Measurement of Neutron Dose Equivalent within and Outside of a LINAC Treatment Vault Using a Neutron Survey Meter

Duong Thanh Tai,Truong Thi Hong Loan,Hiba Omer,Abdelmoneim Sulieman,David A Bradley,Nissren Tamam

doi:10.3390/qubs5040033

Abstract

This work concerns neutron doses associated with the use of a Siemens Primus M5497 electron accelerator, which is operated in the photon mode at 15 MV. The conditions offer a situation within which a fraction of the bremsstrahlung emission energies exceed the photoneutron threshold. For different field sizes, an investigation has been made of neutron dose equivalent values at various measurement locations, including: (i) At the treatment table, at a source-surface distance of 100 cm; (ii) at the level of the floor directly adjacent to the treatment table; and (iii) in the control room and patient waiting area. The evaluated neutron dose equivalent was found to range from 0.0001 to 8.6 mSv/h, notably with the greatest value at the level of the floor directly adjacent to the treatment couch (8.6 mSv/h) exceeding the greatest value on the treatment table (5.5 mSv/h). Low values ranging from unobservable to between 0.0001 to 0.0002 mSv/h neutron dose were recorded around the control room and patient waiting area. For measurements on the floor, the study showed the dose equivalent to be greatest with the jaws closed. These data, most particularly concerning neutron distribution within the treatment room, are of great importance in making steps towards improving patient safety via the provision of protective measures.

Highlights

Worldwide, cancer incidence has been on the rise, presently running at in excess of 19.3 million new cases annually, increasing with population growth and aging
Subsequent to the course of radiation therapy, a value of up to 19% is estimated at 30 years of age, with longer life expectancy and sensitive tissues taken into account [8,9,10]
A direct measurement of equivalent dose rate produced by neutrons from a Siemens Primus M5497 electron accelerator was performed at the Department of Nuclear Medicine

Summary

Introduction

Cancer incidence has been on the rise, presently running at in excess of 19.3 million new cases annually, increasing with population growth and aging. X-rays at potentials of greater than 10 MV can be used for the treatment of deep-seated tumors, as previously mentioned, a situation within which a fraction of the bremsstrahlung emission energies exceeds the photoneutron threshold In use of these high X-ray energies, the generation of secondary neutrons via photonuclear reactions can be expected, produced in the various materials comprising the accelerator head and its components, including the target, filter, collimator, and jaws of the accelerator, all of the items containing heavy isotopes [5]. The photon beams generated at about 10 MV and the greater neutrons can be expected to contribute at a low fraction to the patient’s dose, with the increase in secondary cancer risk For this reason, it is not considered in most dosimetric assessments [6]. This work investigates the neutron dose equivalent for different field sizes at various measurement locations in the radiotherapy department, primarily within the bunker

Materials and Methods

Dose Measurement

Findings

Detector