic evaluation of the specimen showed the typical features of nodular fasciitis. After surgery, the patient was relieved of all symptoms, with no evidence of recurrence at the recent 2-year follow-up.

CONCLUSION

This is the first reported case of intraneural nodular fasciitis presenting with severe radiculopathy. Nodular fasciitis should be considered in the differential diagnosis of severe sciatica. PET may be a useful tool for diagnosing sciatica of unknown origin that cannot be identified using conventional imaging tools.

Positron emission tomography and [18F]BPA: a perspective application to assess tumour extraction of boron in BNCT

Positron emission tomography (PET) has become a key imaging tool in clinical practice and biomedical research to quantify and study biochemical processes in vivo. Physiologically active compounds are tagged with positron emitters (e.g. (18)F, (11)C, (124)I) while maintaining their biological properties, and are administered intravenously in tracer amounts (10(-9)-10(-12)M quantities). The recent physical integration of PET and computed tomography (CT) in hybrid PET/CT scanners allows a combined anatomical and functional imaging: nowadays PET molecular imaging is emerging as powerful pharmacological tool in oncology, neurology and for treatment planning as guidance for radiation therapy. The in vivo pharmacokinetics of boron carrier for BNCT and the quantification of (10)B in living tissue were performed by PET in the late nineties using compartmental models based on PET data. Nowadays PET and PET/CT have been used to address the issue of pharmacokinetic, metabolism and accumulation of BPA in target tissue. The added value of the use of L-[(18)F]FBPA and PET/CT in BNCT is to provide key data on the tumour extraction of (10)B-BPA versus normal tissue and to predict the efficacy of the treatment based on a single-study patient analysis. Due to the complexity of a binary treatment like BNCT, the role of PET/CT is currently to design new criteria for patient enrolment in treatment protocols: the L-[(18)F]BPA/PET methodology could be considered as an important tool in newly designed clinical trials to better estimate the concentration ratio of BPA in the tumour as compared to neighbouring normal tissues. Based on these values for individual patients the decision could be made whether BNCT treatment could be advantageous due to a selective accumulation of BPA in an individual tumour. This approach, applicable in different tumour entities like melanoma, glioblastoma and head and neck malignancies, make this methodology as reliable prognostic and therapeutic indicator for patient undergoing BNCT.

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.

Boron Neutron Capture Therapy in the Treatment of Locally Recurred Head and Neck Cancer

PURPOSE

Head and neck carcinomas that recur locally after conventional irradiation pose a difficult therapeutic problem. We evaluated safety and efficacy of boron neutron capture therapy (BNCT) in the treatment of such cancers.

METHODS AND MATERIALS

Twelve patients with inoperable, recurred, locally advanced (rT3, rT4, or rN2) head and neck cancer were treated with BNCT in a prospective, single-center Phase I-II study. Prior treatments consisted of surgery and conventionally fractionated photon irradiation to a cumulative dose of 56-74 Gy administered with or without concomitant chemotherapy. Tumor responses were assessed using the RECIST (Response Evaluation Criteria in Solid Tumors) criteria and adverse effects using the National Cancer Institute common toxicity grading v3.0. Intravenously administered boronophenylalanine-fructose (BPA-F, 400 mg/kg) was used as the boron carrier. Each patient was scheduled to be treated twice with BNCT.

RESULTS

Ten patients received BNCT twice; 2 were treated once. Ten (83%) patients responded to BNCT, and 2 (17%) had tumor growth stabilization for 5.5 and 7.6 months. The median duration of response was 12.1 months; six responses were ongoing at the time of analysis or death (range, 4.9-19.2 months). Four (33%) patients were alive without recurrence with a median follow-up of 14.0 months (range, 12.8-19.2 months). The most common acute adverse effects were mucositis, fatigue, and local pain; 2 patients had a severe (Grade 3) late adverse effect (xerostomia, 1; dysphagia, 1).

CONCLUSIONS

Boron neutron capture therapy is effective and safe in the treatment of inoperable, locally advanced head and neck carcinomas that recur at previously irradiated sites.