Abstract
Under the collaboration between National Tsing Hua University (NTHU) and Taipei Veterans General Hospital (TVGH), clinical trial of recurrent head-and-neck cancer by Boron Neutron Capture Therapy (BNCT) at Tsing Hua open-pool reactor (THOR) started on 2010. Up to January of 2014, 17 patients were treated. This study is focus on the experience of treatment plannings, the influences on epithermal neutron beam under different size and thickness of treatment setup, as well as the comparison and verification of the transformation of dose file for the protocol 2. The treatment plannings in this study is performed by the in-house designed treatment planning system THORplan. Based on experiences of clinical treatment, different setup should be applied for superficial and deep-seated tumors. For superficial tumors, using collimator gives tissues located inside the irradiation field higher fluxes, and can protect tissues located outside the irradiation field. For deep-seated tumors, there is no need for using collimator. Lithium pad can be used at the beam exit to protect the skin. For tumor after surgical resection, the effect of material assignment of the cavity inside the tumor on the calculational result is investigated. The resulting dose difference is not apparent if the cavity is small. It becomes larger as the size of cavity increases. Different treatment setups, such as lithium pad, can be used to provide skin protection. Currently used lithium pad is composed of 2.5 cm natural lithium and 0.5 cm enriched lithium. A 3 cm-natural lithium can provide similar protection effect. Among Patient 11 to Patient 17 of protocol 1, 3 patients are complete response. The corresponding doses of these tumors have homogeneity index > 0.5, sum of minimum dose > 21 Gy-eq, and sum of average minimum physical dose > 4 Gy. There is no apparent correlation between tumor response and the average dose received. But the minimum dose seems to be an important factor. Protocol 2 of BNCT clinical trial was started on 2014. After receiving one BNCT treatment at NTHU, photon therapy will be performed at TPEVGH. Dose of THORplan can be transformed to RS dose by using RTDOSE code, which can later be read by treatment planning system used in hospital for dose adding purpose. Compared with THORplan3, THORplan4 generates more consistent tissue volumes and dose for dose adding.