Fogliata Antonella, Bolsi Alessandra, Cozzi Luca, Bernier Jacques
Medical Physics Unit, Oncology Institute of Southern Switzerland, Bellinzona, Switzerland.
Radiother Oncol. 2003 Dec;69(3):267-75. doi: 10.1016/j.radonc.2003.10.003.
The objective of this study is to evaluate, at planning and dosimetric level, the potential benefits of the simultaneous integrated boost (SIB) concept with intensity-modulated radiation therapy (IMRT), using a comparative analysis on physical dose distributions corrected for radiobiological models. The concept of SIB at the end of the treatment has been analysed as an alternative acceleration scheme.
Physical dose distributions were computed on a commercial planning system (Varian Cadplan-Helios) for five patients presenting with advanced head and neck carcinomas. Treatment plans were designed using five IMRT beams. Three fractionation strategies were compared in the study: the standard sequential irradiation SEQ of elective and boost volumes, the pure SIB, and a modified SIB (SEQ/SIB), where the actual SIB follows a first phase of conventional fractionation to the elective volume. All physical dose distributions were corrected using a linear quadratic biological model, taking into account also repopulation and time at repopulation onset. Objective quantities, derived from biological dose volume histograms, were used for the analysis.
Physical doses equivalent to 50 and 80 Gy (in fractions of 2 Gy) to elective volume and boost were calculated for the SIB and SEQ/SIB regimes. With SIB 54 and 72 Gy dose levels have to be delivered in 30 fractions, while in the SEQ/SIB scheme 36 Gy are delivered in 20 sessions to the elective volume, and further 18 and 35.5 Gy during the last 10 fractions are delivered to elective volume and boost, respectively (for a total physical dose of 71.5 Gy). The comparison showed: (1) the boost target homogeneity resulted in generally acceptable and comparable among sequential and modified SIB schemes, while it was statistically worse for the pure SIB approach; (2) the fraction of elective target volume not included in the boost volume was characterised by a higher level of dose heterogeneity; (3) the spinal cord never reached tolerance levels and maximum point dose was on average below 38 Gy (biologically corrected to 2 Gy/fraction); and (4) sparing of parotid glands strongly depends on their eventual inclusion in the target volumes: for glands not included or only partially included, it was possible on average to keep the dose to 2/3 of the volume below 29 Gy for all regimes (32 Gy as physical dose).
Feasibility of SIB techniques and in particular of the modified SIB appears to be dosimetrically proven and the results reported here justify the activation of a phase I protocol to verify clinically their impact using IMRT photon-based techniques.
本研究的目的是在计划和剂量测定层面，通过对经放射生物学模型校正的物理剂量分布进行对比分析，评估同步整合加量（SIB）概念与调强放射治疗（IMRT）相结合的潜在益处。已对治疗末期的SIB概念作为一种替代加速方案进行了分析。
在商用计划系统（瓦里安Cadplan - Helios）上，针对5例晚期头颈癌患者计算了物理剂量分布。使用5个IMRT射束设计治疗计划。本研究比较了三种分割策略：选择性体积和加量体积的标准序贯照射SEQ、单纯SIB以及改良SIB（SEQ/SIB），其中实际的SIB在对选择性体积进行第一阶段常规分割之后进行。所有物理剂量分布均使用线性二次生物模型进行校正，同时考虑了再增殖以及再增殖开始的时间。从生物剂量体积直方图得出的客观指标用于分析。
计算了SIB和SEQ/SIB方案中选择性体积和加量体积相当于50 Gy和80 Gy（2 Gy分次）的物理剂量。采用SIB时，必须在30次分割中给予54 Gy和72 Gy的剂量水平，而在SEQ/SIB方案中，在20次照射中给予选择性体积36 Gy的剂量，在最后10次分割中分别再给予选择性体积18 Gy和加量体积35.5 Gy的剂量（物理剂量总计71.5 Gy）。比较结果显示：（1）加量靶区的均匀性在序贯和改良SIB方案中总体上可接受且相当，而对于单纯SIB方法在统计学上较差；（2）未包含在加量体积中的选择性靶区体积部分具有更高水平的剂量异质性；（3）脊髓从未达到耐受水平，最大点剂量平均低于38 Gy（生物校正为2 Gy/分次）；（4）腮腺的 sparing 强烈取决于它们最终是否包含在靶区体积中：对于未包含或仅部分包含的腺体，在所有方案中平均可使2/3体积的剂量低于29 Gy（物理剂量为32 Gy）。
SIB技术，尤其是改良SIB的可行性在剂量测定方面似乎得到了证实，此处报告的结果证明启动一项I期方案以使用基于IMRT光子的技术在临床上验证其影响是合理的。
