Boron neutron capture therapy of skin melanomas at the RA-6 reactor: A procedural approach to beam set up and performance evaluation for upcoming clinical trials

Gadolinium Neutron Capture Therapy for Cats and Dogs with Spontaneous Tumors Using Gd-DTPA

We conducted a clinical veterinary study on neutron capture therapy (NCT) at a neutron-producing accelerator with seven incurable pets with spontaneous tumors and gadolinium as a neutron capture agent (gadolinium neutron capture therapy, or GdNCT). Gadolinium-containing dimeglumine gadopentetate, or Gd-DTPA (Magnevist®, 0.6 mL/kg b.w.), was used. We observed mild and reversible toxicity related to the treatment. However, no significant tumor regression in response to the treatment was observed. In most cases, there was continued tumor growth. Overall clinical improvement after treatment was only temporary. The use of Gd-DTPA for NCT had no significant effects on the life expectancy and quality of life of animals with spontaneous tumors. Further experiments using more advanced gadolinium compounds are needed to improve the effect of GdNCT so that it can become an alternative to boron neutron capture therapy. Such studies are also necessary for further NCT implementation in clinical practice as well as in veterinary medicine.

Boron Neutron Capture Therapy: Current Status and Challenges

Boron neutron capture therapy (BNCT) is a re-emerging therapy with the ability to selectively kill tumor cells. After the boron delivery agents enter the tumor tissue and enrich the tumor cells, the thermal neutrons trigger the fission of the boron atoms, leading to the release of boron atoms and then leading to the release of the α particles (⁴He) and recoil lithium particles (⁷Li), along with the production of large amounts of energy in the narrow region. With the advantages of targeted therapy and low toxicity, BNCT has become a unique method in the field of radiotherapy. Since the beginning of the last century, BNCT has been emerging worldwide and gradually developed into a technology for the treatment of glioblastoma multiforme, head and neck cancer, malignant melanoma, and other cancers. At present, how to develop and innovate more efficient boron delivery agents and establish a more accurate boron-dose measurement system have become the problem faced by the development of BNCT. We discuss the use of boron delivery agents over the past several decades and the corresponding clinical trials and preclinical outcomes. Furthermore, the discussion brings recommendations on the future of boron delivery agents and this therapy.

Experimental studies of boron neutron capture therapy (BNCT) using histone deacetylase inhibitor (HDACI) sodium butyrate, as a complementary drug for the treatment of poorly differentiated thyroid cancer (PDTC)

PURPOSE

The present study analyzed different protocols of administration of boronophenylalanine (BPA) and sodium butyrate (NaB) to increase the BNCT efficacy for poorly differentiated thyroid cancer (PDTC).

MATERIALS AND METHODS

Nude mice implanted with human PDTC cells (WRO) were distributed into four protocols: 1) BPA; 2) BPA + ip NaB; 3) BPA + oral NaB; 4) Control. Biodistribution and histologic studies were performed. LAT (BPA transporter) isoforms gene expression was assessed by RT-PCR.

RESULTS

Tumor growth delay was observed in animals of the Protocol #3 (p < 0.05). NaB (Protocol #2) increased tumor boron uptake 2-h post BPA injection (p < 0.05). On the other hand, NaB upregulated the expression of all the isoforms of the LAT transporter in vitro. Histologic studies showed a significant decrease of mitotic activity and an increase of vacuoles in tumors of Protocol #3. Neutrons alone or combined with NaB caused some tumor growth delay (p < 0.05), while in the BNCT and BNCT + NaB groups, there was a halt in tumor growth in 70 and 80% of the animals, respectively.

CONCLUSIONS

Intraperitoneally administration of NaB increased boron uptake while oral administration for a longer period of time induced tumor growth delay previous to BPA administration. The use of NaB via ip would optimize the irradiation results.

The essential role of radiobiological figures of merit for the assessment and comparison of beam performances in boron neutron capture therapy

PURPOSE

Boron Neutron Capture Therapy (BNCT) is a treatment modality that uses an external neutron beam to selectively inactive boron10-loaded tumor cells. This work presents the development and innovative use of radiobiological probability models to adequately evaluate and compare the therapeutic potential and versatility of beams presenting different neutron energy spectra. M&M: Aforementioned characteristics, collectively refer to as the performance of a beam, were defined on the basis of radiobiological probability models for the first time in BNCT. A model of uncomplicated tumor control probability (UTCP) for HN cancer was introduced. This model considers a NTCP able to predict severe mucositis and a TCP for non-uniform doses derived herein. A systematic study comprising a simplified HN cancer model is presented as a practical application of the introduced radiobiological figures of merit (FOM) for assessing and comparing the performance of different clinical beams. Applications involving treated HN cancer patients were also analyzed.

