Gabriele Parisi

Objective. Proton therapy is increasingly used in oncology due to its enhanced biological effectiveness and precision in targeting tumour tissues. Accurately characterising the radiation quality is, therefore, fundamental. However, the role of fragments in proton therapy remains understudied, mainly due to their low frequency of occurrence and limited impact on the dose. The fragments generated, though, interact differently with biological tissues and may substantially affect the biological response. This work characterises the fragments field generated by a typical clinical proton beam using microdosimetry. Approach. Experiments and Monte Carlo simulations were carried out for this purpose, using a 70.2 MeV proton beam moderated by a lung-equivalent material. Main results. Fragments contributed around 2% to y ¯ F and over 60% to y ¯ D , underscoring their relevance. The detector structure critically influenced their measurement, highlighting the necessity of detector-specific interpretation of spectra when used for biological modelling. Significance. Our results stress the importance of fragment-aware approaches for accurately assessing radiation quality and predicting biological outcomes in proton therapy.

Melanoma is an aggressive disease that arises from mutations in the cells that produce the pigment melanin, melanocytes. Melanoma is characterized by a high mortality rate, due to avoidance of applied therapies and metastasis to other organs. The peculiar features of boron neutron capture therapy (BNCT), particularly its cell-level selectivity, make BNCT a promising modality for melanoma treatment. However, appropriate cellular models should be used to study new therapies or improve the efficacy of existing therapies. Spheroids, which have been used for years for in vitro studies of the efficacy of anti-cancer therapies, have many characteristics shared with tumors through which they can increase the accuracy of the cellular response compared to 2D culture in vitro studies and reduce the use of animals for research in the future. To the best of our knowledge, when we started researching the use of spheroids in BNCT in vitro, there was no publication showing such use. Our study aimed to evaluate the efficacy of a 3D cellular model (spheroids) for testing BNCT on melanoma cells. We assessed boronophenylalanine (¹⁰BPA) uptake using inductively coupled plasma mass spectrometry in both spheroids and 2D cultures of melanoma and melanocytes. DNA damage, Ki67 protein expression, and spheroid growth were analyzed. The experimental groups included: (1) IR_B (neutron flux + 50 µg ¹⁰B/mL), (2) IR (neutron flux alone), (3) C_B (no irradiation, 50 µg ¹⁰B/mL), and (4) C (no irradiation and no treatment with boron). The total absorbed doses were estimated to be 2.1–3.1 Gy for IR_B cells and spheroids as well as 8.3–9.4 Gy for IR_B spheroids, while estimated doses for IR cells were 0.5–1.9 Gy. The results indicated that IR_B spheroids might exhibit a reduced diameter. Melanoma cells in the 3D model showed that their DNA damage levels may be higher than those in the 2D model. Moreover, the Ki67 assay revealed differences in the expression of this marker between irradiated melanoma cell lines. In conclusion, preincubation with ¹⁰BPA enhances BNCT efficacy, leading to cell growth inhibition and increased DNA fragmentation. Differences in DNA damage between 2D and 3D models may be due to dissimilarities in cell metabolism caused by a changed cell architecture.

Boron Neutron-Capture Therapy (BNCT) is a form of radiation therapy that relies on the highly localized and enhanced biological effects of the ¹⁰B neutron capture (BNC) reaction products to selectively kill cancer cells. The efficacy of BNCT is, therefore, strongly dependent on the ¹⁰B spatial microdistribution at a subcellular level. Fluorescent Nuclear Track Detectors (FNTDs) could be a promising technology for measuring ¹⁰B microdistribution. They allow the measurement of the tracks of charged particles, and their biocompatibility allows cell samples to be deposited and grown on their surfaces. If a layer of borated cells is deposited and irradiated by a neutron field, the energy deposited by the BNC products and their trajectories can be measured by analyzing the corresponding tracks. This allows the reconstruction of the position where the measured particles were generated, hence the microdistribution of ¹⁰B. With respect to other techniques developed to measure ¹⁰B microdistribution, FNTDs would be a non-destructive, biocompatible, relatively easy-to-use, and accessible method, allowing the simultaneous measurement of the ¹⁰B microdistribution, the LET of particles, and the evolution of the related biological response on the very same cell sample. An FNTD was tested in three irradiation conditions to study the feasibility of FNTDs for BNCT applications. The FNTD allowed the successful measurement of the correct alpha particle range and mean penetration depth expected for all the radiation fields employed. This work proved the feasibility of FNTD in reconstructing the tracks of the alpha particles produced in typical BNCT conditions, thus the ¹⁰B microdistribution. Further experiments are planned at the University of Pavia’s LENA (Applied Nuclear Energy Laboratory) to test the final set-up coupling the FNTD with borated cell samples.

