The Comparison Of Efficacy Between Altered Thoracic Radiotherapy Fractionation And The Exploration Of Clinical Application Of Circulating Tumor DNA Detected By Different Next-generation Sequencing Approaches In Limited-stage Small Cell Lung Cancer

Part1 Radiotherapy fraction in limited-stage small cell lung cancer in the modern era:Meta-analysis of 8006 reconstructed individual patient dataBackground:The optimal thoracic radiotherapy(TRT)dose and fractionation for limitedstage small cell lung cancer(LS-SCLC)using modern techniques remain unclear.To date,no randomized controlled trials(RCTs)have provided head-to-head comparisons between altered fractionation schedules.An individual-patient data(IPD)meta-analysis is highly desirable in evidence synthesis,and plays a critical role in defining practice in the absence of large,randomized trials.We conducted IPD meta-analysis of the efficacy and safety differences between definitive hypofractionated TRT(HypoTRT),conventionally fractionated TRT(ConvTRT)and hyperfractionated TRT(HyperTRT),especially in modern era using three-dimensional conformal radiotherapy or intensity modulated radiotherapy(3D-CRT/IMRT).Methods:Eligible RCTs,real-world cohorts,and single-arm trials published between January 1,1990,and July 31,2021,were identified in PubMed,EMBASE,and Web of Science.Two meta-analyses of overall survival(OS)were conducted:(i)random-effects meta-analysis based on reconstructed individual-patient data(IPD)of all studies;(ii)Bayesian network meta-analysis based on study-level aggregated data(AD)of RCTs.The incidence of severe radiation-related toxicities between fraction modalities was compared using random-effects meta-regression model.Results:Overall,53 of the 30031 publications met the inclusion criteria,and a total of 8006 IPD were reconstructed.Based on the shared frailty Cox model stratified by study types,OS rates were comparable between HypoTRT and HyperTRT(HR=1.04,95%CI 0.92-1.18)or ConvTRT(HR=0.93,95%CI 0.83-1.06);meanwhile ConvTRT was inferior to HyperTRT(HR=1.12,95%CI 1.03-1.21).After adjusting for key treatment variables,including concurrent chemotherapy,TRT timing and corrected biologically effective dose(BED10),there were no significant differences in OS rates between altered fractionation regimens(HypoTRT vs HyperTRT,adjusted HR=1.05,95%CI 0.93-1.19;ConvTRT vs HyperTRT,adjusted HR=1.00,95%CI 0.90-1.11;HypoTRT vs ConvTRT,adjusted HR=1.05,95%CI 0.91-1.20).In the modern era,survival outcomes of all three schedules,while remain comparable(HypoTRT vs HyperTRT,HR=0.95,95%CI 0.81-1.10;ConvTRT vs HyperTRT,HR=1.09,95%CI 0.98-1.21),have improved significantly.Results of AD-based network meta-analysis were consistent with those of IPD analysis,and HypoTRT was ranked the best regimen within 3D-CRT/IMRT subgroup(SUCRA=81%).There were no significant differences in either severe radiation esophagitis(HypoTRT vs HyperTRT,14%vs 17%,p=0.487;ConvTRT vs HyperTRT,12%vs 17%,p=0.214;HypoTRT vs ConvTRT,14%vs 12%,p=0.769)or radiation pneumonitis(HypoTRT vs HyperTRT,5%vs 3%,p=0.236;ConvTRT vs HyperTRT,5%vs 3%,p=0.299;HypoTRT vs ConvTRT,5%vs 5%,p=0.949)between groups when using modern radiation techniques.Conclusions:In the modern RT era,no significant differences in OS or severe radiationrelated toxicities were observed between altered schedules in LS-SCLC.HypoTRT may be associated with moderate and non-significant OS improvements,which should be further confirmed in prospective randomized phase Ⅲ trials.Part 2 Analysis of risk factors of radiation-induced toxicity in limited-stage small cell lung cancer treated with hypofractionated intensity-modulated radiotherapyObjectives:To compare the incidence of radiation-related toxicities between conventional and hypofractionated intensity-modulated radiation therapy(IMRT)for limited-stage small cell lung cancer(SCLC),and to explore the risk factors of hypofractionated radiotherapy-induced toxicities.Methods:Data were collected from consecutive limited-stage SCLC patients treated with definitive concurrent chemoradiotherapy in Cancer Hospital of Chinese Academy of Medical Sciences between March 2016 to April 2022.The enrolled patients were divided into two groups according to radiation fractionated regimens.Common Terminology Criteria for Adverse Events(CTCAE,version 5.0)was used to evaluate the grade of radiation esophagus injuries and lung injuries.Logistic regression analyses were used to identify factors associated with radiation-related toxicities in the hypofractionated radiotherapy group.Results:Among 211 enrolled patients,108 cases underwent conventional IMRT and 103 patients received hypofractionated IMRT.The cumulative incidences of acute esophagitis grade ≥2[38.8%(42/108)vs 35.0%(36/103),p=0.895]and grade ≥3[1.9%(2/108)vs 5.8%(6/103),p=0.132]were similar between conventional and hypofractionated IMRT group.Late esophagus injuries grade ≥2 occurred in one patient in either group.No differences in the cumulative