RESULTS

The maximum UTCP proved suitable and sensitive to assess the performance of a beam, revealing particularities of the studied sources that the physical FOMs do not highlight. The radiobiological FOMs evaluated in patients showed to be useful tools both for retrospective analysis of the BNCT treatments, and for prospective studies of beam optimization and feasibility.

CONCLUSIONS

The presented developments and applications demonstrated that it is possible to assess and compare performances of completely different beams fairly and adequately by assessing the radiobiological FOM UTCP. Thus, this figure would be a practical and essential aid to guide treatment decisions.

A 13C(d,n)-based epithermal neutron source for Boron Neutron Capture Therapy

PURPOSE

Boron Neutron Capture Therapy (BNCT) requires neutron sources suitable for in-hospital siting. Low-energy particle accelerators working in conjunction with a neutron producing reaction are the most appropriate choice for this purpose. One of the possible nuclear reactions is ¹³C(d,n)¹⁴N. The aim of this work is to evaluate the therapeutic capabilities of the neutron beam produced by this reaction, through a 30mA beam of deuterons of 1.45MeV.

METHODS

A Beam Shaping Assembly design was computationally optimized. Depth dose profiles in a Snyder head phantom were simulated with the MCNP code for a number of BSA configurations. In order to optimize the treatment capabilities, the BSA configuration was determined as the one that allows maximizing both the tumor dose and the penetration depth while keeping doses to healthy tissues under the tolerance limits.

RESULTS

Significant doses to tumor tissues were achieved up to ∼6cm in depth. Peak doses up to 57Gy-Eq can be delivered in a fractionated scheme of 2 irradiations of approximately 1h each. In a single 1h irradiation, lower but still acceptable doses to tumor are also feasible.

CONCLUSIONS

Treatment capabilities obtained here are comparable to those achieved with other accelerator-based neutron sources, making of the ¹³C(d,n)¹⁴N reaction a realistic option for producing therapeutic neutron beams through a low-energy particle accelerator.

Antitumor potential induction and free radicals production in melanoma cells by Boron Neutron Capture Therapy

Antiproliferative and oxidative damage effects occurring in Boron Neutron Capture Therapy (BNCT) in normal fibroblasts and melanoma cell lines were analyzed. Melanoma cells and normal fibroblasts were treated with different concentrations of Boronophenylalanine and irradiated with thermal neutron flux. The cellular viability and the oxidative stress were determined. BNCT induced free radicals production and proliferative potential inhibition in melanoma cells. Therefore, this therapeutic technique could be considered efficient to inhibit growth of melanoma with minimal effects on normal tissues.

First application of dynamic infrared imaging in boron neutron capture therapy for cutaneous malignant melanoma

PURPOSE

The purpose of this study is to assess the potential of dynamic infrared imaging (DIRI) as a functional, noninvasive technique for evaluating the skin acute toxicity and tumor control within the framework of the Argentine boron neutron capture therapy (BNCT) program for cutaneous malignant melanoma.

METHODS

Two patients enrolled in the Argentine phase I/II BNCT clinical trial for cutaneous malignant melanoma were studied with DIRI. An uncooled infrared camera, providing a video output signal, was employed to register the temperature evolution of the normal skin and tumor regions in patients subjected to a mild local cooling (cold stimulus). In order to study the spatial correlation between dose and acute skin reactions, three-dimensional representations of the superficial dose delivered to skin were constructed and cameralike projections of the dose distribution were coregistered with visible and infrared images.

RESULTS

The main erythematous reaction was observed clinically between the second and fifth week post-BNCT. Concurrently, with its clinical onset, a reactive increase above the basal skin temperature was observed with DIRI in the third week post-BNCT within regions that received therapeutic doses. Melanoma nodules appeared as highly localized hyperthermic regions. 2 min after stimulus, these regions reached a temperature plateau and increased in size. Temperature differences with respect to normal skin up to 10 degrees C were observed in the larger nodules.

