Factors that Influence the Need to Start Adaptive Radiotherapy.

Introduction: Adaptive radiotherapy (ART) is an essential approach to account for anatomical and biological uncertainties. Adaptive radiotherapy is, however, time-consuming, and it is unclear which patients are eligible or when is the best time to start ART.

Methods: This prospective study was conducted at Kasr El-Aini Center of Clinical Oncology and Nuclear Medicine, Cairo, Egypt from January 2019 to December 2020. Thirty patients with pathologically proven, limited-stage small cell or stage I-II non-small cell lung cancer who were either not fit for or refused surgery or had stage III disease were recruited and underwent treatment planning to receive 60 Gy on a conventional 3D conformal radiation schedule with platinum-based chemotherapy. All patients underwent computed tomography (CT) planning within 2 and 4 weeks of starting radiation therapy to assess the need for adaptation. Pulmonary function test and echocardiography findings were assessed at the end of treatment and at 3 and 6 months after treatment, and were compared to the baseline.

Results: We found a significant reduction in mean value of the planning target volume (PTV) in the CT scans at the second (331 cm) and fourth (257 cm) weeks of treatment as compared to baseline (342 cm) (-value < 0.0001). Adaptation decreased the dose to the organ at risk with statistical significance and with improvement of the target coverage. At week 2 of radiotherapy, the need for adaptation was correlated to the conformity index ( = 0.0473), esophageal V35 ( = 0.0488), esophageal V50 ( = 0.0295), and its mean dose ( = 0.0087). At week 4 it was correlated to forced expiratory volume in 1 second (FEV1) ( = 0.0303), ratio between the forced expiratory volume in 1 second and the forced vital capacity (FEV1/FVC) ( = 0.0024), and echocardiography ( = 0.0183).

Conclusions: Conformity index and esophageal dose constraints can predict the need for adaptation at week 2, whereas baseline pulmonary function parameters and echocardiography can predict the need for adaptation at week 4 of radiotherapy.