Finnish Dosimetric Practice for Epithermal Neutron Beam Dosimetry in Boron Neutron Capture Therapy

Boron neutron capture therapy (BNCT) is a form of chemically targeted radiotherapy that utilises the high neutron capture cross-section of boron-10 isotope to achieve a preferential dose increase in the tumour. The BNCT dosimetry poses a special challenge as the radiation dose absorbed by the irradiated tissues consists of several dose different components. Dosimetry is important as the effect of the radiation on the tissue is correlated with the radiation dose. Consistent and reliable radiation dose delivery and dosimetry are thus basic requirements for radiotherapy. The international recommendations for are not directly applicable to BNCT dosimetry. The existing dosimetry guidance for BNCT provides recommendations but also calls for investigating for complementary methods for comparison and improved accuracy. In this thesis the quality assurance and stability measurements of the neutron beam monitors used in dose delivery are presented. The beam monitors were found not to be affected by the presence of a phantom in the beam and that the effect of the reactor core power distribution was less than 1%. The weekly stability test with activation detectors has been generally reproducible within the recommended tolerance value of 2%. An established toolkit for epithermal neutron beams for determination of the dose components is presented and applied in an international dosimetric intercomparison. The measured quantities (neutron flux, fast neutron and photon dose) by the groups in the intercomparison were generally in agreement within the stated uncertainties. However, the uncertainties were large, ranging from 3-30% (1 standard deviation), emphasising the importance of dosimetric intercomparisons if clinical data is to be compared between different centers. Measurements with the Exradin type 2M ionisation chamber have been repeated in the epithermal neutron beam in the same measurement configuration over the course of 10 years. The presented results exclude severe sensitivity changes to thermal neutrons that have been reported for this type of chamber. Microdosimetry and polymer gel dosimetry as complementary methods for epithermal neutron beam dosimetry are studied. For microdosimetry the comparison of results with ionisation chambers and computer simulation showed that the photon dose measured with microdosimetry was lower than with the two other methods. The disagreement was within the uncertainties. For neutron dose the simulation and microdosimetry results agreed within 10% while the ionisation chamber technique gave 10-30% lower neutron dose rates than the two other methods. The response of the BANG-3 gel was found to be linear for both photon and epithermal neutron beam irradiation. The dose distribution normalised to dose maximum measured by MAGIC polymer gel was found to agree well with the simulated result near the dose maximum while the spatial difference between measured and simulated 30% isodose line was more than 1 cm. In both the BANG-3 and MAGIC gel studies, the interpretation of the results was complicated by the presence of high-LET radiation.Boorineutronisädehoito (BNCT-hoito) on kemiallisesti kohdennettu sädehoito, jossa säteilyn vaikutus kohdennetaan kasvaimeen hyödyntämällä boori-10 isotoopin neutronikaappausreaktiota ja kasvainsoluihin hakeutuvaa kantaja-ainetta. BNCT:n säteilyannoksen määritys on haasteellista, koska säteilyannos koostuu useista biologisilta vaikutuksiltaan erilaisista annoskomponenteista. Säteilyannoksen määritys on tärkeää, koska sädehoidon vaikutus riippuu potilaan saamasta säteilyannoksesta. Sädehoidon annosmittauksen kansainväliset suositukset eivät suoraan sovellu BNCT annosmittauksiin. Olemassa oleva BNCT annosmittausohjeistus antaa menetelmäsuosituksia, mutta myös kehottaa tutkimaan vaihtoehtoisia annosmittausmenetelmiä tulosten vertailtavuuden ja menetelmien tarkkuuden parantamiseksi. Tässä väitöskirjassa esitetään BNCT-hoidoissa käytettävän neutronisäteilykeilan laadunvarmistusmittauksia ja vertaillaan niitä kansainväliseen suositukseen. Säteilykeilassa oleva testikappale ei vaikuttanut annosmonitorikammion herkkyyteen ja reaktorin tehojakauman vaikutus oli alle 1%. Viikoittainen tasaisuusmittaus on ollut yleisesti suositellun 2% vaihteluvälin rajoissa. Väitöskirjassa esitellään neutronisäteilykeilan annosmittauksiin kehitetty mittavälinekokonaisuus ja sitä käytetään kansainvälisessä annosvertailututkimuksessa. Annosvertailuun osallistuneiden ryhmien mittaustulokset (neutroni vuo, nopeiden neutronien annos ja fotoniannos) olivat yleisesti yhtenevät mittauksiin liittyvien epävarmuuksien puitteissa. Epävarmuusrajat olivat suuret, 3-30% (1 keskihajonta) riippuen mittausmenetelmästä. Tulokset korostavat osaltaan annosvertailujen tärkeyttä, jotta kliinisiä tuloksia eri BNCT-hoitokeskusten välillä voidaan verrata. Otaniemen tutkimusreaktorin neutronikeilassa on tehty 10 vuoden aikana mittauksia samanlaisessa mittausgeometriassa Exradin 2M -mallisella ionisaatiokammiolla. Tässä työssä esitetyt tulokset näistä mittauksista poissulkevat merkittävät herkkyysmuutokset, jollaisia on raportoitu tämän malliselle ionisaatiokammiolle. Väitöskirjassa selvitetään lisäksi verrannollisuuskammiolla ja geeliannosmittareilla saavutettavaa hyötyä epitermisen neutronikeilan annosmittauksissa. Verrannollisuuskammiolla mitattuna fotoniannos oli alhaisempi kuin ionisaatiokammiolla tai tietokonesimulaatiolla laskettu fotoniannos. Neutroniannoksen osalta verrannollisuuskammiomittaukset ja tietokonesimulaatiotulokset olivat yhteneviä 10% tarkkuudella, kun taas ionisaatiokammiomittauksilla saatiin 10-30% alhaisempia neutroniannoksia. BANG-3 -tyyppisen geeliannosmittarin vaste havaittiin lineaariseksi sekä fotoni- että epitermisessä neutronikeilassa. MAGIC-tyyppisen geeliannosmittarin annosmaksimiin normitettu annos vastasi tietokonesimulaation perusteella laskettua annosjakaumaa, mutta yhteneväisyys oli heikompi pienemmän annoksen alueella

