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

Using the photon isoeffective dose formalism to compare and combine BNCT and CIRT in a head and neck tumour

Boron Neutron Capture Therapy (BNCT) is a radiotherapy technique based on the enrichment of tumour cells with suitable 10-boron concentration and on subsequent neutron irradiation. Low-energy neutron irradiation produces a localized deposition of radiation dose caused by boron neutron capture reactions. Boron is vehiculated into tumour cells via proper borated formulations, able to accumulate in the malignancy more than in normal tissues. The neutron capture releases two high-LET charged particles (i.e., an alpha particle and a lithium ion), losing their energy in a distance comparable to the average dimension of one cell. Thus BNCT is selective at the cell level and characterized by high biological effectiveness. As the radiation field is due to the interaction of neutrons with the components of biological tissues and with boron, the dosimetry requires a formalism to express the absorbed dose into photon-equivalent units. This work analyzes a clinical case of an adenoid cystic carcinoma treated with carbon-ion radiotherapy (CIRT), located close to optic nerve and deep-seated as a practical example of how to apply the formalism of BNCT photon isoeffective dose and how to evaluate the BNCT dose distribution against CIRT. The example allows presenting different dosimetrical and radiobiological quantities and drawing conclusions on the potential of BNCT stemming on the clinical result of the CIRT. The patient received CIRT with a dose constraint on the optic nerve, affecting the peripheral part of the Planning Target Volume (PTV). After the treatment, the tumour recurred in this low-dose region. BNCT was simulated for the primary tumour, with the goal to calculate the dose distribution in isoeffective units and a Tumour Control Probability (TCP) to be compared with the one of the original treatment. BNCT was then evaluated for the recurrence in the underdosed region which was not optimally covered by charged particles due to the proximity of the optic nerve. Finally, a combined treatment consisting in BNCT and carbon ion therapy was considered to show the consistency and the potential of the model. For the primary tumour, the photon isoeffective dose distribution due to BNCT was evaluated and the resulted TCP was higher than that obtained for the CIRT. The formalism produced values that are consistent with those of carbon-ion. For the recurrence, BNCT dosimetry produces a similar TCP than that of primary tumour. A combined treatment was finally simulated, showing a TCP comparable to the BNCT-alone with overall dosimetric advantage in the most peripheral parts of the treatment volume. Isoeffective dose formalism is a robust tool to analyze BNCT dosimetry and to compare it with the photon-equivalent dose calculated for carbon-ion treatment. This study introduces for the first time the possibility to combine the dosimetry obtained by two different treatment modalities, showing the potential of exploiting the cellular targeting of BNCT combined with the precision of charged particles in delivering an homogeneous dose distribution in deep-seated tumours.

Profile analysis of adverse events after boron neutron capture therapy for head and neck cancer: a sub-analysis of the JHN002 study

The purpose of this study was to outline the course and profile of adverse events specific to boron neutron capture therapy (BNCT) for head and neck cancer. This was a sub-analysis of the phase II JHN002 trial. Patients received 400 mg/kg borofalan(10B), followed by neutron irradiation. The course of adverse events after BNCT was documented in the JHN002 Look Up study. Patients were grouped into face/front (FF), face/lateral (FL) and neck (N) beam groups according to the point of skin incidence of the epithermal neutron beam axis, and the profile of adverse events dependent on beam incidence position was examined. The courses of adverse events in eight recurrent squamous cell carcinoma (R-SCC) and 13 recurrent or locally advanced non-SCC cases were analyzed. Median interval to complete recovery was 23 days (interquartile range (IQR), 14-48 days) for oral mucositis, 40 days (IQR, 24-56 days) for dermatitis, 58 days (IQR, 53-80 days) for dysgeusia and 156 days (IQR, 82-163 days) for alopecia. In the FF beam group, parotitis (P = 0.007) was less frequent, while oral mucositis (P = 0.032), fatigue (P = 0.002), conjunctivitis (P = 0.001), epistaxis (P = 0.001) and abdominal discomfort (P = 0.029) tended to be more frequent than in the FL and N beam groups. Courses and irradiation site-specific profiles of adverse events in BNCT for head and neck cancer were identified. This profile may be useful for considering interventions to prevent exacerbation of treatment-related adverse events on BNCT.

Detailed dosimetry calculation for in-vitro experiments and its impact on clinical BNCT

PURPOSE

Boron Neutron Capture Therapy (BNCT) is a form of hadrontherapy based on the selective damage caused by the products of neutron capture in ¹⁰B to tumour cells. BNCT dosimetry strongly depends on the parameters of the dose calculation models derived from radiobiological experiments. This works aims at determining an adequate dosimetry for in-vitro experiments involving irradiation of monolayer-cultured cells with photons and BNCT and assessing its impact on clinical settings. M&M: Dose calculations for rat osteosarcoma UMR-106 and human metastatic melanoma Mel-J cell survival experiments were performed using MCNP, transporting uncharged particles for KERMA determinations, and secondary particles (electrons, protons, ¹⁴C, ⁴He and ⁷Li) to compute absorbed dose in cultures. Dose-survival curves were modified according to the dose correction factors determined from computational studies. New radiobiological parameters of the photon isoeffective dose models for osteosarcoma and metastatic melanoma tumours were obtained. Dosimetry implications considering cutaneous melanoma patients treated in Argentina with BNCT were assessed and discussed.

