Combined tumour treatment by coupling conventional radiotherapy to an additional dose contribution from thermal neutrons

Aim: To employ the thermal neutron background in conventional X-rays radiotherapy treatments in order to add a localized neutron dose boost to the patient, enhancing the treatment effectiveness. Background: Conventional linear accelerators for radiotherapy produce fast secondary neutrons with a mean energy of about 1 MeV due to (\u3b3, n) reaction. This neutron field, isotropically distributed, is considered as an extra unaccounted dose during the treatment. Moreover, considering the moderating effect of human body, a thermal neutron field is localized in the tumour area: this neutron background could be employed for Boron Neutron Capture Therapy (BNCT) by previously administering a boron (10B enriched) carrier to the patient, acting as a localized radiosensitizer. The thermal neutron absorption in the 10B enriched tissue will improve radiotherapy effectiveness. Materials and Methods: The feasibility of the proposed method was investigated by using simplified tissue-equivalent phantoms with cavities in correspondence of relevant tissues or organs, suited for dosimetric measurements. A 10 cm 7 10 cm square photon field with different energies was delivered to the phantoms. Additional exposures were implemented, using a compact neutron photo-converter-moderator assembly, with the purpose of modifying the mixed photon-neutron field in the treatment region. Doses due to photons and neutrons were both measured by using radiochromic films and superheated bubble detectors, respectively, and simulated with Monte Carlo codes. Results: For a 10 cm 7 10 cm square photon field with accelerating potentials 6 MV, 10 MV and 15 MV, the neutron dose equivalent in phantom was measured and its values was 0.07 mGy/Gy (neutron dose equivalent / photon absorbed dose at isocentre), 0.99 mGy/Gy and 2.22 mGy/Gy, respectively. For a 18 MV treatment, simulations and measurements quantified the thermal neutron field in the treatment zone in 1.55 7 107 cm 122 Gy 121. Assuming a BNCT- standard 10B concentration in tumour tissue, the calculated additional BNCT dose at 4 cm depth in phantom would be 1.5 mGy-eq/Gy. This ratio would reach 43 mGy- eq/Gy for an intensity modulated radiotherapy treatment (IMRT). When a specifically designed compact neutron photo-converter-moderator assembly is applied to the LINAC to enhance the thermal neutron field, the photon field is modified. Particularly, a 15 MV photon field produces a dose profile very similar to that would be produced by a 6 MV field in absence of the photo-converter-moderator assembly. As far as the thermal neutron field is concerned, more thermal neutrons are present, and thermal neutrons per photon increase of a factor 3 to 12 according to the depth in phantom and to different photoconverter geometries. By contrast, the photo-converter-moderator assembly was found to reduce fast neutrons of a factor 16 in the direction of the incident beam. Conclusions: The parasitic thermal neutron component during conventional high- energy radiotherapy could be exploited to produce additional therapeutic doses if the 10B-carrier was administered to the patient. This radiosensitization effect could be increased by modifying the treatment field by using the specifically designed neutron photo-converter-moderator assembly

MEASUREMENTS OF THE PARASITIC NEUTRON DOSE AT ORGANS FROM MEDICAL LINACS AT DIFFERENT ENERGIES BY USING BUBBLE DETECTORS

Conventional linear accelerators (LINACs) for radiotherapy produce fast secondary neutrons due to photonuclear processes. The neutron presence is considered as an extra undesired dose during the radiotherapy treatment, which could cause secondary radio-induced tumors and malfunctions to cardiological implantable devices. It is thus important to measure the neutron dose contribution to patients during radiotherapy, not only at high-energy LINACs, but also at lower energies, near the giant dipole resonance reaction threshold. In this work, the full body neutron dose equivalent has been measured during single-field radiotherapy sessions carried out at different LINAC energies (15, 10 and 6 MV) by using a tissue equivalent (for neutrons) anthropomorphic phantom together with bubble dosemeters. Results have shown that some neutron photoproduction is still present also at lower energies. As a consequence, emitted photoneutrons cannot be ignored and represent a risk contribution for patients undergoing radiotherapy

BNCT AS RADIOSENSITIZER IN HIGH-ENERGY RADIOTHERAPY TREATMENTS

High-energy linear accelerators for radiotherapy produce fast secondary neutrons due to (\u3b3,n) reaction. Considering the moderating effect of human body, an unavoidable and undesired thermal neutron flux is localized in the tumor area. This study proposes the possibility to employ this neutron background to enhance the radiotherapy efficacy: the thermal neutron peak could be exploited for BNCT applications, delivering an additional therapeutic dose to the photon dose concentrated in tumor cells, acting as a localized radiosensitizer

Radiotherapy dose enhancement using {BNCT} in conventional {LINACs} high-energy treatment: Simulation and experiment

