Purpose Small field dosimetry has been an active area of research for over a decade. It is now known that large dosimetric errors can be introduced if proper detectors or correction factors are not used. The International Atomic Energy Agency (IAEA) through the technical report series No. 483 provides guidelines for small field dosimetry procedures as well as correction factors for most detectors available in the market. The plastic scintillator detector (PSD) Exradin W1 has been found to have a correction factor close to unity; however, it is not designed for beam scanning. To overcome this limitation, the new PSD Exradin W2 has been developed to be used as a scanning as well as a relative dosimeter. Characterization of this detector in small field dosimetry is presented in this study. Methods A 6 MV beam from a Varian‐Edge linac was used to collect data for the characterization of a W2 detector. Cerenkov light ratio (CLR) is corrected through a separate new electrometer system that comes with the W2 detector. The parameters investigated include the dose and dose rate linearity, beam profiles, percent depth dose (PDD), field output factors, and temperature response. The results were compared with Gafchromic film (EBT‐3 film) for beam profiles. The field output factor and temperature response were compared to the Exradin W1 detector. Results The dose linearity measured with 600 MU/min dose rate showed minimal variations (<0.5%) even for small MU, and similar results were seen for dose rate linearity. The comparison of field output factors between the W2 and W1 showed small differences for various depth and field sizes. The temperature response showed small variation when the temperature was varied from 6∘C to 50∘C. The slope was −0.0017false/∘C and −0.0016false/∘C for the W2 and the W1 detector, respectively. The differences in profiles are 0.5% in umbra and penumbra region for 1×1cm2 field size when compared to the EBT‐3 film profile. Conclusions The W2 scintillator detector showed similar dosimetric and temperature properties to the W1 scintillator detector. The main advantage of the W2 detector among other plastic scintillators is the beam scanning capabilities that, combined with its correction factor of 1.0, make it an ideal detector for commissioning of SRS and SBRT techniques.

Independent verification of the dose per monitor unit (MU) to deliver the prescribed dose to a patient has been a mainstay of radiation oncology quality assurance (QA). We discuss the role of secondary dose/MU calculation programs as part of a comprehensive QA program. This report provides guidelines on calculationbased dose/MU verification for intensity modulated radiation therapy (IMRT) or volumetric modulated arc therapy (VMAT) provided by various modalities. We provide a review of various algorithms for "independent/second check" of monitor unit calculations for IMRT/VMAT. The report makes recommendations on the clinical implementation of secondary dose/MU calculation programs; on commissioning and acceptance of various commercially available secondary dose/MU calculation programs; on benchmark QA and periodic QA; and on clinically reasonable action levels for agreement of secondary dose/MU calculation programs. | REPORT OF AAPM TASK GROUP 219 ON INDEPENDENT CALCULATION-BASED DOSE/ MU VERIFICATION FOR IMRT

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A trend is underway toward the use of prepackaged low dose rate brachytherapy sources, which come in the form of strands, coiled line sources, preloaded needles, and sterile cartridge packs. Since the medical physicist is responsible for verification of source strength prior to patient treatment, development of prepackaged source strength verification methods is needed. Existing guidelines are reviewed to establish the situation that medical physicists find with respect to prepackaged sources. This investigation presents an experimental evaluation of the effect of some of these multiseed geometries on source strength measurements. Multiseed strands and coils, whether 125I, 103Pd, or 192Ir can be measured in a chamber with a long, sensitive axial length with a uniform response. Sterile seed cartridge packs can also be measured but require a correction factor to be applied. Sources in needles, however, cannot be measured in the needle since there is too great a variation in needle composition and needle tolerance thickness. Removing these seeds from the needle into a sterile measurement insert, which maintains sterility is a practical source strength verification method, similar to those done for multiple seed configurations in a well chamber with adequate axial uniformity. Values are compared with individual air kerma strength calibrations, and correction factors, are presented' where needed. In each case, care must be taken to maintain sterility as multiple seeds are measured in well chamber inserts.

