Pretreatment quality assurance of volumetric modulated arc therapy on patient CT scan using indirect 3D dosimetry system

Abstract

Purpose: Aim of this study is to clinically implement the COMPASS 3D dosimetry system for pretreatment quality assurance of volumetric modulated arc therapy (VMAT-RapidArc) treatment plans. Methods: For this study, 10 head and neck (H&N) and pelvis VMAT plans dose response from Linac was measured using COMPASS system along with MatriXX Evolution and 3D dose reconstructed in the patient computed tomography (CT) scan. Dose volume histograms and 3D gamma were used to evaluate difference between the measured and calculated values. In order to validate the COMPASS system, dose response for open fields were acquired for both homogeneous and inhomogeneous phantoms. Results: The average dose difference between Eclipse treatment planning system (TPS) calculated and COMPASS measured (homogenous medium) in normalization region, inner region, penumbra region and buildup region was less than ±2%. In inhomogeneous phantom, there was a maximum difference -3.17% in lung, whereas the difference other densities was within ±2%. The systematic increase in the average 3D gamma between the TPS calculated and COMPASS measured for VMAT plans with known dose errors and multi-leaf collimator (MLC) offset errors shows that COMPASS system was sensitive enough to find clinical significant errors. The 3D dose parameters (D95, D1, and average dose) of all H&N and pelvis patients were well within the clinically acceptable tolerance level of ±5%. The average 3D gammas for planning target volumes (PTV) and organ at risks (OAR) of the patients were less than 0.6. Conclusion:The results from this study show that COMPASS along with MatriXX Evolution can be effectively used for pretreatment verification of VMAT plans in the patient anatomy.

Performance evaluation of gated volumetric modulated arc therapy

“…On other hand, the advantage of COMPASS 3D dosimetry system over other QA systems was its capability of performing independent 3D dose reconstruction on patient CT scan using beam model, detector measurement and treatment plan. Literatures have validated the accuracy of dose reconstruction method in COMPASS and proved that COMPASS was adequate to perform QA of IMRT/VMAT treatment (14)(15)(16)(17)(18)(19) . Collapsed cone convolution/superposition algorithm based dose calculation engine in COMPASS system, computes dose distribution in heterogeneous medium (lung) similar to Monte Carlo simulations (20) .…”

“…Therefore it is important to evaluate the feasibility and the dosimetric accuracy of the gated VMAT before its clinical use (1,5) . The gamma agreement index in table 1 does not provide any clinically relevant information about the results (13) , whereas COMPASS system provides the signi-icance of error in PTV and as well as in OAR's (14)(15)(16)(17)(18) . The information provided by DynaLog -iles and traditional 2D planar dosimetry cannot easily be translated onto dose deviations in the tumor and/or at OAR's.…”

“…Despite local inaccuracies in the dose reconstruction, Godart et al (17) have shown that COMPASS system was adequate to perform pretreatment veri-ication of VMAT treatment plans. Few studies have shown the experimental and clinical validation of COMPASS system for both IMRT and VMAT (14)(15)(16)(17)(18)(19) . In this study, we have evaluated the performance of gated volumetric modulated arc therapy by using 2D planar dosimetry, DynaLog Files and COMPASS 3D dosimetry system.…”

Planning and Dosimetric Study of Volumetric Modulated Arc Based Hypofractionated Stereotactic Radiotherapy for Acoustic Schwannoma - 6MV Flattening Filter Free Photon Beam

“…Pretreatment QA was performed in a phantom using chamber, film, 2D array and electronic portal imaging. Each of these devices has been proven useful but has its own limitations (Xin et al, 2012;Thirumalai et al, 2014). Due to involvement of small field size the point dosimetry would be better choice than 2D planar dosimetry.…”

Clinical Experience with Machine Log File Software for Volumetric-Modulated Arc Therapy Techniques

“…W ith the introduction of intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) techniques, the complexity of the treatment plan in radiation oncology has increased along with the need for patient-specifi c pretreatment quality assurance (QA) measurements. Th e need for fast and reliable methods has created a wide variety of available solutions for IMRT QA, including ion chamber, diode array, electronic portal imaging device (EPID), fi lm, and radio-chromic fi lm measurements, which have been extensively studied and are widely accepted (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15). Th e Mobius FX solution (Mobius Medical Systems, Houston, TX) for IMRT QA uses linac treatment logs to calculate and verify the 3D dose delivered.…”