Feasibility Study On Cone Beam Computed Tomography Derived Adaptive Radiothera For Radical Treatment Of Esophageal Cancer

Background and purpose Using kilo-voltage cone beam computed tomography (KV-CBCT) imaging data acquired in the first week five times radiotherapy for esophageal cancer patients receiving radical three-dimensional conformal radiotherapy (3DCRT), to explore the potential for design adaptive radiation therapy (ART) by creating a patient specific planning target volume (PTV). And to investigate the potential reduction in the irradiation dose to the normal tissue for the KV-CBCT image-guided adaptive radiotherapy.Methods and materials10esophageal cancer patients receiving radical3DCRT from October,2010to January,2011were enrolled for the study in the Cancer Hospital of Guangxi Medical University. The PTV of3DCRT plan is defined as clinical target volume (CTV)(included primary site and regional node) plus esophagus outlined3to5cm cranio-caudally and a1-1.5cm circumferential margin. On the linear accelerator, the patients udderwent setup on a daily KV-CBCT acquisition in the treatment position using the Elekta Synergy ⅩⅥ. And no correction for setup error were made for each patient during radiation therapy. KV-CBCT imaging were acquired on Days1to5in the first week radiotherapy, then once per week in the last2-6weeks radiotherapy.8to10KV-CBCT images were acquired for each Patient. The KV-CBCT images were imported into the Pinnacle3, V8.0m planning system, and matched with the planning CT for the same treatment position. Then the same tumor and esophagus in3DCRT plan for the length of the CTV are contoured on each KV-CBCT imaging and imported into3DCRT plan. A composite volume (CTV1) is created by uniting the first Week5CTVs and5mm margin is added to attain PTV1. This new PTV1is the PTV of ART. The same process is repeated using KV-CBCT images Week2to6to created PTV2. Using the same radiation planning parameters in3DCRT to created A new plan (adaptive plan) with PTV1and PTV2. The coverage of the95%prescription isodose is evaluated on PTV1and PTV2with same radiation planning. Dose-volume histograms(DVH) for lung, heart, and spinal cord for3DCRT and ART plan were compared using t test by SPSS13.0statistical software.Results:A total of98KV-CBCT imagings for10cases were analyzed to created ART plan for each patient by modified the primary3DCRT plan. To achieve coverage of the planning target volume with the95%isodose line for the PTV1using similar field arrangement as per primary clinical plan and to get the DVH. In the ART plan,the coverage of the95%prescription isodose for PTV2(99.1%±1.7%)was higher then that of PTV1(95.5%±3.4%)(p=0.03), which to ascertain that the PTV1would provide adequate coverage for the whole duration of the treatment. Comparing ART plan with3DCRT plan for OAR, the Lung’s V20(25.1%VS.26.9%, p=0.001)> V30(14.1%VS.15.4%, p=0.001)and mean dose (14.1Gy VS.15.1Gy, p=0.001), heart’s V40(7.8%VS.13.3%, p=0.002) and mean dose (16.7Gy VS.19.7Gy, p=0.002) and spinal cords max dose(41.5Gy VS.42.9Gy, p=0.018) and mean dose(23.5Gy VS.25.0Gy, p=0.001) in ART plan were significantly lower than those of the3DCRT plan.Conclusions A adaptive radiation therapy can be constructed base on3DCRT using KV-CBCT imaging messages of the first week of treatment. A single plan modification can be performed within the second week of treatment which considerable reduction in dose of the organs at risk.