Inaniwa T, Kanematsu N, Suzuki M, Hawkins R B
Medical Physics Research Program, Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Chiba, Japan.
Phys Med Biol. 2015 May 21;60(10):4105-21. doi: 10.1088/0031-9155/60/10/4105. Epub 2015 May 1.
Carbon-ion radiotherapy treatment plans are designed on the assumption that the beams are delivered instantaneously, irrespective of actual dose-delivery time structure in a treatment session. As the beam lines are fixed in the vertical and horizontal directions at our facility, beam delivery is interrupted in multi-field treatment due to the necessity of patient repositioning within the fields. Single-fractionated treatment for non-small cell lung cancer (NSCLC) is such a case, in which four treatment fields in multiple directions are delivered in one session with patient repositioning during the session. The purpose of this study was to investigate the effects of the period of dose delivery, including interruptions due to patient repositioning, on tumor control probability (TCP) of NSCLC. All clinical doses were weighted by relative biological effectiveness (RBE) evaluated for instantaneous irradiation. The rate equations defined in the microdosimetric kinetic model (MKM) for primary lesions induced in DNA were applied to the single-fractionated treatment of NSCLC. Treatment plans were made for an NSCLC case for various prescribed doses ranging from 25 to 50 Gy (RBE), on the assumption of instantaneous beam delivery. These plans were recalculated by varying the interruption time τ ranging from 0 to 120 min between the second and third fields for continuous irradiations of 3 min per field based on the MKM. The curative doses that would result in a TCP of 90% were deduced for the respective interruption times. The curative dose was 34.5 Gy (RBE) for instantaneous irradiation and 36.6 Gy (RBE), 39.2 Gy (RBE), 41.2 Gy (RBE), 43.3 Gy (RBE) and 44.4 Gy (RBE) for τ = 0 min, 15 min, 30 min, 60 min and 120 min, respectively. The realistic biological effectiveness of therapeutic carbon-ion beam decreased with increasing interruption time. These data suggest that the curative dose can increase by 20% or more compared to the planned dose if the interruption time extends to 30 min or longer. These effects should be considered in carbon-ion radiotherapy treatment planning if a longer dose-delivery procedure time is anticipated.
碳离子放射治疗计划的设计假设是射线瞬间照射，而不考虑治疗过程中实际的剂量输送时间结构。由于我们设施中的射线束在垂直和水平方向上是固定的，在多野治疗中，由于需要在射野内重新定位患者，射线输送会中断。非小细胞肺癌（NSCLC）的单次分割治疗就是这样一种情况，即在一次治疗中通过在治疗过程中重新定位患者来进行多个方向的四个治疗射野的照射。本研究的目的是探讨包括因患者重新定位导致的中断在内的剂量输送时间对NSCLC肿瘤控制概率（TCP）的影响。所有临床剂量均根据瞬时照射评估的相对生物效应（RBE）进行加权。将微剂量动力学模型（MKM）中定义的针对DNA中诱导的原发性损伤的速率方程应用于NSCLC的单次分割治疗。假设射线瞬间照射，针对各种规定剂量范围为25至50 Gy（RBE）的NSCLC病例制定治疗计划。基于MKM，通过改变第二和第三射野之间0至120分钟的中断时间τ，对每个射野连续照射3分钟的情况重新计算这些计划。针对各个中断时间推导得出导致TCP为90%的治愈剂量。瞬时照射的治愈剂量为34.5 Gy（RBE），τ = 0分钟、15分钟、30分钟、60分钟和120分钟时的治愈剂量分别为36.6 Gy（RBE）、39.2 Gy（RBE）、41.2 Gy（RBE）、43.3 Gy（RBE）和44.4 Gy（RBE）。治疗用碳离子束的实际生物效应随中断时间的增加而降低。这些数据表明，如果中断时间延长至30分钟或更长，与计划剂量相比，治愈剂量可增加20%或更多。如果预计剂量输送程序时间较长，在碳离子放射治疗计划中应考虑这些影响。
