Robotic radiosurgery system patient‐specific QA for extracranial treatments using the planar ion chamber array and the cylindrical diode array

Abstract

Robotic radiosurgery system has been increasingly employed for extracranial treatments. This work is aimed to study the feasibility of a cylindrical diode array and a planar ion chamber array for patient‐specific QA with this robotic radiosurgery system and compare their performance. Fiducial markers were implanted in both systems to enable image‐based setup. An in‐house program was developed to postprocess the movie file of the measurements and apply the beam‐by‐beam angular corrections for both systems. The impact of noncoplanar delivery was then assessed by evaluating the angles created by the incident beams with respect to the two detector arrangements and cross‐comparing the planned dose distribution to the measured ones with/without the angular corrections. The sensitivity of detecting the translational (1–3 mm) and the rotational (1°–3°) delivery errors were also evaluated for both systems. Six extracranial patient plans (PTV 7–137 cm3) were measured with these two systems and compared with the calculated doses. The plan dose distributions were calculated with ray‐tracing and the Monte Carlo (MC) method, respectively. With 0.8 by 0.8 mm2 diodes, the output factors measured with the cylindrical diode array agree better with the commissioning data. The maximum angular correction for a given beam is 8.2% for the planar ion chamber array and 2.4% for the cylindrical diode array. The two systems demonstrate a comparable sensitivity of detecting the translational targeting errors, while the cylindrical diode array is more sensitive to the rotational targeting error. The MC method is necessary for dose calculations in the cylindrical diode array phantom because the ray‐tracing algorithm fails to handle the high‐Z diodes and the acrylic phantom. For all the patient plans, the cylindrical diode array/ planar ion chamber array demonstrate 100%/>;92%false(3%/3 mmfalse) passing rates. The feasibility of using both systems for robotic radiosurgery system patient‐specific QA has been demonstrated. For gamma evaluation, 2%/2 mm criteria for cylindrical diode array and 3%/3 mm criteria for planar ion chamber array are suggested. The customized angular correction is necessary as proven by the improved passing rate, especially with the planar ion chamber array system.PACS number: 29.40.‐n

High resolution ion chamber array delivery quality assurance for robotic radiosurgery: Commissioning and validation

“…It is interesting also to remark that 98.2% of the cases yielded pass-rates above 80% for 2%/1 mm. These results indicated the possibility to use Gamma-Index criteria that are tighter than those proposed for lower resolution array based CyberKnife DQA [20] and potentially even tighter than the criteria we recently suggested for film based CyberKnife DQA [7], permitting to decrease the dose difference criteria from 3% to 2% with 1 mm DTA. However, due to the uncertainties related to beam angle and DPP dependence, which are only partially corrected for in our method, the adoption of a 2% dose difference criteria requires caution and further investigation.…”

“…The proposed GammaIndex criteria by the AAPM TG 135 for film based DQA are 2% dose difference (without reference to global or local dose) and 2 mm distance-to-agreement, requiring a pass-rate above 90% [6]. Similar criteria were also used for a recent study involving a planar and a cylindrical array for CyberKnife DQA [20]. However, from our previous analysis performed for film DQA it was demonstrated that with 2%/2 mm criteria small errors during CyberKnife beam delivery remain undetected [7].…”

“…For verification of dose distributions, generally diode or ion-chamber arrays are used, e.g., for IMRT and VMAT, often in combination with rotating phantoms [11] or angular correction factors to minimize the variation of detector angular response [15,16]. For the CyberKnife with its non-isocentric non-coplanar beam arrangements, the usefulness of planar ion-chamber arrays and cylindrical diode arrays has been recently investigated [20] while rotating phantoms currently do MU = Monitor Units, S/I = Superior/Inferior, L/R = Left/Right, A/P = Anterior/Posterior, SDD = source-detector-distance. 2%/2 mm 3D Gamma-Index criteria was used after registration, but before alignment due to uncertainties in measurement plane definition on the phantom CT. 3% and 2%/ 1 mm 2D Gamma-Index criteria was used after alignment in all three directions to evaluate the agreement of the calculated and measured dose distributions.…”

Patient-Specific Quality Assurance in a Multileaf Collimator-Based CyberKnife System Using the Planar Ion Chamber Array

“…[11][12][13] 2D film dosimetry offers superior spatial resolution for small field measurements, but the resulting dose distributions are sensi- The CyberKnife system has a predefined safety zone around the patient based on the patient's size. When we perform the patient-specific QA for a patient with the brain tumor, special attention is required to avoid the collision between the patient-specific QA phantom including Octavius 1000SRS detector and the moving robot arm due to the narrow patient safety zone.…”

Investigation of two linear accelerator head designs for treating brain metastases with hypofractionated volumetric-modulated arc radiotherapy

“…1,6,20 However, ArcCHECK has been demonstrated to be sensitive to errors in patient-specific QA for radiosurgery, including radiosurgery to multiple targets. [21][22][23][24] Another advantage of ArcCHECK is that the measurement and analysis is integrated in the same software. 25 The present study is of retrospective nature and therefore the comparison may be unfair or biased, given a priori knowledge of the BM plans and the fact that there was no time restriction on planning.…”