CONCLUSIONS

Preliminary results suggest that DIRI, enhanced by the application of cold stimuli, may provide useful functional information associated with the metabolism and vasculature of tumors and inflammatory processes related to radiation-induced changes in the skin as well. These capabilities are aimed at complementing the clinical observations and standard imaging techniques, such as CT and Doppler ultrasound.

BNCT for skin melanoma in extremities: updated Argentine clinical results

As part of phase I/II melanoma BNCT clinical trial conducted in Argentina in a cooperative effort of the Argentine Atomic Energy Commission (CNEA) and the Oncology Institute Angel H. Roffo (IOAHR), 7 patients (6 female-1 male) received eight treatment sessions covering ten anatomical areas located in extremities. Mean age of the patients was 64 years (51-74). The treatments were performed between October 2003 and June 2007. All patients presented multiple subcutaneous skin metastases of melanoma and received an infusion containing approximately 14 gr/m(2) of (10)borophenyl-alanine (BPA) followed by the exposition of the area to a mixed thermal-epithermal neutron beam at the RA-6 reactor. The maximum prescribed dose to normal skin ranged from 16.5 to 24 Gy-Eq and normal tissue administered dose varied from 15.8 to 27.5 Gy-Eq. Considering evaluable nodules, 69.3% of overall response and 30.7% of no changes were seen. The toxicity was acceptable, with 3 out of 10 evaluable areas showing ulceration (30% toxicity grade 3).

Unifying dose specification between clinical BNCT centers in the Americas

A dosimetry intercomparison between the boron neutron capture therapy groups of the Massachusetts Institute of Technology (MIT) and the Comisión Nacional de Energía Atómica (CNEA), Argentina was performed to enable combined analyses of NCT patient data between the different centers. In-air and dose versus depth measurements in a rectangular water phantom were performed at the hyperthermal neutron beam facility of the RA-6 reactor, Bariloche. Calculated dose profiles from the CNEA treatment planning system NCTPlan that were calibrated against in-house measurements required normalizations of 1.0 (thermal neutrons), 1.13 (photons), and 0.74 (fast neutrons) to match the dosimetry of MIT.

Numerical assessment of radiation binary targeted therapy for HER-2 positive breast cancers: advanced calculations and radiation dosimetry

In our previous publication (Mundy et al 2006 Phys. Med. Biol. 51 1377) we have described the theoretical assessment of our novel approach in radiation binary targeted therapy for HER-2 positive breast cancers and summarized the future directions in this area of research. In this paper we advanced the numerical analysis to show the detailed radiation dose distribution for various neutron sources in combination with the required boron concentration and allowed radiation skin doses. We once again proved the feasibility of the concept and will use these data and conclusions to start with the experimental verifications.

Implantable self-powered detector for on-line determination of neutron flux in patients during NCT treatment

A novel system to determine thermal neutron flux in real time during NCT treatments was developed in the National Atomic Energy Commission of Argentina. The system is based on a special self-powered detector that can be implanted in patients owing to its small size and biocompatibility. High voltage is not required to operate this kind of detectors, which is a considerable advantage in terms of medical uses. By choosing the appropriate materials, it was possible to obtain a prototype with thermal neutron sensitivity providing for an adequate signal level in typical NCT thermal fluxes. It was also possible to minimize gamma response in order to neglect its contribution.

Voxel model in BNCT treatment planning: performance analysis and improvements

In recent years, many efforts have been made to study the performance of treatment planning systems in deriving an accurate dosimetry of the complex radiation fields involved in boron neutron capture therapy (BNCT). The computational model of the patient's anatomy is one of the main factors involved in this subject. This work presents a detailed analysis of the performance of the 1 cm based voxel reconstruction approach. First, a new and improved material assignment algorithm implemented in NCTPlan treatment planning system for BNCT is described. Based on previous works, the performances of the 1 cm based voxel methods used in the MacNCTPlan and NCTPlan treatment planning systems are compared by standard simulation tests. In addition, the NCTPlan voxel model is benchmarked against in-phantom physical dosimetry of the RA-6 reactor of Argentina. This investigation shows the 1 cm resolution to be accurate enough for all reported tests, even in the extreme cases such as a parallelepiped phantom irradiated through one of its sharp edges. This accuracy can be degraded at very shallow depths in which, to improve the estimates, the anatomy images need to be positioned in a suitable way. Rules for this positioning are presented. The skin is considered one of the organs at risk in all BNCT treatments and, in the particular case of cutaneous melanoma of extremities, limits the delivered dose to the patient. Therefore, the performance of the voxel technique is deeply analysed in these shallow regions. A theoretical analysis is carried out to assess the distortion caused by homogenization and material percentage rounding processes. Then, a new strategy for the treatment of surface voxels is proposed and tested using two different irradiation problems. For a parallelepiped phantom perpendicularly irradiated with a 5 keV neutron source, the large thermal neutron fluence deviation present at shallow depths (from 54% at 0 mm depth to 5% at 4 mm depth) is reduced to 2% on average. Reassigning fluence values in the case of this phantom in angular position produced the maximum deviation in the thermal fluence to decrease from 140% to 23% at the surface of the phantom. Thus, even for the largest deviations, obtained by intentionally placing the phantom in the most disadvantageous position with respect to the voxel grid, the reassignment shows very good performance. Since these results substantially improve the performance of the 1 cm based voxel model in surface boundary regions, the proposed strategy will be implemented in future versions of the NCTPlan code.

