The neutron dose and energy spectrum outside a 20‐MV accelerator treatment room

Abstract

A maze design is discussed for a Therac 20 linear accelerator (manufactured by Atomic Energy of Canada, Ltd.) which reduces the flux of neutrons at the door to permissible levels in controlled areas. The L-shaped design allows for a relatively light door at the end of the maze, consisting of 5.08-cm (2-in.) borated polyethylene and 2-mm lead. A comparison is made between the neutron dose equivalent (DE) calculated by various methods and the DE measured with a variety of portable neutron survey meters. In addition, the neutron energy spectrum outside the maze at 1 m from the door, measured with a polyethylene multisphere LiI system, is reported.

Photoneutron and capture gamma dose calculations for a radiotherapy room made of high density concrete

“…It is seen that among the stud ied an a lyt i cal meth ods, the Wu-McGinley and then French meth ods pro vide better re sults com par ing to MC re sults for neu tron dose equiv a lents at the maze en trance door. The re sults were very sim i lar to the results of Mul ler-Runkel et al, who showed that the French method acts better than Ker sey and Mc Call meth ods in a ra di a tion ther apy room with 20 MeV pho tons [23]. Monte Carlo and ex per i men tal stud ies have shown that an a lyt i cal meth ods over es ti mate the neu tron dose equiv a lent at the maze en trance door [14].…”

A new analytical formula for neutron capture gamma dose calculations in double-bend mazes in radiation therapy

“…of borated polyethylene, most of (n, ) interactions occurred with Boron atoms and gamma rays with average energy of 0.4 MeV released in the process. 15 In another study by Tochilin and LaRiviere, average energy of 3.6 MeV was reported for capture gamma rays. 20 Finally, capture gamma rays are found at the maze entrance door and their effect on maze entrance door shielding should be considered in radiation therapy facilities.…”

“…[1][2][3][4] On the other hand, it is associated with unwanted photonuclear reaction between high energy photons and linac head materials, patient body and treatment room walls. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] Production of photoneutrons occurs through photonuclear reactions, and consequently high energy gamma rays can be generated in the maze, following the capture process of thermalized neutrons. 16 Both photoneutrons and neutron capture gamma rays are considered as undesirable radiations from radiation protection point of view, because they increase the patient and staff whole body radiation dose.…”

“…Prompt capture gamma ray emissions within the maze have been studied by several researchers and the energy range from 2 MeV to 8 MeV has been reported for these gamma rays. 15,21 A study showed that in the mazes with 2 in. of borated polyethylene, most of (n, ) interactions occurred with Boron atoms and gamma rays with average energy of 0.4 MeV released in the process.…”

Δοσιμετρικοί Υπολογισμοί Νετρονίων Σε Επιταχυντές Υψηλής Ενέργειας

“…Οι μέθοδοι αυτές βασίζονται σε πειραματικές μετρήσεις, λαμβάνοντας υπόψη τα επιμέρους γεωμετρικά χαρακτηριστικά των θαλάμων. Ωστόσο έχουν παρατηρηθεί σημαντικές διαφορές ανάμεσα στα αποτελέσματα των υπολογισμών και των πειραματικών μετρήσεων (Muller-Runkel et al 1986). Ειδικότερα, σε περιπτώσεις θαλάμων θεραπείας ειδικής κατασκευής οι διαφορές αυτές είναι μεγάλες και οι ημιεμπειρικές τεχνικές προσδιορισμού της δόσης στο θάλαμο θεραπείας δεν μπορούν να εφαρμοστούν.…”