Pi-En Tsai

Neutron spectra measurement and comparison of the HFR and THOR BNCT beams

This paper aims to measure the spectra of HB11 (high flux reactor, HFR) and the Tsing Hua open-pool reactor (THOR) boron neutron capture therapy (BNCT) beams by multiple activation foils. The self-shielding corrections were made with the aid of MCNP calculations. The initial spectra were adjusted by a sophisticated process named coarse-scaling adjustment using SAND-EX, which can adjust a given coarse-group spectrum into a fine-group structure, i.e. 640 groups, with excellent continuity. The epithermal neutron flux of the THOR beam is about three times of HB11. The thermal neutron flux, boron and gold reaction rates along the central axis of a PMMA phantom are calculated for both adjusted spectra for comparison.

BNCT EPITHERMAL NEUTRON BEAM MAPPING BY USING INDIRECT NEUTRON RADIOGRAPHY

Abstract This paper aims to measure the neutron flux distribution over the cross section of the boron neutron capture therapy epithermal neutron beam at the Tsing Hua Open-pool Reactor (THOR) by using indirect neutron radiography. It is successfully performed using an aluminum plate coupled with an imaging plate (IP). The developed high-resolution image represents the relative distribution of the neutron flux across the aluminum plate. The horizontal profiles of 28Al activity, according to the measurement using IP and calculations using MCNP with different angular source distributions, were given. In addition, horizontal profiles of 56Mn and 198Au activities measured using AuAl and MnNi foils, respectively, were provided. From the comparison between the measurements and calculations, source angular characteristics of the beam were inferred.

A preliminary study on using the radiochromic film for 2D beam profile QC/QA at the THOR BNCT facility

The GAFCHROMIC(®) EBT2 dosimetry film has been studied as a rapid QC/QA tool for 2D dose profile mapping in the BNCT beam at THOR. The pixel values of the EBT2 film image were converted to the 2D dose profile using a dose calibration curve obtained by 6-MV X-ray. The reproducibility of the 2D dose profile measured using the EBT2 film in the PMMA phantom was preliminarily found to be acceptable with uncertainties within about ±2 to ±3.5%. It is found that the EBT2 measured dose profile consisted of both gamma-ray components and neutron contributions. Therefore, the dose profile measured using the EBT2 film is significantly different from the neutron flux profile measured using the indirect neutron radiography method. Further study of the influence of neutrons to the response of the EBT2 film is indispensible for the absolute dose profile determination in a BNCT beam.

Neutron flux mapping inside a cubic and a head PMMA phantom using indirect neutron radiography.

This study aims to measure the two-dimensional (2D) neutron spatial distribution inside a cubic and a head PMMA phantom for the purpose of further comparison with the treatment planning. The measurements were made by using the indirect neutron radiography (INR), which utilized a thin copper foil and the imaging plate. The developed image provides satisfactory spatial resolution and very low statistical error (< 1%). As to the time cost, the whole procedure normally takes less than 3 h. The result shows that the indirect neutron radiography can be a quick and reliable method to provide a 2D neutron spatial distribution inside a phantom.

Quality control and quality assurance procedures at the THOR BNCT facility.

Various quality control (QC) and quality assurance (QA) procedures of the boron neutron capture therapy (BNCT) beam at the Tsing Hua Open-pool Reactor (THOR) are established to ensure beam availability and quality. The QC/QA methods mainly employ foil activation and paired ionization chambers, respectively, for beam intensity check and dose assessment. Beam intensity is monitored on-line by using three dead-time corrected fission chambers. In addition to the periodic QC/QA activities regarding beam quality and the monitoring system, the quick QC/QA performed in an all-in-one phantom will be executed less than 70 min before the clinical treatment to guarantee beam quality. The QC/QA procedures have been gradually established and the actual performance satisfied the preset criteria defined for the BNCT facility at THOR.

Performance evaluation of the source description of the THOR BNCT epithermal neutron beam

This paper aims to evaluate the performance of the source description of the THOR BNCT beam via different measurement techniques in different phantoms. The measurement included (1) the absolute reaction rate measurement of a set of triple activation foils, (2) the neutron and gamma-ray dose rates measured using the paired ionization chamber method, and (3) the relative reaction rate distributions obtained using the indirect neutron radiography. Three source descriptions, THOR-Y09, surface source file RSSA, and THOR-50C, were tested. The comparison results concluded that THOR-Y09 is a well-tested source description not only for neutron components, but also for gamma-ray component.

Increase of the beam intensity for BNCT by changing the core configuration at THOR

In this article, we will consider several core configurations and run the core calculation with MCNP to obtain the neutrons distribution at THOR. The thermal neutron flux inside the vertical tubes (VT-B-VT-E) and the fast neutron flux in the first row facing to the boron neutron capture therapy (BNCT) facility (I3-I5) were tallied for indication. Based on these simulation results, the fuel elements were rearranged during the annual repair period in 2007. The epithermal neutron flux at the center of BNCT beam exit in air was measured again, and the results showed that the beam intensity increased by 50%. Comparing the neutron intensities both in reactor core and at the BNCT beam exit for several core configurations, the results show that the BNCT beam intensity can be increased without decreasing the neutron intensity in core.