Heterogeneity and scatter effects on Ir-192 brachytherapy dose distribution.
We studied the effects of the presence of an air cavity and scatter due to patient size on dose distribution near an Iriduim-192 brachytherapy source (Ir-192). The source was modeled using Monte Carlo (MC) code MCNP5. The Radial dose, gL(r), and the anisotropy function, F(r,θ) specified by the AAPM TG-43 have been determined and compared with the consensus data (AAPM report No. 229). We compared our MC results to the measured dose distribution using an EBT3 Gafchromic® film measurement. The dose was determined in the presence of an air cavity of 3, 5, and 7mm diameters located at 2mm distance from Ir-192. The dose was also determined for Ir-192 centered in 30×30×30cm3and 80×80×80cm3water phantoms. The MC results of gL(r) and F(r,θ) agreed with the consensus data to within 2% and 3%, respectively. The MC and the measured dose distributions agreed well with a maximum difference of 8.2% at the periphery of the film. The dose at 10cm from the Ir-192 source with a full scattering medium (80×80×80cm3) was 7% higher compared to the dose in (30×30×30cm3) water phantom. The dose to water in the presence of a 3, 5, and 7mm diameter air cavity increased by an average of 3%, 6%, and 9%, respectively, compared to the dose with no air cavity. Ignoring scatter effects and the heterogeneity correction in the presence of an air cavity can lead to significant errors in dose delivered to patients.
Department of Physics, King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia.
Alexander F I
AF
Osman
Department of Physics, King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia. Electronic address: maalej@kfupm.edu.sa.
Nabil
N
Maalej
Department of Physics, King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia.
Khateeb
K
Ul-Rahman
Radiation Oncology Department, King Fahd Specialist Hospital, Dammam, Saudi Arabia.
Wamied Abdel
WA
Rahman
D000388:Air; D016880:Anisotropy; D055592:Biophysical Phenomena; D049628:Body Size; D001918:Brachytherapy / Q000379:methods* / Q000706:statistics & numerical data; D003198:Computer Simulation; D005373:Film Dosimetry / Q000706:statistics & numerical data; D006801:Humans; D007496:Iridium Radioisotopes / Q000627:therapeutic use*; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011874:Radiometry / Q000706:statistics & numerical data; D011879:Radiotherapy Dosage; D012542:Scattering, Radiation
D007496:Iridium Radioisotopes
Air cavity; Brachytherapy; Dosimetry; Film; Monte Carlo