< Topic > Not giving the burden to the body of the patient and detecting tumor position in high accuracy, the tumor is detected continually at high detection efficiency and radiation is irradiated to only the malignant tumor effectively and the radiotherapy device of the dynamic tumor which can decrease the being bombed quantity and the radiotherapy program of the dynamic tumor are offered.Solutions It stops controls the tumor position distinction expedient 44 which is distinguished whether or not calculates counting rate the threshold relative expedient 43 which compares with the counting rate of the disappearance line which is acquired from line counting rate calculation expedient 41 and line counting rate calculation expedient 41 and the threshold of the counting rate which is acquired from displacement threshold memory expedient 32 and the tumor displaced to outside radiation lighting spot the disappearance line is detected line detection expedient the displacement threshold memory expedient on the basis of the detection signal of 32 which remembers the threshold of 20 and counting rate and the disappearance line and radiation lighting, or the stop order signalIt possesses with the lighting control means 45 which it outputs.【課題】 患者の体への負担を与えないこと、腫瘍位置を高精度に検出すること、高い検出効率で連続的に腫瘍を検出し放射線を悪性の腫瘍のみに効果的に照射して被爆量を低減することができる動的腫瘍の放射線治療装置および動的腫瘍の放射線治療プログラムを提供する。【解決手段】 消滅γ線を検出するγ線検出手段20と、計数率の閾値を記憶する変位閾値記憶手段32と、消滅γ線の検出信号に基づいて計数率を算出するγ線計数率算出手段41と、γ線計数率算出手段41から取得した消滅γ線の計数率と変位閾値記憶手段32から取得した計数率の閾値とを比較する閾値比較手段43と、腫瘍が放射線照射スポット外へ変位したか否かを判別する腫瘍位置判別手段44と、放射線照射を停止制御する、または停止指示信号を出力する照射制御手段45とを有する。
