Dose specification for Ir-192 high dose rate brachytherapy in terms of dose-to-water-in-medium and dose-to-medium-in-medium

Autor(es)

Fonseca, Gabriel Paiva ^{[1, 2]} ; Tedgren, Asa Carlsson ^{[3, 4]} ; Reniers, Brigitte ^{[1, 5]} ; Nilsson, Josef ^[3] ; Persson, Maria ^[3] ; Yoriyaz, Helio ^[2] ; Verhaegen, Frank ^{[6, 1]}

Afiliação do(s) autor(es)

^[1] Maastricht Univ, Med Ctr, GROW Sch Oncol & Dev Biol, Dept Radiat Oncol MAASTRO, NL-6201 BN Maastricht - Netherlands

^[2] IPEN CNEN SP, Sao Paulo - Brazil

^[3] Karolinska Univ Hosp, Dept Med Phys, Sect Radiotherapy Phys & Engn, Stockholm - Sweden

^[4] Linkoping Univ, Dept Med & Hlth Sci IMH, Med Radiat Phys, Linkoping - Sweden

^[5] Hasselt Univ, CMK, Res Grp NuTeC, B-3590 Diepenbeek - Belgium

^[6] McGill Univ, Dept Oncol, Med Phys Unit, Montreal, PQ H3G 1A4 - Canada

• Tipo de documento: Artigo Científico
• Fonte: Physics in Medicine and Biology; v. 60, n. 11, p. 4565-4579, JUN 7 2015.
• Citações Web of Science: 6

Resumo

Dose calculation in high dose rate brachytherapy with Ir-192 is usually based on the TG-43U1 protocol where all media are considered to be water. Several dose calculation algorithms have been developed that are capable of handling heterogeneities with two possibilities to report dose: dose-to-medium-inmedium (D-m,D-m) and dose-to-water-in-medium (D-w,D-m). The relation between D-m,D-m and D-w,D-m for Ir-192 is the main goal of this study, in particular the dependence of D-w,D-m on the dose calculation approach using either large cavity theory (LCT) or small cavity theory (SCT). A head and neck case was selected due to the presence of media with a large range of atomic numbers relevant to tissues and mass densities such as air, soft tissues and bone interfaces. This case was simulated using a Monte Carlo (MC) code to score: D-m,D-m, D-w,D-m (LCT), mean photon energy and photon fluence. D-w,D-m (SCT) was derived from MC simulations using the ratio between the unrestricted collisional stopping power of the actual medium and water. Differences between D-m,D-m and D-w,D-m (SCT or LCT) can be negligible (<1%) for some tissues e.g. muscle and significant for other tissues with differences of up to 14% for bone. Using SCT or LCT approaches leads to differences between D-w,D-m (SCT) and D-w,D-m (LCT) up to 29% for bone and 36% for teeth. The mean photon energy distribution ranges from 222 keV up to 356 keV. However, results obtained using mean photon energies are not equivalent to the ones obtained using the full, local photon spectrum. This work concludes that it is essential that brachytherapy studies clearly report the dose quantity. It further shows that while differences between D-m,D-m and D-w,D-m (SCT) mainly depend on tissue type, differences between D-m,D-m and D-w,D-m (LCT) are, in addition, significantly dependent on the local photon energy fluence spectrum which varies with distance to implanted sources. (AU)

• Processo FAPESP: 11/22778-8 - Dosimetria 3D baseada em imagens médicas e códigos de Monte Carlo com aplicação em braquiterapia
• Beneficiário: Hélio Yoriyaz
• Modalidade de apoio: Auxílio à Pesquisa - Regular
• Processo FAPESP: 11/23765-7 - Comparação e análise de sistemas de planejamento de tratamento para braquiterapia 3D, utilizando o mcnp5, brachyvision e nucletron
• Beneficiário: Gabriel Paiva Fonseca
• Modalidade de apoio: Bolsas no Exterior - Estágio de Pesquisa - Doutorado
• Processo FAPESP: 11/01913-4 - Modelagem pelo método de Monte Carlo do paciente e das complexidades dos tratamentos braquiterápicos com alta taxa de dose
• Beneficiário: Gabriel Paiva Fonseca
• Modalidade de apoio: Bolsas no Brasil - Doutorado