Ensuring that the desired dose is delivered to the prescribed location for each patient requires a well thought out QA program. Use of pre-treatment QA often requires a disproportionate amount of physics time and resources relative to the number of failures found, and traditional array-based pre-treatment QA methods have been shown to provide low sensitivity to error detection (ref 1). Additional methods must be considered if we are truly to provide complete QA for all patients. Independent in vivo verification of the plan during
delivery is a significant step toward ensuring dose is delivered as prescribed. How does your clinic determine whether plans are delivered accurately during each and every fraction?
Independent automated methods using integrated EPID panels are one solution. The latest release of Adaptivo™ provides improved workflow for daily treatment evaluation. Adaptivo compares exit dosimetry measurements to predicted images to evaluate both accuracy and consistency of delivery. The predicted image is generated based on the plan, planning CT, and a LINAC specific beam model. This provides an independent assessment both that the correct plan is being delivered and that the correct patient setup and alignment occurred each day. Incorrect patient setup on day 1 which is corrected in subsequent fractions is shown in Figure 1.
Adaptivo was designed by clinical physicists with clinical evaluation in mind. Traditional gamma analysis provides no information concerning whether delivery is hotter or cooler than planned. Adaptivo’s hot/cold gamma analysis (Fig 1) is the default view because of the added clinical information it provides. The traditional gamma is given a sign based on if the measured value is hotter (positive/red) or cooler (negative/blue) for ease in evaluation and troubleshooting. Hot/cold gamma is calculated via post-processing of the gamma index map using the following the equation:
where H is the heaviside function.
In addition to confirmation of the patient plan delivery and alignment, weekly average alerts are a mechanism to trigger replanning conversations between the radiation oncologist and medical physicist. Daily differences either due to setup or variable anatomy such as bladder or bowel changes need to be differentiated from longer term changes such as tumor shrinkage or weight loss. Adaptivo facilitates review using weekly average data alerts and treatment delivery trends of the gamma pass rates. In the example shown in Figure 1, replanning triggered by the automatic alerts on the Adaptivo dashboard (Figure 2a) and backed up with trend data (Figure 2b) resulted in improved treatment. In this example, Adaptivo alerts helped facilitate significant reduction in the treatment volume, an increase in tumor dose, and a reduction in dose to normal tissue (Data courtesy of Brian Pomije, MS, DABR Radiation Therapy Physicist, GenesisCare – August 2020).