The increasing interest in hadron therapy has heightened the need for accurate and reliable methods to assess radiation quality and the biological effectiveness of particles used in treatment. Microdosimetry has emerged as a key tool for this, demonstrating its potential, reliability, and suitability. In this context, solid-state microdosimeters offer technological advantages over traditional Tissue-Equivalent Proportional Counters, and recent advancements have further improved their performance and reliability. However, one critical challenge in solid-state microdosimetry is the so-called 'border effect', which can impact measurement accuracy. In this study, the border effect in diamond microdosimeters was thoroughly studied using Ion Beam Induced Charge (IBIC) analysis. The research, relying on experiments conducted at the Surrey Ion Beam Centre, developed an effective method to characterise and quantify the border effect. Geant4 Monte Carlo simulations were also employed to assess the impact of the border effect under typical proton therapy conditions, with a specific model developed and validated to reproduce this effect in simulations. Results showed potential significant variations of up to 40% in ȳ_F and 20% in ȳ_D values, highlighting the importance of accurately characterising the border effect and encouraging further research to mitigate its influence on microdosimetry measurements.

Melanoma is an aggressive disease that arises from mutations in the cells that produce the pigment melanin, melanocytes. Melanoma is characterized by a high mortality rate, due to avoidance of applied therapies and metastasis to other organs [1]. The peculiar features of BNCT, particularly its cell-level selectivity of Boron Neutron Capture Therapy (BNCT), make BNCT a promising modality for melanoma treatment. However, appropriate cellular models should be used to study new therapies or improve the efficacy of existing therapies. Spheroids, which have been used for years for in vitro studies of the efficacy of anti-cancer therapies, have many characteristics shared with tumors by which they can increase the accuracy of the cellular response compared to 2D cultures in vitro studies, and in the future reduce the use of animals for research. To the best of our knowledge, when we started researching the use of spheroids in BNCT therapy in vitro, there was no publication showing such use. Our study aimed to evaluate the efficacy of a 3D cellular model (spheroids) for testing BNCT on melanoma cells. We assessed boronophenylalanine (10BPA) uptake using Inductively Coupled Plasma Mass Spectrometry in both spheroids and 2D cultures of melanoma and melanocytes. DNA damage, Ki67 protein expression, and spheroid growth were analyzed. The experimental groups included: (1) IR_B (neutron flux + 50 µg 10B/ml), (2) IR (neutron flux alone), (3) C_B (no irradiation, 50 µg 10B/ml), and (4) C (no irradiation and no treatment with boron). The total absorbed doses were estimated to 2.1 – 3.1 Gy for IR_B cells and spheroids as well as 8.3 – 9.4 Gy for IR_B spheroids, while estimated doses for IR cells were 0.5 – 1.9 Gy. Results indicated that IR_B spheroids had reduced diameters and significantly higher DNA damage compared to other groups. Melanoma cells in the 3D model showed higher DNA damage levels than those in the 2D model. Moreover, the Ki67 assay revealed differences in the expression of this marker between irradiated melanoma cell lines. In conclusion, preincubation with 10BPA enhances BNCT efficacy, leading to cell growth inhibition and increased DNA fragmentation. Differences in DNA damage between 2D and 3D models may be due to dissimilarities in cell metabolism caused by a changed cell architecture.

The interest in Boron Neutron Capture Therapy (BNCT) has been recently increasing thanks to the latest advancements in accelerator technology which allow to generate the required neutron field from accelerator facilities that could be hosted in hospitals or clinical centres. BNCT is a form of radiation therapy which relies on the highly localised and enhanced biological effects of the boron-10 (B-10) neutron capture (BNC) reaction products to selectively kill cancer cells. The BNC products are low-energy alpha and lithium ions, which are characterised by a high Linear Energy Transfer (LET) and a very short range lower than 9?m. The energy deposition and interaction with critical biological target such as DNA molecules is therefore strongly dependent on the B-10 spatial micro-distribution into the cells. In this framework, the Fluorescent Nuclear Track Detectors (FNTD) could be a promising device for the visualisation of the ion traversals induced in BNCT. FNTD consists of a fluorescent single-crystal aluminium oxide doped with carbon and magnesium, coupled with a Confocal Laser Scanning Microscopy (CLSM) read-out. Its biocompatibility allows to deposit and grow cells samples on its surface. If a layer of borated cells is deposited and irradiated by a neutron field, the energy deposited by the BNC products and their trajectories can be measured by analysing the corresponding track spots induced at different depths of the detector. This allows to reconstruct the position where the measured particles were generated, hence the micro-distribution of B-10. A FNTD was tested in three irradiation conditions to study the feasibility of FNTD for BNCT applications. The device was firstly irradiated by the alpha particles emitted by an Am-241 source (with energy of about 5.5 MeV). The same radiation field moderated by a 23?m layer of Mylar was then used to obtain alpha particles with a lower energy of about 2.5 MeV, thus closer to BNC products. Finally, the FNTD was tested at the University of Pavia’s LENA (Applied Nuclear Energy Laboratory) under a thermal neutron beam. A standard reference material (SRM) consisting of boron implanted on a silicon wafer was placed on the detector surface to reproduce a typical BNCT radiation field. The FNTD allowed to successfully measure the correct alpha particles range and mean penetration depth expected for all the radiation fields employed. This work proved the feasibility of FNTD to reconstruct the tracks of the alpha particles produced in typical BNCT conditions. Hence, FNTD will allow to measure the intra-cellular micro-distribution of B-10, bringing a significant contribution to the advancement of BNCT research. With this purpose, further experiments at LENA irradiating borated cell samples are planned.

