Evaluation of TomoTherapy dose calculations with intrafractional motion and motion compensation

Abstract

Purpose: Anatomical motion, both cyclical and aperiodic, can impact the dose delivered during external beam radiation. In this work, we evaluate the use of a research version of the clinical TomoTherapy â dose calculator to calculate dose with intrafraction rigid motion. We also evaluate the feasibility of a method of motion compensation for helical tomotherapy using the jaws and MLC. Methods: Treatment plans were created using the TomoTherapy treatment planning system. Dose was recalculated for several simple rigid motion traces including a 4 mm step motion applied either longitudinally or transversely, and a sinusoidal motion. The calculated dose volumes were compared to dose measurements that were performed by translating the phantom with the same motion traces used in the calculations. Measurements were made using film and ion chambers. Finally, the delivery plans were modified to compensate for the motion by sweeping the jaws for longitudinal motion and shifting the MLC leaves for transverse motion, and the calculations and measurements were repeated. Results: A transverse step motion shifted the dose that was delivered after the step occurred, but otherwise did not impact the dose distribution. Film measurements agreed with dose calculations to within 2%/2 mm for 99% of dose points within the 50% isodose line. A shift in the MLC leaf delivery pattern successfully compensated for the step motion to within the 3 mm accuracy allowed by the finite leaf widths. A longitudinal step motion impacted the dose in the interior of the target volume to a degree that was dependent on the planning field width and step size. Film measurements agreed with dose calculations to within 2%/2 mm for 98% of dose points within the 50% isodose line. Shifts in the jaw position successfully compensated for the longitudinal step motion. Sinusoidal (breathinglike) motion was also studied, with similar results. Conclusions: A research version of the clinical TomoTherapy dose calculator has been shown to accurately calculate the dose from treatment plans delivered in the presence of arbitrary rigid motion. Modifications to the delivery plan using jaw and MLC leaf shifts that follow the motion can successfully compensate for the target motion.

Evaluation of radixact motion synchrony for 3D respiratory motion: Modeling accuracy and dosimetric fidelity

“…The dosimetric effect of a Synchrony‐enabled treatment for respiratory motion was studied by Schnarr et al, in which Synchrony tracked and compensated for linear respiratory‐mimicking motion, but for only one non‐clinical treatment plan for a cylindrical target 13 . In addition, Chao et al evaluated the accuracy of TomoTherapy dose calculations for Synchrony deliveries using film, but the motion was programmed a priori into the treatment plan instead of using real‐time tracking 14 . Chen et al performed acceptance testing of Synchrony deliveries, 15 but these tests were limited to a single clinical delivery quality assurance (DQA) test for a respiratory with fiducial treatment.…”

Accuracy of TomoEDGE dynamic jaw field widths

“…study from which the original 1% FWHM tolerance was established. Furthermore, the establishment of an appropriate QA tolerance for the asymmetric FWs becomes more relevant with the recent development of motion management utilizing the dynamic jaws 10. The AAPM TG‐148 report for quality assurance of TomoTherapy was published prior to the introduction of dynamic jaw movement and the study suggests that the recommended tolerance limits could be revisited in lieu of the present technology.…”

Tumor tracking using the Radixact system. Review of reports presented at the ESTRO 38 conference in Milan

“…algorytm przewidujący. Ta składowa zbudowanego modelu rekompensuje potencjalne opóźnienia systemowe wynikające z konieczności zebrania i analizy danych dotyczących pozycji guza [2,[12][13][14].…”

“…Stąd podczas prezentacji możliwości systemu Radixact bardzo często podkreśla się, że w porównaniu z bramkowaniem oddechowym, system ten może mieć tzw. 100% cykl pracy [12][13][14].…”

“…Na koniec warto wspomnieć o zgodności dostarczania zaplanowanych rozkładów dawek z danymi pomiarowymi uzyskanymi poprzez odtworzenie ruchomości na fantomie [12][13][14].…”