Peñagarícano José A, Shi Chengyu, Ratanatharathorn Vancerat
Department of Radiation Oncology, University of Arkansas for Medical Sciences, Little Rock, 72205, USA.
Technol Cancer Res Treat. 2005 Dec;4(6):683-9. doi: 10.1177/153303460500400613.
In cranio-spinal axis (CSA) irradiation, patients are usually treated in the prone position with junctions between cranial and spinal fields. Collimator angle and pedestal rotations are introduced to obtain coplanar alignment of the matched junction. Furthermore, daily moving junctions are commonly used to feather out the junctional dose as additional safeguards to avoid radiation myelopathy. Helical tomotherapy integrates linear accelerator and CT technology capable of delivering CSA treatment without geometric matches or feathering of junctions. The patient is treated with helical beams in the supine position. Since CSA is used mainly in the pediatric population, the potential increase in integral dose to structures or the whole body from linac- or tomotherapy-based IMRT raises concerns of increased rates of secondary malignancies. In this study, we will present an integral dose comparison between conventional CSA (3D) and helical delivery to the CSA (TOMO) utilizing the Tomotherapy Hi-ART system for three pediatric patients. Integral dose was calculated for organ at risk (OAR), two targets (PTV-BRAIN and PTV-SPINE), entire planning CT data set and to the healthy tissue (entire CT-DATA SET minus the PTV). Overall integral dose was 8% higher in the TOMO plans for Patients #1 and #3, but 2% lower in Patient #2. DVH analysis shows that TOMO plans give lower doses to larger volumes and higher doses to smaller volumes of tissue in all three cases. The advantages of the TOMO plans are minimization of matched junctions and better sparing of most OARs. With increased computational and memory power in the tomotherapy planning station, the excess integral dose to the healthy tissue can be re-distributed within the patient and in turn the total integral dose can be same or lower than in conventional delivery. The impact of a small increase in overall integral dose and the associated risks of secondary malignancies are unknown. Long-term follow-up is needed to answer this question.
在颅脊柱轴（CSA）照射中，患者通常俯卧位接受治疗，颅部和脊柱野之间有衔接部位。引入准直器角度和治疗床旋转以实现匹配衔接部位的共面校准。此外，日常移动衔接部位通常用于使衔接部位剂量平滑过渡，作为避免放射性脊髓病的额外防护措施。螺旋断层放射治疗集成了直线加速器和CT技术，能够在不进行几何匹配或衔接部位剂量平滑过渡的情况下进行CSA治疗。患者仰卧位接受螺旋束治疗。由于CSA主要用于儿科人群，基于直线加速器或断层放射治疗的调强放疗（IMRT）使结构或全身的积分剂量潜在增加，引发了对继发性恶性肿瘤发生率增加的担忧。在本研究中，我们将展示利用螺旋断层放射治疗Hi-ART系统对三名儿科患者进行常规CSA（3D）和螺旋式CSA（TOMO）治疗时的积分剂量比较。计算了危及器官（OAR）、两个靶区（PTV-BRAIN和PTV-SPINE）、整个计划CT数据集以及健康组织（整个CT数据集减去PTV）的积分剂量。患者1和患者3的TOMO计划总体积分剂量高8%，但患者2低2%。剂量体积直方图（DVH）分析表明，在所有三种情况下，TOMO计划对较大体积组织给予较低剂量，对较小体积组织给予较高剂量。TOMO计划的优势在于使匹配衔接部位最小化，并更好地保护大多数OAR。随着断层放射治疗计划工作站计算能力和内存的增加，健康组织的过量积分剂量可在患者体内重新分配，进而总积分剂量可与传统放疗相同或更低。总体积分剂量的小幅增加及其相关的继发性恶性肿瘤风险的影响尚不清楚。需要长期随访来回答这个问题。
