Mass energy-absorption coefficients and mass collision stopping powers forelectrons in tumors of various histologies

The mass energy-absorption coefficients and electron mass collision stoppin g powers have been calculated for tumors of various histologies. Eleven exc ised or biopsied tumor specimens were considered, including samples from tw o squamous cell lung carcinomas, two sarcomas, three adenoid cystic carcino mas, two melanomas and two rectal carcinomas. The hydrogen, carbon, nitroge n and oxygen composition of the tumor samples was determined. Photon mass e nergy-absorption data in the energy range 1 keV to 20 MeV have been calcula ted using elemental mass energy-absorption coefficients previously calculat ed by Hubbell and Seltzer. Electron mass collision stopping powers for ener gies between 10 keV and 60 MeV were calculated from the values for water us ing the data and methodology described in ICRU Report #37. The ratio of the average mass energy-absorption coefficient of the tumor samples to the coe fficient of water was found to be 0.99 across most of the energies of clini cal interest (>100 keV) except for photon energies of 5 MeV and above for w hich the ratio dropped to 0.48. The ratio of the average electron mass coll ision stopping power of the tumor specimens to that of water was 0.99 for a ll energies. (C) 1999 American Association of Physicists in Medicine. [S009 4-2405(99)01203-1].