Introducing an on-line adaptive procedure for prostate image guided intensity modulate proton therapy
Introducing an on-line adaptive procedure for prostate image guided intensity modulate proton therapy
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DOI：
10.1088/0031-9155/56/15/019
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发表时间：
2011-08-07
影响因子：
3.5
通讯作者：
Mackie, T. R.
中科院分区：
文献类型：
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作者：
Zhang, M.;Westerly, D. C.;Mackie, T. R.
通过在线图像引导（IG），前列腺相对于骨骼解剖的移位可以通过重新调整患者相对于治疗场的位置来纠正。在图像引导强度调制质子治疗（IG-IMPT）中，由于质子范围对其穿过的物质更敏感，重新排列可能会引入大剂量变化。本文对这一效应进行了研究，并提出了一种在线自适应程序来将计划剂量恢复到目标。以真实前列腺患者的CT图像为基础，构建二维拟人化幻像。生成两场横向相对点3d调制和24场全弧远端边缘跟踪（DET）计划，处方为70 Gy到计划目标体积。对于模拟交付，我们考虑了两种类型的过程：非自适应过程和在线自适应过程。在非适应性程序中，仅进行患者重新排列以匹配计划CT中的前列腺位置。在在线自适应过程中，在患者重新排列的基础上，每个质子束的动能从重新排列后获得的在线CT图像中重新确定，随后用于输送。重新计算了不同计划和不同给药程序的单个组分的剂量分布。结果表明，在没有自适应的情况下，3d调制和DET计划都通过在前列腺中存在大的冷点或热点而经历了递送剂量的降解。DET计划比3d调制计划有更差的剂量降解。适应性程序有效地恢复了DET计划中的计划剂量分布，交付的前列腺D(98%)， D（50%）和D（2%）值低于处方的1%。在3d调制计划中，在某些情况下，自适应程序不能有效地减少递送剂量降解，并产生与非自适应程序相似的结果。综上所述，基于二维幻像研究，通过对在线图像重新排列后的质子束束能量进行更新，这一在线自适应过程对于基于pet的IG-IMPT是必要且有效的。无需重新计算和优化剂量，可轻松纳入临床工作流程。
With on-line image guidance (IG), prostate shifts relative to the bony anatomy can be corrected by realigning the patient with respect to the treatment fields. In image guided intensity modulated proton therapy (IG-IMPT), because the proton range is more sensitive to the material it travels through, the realignment may introduce large dose variations. This effect is studied in this work and an on-line adaptive procedure is proposed to restore the planned dose to the target. A 2D anthropomorphic phantom was constructed from a real prostate patient's CT image. Two-field laterally opposing spot 3D-modulation and 24-field full arc distal edge tracking (DET) plans were generated with a prescription of 70 Gy to the planning target volume. For the simulated delivery, we considered two types of procedures: the non-adaptive procedure and the on-line adaptive procedure. In the non-adaptive procedure, only patient realignment to match the prostate location in the planning CT was performed. In the on-line adaptive procedure, on top of the patient realignment, the kinetic energy for each individual proton pencil beam was re-determined from the on-line CT image acquired after the realignment and subsequently used for delivery. Dose distributions were re-calculated for individual fractions for different plans and different delivery procedures. The results show, without adaptive, that both the 3D-modulation and the DET plans experienced delivered dose degradation by having large cold or hot spots in the prostate. The DET plan had worse dose degradation than the 3D-modulation plan. The adaptive procedure effectively restored the planned dose distribution in the DET plan, with delivered prostate D(98%), D(50%) and D(2%) values less than 1% from the prescription. In the 3D-modulation plan, in certain cases the adaptive procedure was not effective to reduce the delivered dose degradation and yield similar results as the non-adaptive procedure. In conclusion, based on this 2D phantom study, by updating the proton pencil beam energy from the on-line image after realignment, this on-line adaptive procedure is necessary and effective for the DET-based IG-IMPT. Without dose re-calculation and re-optimization, it could be easily incorporated into the clinical workflow.