Dosimetric impact of an air passage on intraluminal brachytherapy for bronchus cancer.
The brachytherapy dose calculations used in treatment planning systems (TPSs) have conventionally been performed assuming homogeneous water. Using measurements and a Monte Carlo simulation, we evaluated the dosimetric impact of an air passage on brachytherapy for bronchus cancer. To obtain the geometrical characteristics of an air passage, we analyzed the anatomical information from CT images of patients who underwent intraluminal brachytherapy using a high-dose-rate192Ir source (MicroSelectron V2r®, Nucletron). Using an ionization chamber, we developed a measurement system capable of measuring the peripheral dose with or without an air cavity surrounding the catheter. Air cavities of five different radii (0.3, 0.5, 0.75, 1.25 and 1.5 cm) were modeled by cylindrical tubes surrounding the catheter. A Monte Carlo code (GEANT4) was also used to evaluate the dosimetric impact of the air cavity. Compared with dose calculations in homogeneous water, the measurements and GEANT4 indicated a maximum overdose of 5-8% near the surface of the air cavity (with the maximum radius of 1.5 cm). Conversely, they indicated a minimum overdose of ~1% in the region 3-5 cm from the cavity surface for the smallest radius of 0.3 cm. The dosimetric impact depended on the size and the distance of the air passage, as well as the length of the treatment region. Based on dose calculations in water, the TPS for intraluminal brachytherapy for bronchus cancer had an unexpected overdose of 3-5% for a mean radius of 0.75 cm. This study indicates the need for improvement in dose calculation accuracy with respect to intraluminal brachytherapy for bronchus cancer.
Department of Radiation Oncology, National Cancer Center Hospital, 5-1-1 Tsukiji, Chuo-ku, Tokyo 104-0045, Japan hiokamot@ncc.go.jp.
Hiroyuki
H
Okamoto
Department of Radiation Oncology, National Cancer Center Hospital, 5-1-1 Tsukiji, Chuo-ku, Tokyo 104-0045, Japan.
Akihisa
A
Wakita
Department of Radiation Oncology, National Cancer Center Hospital, 5-1-1 Tsukiji, Chuo-ku, Tokyo 104-0045, Japan.
Satoshi
S
Nakamura
Department of Radiation Oncology, National Cancer Center Hospital, 5-1-1 Tsukiji, Chuo-ku, Tokyo 104-0045, Japan.
Shie
S
Nishioka
Department of Radiation Oncology, National Cancer Center Hospital, 5-1-1 Tsukiji, Chuo-ku, Tokyo 104-0045, Japan.
Ako
A
Aikawa
Department of Radiation Oncology, National Cancer Center Hospital, 5-1-1 Tsukiji, Chuo-ku, Tokyo 104-0045, Japan.
Toru
T
Kato
Department of Radiation Oncology, National Cancer Center Hospital, 5-1-1 Tsukiji, Chuo-ku, Tokyo 104-0045, Japan.
Yoshihisa
Y
Abe
Department of Radiation Oncology, National Cancer Center Hospital, 5-1-1 Tsukiji, Chuo-ku, Tokyo 104-0045, Japan.
Kazuma
K
Kobayashi
Department of Radiation Oncology, National Cancer Center Hospital, 5-1-1 Tsukiji, Chuo-ku, Tokyo 104-0045, Japan.
Koji
K
Inaba
Department of Radiation Oncology, National Cancer Center Hospital, 5-1-1 Tsukiji, Chuo-ku, Tokyo 104-0045, Japan.
Naoya
N
Murakami
Department of Radiation Oncology, National Cancer Center Hospital, 5-1-1 Tsukiji, Chuo-ku, Tokyo 104-0045, Japan.
Jun
J
Itami
D000388:Air; D001918:Brachytherapy / Q000379:methods*; D001980:Bronchi / Q000528:radiation effects; D001984:Bronchial Neoplasms / Q000532:radiotherapy*; D002404:Catheterization; D057785:Catheters; D003198:Computer Simulation; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D009010:Monte Carlo Method; D011829:Radiation Dosage; D011874:Radiometry; D011880:Radiotherapy Planning, Computer-Assisted; D014057:Tomography, X-Ray Computed
HDR; TG-43; TPS; brachytherapy; heterogeneity