Radiation Doses to Staff in a Hybrid Operating Room : An Anthropomorphic Phantom Study with Active Electronic Dosimeters

Objective: To quantify the effects of different imaging settings on radiation exposure to the operator and surgical team in a hybrid operating room (OR). Methods: Measurements to determine scatter radiation in different imaging and geometry settings using an anthropomorphic phantom were performed in a hybrid OR equipped with a robotic C arm interventional angiography system (Artis Zeego; Siemens Healthcare, Erlangen, Germany). The radiation dose (RD) was measured with seven calibrated Philips DoseAware active electronic dosimeters and a Raysafe Xi survey detector, which were placed at different locations in the hybrid OR. The evaluated set ups included low dose, medium dose, and high dose fluoroscopy for abdomen; fluoroscopy fade; roadmap; and digital subtraction angiography (DSA), all using 20 s exposures. The effect of magnification, tube angulation, field size, source to skin distance, and RADPAD protection shields were assessed. Finally RD during cone beam computed tomography (CBCT) was obtained. Results: In the operator position the initial settings with low dose fluoroscopy caused a RD of 1.03 mu Gy. The use of fluorofade did not increase the radiation dose (1.02 mu Gy), whereas the roadmap increased it threefold (2.84 mu Gy). The RD with "normal fluoro" was 4.13 mu Gy and increased to 6.44 mu Gy when high dose fluoroscopy mode was used. Magnification or field size varying from 42 cm to 11 cm led the RD to change from 0.86 mu Gy to 2.10 mu Gy. Decreasing the field of view to 25% of the initial size halved the RD (0.48 mu Gy). The RDs for the left anterior oblique 30 degrees and right anterior oblique 30 degrees were 3.26 mu Gy and 1.63 mu Gy, respectively. DSA increased the cumulative dose 33 fold but the RADPAD shield decreased the DSA RD to 4.92 mu Gy. The RD for CBCT was 47.2 mu Gy. Conclusion: Radiation exposure to operator and personnel can be significantly reduced during hybrid procedures with proper radiation protection and dose optimisation. A set of six behavioural rules were established.Peer reviewe

Effect of the Calibration in Water and the Build-up Cap on the Mg(Ar) Ionization Chamber Measurements

