Dosimetric characterization of an image-guided stereotactic small animal irradiator

Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX, USA.
Physics in Medicine and Biology (Impact Factor: 2.76). 03/2011; 56(8):2585-99. DOI: 10.1088/0031-9155/56/8/016
Source: PubMed


Small animal irradiation provides an important tool used by preclinical studies to assess and optimize new treatment strategies such as stereotactic ablative radiotherapy. Characterization of radiation beams that are clinically and geometrically scaled for the small animal model is uniquely challenging for orthovoltage energies and minute field sizes. The irradiator employs a commercial x-ray device (XRAD 320, Precision x-ray, Inc.) with a custom collimation system to produce 1-10 mm diameter beams and a 50 mm reference beam. Absolute calibrations were performed using the AAPM TG-61 methodology. Beam's half-value layer (HVL) and timer error were measured with an ionization chamber. Percent depth dose (PDD), output factors (OFs) and off-axis ratios were measured using radiochromic film, a diode and a pinpoint ionization chamber at 19.76 and 24.76 cm source-to-surface distance (SSD). PDD measurements were also compared with Monte Carlo (MC) simulations. In-air and in-water absolute calibrations for the reference 50 mm diameter collimator at 19.76 cm SSD were measured as 20.96 and 20.79 Gy min(-1), respectively, agreeing within 0.8%. The HVL at 250 kVp and 15 mAs was measured to be 0.45 mm Cu. The reference field PDD MC simulation results agree with measured data within 3.5%. PDD data demonstrate typical increased penetration with increasing field size and SSD. For collimators larger than 5 mm in diameter, OFs measured using film, an ion chamber and a diode were within 3% agreement.

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    • "However, to ensure the correct utilization of these tools requires accurate and consistent radiation dose output, geometric positioning accuracy, geometric object representation, general image quality and the correct alignment of imaging and radiation isocenters. Some comprehensive protocols have been published to ensure accurate commissioning and dosimetric characterization as well as calibration of the beam alignment (Matinfar et al. 2009; Rodriguez et al. 2009; Tryggestad et al. 2009; Pidikiti et al. 2011; Lindsay et al. 2014). These procedures, although comprehensive , are quite time consuming and are more appropriate for machine commissioning and annual system checks, rather than ongoing monthly or weekly QA. "
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    ABSTRACT: Modern pre-clinical radiation therapy (RT) research requires high precision and accurate dosimetry to facilitate the translation of research findings into clinical practice. Several systems are available that provide precise delivery and on-board imaging capabilities, highlighting the need for a qualitymanagement program (QMP) to ensure consistent and accurate radiation dose delivery. An ongoing, simple, and efficient QMP for image-guided robotic small animal irradiators used in pre-clinical RT research is described. Protocols were developed and implemented to assess the dose output constancy (based on the AAPM TG-61 protocol), cone-beam computed tomography (CBCT) image quality and object representation accuracy (using a custom-designed imaging phantom), CBCT-guided target localization accuracy and consistency of the CBCT-based dose calculation. To facilitate an efficient read-out and limit the user dependence of theQMP data analysis, a semi-automatic image analysis and data representation program was developed using the technical computing software MATLAB. The results of the first 6-mo experience using the suggested QMP for a Small Animal Radiation Research Platform (SARRP) are presented, with data collected on a bi-monthly basis. The dosimetric output constancy was established to be within ±1 %, the consistency of the image resolution was within ±0.2 mm, the accuracy of CBCT-guided target localization was within ±0.5 mm, and dose calculation consistency was within ±2 s (±3%) per treatment beam. Based on these results, this simple quality assurance program allows for the detection of inconsistencies in dosimetric or imaging parameters that are beyond the acceptable variability for a reliable and accurate pre-clinical RT system, on a monthly or bi-monthly basis.
    Health Physics 11/2015; 109(3):S190-S199. DOI:10.1097/HP.0000000000000323 · 1.27 Impact Factor
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    • "Relative dosimetry of very small field sizes. Several studies have determined the relative dosimetry data for kilovoltage x-rays used for intraoperatative radiation therapy (IORT) and animal irradiators often with very small field sizes (Eaton and Duck 2010, Eaton 2012, Ebert et al 2009, Newton et al 2011, Pidikiti et al 2011). The IORT x-ray units typically deliver x-rays with peak potentials of 50 kVp. "
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    ABSTRACT: This topical review provides an up-to-date overview of the theoretical and practical aspects of therapeutic kilovoltage x-ray beam dosimetry. Kilovoltage x-ray beams have the property that the maximum dose occurs very close to the surface and thus, they are predominantly used in the treatment of skin cancers but also have applications for the treatment of other cancers. In addition, kilovoltage x-ray beams are used in intra operative units, within animal irradiators and in on-board imagers on linear accelerators and kilovoltage dosimetry is important in these applications as well. This review covers both reference and relative dosimetry of kilovoltage x-ray beams and provides recommendations for clinical measurements based on the literature to date. In particular, practical aspects for the selection of dosimeter and phantom material are reviewed to provide suitable advice for medical physicists. An overview is also presented of dosimeters other than ionization chambers which can be used for both relative and in vivo dosimetry. Finally, issues related to the treatment planning and the use of Monte Carlo codes for solving radiation transport problems in kilovoltage x-ray beams are presented.
    Physics in Medicine and Biology 02/2014; 59(6):R183-R231. DOI:10.1088/0031-9155/59/6/R183 · 2.76 Impact Factor
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    • "Radiation was carried out using an X-ray image guided small animal irradiator as previously described (7,8). The irradiator is characterized by a high dose rate, small beam size, accurate and precise target localization facilitated through image guidance, resulting in precision-high dose irradiation. "
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    ABSTRACT: The purpose of this study was to develop an aggressive locally advanced orthotopic prostate cancer model for assessing high-dose image-guided radiation therapy combined with biological agents. For this study, we used a modified human prostate cancer (PCa) cell line, PC3, in which we knocked down a tumor suppressor protein, DAB2IP (PC3‑KD). These prostate cancer cells were implanted into the prostate of nude or Copenhagen rats using either open surgical implantation or a minimally invasive procedure under ultrasound guidance. We report that: i) these DAB2IP-deficient PCa cells form a single focus of locally advanced aggressive tumors in both nude and Copenhagen rats; ii) the resulting tumors are highly aggressive and are poorly controlled after treatment with radiation alone; iii) ultrasound-guided tumor cell implantation can be used successfully for tumor development in the rat prostate; iv) precise measurement of the tumor volume and the treatment planning for radiation therapy can be obtained from ultrasound and MRI, respectively; and v) the use of a fiducial marker for enhanced radiotherapy localization in the rat orthotopic tumor. This model recapitulates radiation-resistant prostate cancers which can be used to demonstrate and quantify therapeutic response to combined modality treatments.
    International Journal of Oncology 03/2013; 42(5). DOI:10.3892/ijo.2013.1858 · 3.03 Impact Factor
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