A dosimetric study on the use of bolus materials for treatment of superficial tumors with BNCT.

For treatment of superficially located tumors, such as head and neck cancers that invade the skin, the tumor dose may remain low on the skin when such tumors are treated with epithermal neutrons in boron neutron capture therapy (BNCT). The goal of this study was to examine the effects of bolus material for BNCT of superficial tumors, to verify the calculated (55)Mn(n, gamma) and the (197)Au(n, gamma) activation reaction rates and the neutron and the gamma doses in a phantom irradiated with a bolus, to measure the neutron activation of the bolus materials after irradiation, and according to depth dose distribution, to estimate when it is advantageous to use a bolus in BNCT. The present data show that both paraffin and water gel can be used as a bolus material for BNCT. However, we recommend paraffin for clinical use, since it is durable and can be easily shaped. A 5 mm paraffin bolus increases the surface dose approximately 50%, and its use may be advantageous for treatment of superficial tumors where the planning target volume (PTV) reaches to 6 cm or less in tissue depth.