Determination of the optimal tolerance for MLC positioning in sliding window and VMAT techniques

Abstract

Dynalog analysis provides a feasible method for investigating the optimal tolerance for MLC positioning in dynamic fields. In sliding window treatments, the tolerance of 2 mm was found to be adequate, although it can be reduced to 1.5 mm. In VMAT treatments, the typically used 5 mm tolerance is excessively high. Instead, a tolerance of 2.5 mm is recommended.

Delivering RapidArc®: A comprehensive study on accuracy and long term stability

“…Our results on the MLC errors frequency prove that the machine tolerance can be reduced from the suggested value of 3 mm to 2.5 mm without affect the delivery efficiency (see also Hernandez [18]). Concerning MU delivery, the proposed limit of 0.15 MU/arc [32] can be reduced to 0.1 MU/arc which is more than 6 times greater than the MU delivery error standard deviation measured in this work.…”

“…Two years of clinical activity were extensively and systematically investigated http to assess the long term stability and the accuracy of the system. Unlike published works which partially cover the study of RapidArc delivery performance, both for the data pool statistics and for the restricted analyzed parameters [13][14][15]18], this article provides a robust proof of the clinical RapidArc reliability through the analysis of all the main parameters affecting the RapidArc delivery for a large number of a clinical cases with different degrees of complexity.…”

The use of log file analysis within VMAT audits

“…If an error goes beyond this value in VMAT delivery, an interlock is triggered by the MLC in order to interrupt the gantry rotation. 15 There are no tolerances for TrueBeams as they prioritize the MLC and adjust other beam delivery parameters to allow MLCs to reach planned positions, negating the requirement for a specific tolerance value. (Table 3).…”

“…These results did not differentiate between TPS types and versions, linear accelerator type and treatment site/techniques. Hernandez et al 15 investigated Varian Trilogy and Clinac log files with plans delivered using a single TPS to determine optimal MLC tolerances for IMRT and VMAT.…”

Technical Note: Motion‐perturbation method applied to dosimetry of dynamic MLC target tracking—A proof‐of‐concept

“…If a reasonable tracking system were employed, this relative velocity would be considered rather high for a Varian accelerator, since the leaf speed is typically limited in planning to the published maximum of 2.5 cm/s (Ref. 8) or slightly less, 9 and tracking should slow down the planned leaf speed if the target is moving in the opposite direction. On the other hand, if the leaf is chasing the target, the relative velocity is also unlikely to exceed 3 cm/s.…”