incidence of acute pneumonitis grade ≥2[12.0%(13/108)vs 5.8%(6/103),p=0.172]and late lung injuries grade ≥2[5.6%(6/108)vs 10.7%(11/103),p=0.277]were observed.There was no grade ≥3 lung injuries occurred in either group.Using multiple regression analysis,mean esophageal dose ≥13Gy[OR(odd ratio=3.33),95%CI(confidence interval)1.23-9.01,p=0.018]and the overlapping volume between planning target volume(PTV)and esophageal ≥8cm3(OR=3.99,95%CI 1.2412.79,p=0.020)were identified as the independent risk factors associated with acute esophagitis grade ≥2 in the hypofractionated radiotherapy group.Acute pneumonitis grade ≥2 was correlated with presence of chronic obstructive pulmonary disease(COPD).Late lung injuries grade ≥2 was correlated with tumor location.Conclusions:Hypofractionated IMRT were tolerated with manageable toxicities for limited-stage SCLC patients treated with IMRT.Mean esophageal dose and the overlapping volume between PTV and esophageal were independently predictive factors of acute esophagitis grade ≥2,and COPD and tumor location were valuable factors of lung injuries for limited-stage SCLC patients receiving hyofractionated radiotherapy.Prospective studies are needed to confirm these results.Part 3 The exploration of clinical application of circulating tumor DNA detected by different next-generation sequencing approaches in limited-stage small cell lung cancerObjectives:Circulating tumor DNA(ctDNA)has been used for recurrence risk stratification,prognosis prediction,dynamic recurrence detection in various solid tumors.However,the prognostic value of ctDNA in limited-stage small cell lung cancer(LS-SCLC)is unclear,which may be caused by the unique biological features of SCLC and the limitations of liquid biopsy technology.Due to the rapid response of SCLC cells to chemoradiotherapy,tumor burden reduced significantly after initial treatment,and the concentration of tumor DNA fragments released into blood drops sharply.We have no idea whether increasing the sequencing depth to increase the detection rate of low-abundance mutations at low concentrations is more effective than conventional sequencing depth with broad-spectrum gene panel in SCLC.Therefore,we compare two approaches for ctDNA next-generation sequencing(NGS)and explore the prognostic value of ctDNA in LSSCLC.Methods:We prospectively enrolled 97 LS-SCLC patients treated with radical chemoradiotherapy.Peripheral blood samples were collected at five time points:pretreatment(TP0),at the beginning of thoracic radiotherapy(TP1),at the end of thoracic radiotherapy(TP2),at the end of all treatments(TP3),and at disease progression(TP4).The samples were analyzed by targeted NGS of 474 or 139 cancer-related genes.The primary end point of this study was progression-free survival(PFS).Results:A total of 246 peripheral blood samples were collected from 97 enrolled patients.There was no difference in the proportion of the detected or undetected ctDNA at various time points between the two gene panels.The percentage of detected ctDNA at TPO,TP1,TP2,TP3,and TP4 was 85.7%(2/14),44.0%(40/91),33.3%(22/66),35.6%(26/45),and 73.7%(14/19),respectively.The average number of detected gene mutations was 13,6,1,2,and 6,respectively.The most frequent gene mutations at each time point were TP53 and RB1 genes at TP0-TP4(except for TP2).The median follow-up time for all enrolled patients was 21.07 months(95%confidence interval[CI]19.67-22.63),and the median PFS was 23.53 months(95%CI 14.8-NA).The PFS of patients with detected ctDNA was significantly shorter than that of undetected ctDNA patients at TP1,TP2,and TP3(hazard ratio[HR]=2.26,95%CI 1.22-4.18;HR=2.55,95%CI 1.19-5.47;HR=3.88,95%CI 1.3611.03).After adjusting for clinical factors,only the ctDNA at TP3 was significantly correlated with PFS(HR=3.09,95%CI 1.01-9.50).The negative predictive value(NPV)of TP3-ctDNA detection was 77.5%,and the positive predictive value(PPV)was 50%.When exploring the association between gene mutations detected by ctDNA at various time points with PFS,we observed that only TP3-RB1 gene detection was an independent prognostic factor(HR=8.27,95%CI 2.12-32.24)after adjusting for clinical factors.The NPV of TP3-RB1 gene detection was 74.5%,and the PPV was 80%.The results of dynamic analysis showed that after chemotherapy and radiotherapy intervention,patients with continuous negative or positive-to-negative(undetected in the last testing at the end of thoracic radiotherapy or all treatment)ctDNA or RBI genes detection had better PFS(HR=1.51,95%CI 1.19-1.93;HR=1.73,95%CI 1.23-2.44).Conclusion:ctDNA is a feasible biomarker to predict the prognosis of LS-SCLC,while the predictive efficacy of ctDNA is not consistent at different time points during or after the chemoradiotherapy.ctDNA or RBI genes detection at the end of all treatments is significantly associated the PFS.RB1 detection may have better predictive performance,which needs further confirmation in larger prospective trials.