Dosimetric And Clinical Study In Radiotherapy Of Esophageal Squamous Cell Carcinoma

Objective:To explore the application of RapidArc in esophageal squamous cell carcinoma,compare the differences in target coverage,conformity and homogeneity between RapidArc and s IMRT,and analyze the dosimetric parameters in lung,heart and spinal cord according to tumor loci.Meanwhile,the toxicity incidence and clinical responses of the two techniques were also assessed to provide advice for clinical treatments of esophageal squamous cell carcinoma.Methods:Sixty-eight patients pathologically diagnosed with esophageal squamous cell carcinoma were recruited retrospectively.Each of them underwent simulated position and CT scan to delineate tumor targets and organs at risk with an identical procedure.All the plans were verified by two intermediate and one senior radiation oncologists.Whether concurrent chemotherapy based on 5-fluorouracil or paclitaxel was necessary was decided by three professionals with intermediate or above titles.Patients were subdivided into the RapidArc or s IMRT arm according to the techniques prescribed.We compared the conformation index（CI）,homogeneity index（HI）and monitor units（MU）to evaluate the target coverage and efficacy of the two techniques.While the dosimetric parameters of organs at risk were compared to estimate the organ sparing ability,the toxicity incidence and clinical response rates were compared to assess the feasibility,safety and effectiveness of RapidArc.Results:1. There was no significant difference in demographic characteristics between the two arms（P>0.05）.In radical radiotherapy,RapidArc presented a lower PTVmin （4449.92±803.92c Gy vs 5016.72±595.63c Gy,P=0.020）but a higher D2 （6658.50±170.96c Gy vs 6540.96±110.67c Gy,P=0.014）than s IMRT.No significant difference was observed in other indices（P>0.05）.Besides,CI was higher in RapidArc（0.79±0.06 vs 0.72±0.10,P=0.004）,while its MU was significantly lower （445.52±65.63MU vs 554.62±106.08MU,P=0.000）.However,there was no significant difference in HI（P>0.05）.2. In upper thoracic plans,V₃₀ of lungs,V₃₀,V₄₀ and Dmean of heart and D₂ of spinal cord were significantly lower in RapidArc than s IMRT（P<0.05）.Meanwhile, RapidArc also exhibited lower V₃₀,V₄₀ and Dmean of heart and V₂₀ of spinal cord in middle thoracic plans（P<0.05）.Only V₅ and V₂₀ of spinal cord were better in RapidArc in lower thoracic subgroups（P<0.01）.No other difference in organs at risk showed statistical significance（P>0.05）.3.No radiation injury above grade 3 was observed.The incidence of acute myelotoxicity,acute radiation pneumonitis,acute radiation esophagitis,pulmonary fibrosis,pleural effusion and pericardial effusion were decreased by 12.92%, 10.83%,2.92%,2.50%,5.42%,7.50%in RapidArc respectively,but the differences were not statistically significant（P>0.05）.Clinical responses were evaluated three months after treatment,and RapidArc showed slightly higher CR,PR and DCR rates than s IMRT,which were 36.36%,36.36%and 90.91%respectively.There was no significant difference between the two arms（P>0.05）.Conclusions:1.RapidArc could meet the dosimetric requirements of target coverage of esophageal squamous cell carcinoma.It can also promote the conformity and reduce monitor units remarkably.2. RapidArc performed better in reducing the radiation dosage of high-dose regions oflungs,heart and spinal cord than s IMRT,especially in upper thoracic plans.3. Despite all the advantages in dosimetry,RapidArc did not exhibit superiority in alleviating toxicity or enhancing clinical response rates,whose clinical benefits should be verified further.