Sensitivity of volumetric modulated arc therapy patient specific QA results to multileaf collimator errors and correlation to dose volume histogram based metrics

2013 ◽  
Vol 40 (11) ◽  
pp. 111715 ◽  
Author(s):  
Linda Coleman ◽  
Christina Skourou
Keyword(s):  
Volumetric Modulated Arc Therapy ◽  
Patient Specific ◽  
Multileaf Collimator ◽  
Dose Volume Histogram ◽  
Dose Volume ◽  
Arc Therapy ◽  
Patient Specific Qa

The sensitivity of gamma index analysis to detect multileaf collimator (MLC) positioning errors using Varian TrueBeam EPID and ArcCHECK for patient-specific prostate volumetric-modulated arc therapy (VMAT) quality assurance

2017 ◽  
Vol 17 (1) ◽  
pp. 66-77 ◽  
Author(s):  
Borna Maraghechi ◽  
Jack Davis ◽  
Nicholas Mitchell ◽  
Meeral Shah ◽  
Andre Fleck ◽  
...  
Keyword(s):  
Volumetric Modulated Arc Therapy ◽  
Patient Specific ◽  
Multileaf Collimator ◽  
Control Points ◽  
Dose Distributions ◽  
Positioning Errors ◽  
Gamma Index ◽  
Arc Therapy ◽  
Epid Dosimetry ◽  
Higher Sensitivity

AbstractBackgroundDue to the increased degree of modulation and complexity of volumetric-modulated arc therapy (VMAT) plans, it is necessary to have a pre-treatment patient-specific quality assurance (QA) programme. The gamma index is commonly used to quantitatively compare two dose distributions. In this study we investigated the sensitivity of single- and multi-gamma criteria techniques to detect multileaf collimator (MLC) positioning errors using the Varian TrueBeam Electronic Portal Imaging DeviceTM (EPID) dosimetry and the ArcCHECKTM device.Materials and methodsAll active MLC positions of seven intact prostate patients VMAT plans were randomly changed with a mean value of 0.25, 0.5, 1 and 2 mm and a standard deviation of 0.1 mm on 25, 50, 75 and 100% of the control points. The change in gamma passing rates of six gamma criteria of 3%/3 mm, 3%/2 mm, 3%/1 mm, 2%/2 mm, 2%/1 mm and 1%/1 mm were analysed individually (single-gamma criterion) and as a group (multi-gamma criteria) as a function of the simulated errors. We used the improved and global gamma calculation algorithms with a low dose threshold of 10% in the EPID and ArcCHECK software, respectively. The changes in the planning target volume dose distributions and the organs at risk due to the MLC positioning errors were also studied.ResultsWhen 25, 50, 75 and 100% of the control points were modified by the introduction of the simulated errors, the smallest detectable errors with the EPID were 2, 1, 0.5 and 0.5 mm, respectively, using the multi-gamma criteria technique. Similarly for the single-gamma criteria technique errors as small as 2, 1, 1 and 1 mm applied to 25, 50, 75 and 100% of the control points, respectively, were detectable using a 2%/2 mm criterion. However, the smallest detectable errors with the ArcCHECK when using the multi-gamma criteria technique were 2, 2 and 1 mm when MLC errors were applied on 50, 75 and 100% of the control points. When only 25% of the control points were affected the ArcCHECK were unable to detect any of the errors applied. No noticeable difference was observed in the sensitivity using the single- or the multi-gamma criteria techniques with the ArcCHECK.ConclusionThe Varian TrueBeam EPID dosimetry shows a higher sensitivity in detecting MLC positioning errors compared with the ArcCHECK regardless of using the single- or the multi-gamma criteria techniques. Higher sensitivity was observed using the multi-gamma criteria technique compared with the single-criterion technique when using the EPID.

scholarly journals Can clinically relevant dose errors in patient anatomy be detected by gamma passing rate or modulation complexity score in volumetric-modulated arc therapy for intracranial tumors?

