Alternatives to patient specific verification measurements in proton therapy: a comparative experimental study with intentional errors

Abstract

Patient specific verification (PSV) measurements for pencil beam scanning (PBS) proton therapy are resource-consuming and necessitate substantial beam time outside of clinical hours. As such, efforts to safely reduce the PSV-bottleneck in the clinical work-flow are of great interest. Here, capabilities of current PSV methods to ensure the treatment integrity were investigated and compared to an alternative approach of reconstructing the dose distribution directly from the machine control- or delivery log files with the help of an independent dose calculation (IDC). Scenarios representing a wide range of delivery or work-flow failures were identified (e.g. error in spot position, air gap or pre-absorber setting) and machine files were altered accordingly. This yielded 21 corrupted treatment files, which were delivered and measured with our clinical PSV protocol. IDC machine- and log file checks were also conducted and their sensitivity at detecting the errors compared to the measurements. Although some of the failure scenarios induced clinically relevant dose deviations in the patient geometry, the PSV measurement protocol only detected one out of 21 error scenarios. However, 11 and all 21 error scenarios were detected using dose reconstructions based on the log and machine files respectively. Our data suggests that, although commonly used in particle therapy centers, PSV measurements do a poor job detecting data transfer failures and imperfect delivery machine performance. Machine- and log-file IDCs have been shown to successfully detect erroneous work-flows and to represent a reliable addition to the QA procedure, with the potential to replace PSV.

Dosimetric influence of deformable image registration uncertainties on propagated structures for online daily adaptive proton therapy of lung cancer patients

“…After the delivery, however, a careful structure revision and correction are necessary. A full plan reoptimisation used in this study (a new spot placement, constraint optimisation [27,28]) has the advantage that it allows for an improved plan quality in case of favourable anatomy and also works in the case of major anatomical changes, where the simpler approach of restoring the dose on the new anatomy independent from the daily structures [67] might fail. As part of the offline quality assurance after the delivery, the delivered DAPT dose can then be reconstructed from the delivery logfile, using the daily CT and a MC dose calculation [30,68], as in such an online workflow, no patient specific dose measurements are possible.…”

“…At PSI an online DAPT workflow has recently been developed [25] and successfully tested for nondeforming anatomies on a phantom [26]. In the DAPT workflow a daily CT is acquired in treatment position, contours are transferred and a plan is reoptimised online [27], followed by a fast clinical and measurement-free physical quality assurance [28]. After the delivery, the dose is reconstructed on the planning CT [29,30].…”

A Modular System for Treating Moving Anatomical Targets With Scanned Ion Beams at Multiple Facilities: Pre-Clinical Testing for Quality and Safety of Beam Delivery

“…The procedure and phantoms were modified in our study for motion compensation. Further, Matter et al (56) investigated the capabilities of various plan verification procedures to ensure the integrity of treatment plans under a variety of planning errors. Of the measured errors, two cases were relevant considerations for motion-synchronized deliveries with the M-DDS: the "all spots shifted randomly" case, and the "increase in spot weights" case.…”

Daily adaptive proton therapy – the key to innovative planning approaches for paranasal cancer treatments

“…As for fast planning and plan QA, we have previously demonstrated that the complete optimization of plans can be performed in just a few seconds [13], whereas efficient independent dose calculations, based on machine control files, provided a fast and sensitive alternative to plan specific QA measurements [14,33]. Finally, although accurate contour propagation and dose accumulation for deformable geometries are still challenging [34], for the paranasal sinuses spatial transformations between daily datasets are predominantly rigid, simplifying both processes considerably.…”

“…With DAPT, both the daily anatomy and patient setup variations can be directly included in the daily plan optimization, allowing for reduced margins and irradiation of surrounding healthy tissue. As such, previous studies showed that a highly efficient DAPT workflow including the plan-of-the-day generation and validation might be feasible in less than five minutes after inroom 3D imaging [13,14].…”