RESULTS

KERMA values for the monolayer-cultured cells overestimate absorbed doses of radiation components of interest in BNCT. Detailed dose calculations for the osteosarcoma irradiation increased the relative biological effectiveness factor RBE_1% of the neutron component in more than 30%. The analysis based on melanoma cases reveals that the use of survival curves based on KERMA leads to an underestimation of the tumour doses delivered to patients.

CONCLUSIONS

Considering detailed dose calculation for in-vitro experiments significantly impact on the prediction of the tumor control in patients. Therefore, proposed methods are clinically relevant.

A Critical Review of Radiation Therapy: From Particle Beam Therapy (Proton, Carbon, and BNCT) to Beyond

In this paper, we discuss the role of particle therapy—a novel radiation therapy (RT) that has shown rapid progress and widespread use in recent years—in multidisciplinary treatment. Three types of particle therapies are currently used for cancer treatment: proton beam therapy (PBT), carbon-ion beam therapy (CIBT), and boron neutron capture therapy (BNCT). PBT and CIBT have been reported to have excellent therapeutic results owing to the physical characteristics of their Bragg peaks. Variable drug therapies, such as chemotherapy, hormone therapy, and immunotherapy, are combined in various treatment strategies, and treatment effects have been improved. BNCT has a high dose concentration for cancer in terms of nuclear reactions with boron. BNCT is a next-generation RT that can achieve cancer cell-selective therapeutic effects, and its effectiveness strongly depends on the selective ¹⁰B accumulation in cancer cells by concomitant boron preparation. Therefore, drug delivery research, including nanoparticles, is highly desirable. In this review, we introduce both clinical and basic aspects of particle beam therapy from the perspective of multidisciplinary treatment, which is expected to expand further in the future.

A Novel Approach to Design and Evaluate BNCT Neutron Beams Combining Physical, Radiobiological, and Dosimetric Figures of Merit

(1) Background:The quality of neutron beams for Boron Neutron Capture Therapy (BNCT) is currently defined by its physical characteristics in air. Recommendations exist to define whether a designed beam is useful for clinical treatment. This work presents a new way to evaluate neutron beams based on their clinical performance and on their safety, employing radiobiological quantities. (2) Methods: The case study is a neutron beam for deep-seated tumors from a 5 MeV proton beam coupled to a beryllium target. Physical Figures of Merit were used to design five beams; however, they did not allow a clear ranking of their quality in terms of therapeutic potential. The latter was then evaluated based on in-phantom dose distributions and on the calculation of the Uncomplicated Tumor Control Probability (UTCP). The safety of the beams was also evaluated calculating the in-patient out-of-beam dosimetry. (3) Results: All the beams ensured a UTCP comparable to the one of a clinical beam in phantom; the safety criterion allowed to choose the best candidate. When this was tested in the treatment planning of a real patient treated in Finland, the UTCP was still comparable to the one of the clinical beam. (4) Conclusions: Even when standard physical recommendations are not met, radiobiological and dosimetric criteria demonstrate to be a valid tool to select an effective and safe beam for patient treatment.

Boron neutron capture therapy using cyclotron-based epithermal neutron source and borofalan (10B) for recurrent or locally advanced head and neck cancer (JHN002): An open-label phase II trial

BACKGROUND AND PURPOSE

Boron neutron capture therapy (BNCT) can be performed without reactors due to development of cyclotron-based epithermal neutron source (C-BENS), which is optimized for treatment for deeper-seated tumors. The purpose of this study was to evaluate efficacy and safety of cyclotron-based BNCT with borofalan (¹⁰B) for recurrent or locally advanced head and neck cancer.

MATERIALS AND METHODS

In this open-label, phase II JHN002 trial of BNCT using C-BENS with borofalan (¹⁰B), patients with recurrent squamous cell carcinoma (R-SCC) or with recurrent/locally advanced non-squamous cell carcinoma (R/LA-nSCC) of the head and neck were intravenously administered 400 mg/kg borofalan (¹⁰B), followed by neutron irradiation. The tumor dose was determined passively as the mucosal maximum dose of 12 Gy-Eq. The primary endpoint was the objective response rate (ORR). Post-trial observational JHN002 Look Up study was planned for evaluating locoregional progression-free survival (LRPFS).

RESULTS

Eight R-SCC and 13 R/LA-nSCC patients were enrolled. All R-SCC patients had prior radiotherapy with a median dose of 65.5 Gy (range, 59.4-76.0 Gy). The ORR for all patients was 71%, and complete response/partial response were 50%/25% in R-SCC and 8%/62% in R/LA-nSCC. The 2-year overall survival for R-SCC and R/LA-nSCC were 58% and 100%, respectively. The median LRPFS was 11.5 months for R-SCC. Frequently observed adverse events included alopecia (95%), hyperamylasemia (86%), and nausea (81%).

CONCLUSION

These data suggest that BNCT using C-BENS with borofalan (¹⁰B) is a promising treatment option for patients with R-SCC or R/LA-nSCC of the head and neck.