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.
- 3D dosimetry
- Monte Carlo
- proton beam
Gorjiara, T., Kuncic, Z., Doran, S., Adamovics, J., & Baldock, C. (2012). Water and tissue equivalence of a new PRESAGE® formulation for 3D proton beam dosimetry: a Monte Carlo study. Medical Physics, 39(11), 7071-7079. https://doi.org/10.1118/1.4757922