The advent of improved digital imaging modalities in diagnostic and therapy is fast making conventional films a nonexistent entity. However, several radiotherapy centers still persist with film for performing quality assurance (QA) tests. This paper investigates the feasibility of using a diagnostic computed radiography (CR) system as a QA tool in radiotherapy. QA tests such as light field congruence, field size verification, determination of radiation isocentre size, multileaf collimator (MLC) check and determination of isocentric shift for stereotactic radiosurgery (SRS) were performed and compared with film. The maximum variation observed between CR and film was 0.4 mm for field size verification, -0.13 mm for the radiation isocentre size check, 0.77 for MLC check and -0.1 mm for isocentric shift using the Winston Lutz test tool for SRS QA. From these results obtained with the CR it is concluded that a diagnostic CR system can be an excellent cost-effective digital alternative to therapy film as a tool for QA in radiotherapy.

Background: The IAEA recommends a quality assurance program in radiotherapy to ensure safe and effective treatments. In this study, radiotherapy departments were surveyed on their current practice including the extent and depth of quality assurance activities. Methods: Radiotherapy departments were voluntarily surveyed in three stages, firstly, in basic facility information, secondly, in quality assurance activities and treatment techniques, and thirdly, in a snapshot of quality assurance, departmental and treatment activities. Results: The IAEA received completed surveys from 381 radiotherapy departments throughout the world with 100 radiotherapy departments completing all three surveys. Dominant patterns were found in linac-based radiotherapy with access to treatment planning systems for 3D-CRT and 3D imaging. Staffing levels for major staff groups were on average in the range recommended by the IAEA. The modal patient workload per EBRT unit was as expected in the range of 21-30 patients per day, however significant instances of high workload (more than 50 patients per day per treatment unit) were reported. Staffing levels were found to correlate with amount of treatment equipment and patient workload. In a self-assessment of quality assurance performance, most radiotherapy departments reported that they would perform at least 60% of the quality assurance activities itemized in the second survey, with particular strength in equipment quality control. In a snapshot survey of quality assurance performance, again equipment quality control practice was well developed, particularly for the treatment equipment. Conclusions: The IAEA surveys provide a snapshot of current radiotherapy practice including quality assurance activities.

Dose area product is particularly useful for machines. In the initial stages of the dose ANGIOGRAPHY assessing and comparing radiation dose from auditing, tabletop dose rates were same in fluoroscopy procedures as it provides an both the systems. The dose rates for low

Purpose: To calibrate an amorphous Silicon (aSi) Electronic Portal Imaging Device (EPID) for dosimetric evaluation of Intensity Modulated Radiation Therapy (IMRT). Methods and Materials: This study was performed using a 6 MV photon beam of a Primus linear accelerator with an aSi EPID. A water‐filled penta step‐phantom of perspex was fabricated for calibrating the EPID. Absolute dosimetry was performed using a calibrated 0.14 cc ion chamber. A polystyrene slab with 21 bores (each separated by 1 cm) to accommodate the ion chamber was used for measuring dose below each step of the phantom. The EPID was calibrated at a source to detector distance of 150 cm. The calibration procedure involved: i) Acquisition of Electronic Portal Images (EPIs) with the centre of the step‐phantom positioned at isocentre for 1, 2 and 3 monitoring unit settings. ii) Measurement of the dose profile below the step‐phantom with the ion chamber placed at pre‐determined positions on the polystyrene slab iii) Acquisition of an EPI with the centre of the step‐phantom at isocentre and the polystyrene slab fixed onto the surface of the flat panel detector. This was used to locate the positions of the ion chamber with respect to the step‐phantom. iv) Plotting the calibration graph for pixel values (averaged over ROI of 10 × 12 pixels) and dose. EPIs of IMRT segments were acquired with the EPID in the ‘port‐during’ mode for each field. All the individually acquired segments were added using codes developed in MATLAB (version 6.5) to get the fluence map. Results: The pixel values of the EPIs were found to increase linearly with dose. The fluence maps acquired using the calibrated EPID were verified with the planned fluence maps. Conclusion: Therefore it is concluded that EPID could be used as a dosimetric verification tool for IMRT.

Purpose: To evaluate the geometric accuracy and image quality of kV CBCT based image guided Radiotherapy system. Methods: A cube phantom with a radio opaque marker was used to determine the geometric accuracy of the isocenter of the CBCT unit. The cube phantom is positioned such that the radio‐opaque ball is at the isocenter. Radiographic images were acquired at various gantry angles and the ball center is matched with the imager center on the OBI software. The image quality assessment was performed with a CatPhan phantom that has objects to asses the low contrast resolution, uniformity of HU, geometric accuracy and special resolution. CBCT images of the phantom were acquired for Full Fan beam (FF) and Half Fan beam (HF) for large field of view. The radiation dose was estimated with a CTDI pelvic phantomResults: The maximum isocentre shift estimated with the Winston‐Lutz test tool was <1mm for most gantry angles. The maximum variation in the HU uniformity was 15 in one region and the rest were within 10 units for FF beam. The special resolution was 8lp /mm for FF beam and 4lp/mm for HF beam. The low contrast resolution, about 5 of the 1% supra slice discs were seen and about two .5% supra slice discs were seen with FF beam. CBCT images of the CatPhan with FF beam during a regular QA showed a ring artifact that was not reflected in patient images. This was identified to be due to a shift in the position of the bow‐tie filter that was subsequently corrected. Conclusion: This work shows that the CBCT image guidance system is suitable for position verification in Radiotherapy application. However, it is essential to have a periodic quality assurance program for CBCT in place to identify issues due to mechanical misalignment