Tissue equivalency of phantom materials for neutron dosimetry in proton therapy.
OBJECTIVE
Previous Monte Carlo and experimental studies involving secondary neutrons in proton therapy have employed a number of phantom materials that are designed to represent human tissue. In this study, the authors determined the suitability of common phantom materials for dosimetry of secondary neutrons, specifically for pediatric and intracranial proton therapy treatments.


METHODS
This was achieved through comparison of the absorbed dose and dose equivalent from neutrons generated within the phantom materials and various ICRP tissues. The phantom materials chosen for comparison were Lucite, liquid water, solid water, and A150 tissue equivalent plastic, These phantom materials were compared to brain, muscle, and adipose tissues.


RESULTS
The magnitude of the doses observed were smaller than those reported in previous experimental and Monte Carlo studies, which incorporated neutrons generated in the treatment head. The results show that for both neutron absorbed dose and dose equivalent, no single phantom material gives agreement with tissue within 5% at all the points considered. Solid water gave the smallest mean variation with the tissues out of field where neutrons are the primary contributor to the total dose.


CONCLUSIONS
Of the phantom materials considered, solid water shows best agreement with tissues out of field.
Dowdell
Stephen
S
Centre for Medical Radiation Physics, University of Wollongong, Wollongong, New South Wales 2522, Australia. sjd431@uow.edu.au
Clasie
Ben
B
Wroe
Andrew
A
Guatelli
Susanna
S
Metcalfe
Peter
P
Schulte
Reinhard
R
Rosenfeld
Anatoly
A
D007390:International Agencies; D009010:Monte Carlo Method; D009502:Neutrons; D019047:Phantoms, Imaging; D061766:Proton Therapy; D011835:Radiation Protection; D011874:Radiometry / Q000295:instrumentation*; D011879:Radiotherapy Dosage; D011522:Protons
D011522:Protons