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

Abstract

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 10B 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.

Unifying dose specification between clinical BNCT centers in the Americas

“…The data measured by CAB in this phantom are used to benchmark the treatment planning software NCTPlan utilized by the CNEA for dose calculations. 5 Examining the calibrated output from NCT-Plan enabled a quantitative comparison between the dose prescribed by CNEA to that measured and so prescribed by MIT for the four individual dose components including that from thermal neutron capture in boron. A fourth-order polynomial was fit using the least-squares method to the MIT dose measurements and the CNEA NCTPlan calculation was TABLE I.…”

“…Although identical ionization chambers are employed, the two groups convert ionization response to absorbed dose differently. The CAB group empirically determines the thermal neutron sensitivities of each chamber 5,7 and subtracts a scaled response from each measurement based upon the measured thermal neutron fluence to then determine the photon and fast neutron doses from the residual ionization currents as initially proposed by Rogus et al 8 The MIT group, however, now includes the thermal neutron response as part of the neutron sensitivity of each chamber and determines the dose from neutrons of all energies. 9 To complete the intercomparison, CNEA computed a treatment plan using the Monte Carlo based NCTPlan ordinarily used for dose calculations in their clinical trials.…”

“…Dosimetry measurements were performed by each group using detectors and methods applicable to their respective clinical protocols in the hyperthermal neutron beam of the RA-6 reactor in Bariloche where patients have been treated in a clinical trial of BNCT for peripheral melanoma. 5,6 Archived data from previous melanoma irradiations performed at MIT are available and can be added to current protocol results from CNEA once dose normalizations are complete. This study also provides a linkage through the MIT measurements between CAB dosimetry and other International Dosimetry Exchange participants in Europe.…”

Dynamic infrared imaging for biological and medical applications in Boron neutron capture therapy

“…The importance of this fact has encouraged our group to improve the computational dosimetry of our patients, continuously progressing towards a more accurate modeling of the dose distribution. [10][11][12] In this context, DIRI became an option to study, non-invasively, the evolution of normal tissue reactions and melanoma control. Together with clinical observation, computed tomography scans and high resolution Doppler ultrasound, DIRI was employed before and after the treatment of melanoma patients with BNCT.…”

Boron Neutron Capture Therapy: Current Status and Challenges

“…planned to enroll 30 melanoma patients for a clinical trial, and they reported the first results of BNCT for the treatment of melanoma. For the first patient, they administered BPA-F at 14 g/m 2 for more than 1.5 h, based on the area of the skin at the affected area ( 94 , 95 ). Results showed that 19 of the 25 nodules were complete response (CR) within 4 weeks of BNCT treatment.…”