Retrospective analysis of target volume dose coverage using CBCT acquired for accelerated hypo-fractionated radiation therapy (AHFRT) in lung cancer

Abstract

Objective To assess target volume dose coverage using cone-beam computed tomography scans (CBCT) acquired for AHFRT. Materials and Methods Nine patients were investigated in this study. Dose prescription was 60 Gy to the PTV (ITV plus 5 mm margins) delivered in 3, 5 or 8 fractions with volumetric modulated arc therapy (VMAT), using 3–5 arcs, 6 MV energy beam and the Novalis Tx linac. Patients were supine on a cushion or a thoracic support. All but 2 patients had arms over the head. ExacTrac was used on patient's bony structures enabling fine 6D table position movements followed by CBCT for ITV 3D positioning. During treatment, Exactrac snap verifications monitored the patient. Twenty CBCT were randomly selected to re-calculate dose coverage to the target in patient's treatment position, having tested the feasibility on phantom (results presented separately). DVHs were analyzed and for 3 patients, session dose distribution reproducibility was assessed. Results Mean median dose percentage difference coverage (CTCBCT) PTV and ITV was 0.01 ± 2.41 and −0.08 ± 2.67 respectively. Mean minimum and maximum dose percentage difference coverage (CT-CBCT) of ITV was 0.415 ± 2.83 and −1.21 ± 2.62 respectively. One patient showed systematic differences larger than −4%, due to image CBCT problems and without this patient, previous reported values changed to 0.81 ± 1.46, 0.88 ± 1.36, 1.23 ± 2.11and −0.2 ± 0.93. Dose targets coverage reproducibility, means standard deviation, was less than 1.8%. Conclusions This preliminary study showed that good patients positioning leads to dose distribution reproducibility respect to simulation as verified using CBCT.