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Ethylene‐vinyl acetate foam as a new lung substitute in radiotherapy
Author(s) -
Marqués Enrique,
Mancha Pedro J.
Publication year - 2018
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1002/mp.12781
Subject(s) - materials science , imaging phantom , dosimetry , absorbed dose , ethylene vinyl acetate , composite material , nuclear medicine , copolymer , medicine , polymer
Purpose The purpose of this study was to evaluate ethylene‐vinyl acetate (EVA) foam as a new lung substitute in radiotherapy and to study its physical and dosimetric characteristics. Methods We calculated the ideal vinyl acetate (VA) content of EVA foam sheets to mimic the physical and dosimetric characteristics of the ICRU lung tissue. We also computed the water‐to‐medium mass collision stopping power ratios, mass attenuation coefficients, CT numbers, effective atomic numbers and electron densities for: ICRU lung tissue, the RANDO commercial phantom, scaled WATER and EVA foam sheets with varying VA contents in a range between the minimum and maximum values supplied by the manufacturer. For all these substitutes, we simulated percent depth‐dose curves with EGSnrc Monte Carlo (MC PDDs) in a water‐lung substitute‐water slab phantom expressed as dose‐to‐medium and dose‐to‐water for 3 × 3‐ and 10 × 10‐cm 2 field sizes. PDD for the 10 × 10‐cm 2 field size was also calculated with the MultiGrid Superposition algorithm (MGS PDD) for a relative electron density to water ratio of 0.26. The latter was compared with the MC PDDs in dose‐to‐water for scaled WATER and EVA foam sheets with the VA content that was most similar to the calculated ideal content that is physically achievable in practice. Results We calculated an ideal VA content of 55%; however, the maximum physically achievable content with current manufacturing techniques is 40%. The physical characteristics of the EVA foam sheets with a VA content of 40% (EVA40) are very close to those of the ICRU lung reference. The physical densities of the EVA40 foam sheets ranged from 0.030 to 0.965 g/cm 3 , almost covering the entire physical density range of the inflated/deflated lung (0.260–1.050 g/cm 3 ). Its mass attenuation coefficient at the effective energy of a 6‐MV photon beam agrees within 0.8% of the ICRU reference value, and its CT number agrees within 6 HU. The effective atomic number for EVA40 varies by less than 0.42 of the ICRU value, and its effective electron density is within 0.9%. PDDs expressed in dose‐to‐medium and dose‐to‐water agree with the ICRU curve within 2% in all regions. PDDs calculated with both MC and MGS were within 1.5%. Conclusions The EVA40 is an excellent cork‐like lung substitute for radiotherapy applications. From a sole material used in footwear, it is possible to obtain a lung substitute that mimics the physical and dosimetric characteristics of ICRU lung tissue even better than the RANDO commercial phantom.