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Multiwalled Carbon Nanotubes and Radiation Dose Enhancement

S Ashmeg1*, P Zygmanski2, T Gayle1, E Eisenbraun3, E Holupka1, (1) Beth Israel Deaconess Medical Center, Boston, MA, (2) Brigham & Women's Hospital, Boston, MA,(3) SUNY Polytechnic Institute

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: study the effect of multiwalled carbon nanotubes on enhancing the radiation dose in external beam therapy.


Methods: dose to water is measured in an in-house made phantom where a farmer chamber was placed vertically and surrounded by a water bath. To the proximal water volume, multi-walled carbon nanotubes (MWCNTs) were added and the ratio of water + MWCNTs to the water only measurement was calculated, determining the dose enhancement ratio (DER). The measurements were repeated for two energies (6MV and 10MV), for two ion chamber positions (the bottom of the cylinder vs. mid-length), two MWCNTs concentrations and for graphite vs MWCNTs.


Results: The four sets of measurements results are plotted in the graph below, with the dose enhancement factor (DEF) defined as:
DEF = (Dose to water+MWCNTs)/(Dose to water only)

Set 1: The ion chamber is at the bottom of the water cylinder, 1.5 cc of MWCNTs added to water
Set 2: The ion chamber is midway of the depth of the water cylinder, 1.5 cc of MWCNTs
Set 2':The ion chamber is midway of the depth of the water cylinder, 1 cc of MWCNTs
Set 3: The ion chamber is midway of the depth of the water cylinder, 1.5 cc of graphite

The DEF is higher than 1.025 for 6MV, set 2 and lower when the MWCNTs concentration is lower or when the ion chamber is placed in the bottom of the phantom. Adding graphite to the water phantom did not increase the measured dose.The DEF decreases with increasing the photon's energy.


Conclusion: to the high aspect ratio of the multi-walled carbon nanotubes, and despite their low atomic number, a scientifically significant dose increase is measured (p-value = 0.0001).

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