AbstractAim To employ the thermal neutron background that affects the patient during a traditional high-energy radiotherapy treatment for {BNCT} (Boron Neutron Capture Therapy) in order to enhance radiotherapy effectiveness. Background Conventional high-energy (15–25 MV) linear accelerators (LINACs) for radiotherapy produce fast secondary neutrons in the gantry with a mean energy of about 1 MeV due to (γ, n) reaction. This neutron flux, isotropically distributed, is considered as an unavoidable undesired dose during the treatment. Considering the moderating effect of human body, a thermal neutron fluence is localized in the tumour area: this neutron background could be employed for {BNCT} by previously administering 10B-Phenyl-Alanine (10BPA) to the patient. Materials and methods Monte Carlo simulations (MCNP4B-GN code) were performed to estimate the total amount of neutrons outside and inside human body during a traditional X-ray radiotherapy treatment. Moreover, a simplified tissue equivalent anthropomorphic phantom was used together with bubble detectors for thermal and fast neutron to evaluate the moderation effect of human body. Results Simulation and experimental results confirm the thermal neutron background during radiotherapy of 1.55E07 cm−2 Gy−1. The {BNCT} equivalent dose delivered at 4 cm depth in phantom is 1.5 mGy-eq/Gy, that is about 3 Gy-eq (4 of X-rays dose) for a 70 Gy {IMRT} treatment. Conclusions The thermal neutron component during a traditional high-energy radiotherapy treatment could produce a localized {BNCT} effect, with a localized therapeutic dose enhancement, corresponding to 4 or more of photon dose, following tumour characteristics. This {BNCT} additional dose could thus improve radiotherapy, acting as a localized radio-sensitizer

Radiotherapy dose enhancement using BNCT in conventional LINACs high-energy treatment: Simulation and experiment

AimTo employ the thermal neutron background that affects the patient during a traditional high-energy radiotherapy treatment for BNCT (Boron Neutron Capture Therapy) in order to enhance radiotherapy effectiveness.BackgroundConventional high-energy (15–25[[ce:hsp sp="0.25"/]]MV) linear accelerators (LINACs) for radiotherapy produce fast secondary neutrons in the gantry with a mean energy of about 1[[ce:hsp sp="0.25"/]]MeV due to (γ, n) reaction. This neutron flux, isotropically distributed, is considered as an unavoidable undesired dose during the treatment. Considering the moderating effect of human body, a thermal neutron fluence is localized in the tumour area: this neutron background could be employed for BNCT by previously administering 10B-Phenyl-Alanine (10BPA) to the patient.Materials and methodsMonte Carlo simulations (MCNP4B-GN code) were performed to estimate the total amount of neutrons outside and inside human body during a traditional X-ray radiotherapy treatment.Moreover, a simplified tissue equivalent anthropomorphic phantom was used together with bubble detectors for thermal and fast neutron to evaluate the moderation effect of human body.ResultsSimulation and experimental results confirm the thermal neutron background during radiotherapy of 1.55E07[[ce:hsp sp="0.25"/]]cm−2[[ce:hsp sp="0.25"/]]Gy−1.The BNCT equivalent dose delivered at 4[[ce:hsp sp="0.25"/]]cm depth in phantom is 1.5[[ce:hsp sp="0.25"/]]mGy-eq/Gy, that is about 3[[ce:hsp sp="0.25"/]]Gy-eq (4% of X-rays dose) for a 70[[ce:hsp sp="0.25"/]]Gy IMRT treatment.ConclusionsThe thermal neutron component during a traditional high-energy radiotherapy treatment could produce a localized BNCT effect, with a localized therapeutic dose enhancement, corresponding to 4% or more of photon dose, following tumour characteristics. This BNCT additional dose could thus improve radiotherapy, acting as a localized radio-sensitizer

Studio di una schermatura per neutroni prodotti mediante acceleratori radioterapici ospedalieri

Lo studio di schermature per neutroni si rivela essenziale in svariate applicazioni scientifiche e mediche. Tali particelle sono difatti utilizzate in radioterapie per cattura neutronica, e.g. Boron Neutron Capture Therapy (BNCT), e causano danneggiamenti di dispositivi elettronici, in particolare dei Dispositivi Cardiaci Impiantabili quali Pacemaker e Defibrillatori. Inoltre, applicazioni radioprotezionistiche richiedono la valutazione e la riduzione della dose conferita dai neutroni in caso di viaggi aerei e missioni spaziali. I fasci neutronici sono oggetto di interessanti studi poich\ue9 la capacit\ue0 di trasferire una dose a un tessuto varia sensibilmente con l\u2019energia. Inoltre, tali particelle sono in grado di attivare diversi materiali con la necessit\ue0 di valutare eventuali dosi da particelle secondarie. Considerando tali peculiarit\ue0 si \ue8 studiato uno schermo per neutroni, il \u201cQuick Boron\u201d (QB), che si presenta in due versioni: rigida e flessibile. Tale materiale, testato sia sperimentalmente sia attraverso simulazioni Monte Carlo, deve le sue qualit\ue0 schermanti alla presenza del boro-10, isotopo con un\u2019elevata sezione d\u2019urto di cattura neutronica per la zona a energie termiche ( = 3840 a E=0.025 eV). Inoltre, nello studio si \ue8 valutato l\u2019accoppiamento del QB con un materiale termalizzante al fine di costituire uno schermo eterogeneo sensibile a un pi\uf9 ampio range energetico

Design and simulation of an optimized e-linac based neutron source for {BNCT} research

Abstract The paper is focused on the study of a novel photo-neutron source for {BNCT} preclinical research based on medical electron Linacs. Previous studies by the authors already demonstrated the possibility to obtain a mixed thermal and epithermal neutron flux of the order of 107 cm−2 s−1. This paper investigates possible Linac’s modifications and a new photo-converter design to rise the neutron flux above 5 107 cm−2 s−1, also reducing the gamma contamination