I3N, Department of Physics, University of Aveiro, Aveiro, Portugal.
Radiat Oncol. 2010 Jun 22;5:57. doi: 10.1186/1748-717X-5-57.
To quantify the radiobiological advantages obtained by an Improved Forward Planning technique (IFP) and two IMRT techniques using different fractionation schemes for the irradiation of head and neck tumours. The conventional radiation therapy technique (CONVT) was used here as a benchmark.
Seven patients with head and neck tumours were selected for this retrospective planning study. The PTV1 included the primary tumour, PTV2 the high risk lymph nodes and PTV3 the low risk lymph nodes. Except for the conventional technique where a maximum dose of 64.8 Gy was prescribed to the PTV1, 70.2 Gy, 59.4 Gy and 50.4 Gy were prescribed respectively to PTV1, PTV2 and PTV3. Except for IMRT2, all techniques were delivered by three sequential phases. The IFP technique used five to seven directions with a total of 15 to 21 beams. The IMRT techniques used five to nine directions and around 80 segments. The first, IMRT1, was prescribed with the conventional fractionation scheme of 1.8 Gy per fraction delivered in 39 fractions by three treatment phases. The second, IMRT2, simultaneously irradiated the PTV2 and PTV3 with 59.4 Gy and 50.4 Gy in 28 fractions, respectively, while the PTV1 was boosted with six subsequent fractions of 1.8 Gy. Tissue response was calculated using the relative seriality model and the Poisson Linear-Quadratic-Time model to simulate repopulation in the primary tumour.
The average probability of total tumour control increased from 38% with CONVT to 80% with IFP, to 85% with IMRT1 and 89% with IMRT2. The shorter treatment time and larger dose per fraction obtained with IMRT2 resulted in an 11% increase in the probability of control in the PTV1 with respect to IFP and 7% relatively to IMRT1 (p < 0.05). The average probability of total patient complications was reduced from 80% with CONVT to 61% with IFP and 31% with IMRT. The corresponding probability of complications in the ipsilateral parotid was 63%, 42% and 20%; in the contralateral parotid it was 50%, 20% and 9%; in the oral cavity it was 2%, 15% and 4% and in the mandible it was 1%, 5% and 3%, respectively.
A significant improvement in treatment outcome was obtained with IMRT compared to conventional radiation therapy. The practical and biological advantages of IMRT2, employing a shorter treatment time, may outweigh the small differences obtained in the organs at risk between the two IMRT techniques. This technique is therefore presently being used in the clinic for selected patients with head and neck tumours. A significant improvement in the quality of the dose distribution was obtained with IFP compared to CONVT. Thus, this beam arrangement is used in the clinical routine as an alternative to IMRT.
通过使用不同分割方案的改进正向计划技术（IFP）和两种调强放疗技术（IMRT）对头颈部肿瘤进行照射，量化获得的放射生物学优势。这里将常规放疗技术（CONVT）用作基准。
选择了七名头颈部肿瘤患者进行这项回顾性计划研究。PTV1 包括原发肿瘤，PTV2 包括高危淋巴结，PTV3 包括低危淋巴结。除了将 64.8 Gy 的最大剂量规定给 PTV1 的常规技术外，分别将 70.2 Gy、59.4 Gy 和 50.4 Gy 规定给 PTV1、PTV2 和 PTV3。除了 IMRT2 之外，所有技术均通过三个连续阶段进行输送。IFP 技术使用五个至七个方向，总共使用 15 至 21 个光束。IMRT 技术使用五个至九个方向和约 80 个节段。第一个，IMRT1，采用传统的 1.8 Gy 分割方案，分 39 次治疗，共三个治疗阶段。第二个，IMRT2，同时以 59.4 Gy 和 50.4 Gy 分别照射 PTV2 和 PTV3，同时对 PTV1 进行六个后续 1.8 Gy 分次的 boost。使用相对串行性模型和泊松线性二次时间模型计算组织反应，以模拟原发肿瘤中的再群体化。
与 CONVT 相比，总肿瘤控制的平均概率从 38%增加到 IFP 的 80%，到 IMRT1 的 85%和 IMRT2 的 89%。IMRT2 获得的较短治疗时间和较大的分割剂量导致 PTV1 中控制概率相对于 IFP 增加了 11%，相对于 IMRT1 增加了 7%（p<0.05）。与 CONVT 相比，总患者并发症的平均概率从 80%降低到 IFP 的 61%和 IMRT 的 31%。同侧腮腺的相应并发症概率为 63%、42%和 20%；对侧腮腺为 50%、20%和 9%；口腔为 2%、15%和 4%；下颌骨为 1%、5%和 3%。
与常规放疗相比，IMRT 治疗结果显著改善。IMRT2 的实际和生物学优势，采用较短的治疗时间，可能超过两种 IMRT 技术在危险器官之间获得的微小差异。因此，目前该技术正在临床中用于某些头颈部肿瘤患者。与 CONVT 相比，IFP 获得了显著改善的剂量分布质量。因此，该光束布置在临床常规中用作 IMRT 的替代方案。
