Quantitative Assessment of the Quality of Irradiation Planning for Patients with Metastatic Lesions of the Spine

Purpose: To conduct a quantitative analysis of the quality of irradiation planning for patients with metastatic lesions of the spine, to assess the dose load on critical organs for this category of patients, to establish the relationship between patient survival and the homogeneity index.
Material and methods: A quantitative analysis of stereotactic irradiation plans for 65 treated patients with simultaneous integrated boost (SIB) was performed. Plans (not implemented) were simulated for a group of patients with an increased prescribed dose to the affected vertebra, including an invisible expected zone of microscopic spread of malignant cells. Dose loads in critical organs for irradiation plans using IMRT and VMAT technology with metastatic lesions of the spine were estimated for both groups. Homogeneity indices were calculated.
Results: The results of the quantitative analysis of the plans for stereotactic irradiation of patients showed that the doses in critical organs in the simulated irradiation plans slightly exceed the same doses, but, nevertheless, are comparable with the characteristics of the integrated boost (SIB) technique and fit into the tolerable dose values in accordance with international criteria. The characteristics are also comparable in terms of the homogeneity index. The hypothesis of the effect on the life expectancy of patients after RT, including the value of the homogeneity index as one of the factors affecting survival times, was not statistically confirmed. The simulated irradiation plans for patients with an increased prescribed dose to the affected vertebra, including an invisible expected zone of microscopic spread of malignant cells, can be applied to the implementation and treatment of patients with metastatic lesions of the spine. Homogeneity indices H I were calculated. It was shown that the survival time for patients with a dose to the PTV of 25 Gy with HI ≥ 0.15 is limited to 18 months, and for HI ≤ 0.15 it increases to 29 months with a statistical significance level of p = 0.647. Similarly, the survival time for patients with a dose to the PTV of 30 Gy with HI ≥ 0.15 is limited to 16 months, and for HI ≤ 0.15 it increases to 29 months with a statistical significance level of p = 0.936, which reflects the absence of differences between the groups.
Conclusions: The obtained results indicate that the hypothesis about the influence of the homogeneity index on life expectancy is not confirmed. For final conclusions, it is necessary to continue the study, possibly with an increase in the sample or the inclusion of additional influencing factors.

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