基于混合准则的IMRT计划优化

在适形调强放射治疗计划优化方法中,基于广义等效均匀剂量(gEUD)的生物优化不能较好地控制靶区剂量覆盖特性,基于剂量体积(DV)的物理优化不能反映组织对剂量的非线性反应,为此提出一种基于gEUD生物准则和物理准则(最小剂量和平均剂量)混合准则约束的方法,结合两类准则的优势,更好地兼顾靶区剂量覆盖特性和保护危及器官。采用10例前列腺病例数据仿真,从剂量学和生物学两方面比较和评价。混合准则优化较物理准则优化能够在保证靶区剂量覆盖特性相似的前提下,降低危及器官的剂量,直肠的平均剂量、V₅₀和V₆₀,膀胱的平均剂量、V₆₅、V₇₀、V₇₅、正常组织并发症概率(NTCP)和gEUD有统计学显著差异(P<0.05)。混合准则优化与生物准则优化相比,一方面靶区剂量覆盖特性得到很大改善,靶区剂量统计指标和生物指标均有显著性差异(P<0.05);另一方面危及器官得到保护,表现在直肠平均剂量、V₅₀、V₆₀、V₇₅、NTCP和gEUD,膀胱V₇₅和gEUD有显著性差异(P<0.05)。总之,在保证靶区放疗剂量的同时,基于gEUD的混合准则放疗优化能够减少危及器官的照射剂量,为进一步改善靶区剂量覆盖特性、提高治疗增益比提供可能。

IMRT Plan Optimization Based on Hybrid Criteria

In optimization methods of conformal intensity modulated radiation therapy, the performance of biological optimization based on generalized equivalent uniform dose (gEUD) still requires improvement to control the target dose coverage precisely, while physical optimization based on dose volume does not reflect the nonlinear response of tissue to dose. Hence, a hybrid criteria optimization method integrating the biological criteria (generalized equivalent uniform dose: gEUD) and physical criteria (minimum dose, mean dose) was proposed in this paper. The new algorithm,taking full advantages of these two kinds of criteria, gave consideration to both the dose coverage of the target area and the protection of the organ.Its feasibility was tested on ten prostate cases through evaluation and comparison from the perspective of dosimetry and biology. Compared with physical criteria optimization, the hybrid criteria optimization reduced dose to the organs at risk on the premise that dose coverage characteristics of target were similar, and at the significance level of 0.05, the mean dose for rectum, V₅₀ and V₆₀ of rectum, the mean dose for bladder, V₆₅,V₇₀,V₇₅,NTCP and gEUD of bladder were significantly different (P<0.05). Moreover, compared with gEUD based biological optimization, on the one hand the target dose coverage characteristics have been greatly improved with dose statistics, and the biological indicators were significantly different (P<0.05); on the other hand, organs at risk got better protection with significant difference (P<0.05) in rectal average dose, V₅₀, V₆₀, V₇₅, NTCP and gEUD as well as in bladder V₇₅ and gEUD. In conclusion, gEUD-based hybrid criteria optimization could reduce the dose to OAR that may be helpful to further improve the dose coverage of PTV and to increase the gain ratio of radio therapy while guarantying the dose to PTV.