Computed Tomography Number Changes of Gross Tumor Volume with MVCT Scans in Tomotherapy May Detect Early the Radiosensitivity of Non–small Cell Lung Cancer Patients

Abstract

Evidences have showed that the computed tomography number (CTN) for tumor and certain normal structures can change after irradiation. We explored whether CTN changes of gross tumor volume with MVCT scans in Tomotherapy may be an early indicator for the radiosensitivity of NSCLC patients. Patients with stage I to III non-small cell lung cancer were eligible in this prospective study. MVCT scans were acquired during tomotherapy. The distribution of CTN and the mean values from the first treatment to the 15th treatment were collected based on the GTV generated on daily MVCT. The dose-response curve for decreased CTN of patients was quantified using the slope of a linear regression. The CTN decreased per Gy ( ΔHU/Gy ) for each patient was calculated after the 15th tomotherapy. Follow-up CT was taken after the whole radiation therapy completed, based on which the post-treatment tumor responses were assessed by two thoracic radiologists. According to the tumor responses, a cut-off value for ΔHU/Gy was calculated by SPSS software. From Jun. 2015 to Dec. 2016, 32 eligible patients were enrolled in this study. Males: 19 (60%), Females: 13 (40%), median age: 61.7 years (range 43.3-70.9). The median radiation dose was 60Gy (range 54-63Gy). In the whole group, the mean CTN was decreased by 37.35 ± 27.07 HU from the first treatment to the 15th treatment. The mean GTV was reduced by 10.26 ± 10.15 cm3. The CTN decreased per Gy (ΔHU/Gy) was ranged from 0.37 to 2.37 among all patients. Seven patients (21.9%) reached CR, 18 patients (56.2%) reached PR, and 7 patients (21.9%) reached SD after the complete tomotherapy. The mean CTN reduction ranged from 28.1 HU to 64.0 HU in patients whose post-treatment tumor responses were CR or PR and the CTN changes were linearly correlated with the radiation dose (R2= 0.87，p＜0.001). The mean CTN changes in the left 7 patients were ranged from 9.9 HU to 26.2 HU. The cut off value for ΔHU/Gy was 0.97, above which patients could have a better radiosensitivity and a further favorable post-treatment tumor response. On an early and quantitative scale, the CTN changes of MVCT in tomotherapy may early detect the radiosensitivity of NSCLC patients. Further studies included larger numbers of patients are expected to validate such a finding and explore whether CTN changes of MVCT hold the potential to optimize treatment by adjusting radiation intensity or modifying the therapeutic regimen, based on the observed radiosensitivity of patients.