Feasibility of Shrinking Field Radiation Therapy through 18F-FDG PET/CT after 40 Gy for Stage III Non-Small Cell Lung Cancers

Objective: To explore the feasibility of shrinking field technique after 40 Gy radiation through 18F-FDG PET/CT during treatment for patients with stage Ⅲ non-small cell lung cancer (NSCLC).
Methods: In 66 consecutivepatients with local-advanced NSCLC, 18F-FDG PET/CT scanning was performed prior to treatment and repeatedafter 40 Gy. Conventionally fractionated IMRT or CRT plans to a median total dose of 66Gy (range, 60-78Gy)were generated. The target volumes were delineated in composite images of CT and PET. Plan 1 was designedfor 40 Gy to the initial planning target volume (PTV) with a subsequent 20-28 Gy-boost to the shrunken PTV.Plan 2 was delivering the same dose to the initial PTV without shrinking field. Accumulated doses of normaltissues were calculated using deformable image registration during the treatment course.
Results: The medianGTV and PTV reduction were 35% and 30% after 40 Gy treatment. Target volume reduction was correlatedwith chemotherapy and sex. In plan 2, delivering the same dose to the initial PTV could have only been achievedin 10 (15.2%) patients. Significant differences (p<0.05) were observed regarding doses to the lung, spinal cord,esophagus and heart.
Conclusions: Radiotherapy adaptive to tumor shrinkage determined by repeated 18F-FDGPET/CT after 40 Gy during treatment course might be feasible to spare more normal tissues, and has the potentialto allow dose escalation and increased local control.