2017 ◽  
Vol 58 (5) ◽  
pp. 685-692 ◽  
Author(s):  
Shingo Ohira ◽  
Yoshihiro Ueda ◽  
Masaru Isono ◽  
Akira Masaoka ◽  
Misaki Hashimoto ◽  
...  
Keyword(s):  
Volumetric Modulated Arc Therapy ◽  
Patient Specific ◽  
Array Detector ◽  
Intracranial Tumors ◽  
Clinical Dose ◽  
Complexity Score ◽  
Passing Rate ◽  
Arc Therapy ◽  
Patient Specific Qa ◽  
Gamma Passing Rate

Abstract We investigated whether methods conventionally used to evaluate patient-specific QA in volumetric-modulated arc therapy (VMAT) for intracranial tumors detect clinically relevant dosimetric errors. VMAT plans with coplanar arcs were designed for 37 intracranial tumors. Dosimetric accuracy was validated by using a 3D array detector. Dose deviations between the measured and planned doses were evaluated by gamma analysis. In addition, modulation complexity score for VMAT (MCSv) for each plan was calculated. Three-dimensional dose distributions in patient anatomy were reconstructed using 3DVH software, and clinical deviations in dosimetric parameters between the 3DVH doses and planned doses were calculated. The gamma passing rate (GPR)/MCSv and the clinical dose deviation were evaluated using Pearson's correlation coefficient. Significant correlation (P < 0.05) between the clinical dose deviation and GPR was observed with both the 3%/3 mm and 2%/2 mm criteria in clinical target volume (D99), brain (D2), brainstem (D2) and chiasm (D2), albeit that the correlations were not ‘strong’ (0.38 < |r| < 0.54). The maximum dose deviations of brainstem were up to 4.9 Gy and 2.9 Gy for Dmax and D%, respectively in the case of high GPR (98.2% with 3%/3 mm criteria). Regarding MCSv, none of the evaluated organs showed a significant correlation with clinical dose deviation, and correlations were ‘weak’ or absent (0.01 < |r| < 0.21). The use of high GPR and MCSv values does not always detect dosimetric errors in a patient. Therefore, in-depth analysis with the DVH for patient-specific QA is considered to be preferable for guaranteeing safe dose delivery.

scholarly journals Dose–volume histogram analysis and clinical evaluation of knowledge-based plans with manual objective constraints for pharyngeal cancer

2020 ◽  
Vol 61 (3) ◽  
pp. 499-505 ◽  
Author(s):  
Takuya Uehara ◽  
Hajime Monzen ◽  
Mikoto Tamura ◽  
Kazuki Ishikawa ◽  
Hiroshi Doi ◽  
...  
Keyword(s):  
Spinal Cord ◽  
Volumetric Modulated Arc Therapy ◽  
Intensity Modulated Radiation Therapy ◽  
Target Volume ◽  
Dose Volume Histogram ◽  
Parotid Glands ◽  
Pharyngeal Cancer ◽  
Knowledge Based ◽  
Dose Volume ◽  
Arc Therapy

Abstract The present study aimed to evaluate whether knowledge-based plans (KBP) from a single optimization could be used clinically, and to compare dose–volume histogram (DVH) parameters and plan quality between KBP with (KBPCONST) and without (KBPORIG) manual objective constraints and clinical manual optimized (CMO) plans for pharyngeal cancer. KBPs were produced from a system trained on clinical plans from 55 patients with pharyngeal cancer who had undergone intensity-modulated radiation therapy or volumetric-modulated arc therapy (VMAT). For another 15 patients, DVH parameters of KBPCONST and KBPORIG from a single optimization were compared with CMO plans with respect to the planning target volume (D98%, D50%, D2%), brainstem maximum dose (Dmax), spinal cord Dmax, parotid gland median and mean dose (Dmed and Dmean), monitor units and modulation complexity score for VMAT. The Dmax of spinal cord and brainstem and the Dmed and Dmean of ipsilateral parotid glands were unacceptably high for KBPORIG, although the KBPCONST DVH parameters met our goal for most patients. KBPCONST and CMO plans produced comparable DVH parameters. The monitor units of KBPCONST were significantly lower than those of the CMO plans (P < 0.001). Dose distribution of the KBPCONST was better than or comparable to that of the CMO plans for 13 (87%) of the 15 patients. In conclusion, KBPORIG was found to be clinically unacceptable, while KBPCONST from a single optimization was comparable or superior to CMO plans for most patients with head and neck cancer.

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