テラハラ　アツロウ   Terahara Atsuro   寺原　敦朗    所属   東邦大学  医学部 医学科（大森病院）    職種   教授
言語種別	英語
発表タイトル	Volume Dose Prescription in Stereotactic Body Radiotherapy for Lung Cancer
会議名	ECCO 16 (European Multidisciplinary Cancer Congress)
学会区分	国際学会
発表形式	ポスター掲示
講演区分	一般
発表者・共同発表者	◎Terahara A†, Saotome N†, Miyamoto K†, Omori M†
発表年月日	2011/09/26
開催地 （都市, 国名）	ストックホルム、スウェーデン
概要	Background: 3D treatment planning system and dose-volume calculations are commonly used now and the dose prescription method is changing. The reference point dose was recommended for prescription, however, volume dose Is becoming popular for IMRT and also for 3D-CRT. In stereotactic body radiotherapy (SBRT), PTV for early stage lung cancer usually includes low density lung field area around tumor volume. Because of that, the periphery of PTV tends to receive relatively lower dose even with appropriate leaf margin of 5mm.  Material and methods: We analyze dose distributions in four cases with lung cancer treated by SBRT. We calculated dose distributions with Xio 4.5 using superposition algorithm. PTV margin was added 5mm around CTV, and leaf margin of 3 to 5 mm was also added for SBRT. We prescribed by isocenter dose in clinical practice. We compared doses for CTV with those for PTV. We also moved isocenter by 5mm, which is the same as PTV margin, to 6 directions and the same dose comparison was made in each movement.  Results: D95, minimum dose (DMin), and mean dose (DMean) for PTV were 89.5, 80.2, and 96.0% of the prescription dose on an average respectively, and they were lower than those for CTV, that were 95.9, 92.8, and 98.9%. With the shift of isocenter, D95, DMin, and DMean for CTV were reduced to 94.5, 88.5, and 98.5% on an average respectively, which were still much higher than those for PTV. Even though the reduction of CTV dose was largest, DMin was an average of 85.7%, when isocenter moved to cranial and caudal direction, it was higher than that of PTV dose of 80.2%. Conclusions: If we add appropriate leaf margin around PTV, the dose reduction for CTV by isocenter shift in the range of PTV margin was relatively small. Therefore, It is not considered essential to cover the whole PTV by high dose volume when sufficient margin is added around CTV.