Paper Information

Journal:   JOURNAL OF BIOMEDICAL PHYSICS AND ENGINEERING   2018 , Volume 8 , Number 1; Page(s) 3 To 12.
 
Paper: 

ASSESSMENT OF NEUTRON CONTAMINATION ORIGINATING FROM THE PRESENCE OF WEDGE AND BLOCK IN PHOTON BEAM RADIOTHERAPY

 
 
Author(s):  BAHREYNI TOOSSI M.T., KHAJETASH B.*, GHORBANI M.
 
* MEDICAL PHYSICS DEPARTMENT, FACULTY OF MEDICINE, MASHHAD UNIVERSITY OF MEDICAL SCIENCES, PARDISE DANESHGAH, VAKIL ABAD BLVD., MASHHAD, IRAN
 
Abstract: 

Background: One of the main causes of induction of secondary cancer in radiation therapy is neutron contamination received by patients during treatment.
Objective: In the present study the impact of wedge and block on neutron contamination production is investigated. The evaluations are conducted for a 15 MV Siemens Primus linear accelerator.
Methods: Simulations were performed using MCNPX Monte Carlo code.30o, 45o and 60o wedges and a cerrobend block with dimensions of 1.5 × 1.5 × 7 cm3 were simulated. The investigation were performed in the 10 × 10 cm2 field size at source to surface distance of 100 cm for depth of 0.5, 2, 3 and 4 cm in a water phantom.
Neutron dose was calculated using F4 tally with flux to dose conversion factors and F6 tally.
Results: Results showed that the presence of wedge increases the neutron contamination when the wedge factor was considered. In addition, 45o wedge produced the most amount of neutron contamination. If the block is in the center of the field, the cerrobend block caused less neutron contamination than the open field due to absorption of neutrons and photon attenuation. The results showed that neutron contamination is less in steeper depths. The results for two tallies showed practically equivalent results.
Conclusion: Wedge causes neutron contamination hence should be considered in therapeutic protocols in which wedge is used. In terms of clinical aspects, the results of this study show that superficial tissues such as skin will tolerate more neutron contamination than the deep tissues.

 
Keyword(s): NEUTRON CONTAMINATION, WEDGE, CERROBEND BLOCK, SIEMENS PRIMUS LINAC, MONTE CARLO SIMULATION
 
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