(1) Background: The Exradin W2 is a commercially available scintillator detector designed for reference and relative dosimetry in small fields. In this work, we investigated the performance of the W2 scintillator in a 10 MV flattening-filter-free photon beam and compared it to the performance of ion chambers designed for small field measurements. (2) Methods: We measured beam profiles and percent depth dose curves with each detector and investigated the linearity of each system based on dose per pulse (DPP) and pulse repetition frequency. (3) Results: We found excellent agreement between the W2 scintillator and the ion chambers for beam profiles and percent depth dose curves. Our results also showed that the two-voltage method of calculating the ion recombination correction factor was sufficient to correct for the ion recombination effect of ion chambers, even at the highest DPP. (4) Conclusions: These findings show that the W2 scintillator shows excellent agreement with ion chambers in high DPP conditions.

PurposeElectronic portal imaging devices (EPIDs) have been widely utilized for patient‐specific quality assurance (PSQA) and their use for transit dosimetry applications is emerging. Yet there are no specific guidelines on the potential uses, limitations, and correct utilization of EPIDs for these purposes. The American Association of Physicists in Medicine (AAPM) Task Group 307 (TG‐307) provides a comprehensive review of the physics, modeling, algorithms and clinical experience with EPID‐based pre‐treatment and transit dosimetry techniques. This review also includes the limitations and challenges in the clinical implementation of EPIDs, including recommendations for commissioning, calibration and validation, routine QA, tolerance levels for gamma analysis and risk‐based analysis.MethodsCharacteristics of the currently available EPID systems and EPID‐based PSQA techniques are reviewed. The details of the physics, modeling, and algorithms for both pre‐treatment and transit dosimetry methods are discussed, including clinical experience with different EPID dosimetry systems. Commissioning, calibration, and validation, tolerance levels and recommended tests, are reviewed, and analyzed. Risk‐based analysis for EPID dosimetry is also addressed.ResultsClinical experience, commissioning methods and tolerances for EPID‐based PSQA system are described for pre‐treatment and transit dosimetry applications. The sensitivity, specificity, and clinical results for EPID dosimetry techniques are presented as well as examples of patient‐related and machine‐related error detection by these dosimetry solutions. Limitations and challenges in clinical implementation of EPIDs for dosimetric purposes are discussed and acceptance and rejection criteria are outlined. Potential causes of and evaluations of pre‐treatment and transit dosimetry failures are discussed. Guidelines and recommendations developed in this report are based on the extensive published data on EPID QA along with the clinical experience of the TG‐307 members.ConclusionTG‐307 focused on the commercially available EPID‐based dosimetric tools and provides guidance for medical physicists in the clinical implementation of EPID‐based patient‐specific pre‐treatment and transit dosimetry QA solutions including intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) treatments.

A series of measurements were undertaken using both high sensitivity radiochromic film and new lithium fluoride thermoluminescent dosimeters in a liquid water medium to define the radial dose function of 90Sr/90Y beta emitting intravascular brachytherapy sources more accurately. These measurements of a single 5 French source pellet served to verify current Monte Carlo transport models and extrapolation chamber measurements of the radial dose function, thus providing the recommended independent published measurements for g(r) of these sources. A slight deviation in the published radial dose function at depth leads the authors to recommend that treatment planning be performed using updated g(r) values from current Monte Carlo transport models verified by measurements such as those shown in this investigation.

Despite their lower cost and high content flexibility, a limitation of in-house-prepared arrays has been their susceptibility to quality control (QC) issues and lack of QC standards across laboratories. Therefore, we developed a novel three-color array system that allows prehybridization QC as well as the Matarray software to facilitate acquisition of accurate gene expression data. In this study, we compared performance of our rat cDNA array to the Affymetrix RG-U34A and Agilent G4130A arrays using 2,824 UniGenes represented on all three arrays. Before data filtering, poor interplatform agreement was observed; however, after data filtering, differentially expressed UniGenes exhibited correlation coefficients of 0.91, 0.88, and 0.92 between the Affymetrix vs. Agilent, Affymetrix vs. cDNA, and Agilent vs. cDNA arrays, respectively. The Affymetrix, Agilent, and cDNA arrays agreed well with quantitative RT-PCR conducted on 42 UniGenes, yielding correlation coefficients of 0.90, 0.90, and 0.96, respectively. Each platform underestimated ratios relative to quantitative RT-PCR, possessing respective slopes of 0.86 ( R2 = 0.81), 0.65 ( R2 = 0.81), and 0.70 ( R2 = 0.92). Overall, these data show that the combination of our novel technical and analytic approaches yield an accurate platform for functional genomics that is concordant with commercial discovery arrays in terms of identifying regulated genes and pathways.