Biological effect of dose distortion by fiducial markers in spot-scanning proton therapy with a limited number of fields:A simulation study

在精确的质子点扫描治疗中，在照射过程中通过透视x射线的连续目标跟踪不仅对呼吸运动的肺和肝肿瘤有益，而且对相对静止的前列腺肿瘤也有益。植入的金标记已被用于通过荧光透视定位靶体积，效果很好。然而，最近的研究表明，金标记物可能导致质子治疗中的剂量明显不足。本研究的重点是前列腺癌，并探讨了多场照射的可能性，通过使用Monte Carlo模拟肿瘤控制概率（TCP）的标记物改善剂量不足的影响。发现当使用两个或更多个场时，1.5mm直径的标记不影响TCP。另一方面，如果标记直径为2mm，则需要多于两个照射场来抑制TCP的降低小于3%。建议使用1.5 mm标记，以避免TCP减少，并保留周围的关键器官，只要标记在X线透视上可见。当植入2 mm标记时，应使用两个以上的射野，标记不应靠近任何射束的远端边缘放置。

In accurate proton spot-scanning therapy, continuous target tracking by fluoroscopic x ray during irradiation is beneficial not only for respiratory moving tumors of lung and liver but also for relatively stationary tumors of prostate. Implanted gold markers have been used with great effect for positioning the target volume by a fluoroscopy. However, recent studies have revealed that gold markers can cause a significant underdose in proton therapy. This research focuses on prostate cancer and explores the possibility that multiple-field irradiation improves the underdose effect by markers on tumor-control probability (TCP) by using a Monte Carlo simulation. It was found that the marker of 1.5 mm diameter does not affect the TCPs when two or more fields are used. On the other hand, if the marker diameter is 2 mm, more than two irradiation fields are required to suppress the decrease in TCP by less than 3%. It is recommended that 1.5-mm markers be used to avoid the reduction of TCP as well as to spare the surrounding critical organs, as long as the markers are visible on x-ray fluoroscopy. When 2-mm markers are implanted, more than two fields should be used and the markers should not be placed close to the distal edge of any of the beams.