Elsevier

Physica Medica

Volume 31, Issue 5, July 2015, Pages 529-535
Physica Medica

Technical notes
Comprehensive quality assurance phantom for the small animal radiation research platform (SARRP)

https://doi.org/10.1016/j.ejmp.2015.04.010Get rights and content

Highlights

  • We developed a comprehensive quality assurance (QA) phantom.

  • The phantom can be used for small animal radiation research platforms (SARRP).

  • The QA tasks include dosimetry, treatment planning system, and imaging.

Abstract

Purpose

To develop and test the suitability and performance of a comprehensive quality assurance (QA) phantom for the Small Animal Radiation Research Platform (SARRP).

Methods and materials

A QA phantom was developed for carrying out daily, monthly and annual QA tasks including: imaging, dosimetry and treatment planning system (TPS) performance evaluation of the SARRP. The QA phantom consists of 15 (60 × 60 × 5 mm3) kV-energy tissue equivalent solid water slabs. The phantom can incorporate optically stimulated luminescence dosimeters (OSLD), Mosfet or film. One slab, with inserts and another slab with hole patterns are particularly designed for image QA.

Results

Output constancy measurement results showed daily variations within 3%. Using the Mosfet in phantom as target, results showed that the difference between TPS calculations and measurements was within 5%. Annual QA results for the Percentage depth dose (PDD) curves, lateral beam profiles, beam flatness and beam profile symmetry were found consistent with results obtained at commissioning. PDD curves obtained using film and OSLDs showed good agreement. Image QA was performed monthly, with image-quality parameters assessed in terms of CBCT image geometric accuracy, CT number accuracy, image spatial resolution, noise and image uniformity.

Conclusions

The results show that the developed QA phantom can be employed as a tool for comprehensive performance evaluation of the SARRP. The study provides a useful reference for development of a comprehensive quality assurance program for the SARRP and other similar small animal irradiators, with proposed tolerances and frequency of required tests.

Introduction

The small animal radiation research platform (SARRP) is an isocentric irradiation system that combines a micro irradiator, cone beam CT imaging, and a treatment planning system [1]. The SARRP allows for image-guided radiotherapy research to be conducted at preclinical level [2], [3]. By mimicking the clinical system, the SARRP has the capabilities to deliver conformal dose distribution with precision and accuracy to the target volume while minimizing dose to healthy tissue [4].

Use of the SARRP for conducting preclinical research on small animals has become more common over the past years in different institutions across the world. There is, therefore, also increasing need for developing quality assurance tools and protocols with recommended tolerance levels for such small animal radiotherapy systems. In previous work, Ngwa et al. [5] developed a Mosfet phantom, using Mosfet dosimeters for facilitating SARRP QA tasks which may warrant daily evaluation. Other work on the commissioning and calibration of the SARRP using gafchromic (EBT2) film has been reported, covering dosimetry tasks such as: measurements of beam profiles, percent depth dose and isocenter congruency test [6], [7]. The purpose of this work is to develop and test the suitability and performance of a comprehensive QA phantom for the SARRP. This phantom was developed as a tool for carrying out daily, monthly and annual QA tasks including: imaging, dosimetry and treatment planning system (TPS) performance evaluation. The results should provide a useful reference for development of a comprehensive quality assurance program with proposed tolerances for the SARRP and potentially other small animal irradiators.

Section snippets

SARRP

A SARRP (Gulmay Medical Inc, 480 Brodgon Rd, Suwanee, GA USA) consists of an x-ray tube mounted on a gantry, with a robotic stage serving as a couch on which the animal is placed. This robotic stage has four degree of freedom x, y z, and φ (couch angle). In imaging mode an SARRP typically operates at 60–80 kVp and 0.5 mA using 1 mm of Al filtration. In therapy mode, it typically operates at 175–220 kVp with 0.15 mm of Cu filtration. The SARRP uses isocentric design in both modes and employs a

Results

The output constancy QA results for different field sizes (Fig. 3) showed maximum differences of 2.5%, 2.3%, 2.01%, and 1.89%, respectively, for open field (20 × 20 cm2), 3 × 3 mm, 5 × 5 mm2, and 12 mm fields. The results are within the tolerances (3% for daily QA) recommended by AAPM Task report 40 and 142 [14], [15].

Figure 4 shows the lateral profile for field size of 5 × 5 mm2 and 12 mm at two depths (0 mm and 10 mm). Analyzed results (Table 1) show the beam flatness results between 1.78%

Discussion

The investigated QA phantom provides an effective comprehensive QA tool for performing daily, monthly, and annual SARRP QA. The results for output check and beam profile (flatness, symmetry, and penumbra) are consistent with the expected reference values. Based on our results over many months using different dosimeters, a recommended tolerance for output measurements could be 3% similar to clinical systems. Results using film (EBT3) showed good 2D dosimetry; however, use of film is laborious

Conclusion

As the use of the SARRP and other small animal irradiators continues to increase across the globe, the need for tools to facilitate different QA tasks or comprehensive QA are also increasing. The QA phantom developed in this work provides one such tool. The results serve as a useful reference for development of a comprehensive quality assurance program, with proposed tolerances and frequency of required tests.

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