  Adaptive radiation therapy (ART) could protect organs at risk (OARs) while
maintain high dose coverage to targets. However, there still lack efficient
online patient QA methods. We aim to develop a clinically relevant online
patient quality assurance (QA) solution for ART using daily CT scans and
electronic portal imaging device (EPID)-based in vivo dosimetry. Ten patients
with rectal cancer at our center were included. Patients' daily CT scans and
portal images were collected to generate reconstructed 3D dose distributions.
Contours of targets and OARs were recontoured on these daily CT scans by a
clinician or an auto-segmentation algorithm, then dose-volume indices were
calculated, and the percent deviation of these indices to their original plans
were determined. This deviation was regarded as the metric for clinically
relevant patient QA. The tolerance level was obtained using a 95% interval of
the QA metric distribution. These deviations could be further divided into
anatomically relevant or delivery relevant indicators for error source
analysis. Finally, our QA solution was validated on an additional six clinical
patients. In rectal cancer, the lower and upper tolerance of the QA metric for
PTV {\Delta}D95 (%) were [-3.11%, 2.35%], and for PTV {\Delta}D2 (%) were
[-0.78%, 3.23%]. In validation, the 68% for PTV {\Delta}D95 (%) and the 79% for
PTV {\Delta}D2 ({%)of the 28 fractions are within tolerances of the QA metrics.
By using four or more out-of-tolerance QA metrics as an action level, there
were 5 fractions (18%) have four or more out-of-tolerance QA metrics in
validation patient dataset. The online patient QA solution using daily CT scans
and EPID-based in vivo dosimetry is clinically feasible. Source of error
analysis has the potential for distinguishing sources of error and guiding ART
for future treatments.
