Adaptive tree multigrids and simplified spherical harmonics approximation in deterministic neutral and charged particle transport

A new deterministic three-dimensional neutral and charged particle transport code, MultiTrans, has been developed. In the novel approach, the adaptive tree multigrid technique is used in conjunction with simplified spherical harmonics approximation of the Boltzmann transport equation. The development of the new radiation transport code started in the framework of the Finnish boron neutron capture therapy (BNCT) project. Since the application of the MultiTrans code to BNCT dose planning problems, the testing and development of the MultiTrans code has continued in conventional radiotherapy and reactor physics applications. In this thesis, an overview of different numerical radiation transport methods is first given. Special features of the simplified spherical harmonics method and the adaptive tree multigrid technique are then reviewed. The usefulness of the new MultiTrans code has been indicated by verifying and validating the code performance for different types of neutral and charged particle transport problems, reported in separate publications.Väitöstutkimuksen tuloksena on kehitetty uusi tietokoneohjelma varauksettomien ja varauksellisten hiukkasten kuten neutronien, fotonien ja elektronien etenemisen mallinnukseen. MultiTrans-ohjelma mahdollistaa säteilyn etenemisen mallinnuksen mielivaltaisessa 3D-geometriassa. Laskentageometria generoidaan suoraan CAD-mallista, jolloin voidaan käyttää moderneja suunnittelutyökaluja. Laskentaverkko on puumaisesti itsetarkentuva materiaalien rajapinnoilla, joissa hila muodostuu automaattisesti hienojakoisimmaksi. Näin monimutkainenkin geometria voidaan kuvata yksityiskohtaisesti merkittävästi pienemmällä hilapisteiden määrällä verrattuna tasajakoiseen hilaan. Laskentaverkon puumaisuudesta seuraa että ongelmalle löytyy aina myös karkeammat hilaesitykset. Tällöin kuljetusyhtälön iteratiivisessa ratkaisussa voidaan käyttää ns. moniverkkotekniikkaa jossa ongelma ratkaistaan ensin hyvin karkeassa esityksessä ja tätä ratkaisua käytetään alkuarvauksena yhä hienojakoisemmissa hiloissa. Näin nopeutetaan iteratiivisen ratkaisun löytymistä huomattavasti. Myös laskentaverkon puumaisuus ja sen myötä hilapisteiden vähäisempi määrä nopeuttaa iteratiivista ratkaisua. Kyseessä on tiettävästä ensimmäinen puumoniverkkotekniikan sovellutus säteilyn etenemisen mallinnukseen. MultiTransia on testattu erilaisten sädehoitojen (esimerkiksi VTT:n Otaniemen ydintutkimusreaktorilla annettavan boorineutronikaappaushoidon) sekä reaktorifysiikan laskentaongelmiin. Ongelmaksi on jossain määrin osoittautunut säteilyn kulkeutumisyhtälölle käytetty yksinkertaistettu palloharmoninen kehitelmä, jonka tarkkuus ei kaikissa tapauksissa vastaa asetettuja vaatimuksia

Epithermal Neutron Beam Interference with Cardiac Pacemakers

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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