James M. Hevezi

Slice Wars vs Dose Wars in Multiple-Row Detector CT

force behind the slice wars. However, the increasing number of slicesandtheincreasingcomplexity in the performance of cardiac CT imaginghasledtothedevelopment of protocols that can yield high radiation dose (expressed in terms of “effective dose”). In general, the demand for shorter scan times (high temporal resolution) and thinner slices (high spatial resolution) requires higher tube current to maintain good image quality. In

Intensifying screen for xeroradiography.

A high-atomic-number rare gas has been incorporated into xeroradiographic cassettes in order to increase the sensitivity of the process to x radiation. Preliminary results indicate that krypton gas at 1-atm pressure increases the sensitivity by approximately a factor of 2 in the mammography energy region.

Optimizing CT dose and image quality for radiotherapy patients.

With the successes of CT dose reduction programs such as Image Gently [1] and Image WiselyTM 2], many organizations have signed n to these programs, and CT proocols across the country have been djusted to match CT dose to the mage quality necessary for a given iagnostic examination. Most of he protocols call for lower doses ompared with the technique in use reviously to scan patients, again n the basis of obtaining sufficient mage quality to allow a diagnosis o be made. With the increased meia attention to CT protocol errors nd misadministrations using highose CT techniques and the inreased frequency of physicians’ orering CT studies to obtain diagnoses, here has been a plethora of articles sugesting CT dose reduction strategies in he recent literature [3-6]. Although CT dose reduction strtegies have been used across the ountry in response to these efforts, hey may not apply to all patients ho require CT scans for their medcal conditions. In particular, patients resenting for CT scans for radioherapy planning may not benefit rom the extremely reduced dose trategies. These patients will have igh-energy x-radiation (an order of agnitude greater than what is reeived with imaging) through the rea being scanned for planning puroses (about 10-80 Gy), and the CT ose (about 1-100 mGy) presents nly a small fraction of the dose the atients will receive to control their disease. In fact, the new techniques in radiation oncology will use further low-energy imaging techniques to align patients during their radiotherapy procedures (“image-guided radiation therapy”). Hence, as mentioned, the CT planning doses will not be of great concern to these patients and their attending radiation oncologists. From the viewpoint of obtaining sufficient image quality for the myriad radiotherapy planning procedures in use today, radiology and radiation oncology department staff members should consult with the attending radiation oncologist to adjust CT scan protocols to obtain sufficient CT image rendition for the planning procedure at hand. This may require an actual increase in CT scan technique from that used for reduced-dose diagnostic techniques. This is especially important when using CT imaging for planning whose image sets will be fused with those from other imaging modalities, such as MRI or PET/CT, to allow the radiation oncologist to accurately contour the tumor targets that will be the subject of the radiotherapy procedure. Image fusion requires matching anatomic regions in both the CT image set and the MRI data, for example, to attack intracranial tumors that are more visible on the MRI data sets. If the CT data set for this fusion is suboptimal (“noisy”) because a reduced-dose CT technique was used, the image fusion may not be rendered accurately,

SU‐GG‐T‐339: New Small Volume Scanner for Radiosurgery Beam Data Collection

Purpose: To determine the minimum dimensions of a water tank for small field Radiosurgery(SRS) and Stereotactic Body Radiation Therapy(SBRT) beam data collection. In addition, to describe the use of the small‐volume tank in its movement to measure direct SAD data, such as TMR/TPR. Methods and Materials: After several iterations in tank design, a cylindrical water tank with dimensions 20 cm diameter and 40 cm high was felt to have enough scatter volume to yield results to full size water tank for SRS and SBRT beam data collection. The entire tank movement is directed by the usual 3D drives (X,Y,Z). A separate vertical drive in the tank can move the detector probe independently of the external drive such that it can be synchronized with the external Z‐drive to keep the detector at a fixed SAD to obtain direct TPR/TMR profiles. For radial, transverse and diagonal profiles, the whole tank is moved across the beam to accumulate cross profiles at various depths determined by the vertical drive in the tank. PDD measurements can also be obtained. Results: Complete sets of beam data for a CyberKnife® SRS treatment unit were obtained with the new scanner (Output factors, Off‐Center Ratios and TPR data) and compared to data taken with a large water tank scanner. All data compared favorably, with the greatest deviation appearing for the 60 mm collimator and 300 mm depth, where the small tank showed values past the penumbra region of about 0.5% less. Total scanning time for a single collimator to obtain TPR data and 10 cross profiles at 5 depths was under 10 minutes. Conclusion: A small volume scanning system was found to yield beam scanning results virtually identical to those obtained with a large water tank for small fields, with less acquisition time.

Mammographic Image Quality

Production of good quality radiographic images of the breast that are of diagnostic value place severe restrictions on the entire imaging system and, in particular, the recording media. A parallel clinical and physical investigation is in progress to evaluate the diagnostic capabilities of the three types of recording media presently in mammography. These will be described and initial results of the evaluation program given.