Pedraza R, Rojas EL, Mitsoura E

Language: English
References: 8
Page: 33-40
PDF size: 338.66 Kb.

ABSTRACT

Monte Carlo simulations were done to characterize a radioactive Nucletron Classic ¹⁹² Ir source with 6 Leipzig applicators (3 for the horizontal loading position and 3 for the vertical loading position) used in clinical treatments to irradiate superficial cancerous or non-cancerous lesions. The dosimetric characterization was made for each source-applicator system using the MCNP4C2 code. The percentage depth dose (PDD), the maximum dose rate and the dose profiles expressed as a percentage with respect to the maximum dose and the dose distribution curves were obtained. The maximum dose rate values absorbed in water for a 370 GBq source are: 4.53 cGy/s ± 0.1268, 4.46 cGy/s ± 0.0783, 4.49 cGy/s ± 0.1268 for the 1, 2 and 3 cm diameter applicators and the source with a horizontal position respectively. When the source is in a vertical position, the following was obtained: 2.70 cGy/s ± 0.0393, 2.68 cGy/s ± 0.1226 and 2.65 cGy/s ± 0.1171 for 1, 2 and 3 cm aperture respectively. Characterized the 6 source-applicator systems in the longitudinal, transverse and radial axes, the 100%, 95%, 90%, 80%, 70%, 60%, 50%, 40% and 30% dose distribution curves were built. These distributions were normalized at 0.05 cm depth along the central axis of the applicator. Our surface dose rate values have a maximum relative difference of 2.24% with those of Evans for the horizontal applicator with 3 cm in aperture (experimentally obtained) and 0.67 % with those of Leon (calculated by MC). The PDD values obtained are statistically the same as those of Evans on the surface, but differ by 0.28 % at the depth of 2 mm, 2.46 % at 5 mm and 5.2 % at 10 mm. The surface dose profiles coincide with those of Leon and Evans and differ by 0.53% at 4 mm depth as maximum. Source position is critical since the maximum dose rate values differ considerably between the horizontal source position and the vertical source position, for the same applicator aperture. However, the dose distributions at depths smaller than 2 mm in both cases are similar, showing a maximum difference of 1.5%.

REFERENCES

1. Faiz MK. The physics of radiation therapy, 3a Edition, Lippincott Williams & Wilkins, 2003.

2. Nath R, Anderson LL, Luxton G, Weaver KA, Williamson JF, Meigooni AS. Dosimetry of interstitial brachytherapy sources: Recommendations of the AAPM Radiation Therapy Committee Task Group No. 43, Med Phys 1995; 22, 209-234.

3. Rivard MJ, Coursey BM, DeWerd LA et al. Update of AAPM Task Group no.43 report: A revised AAPM protocol for brachytherapy dose calculations. Med Phys 2004; 31: 633-674.

4. Evans MDC, Yassa MMS, Podgorsak EB, Roman TN, Schreiner LJ, Souhami L. Surface applicators for high dose rate brachytherapy in aids-related Kaposi’s sarcoma. Int J Radiation Oncology Biol Phys 1997; 39(3): 769-774.

5. Nucletron, Leipzig Applicator Set User Guide, Part number 085.40 (2004).

6. Los Alamos Nacional Laboratory, Monte Carlo N-Particle Transport Code System, Los Alamos, New Mexico, June 2001.

7. Hwnag IM, Leung HWC. Dosimetry characteristics of Leipzig applicators. In: Mould RF, Gurtler MW, editors. Proceedings of the 1st Far East Radiotherapy Treatment Planning Workshop. Veenendaal, The Netherlands; Nucletron-Oldelft; 1996: 88-89.

8. León Blasco MA. Aplicación del Código de Monte Carlo MCNP a la dosimetría en braquiterapia con aplicador Leipzig. Estudio en medios homogéneo y heterogéneo. PhD Thesis, Valencia. Spain, June 2005.