Abstract
Effect of a lead block on alveolar bone protection in image-guided high-dose-rate interstitial brachytherapy for tongue cancer: Using model-based dose calculation algorithms to correct for inhomogeneity
- Department of Oral Radiology, Osaka Dental University, Osaka, Japan
- Department of Radiology, Kansai Medical University Medical Center, Osaka, Japan
- Department of Radiology, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, Japan
- Department of Radiation Oncology, Osaka Rosai Hospital, Osaka, Japan
- Department of Radiology, Fukuchiyama City Hospital, Kyoto, Japan
- Department of Medical Physics, Graduate School of Medical Sciences, Kindai University, Osaka, Japan
- Department of Radiation Oncology, Graduate School of Medicine, Osaka University, Osaka, Japan
- Department of Radiation Oncology, National Hospital Organization Osaka National Hospital, Osaka, Japan
- Department of Radiation Oncology, Osaka Medical and Pharmaceutical University, Osaka, Japan
- Department of Radiology, Kansai Medical University, Osaka, Japan
- Department of Radiation Oncology, National Cancer Center Hospital, Tokyo, Japan
- Center of Radiotherapy, National Institute of Oncology, Department of Oncology, Semmelweis University, Budapest, Hungary
- Department of Radiotherapy and Oncology, University Hospital Frankfurt, Goethe University Frankfurt, Frankfurt am Main, Germany
Introduction
The purpose of this study was to evaluate the effect of a lead block for alveolar bone protection in image-guided high-dose-rate interstitial brachytherapy for tongue cancer.
Material and methods
We treated 6 patients and delivered 5,400 cGy in 9 fractions using a lead block. Effects of lead block (median thickness, 4 mm) on dose attenuation by distance were visually examined using TG-43 formalism-based dose distribution curves to determine whether or not the area with the highest dose is located in the alveolar bone, where there is a high-risk of infection. Dose re-calculations were performed using TG-186 formalism with advanced collapsed cone engine (ACE) for inhomogeneity correction set to cortical bone density for the whole mandible and alveolar bone, water density for clinical target volume (CTV), air density for outside body and lead density, and silastic density for lead block and its’ silicon replica, respectively.
Results
The highest dose was detected outside the alveolar bone in five of the six cases. For dose-volume histogram analysis, median minimum doses delivered per fraction to the 0.1 cm3 of alveolar bone (D0.1cm3TG-43, ACE-silicon, and ACE-lead) were 344.3 (range, 262.9-427.4) cGy, 336.6 (253.3-425.0) cGy, and 169.7 (114.9-233.3) cGy, respectively. D0.1cm3ACE-lead was significantly lower than other parameters. No significant difference was observed between CTV-related parameters.
Conclusions
The results suggested that using a lead block for alveolar bone protection with a thickness of about 4 mm, can shift the highest dose area to non-alveolar regions. In addition, it reduced D0.1cm3 of alveolar bone to about half, without affecting tumor dose.
Keywords
brachytherapy, tongue cancer, lead block, bone protection, inhomogeneity correction
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