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Feasibility of a Newly Developed Water-Equivalent Bolus Technique in Accelerator-Based Boron Neutron Capture Therapy for Skin Tumors

K Hirose

K Hirose1*, K Arai1 , T Harada1 , R Shimokomaki1 , T Motoyanagi1 , T Kato1 , Y Takai1 , (1) Southern Tohoku BNCT Research Center, Koriyama, Fukushima, Japan


SU-I-GPD-T-154 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: The aim was to evaluate a newly developed technique with a water-equivalent bolus (WEB) in accelerator-based BNCT.

Methods: The simulated patient with malignant melanoma lesions localized in a sole, an arch, and a thumb of a unilateral foot was played by a healthy man. A WEB was prepared as follows: Urethane foam cut down into the size of 3-cm larger than the superficial lesion was infiltrated with distilled water with deaeration. The lesions bordered by a catheter were covered with a WEB, and CT scan was performed. The tumor is depicted as a region with 5-mm thickness. A WEB was delineated as water. This was placed into air for calculation in condition with no bolus. For comparison with bolus-like effect of a covered collimator, the outline of an imaginary collimator cover was set as a mass of polycarbonate or a water tank filled with 5-50-mm thickness. For calculation of photon-equivalent dose (Gy-Eq), blood ¹⁰B concentrations, ¹⁰B tumor/blood concentration ratio, and CBE factor for ¹⁰B(n,α)⁷Li reaction were assumed to be 25ppm, 3.5, and 4.0. Then, irradiation condition was defined as tumor Dmin of 30Gy-Eq.

Results: In condition with no bolus, irradiation time was 185.6±56.4min, and tumor Dmax and Dmean were 110.7±31.6Gy-Eq, and 66.2±13.0Gy-Eq, respectively. Skin Dmax was larger than 18Gy-Eq in all cases. In condition with WEB technique, irradiation time was 48.4±15.9min. Tumor Dmax and Dmean were 58.5±5.3Gy-Eq and 48.2±4.2Gy-Eq with good dose homogeneity and within skin tolerable dose (12.7±1.6Gy-Eq). The bolus-like effect of covered collimator with a mass of polycarbonate or water tank was not sufficient. Dose homogeneity and irradiation time were even worse than the condition with a water-equivalent bolus.

Conclusion: Our results revealed that the newly developed WEB technique could have a great effectiveness on dose improvement of accelerator-based BNCT for skin tumors.

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