How the detector resolution affects the clinical significance of SBRT pre-treatment quality assurance results

PurposeTo assess the efficiency of combined use of ArcCheck® detector (AC) and portal dosimetry (PDIP) for delivery quality assurance of head and neck and prostate volumetric‐modulated arc therapy.Materials and methodsMeasurement processes were studied with the Gamma index method according to three analysis protocols. The detection sensitivity to technical errors of each individual or combined measurement processes was studied by inserting collimator, dose and MLC opening error into five head and neck and five prostate initial treatment plans. A total of 220 plans were created and 660 analyses were conducted by comparing measurements to error free planned dose matrix.ResultsFor head and neck localization, collimator errors could be detected from 2° for AC and 3° for PDIP. Dose and MLC errors could be detected from 2% and 0.5 mm for AC and PDIP. Depending on the analysis protocol, the detection sensitivity of total simulated errors ranged from 54% to 88% for AC vs 40% to 74% for PDIP and 58% to 92% for the combined process. For the prostate localization, collimator errors could be detected from 4° for AC while they could not be detected by PDIP. Dose and MLC errors could be detected from 3% and 0.5 mm for AC and PDIP. The detection sensitivity of total simulated errors ranged from 30% to 56% for AC vs 16% to 38% for PDIP and 30% to 58% for combined process.ConclusionThe combined use of the two measurement processes did not statistically improve the detectability of technical errors compared to use of single process.

Section: Discussionmentioning

confidence: 94%

Section: Discussionmentioning

confidence: 99%

Assessment of combined use of ArcCheck^® detector and portal dosimetry for delivery quality assurance of head and neck and prostate volumetric‐modulated arc therapy

Moliner

Sorro

Verstraet

et al. 2018

“…The γ ‐metric, the standard technique used to evaluate the agreement between planned and measured dose,9 can be obtained not only in a two‐dimensional way but also three‐dimensionally, allowing the evaluation of the whole volumetric dose distribution. Nowadays, PTW Octavius ® ‐4D is widely used in the QA process, and its performances were already evaluated also for stereotactic treatments,10, 11, 12 with flattening filter free (FFF) technology13 or for testing respiratory‐gated VMAT delivery 14. In spite of this, some aspects of its performances were only partially investigated 1, 15, 16.…”

Section: Introductionmentioning

confidence: 99%

Practical application of Octavius^®‐4D: Characteristics and criticalities for IMRT and VMAT verification

Urso

Lorusso

Marzoli

et al. 2018

Octavius®‐4D is a very effective device in radiotherapy treatment quality assurance (QA), due to its simple set‐up and analysis package. However, even if it is widely used, its main characteristics and criticalities were only partially investigated. Taking start from its commissioning, the aim of this work was to study the main dependencies of the device response. The outcome dependence was studied comparing results by different delivery techniques [Intensity Modulated Radiation Therapy, IMRT (n = 29) and RapidArc, RA (n = 15)], anatomical regions [15 head/neck, 19 pelvis and 10 pancreas] and linear accelerators [DHX (n = 14) and Trilogy (n = 30)]. Moreover, the agreement dependency on the section of the phantom was assessed. Plan evaluations obtained by 2D, 3D, and volumetric γ‐index (both local and global) were also compared. Generally, high dose gradient resulted critically managed by the assembly, with a smoother effect in RA technique. Worse agreements emerged in the 2D γ‐index vs those of 3D and volumetric (P < 0.001), that were instead statistically comparable in global metric (P > 0.300). Volumetric plan evaluation was coherent with the average of passing rates on the 3 phantom axes (r ≥ 0.9), but transversal section provided best agreements vs sagittal and coronal ones (P < 0.050). The three studied districts furnished comparable results (P > 0.050) while the two LINACs provided different agreements (P < 0.005). The study pointed out that the phantom transversal section better fits the planned dose distribution, so this should be accounted when a two‐dimensional evaluation is needed. Moreover, the major reliability of the 3D metric with respect to the 2D one, as it better agrees with the dosimetric evaluation on the whole volume, suggests that it should be preferred in a two‐dimensional evaluation. Better agreements, obtained with RA vs IMRT technique, confirm that Octavius®‐4D is specifically conceived for rotational delivery. Lastly, the assembly resulted sensitive to different technology.

“…The 1 cm detector distance could be detrimental for SRS QA. 11 Metastasis is often on the order of millimeters. Due to the steep dose gradients, the large detector spacing could prevent the dose profile near a metastasis from being measured to a degree sufficient to verify dose delivery accuracy.…”

Section: Introductionmentioning

confidence: 99%

Patient‐specific dose quality assurance of single‐isocenter multiple brain metastasis stereotactic radiosurgery using PTW Octavius 4D

McCulloch¹,

Pawlowski²,

Kirby³

et al. 2020

Purpose Single‐isocenter multiple brain metastasis stereotactic radiosurgery is an efficient treatment modality increasing in clinical practice. The need to provide accurate, patient‐specific quality assurance (QA) for these plans is met by several options. This study reviews some of these options and explores the use of the Octavius 4D as a solution for patient‐specific plan quality assurance. Methods The Octavius 4D Modular Phantom (O4D) with the 1000 SRS array was evaluated in this study. The array consists of 977 liquid‐filled ion chambers. The center 5.5 cm × 5.5 cm area has a detector spacing of 2.5 mm. The ability of the O4D to reconstruct three‐dimensional (3D) dose was validated against a 3D gel dosimeter, ion chamber, and film measurements. After validation, 15 patients with 2–11 targets had their plans delivered to the phantom. The criteria used for the gamma calculation was 3%/1 mm. The portion of targets which were measurable by the phantom was countable. The accompanying software compiled the measured doses allowing each target to be counted from the measured dose distribution. Results Spatial resolution was sufficient to verify the high dose distributions characteristic of SRS. Amongst the 15 patients there were 74 targets. Of the 74 targets, 61 (82%) of them were visible on the measured dose distribution. The average gamma passing rate was 99.3% (with sample standard deviation of 0.68%). Conclusions The high resolution provided by the O4D with 1000 SRS board insert allows for very high‐resolution measurement. This high resolution in turn can allow for high gamma passing rates. The O4D with the 1000 SRS array is an acceptable method of performing quality assurance for single‐isocenter multiple brain metastasis SRS.