Dose planning with comparison to in vivo dosimetry for epithermal neutron irradiation of the dog brain

Abstract

Boron neutron capture therapy (BNCT) is an experimental type of radiotherapy, presently being used to treat glioblastoma and melanoma. To improve patient safety and to determine the radiobiological characteristics of the epithermal neutron beam of Finnish BNCT facility (FiR 1) dose-response studies were carried on the brain of dogs before starting the clinical trials. A dose planning procedure was developed and uncertainties of the epithermal neutron-induced doses were estimated. The accuracy of the method of computing physical doses was assessed by comparing with in vivo dosimetry. Individual radiation dose plans were computed using magnetic resonance images of the heads of 15 Beagle dogs and the computational model of the FiR 1 epithermal neutron beam. For in vivo dosimetry, the thermal neutron fluences were measured using Mn activation foils and the gamma-ray doses with MCP-7s type thermoluminescent detectors placed both on the skin surface of the head and in the oral cavity. The degree of uncertainty of the reference doses at the thermal neutron maximum was estimated using a dose-planning program. The estimated uncertainty (+/-1 standard deviation) in the total physical reference dose was +/-8.9%. The calculated and the measured dose values agreed within the uncertainties at the point of beam entry. The conclusion is that the dose delivery to the tissue can be verified in a practical and reliable fashion by placing an activation dosimeter and a TL detector at the beam entry point on the skin surface with homogeneous tissues below. However, the point doses cannot be calculated correctly in the inhomogeneous area near air cavities of the head model with this type of dose-planning program. This calls for attention in dose planning in human clinical trials in the corresponding areas.

Prompt gamma tomography during BNCT—a feasibility study

“…One in which the system directly determines the boron absorbed dose through the neutron capture events in boron (as well as other capture events), and one in which the measured boron count rate is normalised against the count rate measured for hydrogen in order to determine the boron concentration distribution (see refs. [16], [17]). The determination of the boron concentration is arguably less interesting, as it would then require the use of a priori (e.g.…”

“…in the verification and monitoring of the treatment actually performed. Generally, foils and thermo-luminescent dosimeters (TLDs) have been used to assess the neutron and gamma dose at the skin of the patient [16], [17]. As these measurements give no information about the boron uptake in deep-seated tissues their clinical significance for boron dosimetry is deficient.…”

Novel Pharmacological and Magnetic Resonance Strategies to Enhance Boron Neutron Capture Therapy (BNCT) Efficacy in the Clinical Treatment of Malignant Glioma

“…To overcome this, the use of higher energy epithermal neutron beams was pursued because of their greater tissue penetrating properties. Indeed, when epithermal neutrons penetrate tissues, they are slowed down into the thermal neutron range (Seppälä et al, 2002, Coderre et al, 1997 by means of collisions with atoms (Fig. 2).…”