Non Peer reviewe

MAGIC polymer gel for dosimetric verification in boron neutron capture therapy

"Radiation-sensitive polymer gels are among the most promising three-dimensional dose verification tools developed to date. We tested the normoxic polymer gel dosimeter known by the acronym MAGIC (methacrylic and ascorbic acid in gelatin initiated by copper) to evaluate its use in boron neutron capture therapy (BNCT) dosimetry. We irradiated a large cylindrical gel phantom (diameter: 10 cm; length: 20 cm) in the epithermal neutron beam of the Finnish BNCT facility at the FiR 1 nuclear reactor. Neutron irradiation was simulated with a Monte Carlo radiation transport code MCNP. To compare dose-response, gel samples from the same production batch were also irradiated with 6 MV photons from a medical linear accelerator. Irradiated gel phantoms then underwent magnetic resonance imaging to determine their R2 relaxation rate maps. The measured and normalized dose distribution in the epithermal neutron beam was compared with the dose distribution calculated by computer simulation. The results support the feasibility of using MAGIC gel in BNCT dosimetry.""Radiation-sensitive polymer gels are among the most promising three-dimensional dose verification tools developed to date. We tested the normoxic polymer gel dosimeter known by the acronym MAGIC (methacrylic and ascorbic acid in gelatin initiated by copper) to evaluate its use in boron neutron capture therapy (BNCT) dosimetry. We irradiated a large cylindrical gel phantom (diameter: 10 cm; length: 20 cm) in the epithermal neutron beam of the Finnish BNCT facility at the FiR 1 nuclear reactor. Neutron irradiation was simulated with a Monte Carlo radiation transport code MCNP. To compare dose-response, gel samples from the same production batch were also irradiated with 6 MV photons from a medical linear accelerator. Irradiated gel phantoms then underwent magnetic resonance imaging to determine their R2 relaxation rate maps. The measured and normalized dose distribution in the epithermal neutron beam was compared with the dose distribution calculated by computer simulation. The results support the feasibility of using MAGIC gel in BNCT dosimetry.""Radiation-sensitive polymer gels are among the most promising three-dimensional dose verification tools developed to date. We tested the normoxic polymer gel dosimeter known by the acronym MAGIC (methacrylic and ascorbic acid in gelatin initiated by copper) to evaluate its use in boron neutron capture therapy (BNCT) dosimetry. We irradiated a large cylindrical gel phantom (diameter: 10 cm; length: 20 cm) in the epithermal neutron beam of the Finnish BNCT facility at the FiR 1 nuclear reactor. Neutron irradiation was simulated with a Monte Carlo radiation transport code MCNP. To compare dose-response, gel samples from the same production batch were also irradiated with 6 MV photons from a medical linear accelerator. Irradiated gel phantoms then underwent magnetic resonance imaging to determine their R2 relaxation rate maps. The measured and normalized dose distribution in the epithermal neutron beam was compared with the dose distribution calculated by computer simulation. The results support the feasibility of using MAGIC gel in BNCT dosimetry."Peer reviewe

Intraoperative CBCT imaging in endovascular abdomen aneurysm repair-Optimization of exposure parameters using a stent phantom

Cone beam computed tomography (CBCT) may provide essential additional image guidance to endovascular abdominal aneurysm repair (EVAR) operations but also significant radiation exposure to patients if scans are not carefully optimized. The purpose of our study was to define the image quality requirements for intraoperative EVAR CBCT imaging and to optimize the CBCT exposure parameters accordingly. A Multi-Energy CT phantom simulating a large patient was used by replacing the central phantom cylinder with a custom water-filled insert including an EVAR stent. Different exposure parameters covering a range of radiation qualities and dose levels were used to define the optimal image quality level regarding stent graft evaluation (compressed, bent, or collapsed). The radiation dose was measured with a calibrated air kerma-area product (KAP) meter and organ doses were calculated based on Monte Carlo simulations and a mathematical patient model. Based on the results, updated exposure parameters with the highest mean energy and lowest dose level available were recommended. With the updated protocol, the radiation exposure could be significantly decreased. The KAP value decreased from 9720 mu Gy center dot m(2) to 440 mu Gy center dot m(2) and reference point air kerma from 351 mGy to 16 mGy (a reduction of 96%) and organ doses of the organs in the irradiated region decreased on an average 91%. The new protocol resulted in acceptable clinical image quality based on testing with clinical cases.Peer reviewe