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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.

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.

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 7×4 cm2 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.

This article reports on the progress of the modeling and experimental characterization of the RA-6 reactor neutron beam, designed for the upcoming BNCT clinical trials of skin melanoma, and presents the first theoretical analysis of such beam performance. The aspects relating to surface source modeling and assessment, beam dosimetry,treatment planning system calibration, and treatment planning optimization are presented herein. Several methods and criteria were established in order to provide guidance for future clinical studies conducted in this facility. Following a realistic model, the theoretical analysis was based on a clinical case of malignant melanoma in extremities. Owing to the complex geometry of the tumor, this particular clinical case represents one of the most difficult lesions to be treated. This article discusses the thorough evaluation stage that has led to the optimization of the treatment planning procedure. Two candidate plans were proposed, and dose–volume distributions in the target volume were evaluated on the basis of the application of a series of criteria that define the critical normal structures which limit the dose delivered. In spite of the complexity of the clinical case under review, results showed that only 4% of the tumor volume is underdosed in cases of mean blood 10 B concentration values, even in the most unfavorable analysis. The overall results suggest that this BNCT facility is prepared to rigorously explore the clinical efficacy of the RA-6 beam and the BNCT treatment modality for peripheral melanomas.

A previous work concerning tumor control and skin damage in cutaneous melanoma treatments with BNCT has been extended to include doses, volumes and responses of 104 subcutaneous lesions from all patients treated in Argentina. Acute skin reactions were also scored for these patients, and cumulative dose-area histograms and dose-based figures of merit for skin were calculated. Broadening the tumor response analysis with the latest data showed that the (minimum or mean) tumor dose is not a good predictor of the observed clinical outcome by itself. However, when the tumor volume was included in the model as second explicative variable, the dose increases its significance and becomes a critical variable jointly with the volume (p-values0.05). A preliminary analysis to estimate control doses for two groups of tumor sizes revealed that for small tumor volumes (0.1cm(3)) doses greater than 20 Gy-Eq produce a high tumor control (80%). However, when tumor volumes are larger than 0.1cm(3), control is moderate (40%) even for minimum doses up to 40 Gy-Eq. Some quantities based on skin doses, areas and complication probabilities were proposed as candidates for predicting the severity of the early skin reactions. With the current data, all the evaluated figures of merit derived similar results: ulceration is present among the cases for which these quantities take the highest values.

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).

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.

The RA-6 reactor located at Bariloche Atomic Center, is a pool type one with 500kW of nominal power and U 90% enriched fuel owned and operated by CN.E.A.