gms | German Medical Science

48th Meeting of the Particle Therapy Co-Operative Group

Particle Therapy Co-Operative Group (PTCOG)

28.09. - 03.10.2009, Heidelberg

Analytic estimates of secondary neutron dose in double scattering and uniform scanning modes of proton therapy

Meeting Abstract

Search Medline for

  • V. Anferov - Indiana University Cyclotron Facility, Bloomington, USA

PTCOG 48. Meeting of the Particle Therapy Co-Operative Group. Heidelberg, 28.09.-03.10.2009. Düsseldorf: German Medical Science GMS Publishing House; 2009. Doc09ptcog011

doi: 10.3205/09ptcog011, urn:nbn:de:0183-09ptcog0118

Published: September 24, 2009

© 2009 Anferov.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( You are free: to Share – to copy, distribute and transmit the work, provided the original author and source are credited.



Purpose: Proton beam losses in the treatment nozzle generate secondary neutrons, which bring unwanted out of field dose during treatments. The purpose of this study is to develop an analytic method for estimating neutron dose to a particular organ at risk during proton therapy.

Methods: Based upon radiation shielding calculation methods proposed by Sullivan, we have developed an analytical model for converting the proton beam losses in the nozzle components and in the treatment volume into the secondary neutron dose at a point of interest. Using MCNPx Monte Carlo code we have benchmarked the neutron dose rates generated by proton beam stopped at various media.

Results: The Monte Carlo calculations suggest that the neutron production in water laterally to the incident beam direction is about factor of five smaller than in iron or copper. This indicates that the neutron dose to a distant organ at risk will be predominated by the protons lost in the patient collimator. Furthermore, the analytical estimates suggest that the neutron dose scales linearly with the number of protons lost in the patient aperture, which means that the neutron dose is very sensitive to the beam usage efficiency.

Conclusion: The results of the study suggest that dominant part of the secondary neutron dose to the patient results from the patient specific aperture. Improving conformity of the radiation field to the patient specific aperture can significantly reduce secondary neutron dose to the patient. Therefore, it is important to increase the number of available generic field sizes in double scattering systems as well as in uniform scanning nozzles.