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. 2019 Apr-Jun;44(2):91-98.
doi: 10.4103/jmp.JMP_4_19.

Clinical Evaluation of a Two-dimensional Liquid-Filled Ion chamber Detector Array for Verification of High Modulation Small Fields in Radiotherapy

Miljenko Markovic  1 , Ganesh Narayanasamy  2 , Sotirios Stathakis  1 , Panayiotis Mavroidis  3 , Ines-Ana Jurkovic  1 , Daniel Saenz  1 , Niko Papanikolaou  1
Affiliations

Clinical Evaluation of a Two-dimensional Liquid-Filled Ion chamber Detector Array for Verification of High Modulation Small Fields in Radiotherapy

Miljenko Markovic et al. J Med Phys. 2019 Apr-Jun.

Abstract

Introduction: Clinical evaluation of a two-dimensional (2D) liquid-filled ion chamber detector array used in the verification of highly modulated small beams of stereotactic body radiation therapy (SBRT) has been conducted.

Materials and methods: Measurements with the Octavius 1000 SRS (PTW, Freiburg, Germany) detector with 977 liquid-filled ion chambers were compared against EDR2 film and PTW Octavius Seven29. The performance of detector array has been evaluated on ten SBRT patient plans. Dose profiles of individual and composite fields' calculated using Pinnacle3 treatment planning system were compared against measurements with Octavius 1000 SRS detector array, EDR2 film, and Octavius Seven29 detector. Gamma index and profile comparison were used in the evaluation and assessment of the detector's performance.

Results: The Gamma index measurements show agreement between Pinnacle3 computations and Octavius 1000 SRS array, PTW Octavius Seven29, and EDR2 film for >90% of the points using 2%, 2 mm tolerance criteria. Profiles obtained with the Octavius 1000 SRS were in agreement with the EDR2 film profiles, demonstrating the detector's superior sampling rate.

Conclusions: The Octavius 1000 SRS is a dosimetrically accurate device to perform quality assurance checks in SBRT treatments. The broad range of measurements performed in this study quantified the dosimetric accuracy of Octavius 1000 SRS detector in the clinical setup of the small fields in radiotherapy.

Keywords: High-density dosimeter; ion chamber; liquid-filled ion chamber; quality assurance; stereotactic body radiation therapy quality assurance.

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Conflict of interest statement

There are no conflicts of interest.

Figures

Figure 1
Figure 1
(a) The standard setup used for Octavius 1000 SRS measurements with the detector array placed between two slabs of plastic water. The source to surface distance is 95 cm and the effective point of measurement is set at 100 cm from the radiation source. (b) Experimental setup for the measurements using an EDR2 film. A 5 cm plastic water phantom is placed on top of the EDR2 film such that the point of measurement is set at 100 cm from the radiation source. The plastic water slab used for backscatter has a 5-cm thickness
Figure 2
Figure 2
(a): The setup that was used for the measurements that were acquired using Octavius 1000 SRS array and Octavius phantom. The detector array is placed in the Octavius phantom at a source to surface distance of 84 cm and the effective point of measurement is set at 100 cm from the radiation source. (b) Experimental setup for the measurements using an EDR2 film placed in the Octavius phantom. The point of measurement is set to be at 100 cm from the radiation source
Figure 3
Figure 3
Comparison of the profiles measured in Octavius 1000 SRS and EDR2 film for a single field exposure using setup outlined in Figure 1 with a 5 cm slab phantom (left column). The gamma analysis results calculated with 3% and 3 mm tolerances (middle column) and 2% and 2 mm (right column) are also shown
Figure 4
Figure 4
Comparison of profiles measured using Octavius 1000 SRS, Octavius Seven29 and EDR2 film for a single field exposure based on setup shown in Figure 2 using the Octavius phantom (left). The gamma analysis results between the Octavius SRS 1000 and Seven29 against the EDR2 film measurements were calculated using tolerances of 3% and 3 mm (middle) and 2% and 2 mm (right)
Figure 5
Figure 5
Comparison of the measured profiles of Octavius 1000 SRS, Octavius Seven29 and EDR2 film for the composite field exposure based on setup in Figure 2 using the Octavius phantom (left). The gamma factors between the Octavius SRS 1000 and Seven29 against the EDR2 film were calculated using tolerances of 3% and 3 mm (middle) and 2% and 2 mm (right)
Figure 6
Figure 6
Comparison between the measured profiles of the Octavius SRS 1000 and EDR2 film for a single field exposure measured at 5 cm depth (left), 15 cm depth (middle) and the comparison between gammas for two different depths (right)
Figure 7
Figure 7
Linear profiles of Octavius 1000 SRS, Octavius Seven29 and EDR2 film. Shown below are the passing rate for gamma criterion comparison between Octavius 1000 SRS and EDR2 film and Octavius Seven29 and EDR2 film
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