Purpose: To evaluate the water and tissue equivalence of a new PRESAGE^® 3D dosimeter for proton therapy.

Methods: The GEANT4 software toolkit was used to calculate and compare total dose delivered by a proton beam with mean energy 62 MeV in a PRESAGE^® dosimeter, water, and soft tissue. The dose delivered by primary protons and secondary particles was calculated. Depth-dose profiles and isodose contours of deposited energy were compared for the materials of interest.

Results: The proton beam range was found to be ≈27 mm for PRESAGE^®, 29.9 mm for soft tissue, and 30.5 mm for water. This can be attributed to the lower collisional stopping power of water compared to soft tissue and PRESAGE^®. The difference between total dose delivered in PRESAGE^® and total dose delivered in water or tissue is less than 2% across the entire water/tissue equivalent range of the proton beam. The largest difference between total dose in PRESAGE^® and total dose in water is 1.4%, while for soft tissue it is 1.8%. In both cases, this occurs at the distal end of the beam. Nevertheless, the authors find that PRESAGE^® dosimeter is overall more tissue-equivalent than water-equivalent before the Bragg peak. After the Bragg peak, the differences in the depth doses are found to be due to differences in primary proton energy deposition; PRESAGE^® and soft tissue stop protons more rapidly than water. The dose delivered by secondary electrons in the PRESAGE^® differs by less than 1% from that in soft tissue and water. The contribution of secondary particles to the total dose is less than 4% for electrons and ≈1% for protons in all the materials of interest.

Conclusions: These results demonstrate that the new PRESAGE^® formula may be considered both a tissue- and water-equivalent 3D dosimeter for a 62 MeV proton beam. The results further suggest that tissue-equivalent thickness may provide better dosimetric and geometric accuracy than water-equivalent thickness for 3D dosimetry of this proton beam.

Item Type:	Refereed Article
Keywords:	3D dosimetry, PRESAGE, proton beam, Monte Carlo, GEANT4
Research Division:	Physical Sciences
Research Group:	Medical and biological physics
Research Field:	Medical physics
Objective Division:	Health
Objective Group:	Other health
Objective Field:	Other health not elsewhere classified
UTAS Author:	Baldock, C (Professor Clive Baldock)
ID Code:	97826
Year Published:	2012
Web of Science® Times Cited:	24
Deposited By:	Office of the School of Engineering
Deposited On:	2015-01-14
Last Modified:	2017-11-01
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