On the impact of longitudinal breathing motion randomness for tomotherapy delivery

Abstract

The purpose of this study is to explain the unplanned longitudinal dose modulations that appear in helical tomotherapy (HT) dose distributions in the presence of irregular patient breathing. This explanation is developed by the use of longitudinal (1D) simulations of mock and surrogate data and tested with a fully 4D HT delivered plan. The 1D simulations use a typical mock breathing function which allows for more flexibility to adjust various parameters. These simplified simulations are then made more realistic by using 100 surrogate waveforms all similarly scaled to produce longitudinal breathing displacements. The results include the observation that, with many waveforms used simultaneously, a voxel-by-voxel probability of a dose error from breathing is found to be proportional to the realistically random breathing amplitude relative to the beam width if the PTV is larger than the beam width and the breathing displacement amplitude. The 4D experimental test confirms that regular breathing will not result in these modulations because of the insensitivity to leaf motion for low frequency dynamics such as breathing. These modulations mostly result from a varying average of the breathing displacements along the beam edge gradients. Regular breathing has no displacement variation over many breathing cycles. Some low frequency interference is also possible in real situations. In the absence of more sophisticated motion management, methods that reduce the breathing amplitude or make the breathing very regular are indicated. However, for typical breathing patterns and magnitudes, motion management techniques may not be required with HT because typical breathing occurs mostly between fundamental HT treatment temporal and spatial scales. A movement beyond only discussing margins is encouraged for intensity modulated radiotherapy such that patient and machine motion interference will be minimized and beneficial averaging maximized. These results are found for homogeneous and longitudinal on-axis delivery for unplanned longitudinal dose modulations.

Impact of motion induced artifacts on automatic registration of lung tumors in Tomotherapy

“…different from 5 s) during the whole treatment, by selecting an appropriate but still comfortable breathing period. Fortunately, such aliasing is not relevant for the helical treatment delivery, the latter being rather insensitive to beam and tumor motion interplay effects [29][30][31]. Secondly, the influence of surrounding tissues or bones in the registration procedure may result in erroneous tumor positioning.…”

A study of longitudinal tumor motion in helical tomotherapy using a cylindrical phantom

“…Several other authors have found no significant dose difference using sinusoidal waveforms. ( 9 , 10 ) Chaudhari et al ( 14 ) have observed more significant differences using real patient rather than sinusoidal breathing patterns between dose distributions for treatments to static versus moving targets. They have observed larger errors due to motion in real patients only for cases of the breathing pattern with a drift toward inhalation (motion drifting inferiorly).…”

“…( 7 , 11 – 13 ) Other studies have found that there are significant effects, even with sinusoidal motion ( 6 ) or with only real patient breathing patterns. ( 9 , 14 ) …”

Surface Dose in the Treatment of Breast Cancer with Helical Tomotherapy

“…In this case, the results should be an approach to show the effects of a vertical and lateral motion of a typical patient with regular shallow breathing patterns on the surface dose. The dose effects of longitudinal breathing were not measured, as actual research found only small dose deviations for the typical breathing motion patterns [8]. The results of the patients showed a homogeneous dose distribution for both HT and 3D-CRT, with discrete advantages for the latter.…”

“…In each setup, a comparison between surface doses displayed in the planning software and measured doses was done, although other studies found, that the validity of the plan doses is limited near the air-to-skin transition [13]. Since the latest research has shown that the longitudinal breathing motion-induced dose error in the treatment of breast cancer with HT is relatively insignificant for typical breathing patterns, this study investigates the possible dose effects of motion in a transverse plane in the radiation field [8].…”