Consistency and reproducibility of the VMAT plan delivery using three independent validation methods

Abstract

The complexity of VMAT delivery requires new methods and potentially new tools for the commissioning of these systems. It appears that great consideration is needed for quality assurance (QA) of these treatments since there are limited devices that are dedicated to the QA of rotational delivery. In this present study, we have evaluated the consistency and reproducibility of one prostate and one lung VMAT plans for 31 consecutive days using three different approaches: 1) MLC DynaLog files, 2) in vivo measurements using the multiwire ionization chamber DAVID, and 3) using PTWseven29 2D ARRAY with the OCTAVIUS phantom at our Varian Clinac linear accelerator. Overall, the three methods of testing the reproducibility and consistency of the VMAT delivery were in agreement with each other. All methods showed minimal daily deviations that contributed to clinically insignificant dose variations from day to day. Based on our results, we conclude that the VMAT delivery using a Varian 2100CD linear accelerator equipped with 120 MLC is highly reproducible.PACS numbers: 87.55.Qr and 87.56.Fc

The effect of MLC speed and acceleration on the plan delivery accuracy of VMAT

“…Therefore, pre-treatment quality assurance (QA) for each patient is routinely performed in the clinic for verification that the plan is delivered as intended.3,5-9 Another method of verification to determine whether a VMAT plan is deliverable as intended or not is the analysis of dynamic log files registered in the linac control system during delivery. [10][11][12][13][14] As a further method of anal ysis, it has been suggested that the dose distribution in patient CT images be reconstructed with those dynamic log files and compared with that of the original treatment plan. 15 On the other hand, several studies have suggested modu lation indices for VMAT, which can quantify and evaluate the degree of modulation at the planning stage to verify the plan delivery accuracy.…”

The use of log file analysis within VMAT audits

“…[9][10][11] In addition, log file analysis can be used to assess the actual/relative delivered dose reconstructed on the patient anatomy using the patient's original CT image set 10,12 or the on-treatment cone-beam CT image set. 13 The use of log files within a radiotherapy VMAT dosimetry audit has been reported for Elekta linear accelerators 14 (Elekta AB, Stockholm, Sweden) but not for Varian linear accelerators.…”

Study of impacts of different evaluation criteria on gamma pass rates in VMAT QA using MatriXX and EPID

“…However, the system has some issues that must be addressed, like electronic disequilibrium produced by insufficient build up material in EPID, inaccuracies in dose measurements created by scattered photons from the phosphor screen, and back scattered radiation from the support arms. Because the position of EPID is fixed with respect to the gantry, it is impossible to asses any errors in the gantry rotation [8]. Furthermore, EPID exhibits a small sag in its position due to gravity; this displacement also contributes to the reduction of pass rates, especially in VMAT plans in which gantry continuously rotates.…”

“…The diode-detector-based MapCHECK (Sun Nuclear Corporation, US) [7], the ion-chamber based Seven29 2D array (PTW, Germany) [8,9], and MatriXX (IBA Dosimetry, Germany) [10][11][12][13][14] are commonly used commercial 2D detector arrays. The MatriXX array has a linear response with dose and it is independent of energy [12].…”