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Variations in energy spectra and water-to-material stopping-power ratios in three-dimensional conformal and intensity-modulated photon fields

, : Variations in energy spectra and water-to-material stopping-power ratios in three-dimensional conformal and intensity-modulated photon fields. Medical Physics 34(4): 1388-1397

Because of complex dose distributions and dose gradients that are created in three-dimensional conformal radiotherapy (3D-CRT) and intensity-modulated radiation therapy (IMRT), photon- and electron-energy spectra might change significantly with spatial locations and doses. This study examined variations in photon- and electron-energy spectra in 3D-CRT and IMRT photon fields. The effects of spectral variations on water-to-material stopping-power ratios used in Monte Carlo treatment planning systems and the responses of energy-dependent dosimeters, such as thermoluminescent dosimeters (TLDs) and radiographic films were further studied. The EGSnrc Monte Carlo code was used to simulate megavoltage 3D-CRT and IMRT photon fields. The photon- and electron-energy spectra were calculated in 3D water phantoms and anthropomorphic phantoms based on the fluence scored in voxel grids. We then obtained the water-to-material stopping-power ratios in the local voxels using the Spencer-Attix cavity theory. Changes in the responses of films and TLDs were estimated based on the calculated local energy spectra and published data on the dosimeter energy dependency. Results showed that the photon-energy spectra strongly depended on spatial positions and doses in both the 3D-CRT and IMRT fields. The relative fraction of low-energy photons (< 100 keV) increased inversely with the photon dose in low-dose regions of the fields. A similar but smaller effect was observed for electrons in the phantoms. The maximum variation of the water-to-material stopping-power ratio over the range of calculated dose for both 3D-CRT and IMRT was negligible (< 1.0%) for ICRU tissue, cortical bone, and soft bone and less than 3.6% for dry air and lung. Because of spectral softening at low doses, radiographic films in the phantoms could over-respond to dose by more than 30%, whereas the over-response of TLDs was less than 10%. Thus, spatial variations of the photon- and electron-energy spectra should be considered as important factors in 3D-CRT and IMRT dosimetry.


PMID: 17500470

DOI: 10.1118/1.2710550

Other references

Burrini, Ag, 1970: Research on the ultrastructure of the intestines of insects. vI. the absorption of glucides using autoradiography. Redia 71, (ser 3) 52 183-188

Hraste, J.; Kordić, S.; Kosovel, Z.; Leusić, Z.; Mise, I.; Smerdelj, S., 1972: Development and promotion of dentistry in the Socialist Republic of Croatia. Acta Stomatologica Croatica 7(3): 125-136

Amiri, F.; Ghiyasvandian, S.; Navab, E.; Zakerimoghadam, M., 2017: Corneal transplantation: A new view of life. The consequences of a corneal transplant are evaluated and classified by care providers, but understanding and interpretation of the results varies between patients, and creates different views for them and influences their lives in different ways...

Fliedner, T.M.; Cronkite, E.P.; Bond, V.P., 1963: Studies on myelocytic cell turnover in bone marrow and blood. Nuclear-Medizin 2: Suppl 1:279-94

Falck, J.; Mailand, N.; Syljuåsen, R.G.; Bartek, J.; Lukas, J., 2001: The ATM-Chk2-Cdc25A checkpoint pathway guards against radioresistant DNA synthesis. When exposed to ionizing radiation (IR), eukaryotic cells activate checkpoint pathways to delay the progression of the cell cycle. Defects in the IR-induced S-phase checkpoint cause 'radioresistant DNA synthesis', a phenomenon that has b...

Kronenberger, W.G.; Thompson, R.J., 1992: Psychological adaptation of mothers of children with spina bifida: association with dimensions of social relationships. Investigated the hypothesis that dimensions of social relationships such as family support, conflict, and control; marital quality/support, social support, and social coping are associated with the psychological adjustment of mothers of children w...

Kornberg, A.; Spudich, J.A.; Nelson, D.L.; Deutscher, M.P., 1968: Origin of proteins in sporulation. Annual Review of Biochemistry 37: 51-78

Jackson, P., 1969: Traffic accident--back on the road. Canadian Journal of Occupational Therapy. Revue Canadienne D'ergotherapie 36(2): 61-4 Passim

McTiernan, C.D.; Alarcon, E.Isaac.; Hallett-Tapley, G.L.; Murillo-Lopez, J.; Arratia-Perez, R.; Netto-Ferreira, J.Carlos.; Scaiano, J.C., 2013: Electron transfer from the benzophenone triplet excited state directs the photochemical synthesis of gold nanoparticles. The rarely recognized electron donating ability of the benzophenone triplet excited state provides an unusual route for the photochemical synthesis of gold nanoparticles.

Kousalya, G.; Ayyavoo, R.; Krishnamurthy, C.S.; Kandaswamy, T.K.; Bhaskaran, S., 1971: Effect of spacing, roguing and weeding on the incidence of rosette disease of groundnut with observations on the aphid vector, Aphis craccivora Koch. In field tests in 1964 at two places in Tamil Nadu, India, the effects of spacing, roguing and weeding on the incidence of rosette disease of groundnut and its vector Aphis craccivora Koch were investigated. Eight spacings (varying from 6 X 6 in....