Comparison of the performance of two NCT treatment planning systems using the therapeutic beam of the RA-6 reactor

This work evaluates the performance of two NCT treatment planning systems: NCTPlan, developed by the CNEA and the Harvard-MIT group, and SERA, developed by the INEEL/Montana State University group. The study was performed in some simple geometries with the therapeutical hyperthermal beam of the RA-6 facility at Bariloche, Argentina. The first geometry was a rectangular phantom and calculations and measurements were made along the central beam axis and along a parellel axis, 4 cm apart from the central beam axis. Measurements and calculations were also performed in a cylindrical phantom, to explore the behavior of the treatment planning systems in a geometry simulating an extremity, in accordance with the CNEA clinical protocol. Comments on differences in source definitions and cross sections libraries are also included in the text. It can be seen that both codes give acceptable results on the central beam axis and on a lateral axis, showing good agreement with experimental results.

A new approach to determine tumor-to-blood 10B concentration ratios from the clinical outcome of a BNCT treatment

A new approach to determine the tumor-to-blood (10)B concentration ratio in boron neutron capture therapy (BNCT) is introduced. It is a statistical method, which uses maximum likelihood estimation on the clinical outcome of a BNCT treatment. Its performance is shown in a clinical case of cutaneous multiple nodular melanomas. The calculations involve a detailed dosimetry analysis, the determination of tumor control probabilities for the different nodules, the maximum likelihood estimation itself, and a parametric bootstrap to obtain confidence intervals for the tumor-to-blood ratio. The obtained ratio is 3.05 +/- 0.46 with a 95%-confidence interval. These results are consistent with those found in literature. Moreover, a single patient with multiple nodules proves enough to get statistically relevant results. The proposed method does not involve surgery and can be performed after a BNCT treatment without being invasive for the patient.

BNCT dose calculation in irregular fields using the sector integration method

Irregular fields for boron neutron capture therapy (BNCT) have been already proposed to spare normal tissue in the treatment of superficial tumors. This added dependence would require custom measurements and/or to have a secondary calculation system. As a first step, we implemented the sector-integration method for irregular field calculation in a homogeneous medium and on the central beam axis. The dosimetric responses (fast neutron and photon dose and thermal neutron flux), are calculated by sector integrating the measured responses of circular fields over the field boundary. The measurements were carried out at our BNCT facility, the RA-6 reactor (Argentina). The input data were dosimetric responses for circular fields measured at different depths in a water phantom using ionisation and activation techniques. Circular fields were formed by shielding the beam with two plates: borated polyethilene plus lead. As a test, the dosimetric responses of a 7x4 cm(2) rectangular field, were measured and compared to calculations, yielding differences less than 3% in equivalent dose at any depth indicating that the tool is suitable for redundant calculations.

First BNCT treatment of a skin melanoma in Argentina: dosimetric analysis and clinical outcome

A Phase I/II protocol for treating cutaneuos melanomas with BNCT was designed in Argentina by the Comisión Nacional de Energía Atómica and the medical center Instituto Roffo. The first of a cohort of thirty planned patients was treated on October 9, 2003. This article depicts the protocol-based procedure and describes the first clinical case, treatment regime and planning, patient irradiation, retrospective dosimetric analysis and clinical outcome. Considering the low acute skin toxicity and the complete response in 21 of the 25 subcutaneous melanoma nodules treated, a second irradiation was performed in a different location of the extremity of the same patient. The corresponding clinical outcome is still under evaluation.