Measurements of neutron fluence in high energy linear accelerator 18MV

Postgraduate Thesis uoadl:2768796 430 Read counter

Unit:
Διατμηματικό ΠΜΣ Ιατρική Φυσική-Ακτινοφυσική
Library of the School of Health Sciences
Deposit date:
2018-06-12
Year:
2018
Author:
Papadopoulos Konstantinos
Supervisors info:
Παντελής Καραΐσκος, Καθηγητής, Ιατρική, ΕΚΠΑ
Ίων Σταματελάτος, Ερευνητής Α', ΕΚΕΦΕ «Δημόκριτος»
Παναγιώτης Παπαγιάννης, Αναπληρωτής Καθηγητής, Ιατρική, ΕΚΠΑ
Original Title:
Μέτρηση ροής νετρονίων σε ιατρικό γραμμικό επιταχυντή 18MV
Languages:
Greek
Translated title:
Measurements of neutron fluence in high energy linear accelerator 18MV
Summary:
High energy linear accelerators (> 10MV) produce neutrons mainly thorough (γ,n) interactions of photons with nuclei of high atomic number materials that constitute the linear accelerator head and beam collimation system, such as target, flattening filter, primary collimators, jaws and head shielding. These neutrons have to be taken into consideration in the shielding design of the treatment room and maze and also increase the out-of-field radiation dose of patients undergoing radiation therapy with high-energy photon beams.
In the present work we validated the hypothesis that a generalized neutron source geometry representing the accelerator head can adequately simulate the neutron source in the therapy treatment room. The experimental study was performed at an Elekta Synergy1 18 MV linear accelerator. Neutron fluence measurements at the isocenter were performed using Au, Co, In and Cu activation foils (bare and Cd covered). The foil activity was determined using a calibrated high purity germanium detector. The neutron source and treatment room configuration were simulated using the Monte Carlo code MCNP5. Different simplified accelerator head geometries were examined. The neutron energy spectrum was taken from an analytical expression derived by Tosi et al 1991. The results of the simulations enabled spectrum averaged cross-sections to be derived. It was concluded that the optimal accelerator head geometry consisted of a point neutron source in the center of a spherical shell composed of tungsten of 10 cm in thickness. This work contributes towards the development of a cost effective generic methodology for optimization of the design of clinical linear accelerators radiation shielding configuration as well as the protection of staff and patients in radiotherapy using high energy accelerators.
Main subject category:
Health Sciences
Keywords:
Neutron, Fluence, Linac, Simulations, Foils
Index:
No
Number of index pages:
0
Contains images:
Yes
Number of references:
34
Number of pages:
75
Papadopoulos Konstantinos Master.pdf (1 MB) Open in new window