

@mastersthesis {6421,
	title = {Dosimetry and heterogeneity effects in the d(48.5)+{Be} neutron beam at the {Harper} {Hospital} superconducting cyclotron},
	year = {1999},
	note = {9933032},
	school = {Wayne State University},
	type = {phdPh.{D}.},
	address = {Ann Arbor},
	abstract = {To implement the tissue heterogeneity corrections into neutron therapy treatment planning the influences of heterogeneities on the dose distribution were examined in Harper Hospital superconducting cyclotron d(48.5)+Be beam. Comprehensive sets of measurements were done using ionization detectors and TLD-300 in phantoms consisting of different materials: tissue-equivalent (A150), bone-equivalent (B100 and B110), lung equivalent (LNSR4) and adipose equivalent (AVBRIII) plastics. The measurements were done at the interfaces as well as inside and around the materials under conditions of secondary charged particle equilibrium. In addition scans in a water phantom were done in the vicinity of the heterogeneities to simulate various clinical situations. The dose in the interface region between A150, B100 and AVBRIII characterized by a build-up or build-down pattern, depending on the ratio of these materials. No such effects were found between LNSR4 and A150 plastics. The perturbations caused by the introduction of the heterogeneity compared to homogeneous phantom could be explained by the kerma and density effects. To prove that the semi-empirical methods of heterogeneity corrections used in photon dosimetry may be applied to neutron calculations scaling parameters were derived to convert the dose distribution from one phantom material to another. Scaling factor defined as the product of the density and the kerma ratio gave the best agreement with the experimental results. The heterogeneity correction methods based on the Modified Power Law and Equivalent TAR were tested. The correction factor used with the Modified Power Law method was altered to account for the material kerma while the density parameter used in the original formula was replaced by the scaling factor defined above. The application of this method resulted in good agreement between the measurements and calculations at the points behind the heterogeneities. Different set of scaling factors derived from Tissue-to Maximum Ratio measurements in various phantoms was used with the Equivalent TAR method. The agreement of this method with the measurements performed lateral to the heterogeneities was less accurate, although the dose perturbation observed at these points was small. A clinical example of dose calculation in lung region was tested. A pattern of dose perturbation due to the lung material similar to that of 4 MV photon beam was observed. The results demonstrate that Modified Power Law method may be used in this situation. The experimental data may be used in future modeling of the d(48.5)+Be neutron beam at the Harper Hospital superconducting cyclotron.},
	keywords = {0756:Radiation, 0992:Oncology, Cyclotron, Dosimetry, Health and environmental sciences, Neutron beam, Oncology, Pure sciences, Radiation, Superconducting cyclotron},
	url = {http://search.proquest.com/docview/304534181?accountid=14270},
	author = {Yudelev, Mark}
}