Objective. Microdosimetry is gaining increasing interest in particle therapy. Thanks to the advancements in microdosimeter technologies and the increasing number of experimental studies carried out in hadron therapy frameworks, it is proving to be a reliable experimental technique for radiation quality characterisation, quality assurance, and radiobiology studies. However, considering the variety of detectors used for microdosimetry, it is important to ensure the consistency of microdosimetric results measured with different types of microdosimeters. Approach. This work presents a novel multi-thickness microdosimeter and a methodology to characterise the radiation quality of a clinical carbon-ion beam. The novel device is a diamond detector made of three sensitive volumes (SVs) of different thicknesses: 2, 6 and 12 µm. The SVs, which operate simultaneously, were accurately aligned and laterally positioned within 3 mm. This alignment allowed for a comparison of the results with a negligible impact of the SVs alignment and their lateral positioning, ensuring the homogeneity of the measured radiation quality. An experimental campaign was carried out at MedAustron using a carbon-ion beam of typical clinical energy (284.7 MeV u⁻¹). Main results. The measurement results allowed for a meticulous interpretation of its radiation quality, highlighting the effect of the SV thickness. The consistency of the microdosimetric spectra measured by detectors of different thicknesses is discussed by critically analysing the spectra and the differences observed. Significance. The methodology presented will be highly valuable for future experiments investigating the effects of the target volume size in radiobiology and could be easily adapted to the other particles employed in hadron therapy for clinical (i.e. protons) and for research purposes (e.g. helium, lithium and oxygen ions).

The interest in microdosimetry is growing thanks to the advancement in microdosimetric technologies, improving detector performance and reliability. Herein, the fabrication and characterization of a novel diamond‐based microdosimeter are proposed. The microdosimeter consists of an array of single‐crystal diamond Schottky diodes about 1.5 μm thick connected in parallel. The detector prototypes are characterized using the ion beam‐induced charge technique, employing a 6 MeV carbon ions microbeam. Despite a good overall response, the first prototypes are affected by the “bridge effect”: a charge collection beneath the metallic bridges connecting the sensitive volumes (SVs), which alters the energy deposition spectrum. To mitigate the bridge effect, different technological solutions are explored: the selective growth of intrinsic diamond layers and the use of an insulating material such as photoresist. These second prototypes reveal a good SV spatial definition without any charge collection from the bridges and a good response homogeneity within the SVs ranging between 3% and 5% full‐width‐half‐maximum among the different prototypes. While the cell‐like thickness and lateral dimensions of SVs make the diamond microdosimeter array ideal for radiobiological applications, its array configuration can make it highly versatile to perform under different fluence rate conditions in particle therapy.

The interest in hadron therapy is growing fast thanks to the latest technological advances in accelerators and delivery technologies, to the development of more and more efficient and comprehensive treatment planning tools, and due to its increasing clinical adoption proving its efficacy. A precise and reliable beam quality assessment and an accurate and effective inclusion of the biological effectiveness of different radiation qualities are fundamental to exploit at best its advantages with respect to conventional radiotherapy. Currently, in clinical practice, the quality assurance (QA) is carried out by means of conventional dosimetry, while the biological effectiveness of the radiation is taken into account considering the Relative Biological Effectiveness (RBE). The RBE is considered a constant value for protons and it is estimated as a function of the absorbed dose in case of carbon ions. In this framework, microdosimetry could bring a significant improvement to both QA and RBE estimation. By measuring the energy deposited by the radiation into cellular or sub-cellular volumes, microdosimetry could provide a unique characterisation of the beam quality on one hand, and a direct link to radiobiology on the other. Different detectors have been developed for microdosimetry, from the more conventional tissue equivalent proportional counter (TEPC), silicon-based and diamond-based solid-state detectors, to ΔE-E telescope detectors, gas electrons multiplier (GEM), hybrid microdosimeters and a micro-bolometer based on Superconducting QUantum Interference Device (SQUID) technology. However, because of their different advantages and drawbacks, a standard device and an accredited experimental methodology have not been unequivocally identified yet. The establishment of accepted microdosimetry standard protocols and code of practice is needed before the technique could be employed in clinical practice. Hoping to help creating a solid ground on which future research, development and collaborations could be planned and inspired, a comprehensive state of the art of the detector technologies developed for microdosimetry is presented in this review, discussing their use in clinical hadron therapy conditions and considering their advantages and drawbacks.