Towards online patient imaging during helical radiotherapy.

Exit-detector data from helical radiation therapy have been studied extensively for delivery verification and dose reconstruction. Since the same radiation source is used for both imaging and treatment, this work investigates the possibility of utilising exit-detector raw data for imaging purposes. This gives rise to potential clinical applications such as retrospective daily setup verification and inter-fractional setup error detection. The exit-detector raw data were acquired and independently analysed using Python programming language. The raw data were extracted from the treatment machine's onboard computer, and converted into 2D array files. The contours of objects (phantom or patient) were acquired by applying a logarithmic function to the ratio of two sinograms, one with the object in the beam and one without. The setup variation between any two treatment deliveries can be detected by applying the same function to their corresponding exit-detector sinograms. The contour of the object was well defined by the secondary radiation from the treatment beam and validated with the imaging beam, although no internal structures were discernible due to the interference from the primary radiation. The sensitivity of the setup variation detection was down to 2 mm, which was mainly limited by the resolution of the exit-detector itself. The exit-detector data from treatment procedures contain valuable photon exit fluence maps which can be utilised for contour definition and verification of patient alignment without reconstruction.

Clinical accuracy of ExacTrac intracranial frameless stereotactic system.

PURPOSE: In this paper, the authors assess the accuracy of the Brainlab ExacTrac system for frameless intracranial stereotactic treatments in clinical practice. METHODS: They recorded couch angle and image fusion results (comprising lateral, longitudinal, and vertical shifts, and rotation corrections about these axes) for 109 stereotactic radiosurgery and 166 stereotactic radiotherapy patient treatments. Frameless stereotactic treatments involve iterative 6D image fusion corrections applied until the results conform to customizable pass criteria, theirs being 0.7 mm and 0.5° for each axis. The planning CT slice thickness was 1.25 mm. It has been reported in the literature that the CT slices' thickness impacts the accuracy of localization to bony anatomy. The principle of invariance with respect to patient orientation was used to determine spatial accuracy. RESULTS: The data for radiosurgery comprised 927 image pairs, of which 532 passed (pass ratio of 57.4%). The data for radiotherapy comprised 15983 image pairs, of which 10 050 passed (pass ratio of 62.9%). For stereotactic radiotherapy, the combined uncertainty of ExacTrac calibration, image fusion, and intrafraction motion was (95% confidence interval) 0.290-0.302 and 0.306-0.319 mm in the longitudinal and lateral axes, respectively. The combined uncertainty of image fusion and intrafraction motion in the anterior-posterior coordinates was 0.174-0.182 mm. For stereotactic radiosurgery, the equivalent ranges are 0.323-0.393, 0.337-0.409, and 0.231-0.281 mm. The overall spatial accuracy was 1.24 mm for stereotactic radiotherapy (SRT) and 1.35 mm for stereotactic radiosurgery (SRS). CONCLUSIONS: The ExacTrac intracranial frameless stereotactic system spatial accuracy is adequate for clinical practice, and with the same pass criteria, SRT is more accurate than SRS. They now use frameless stereotaxy exclusively at their center.

In-vivo dosimetry from total body irradiation patients (2000-2006): results and analysis.

In-vivo dosimetry is an important technique to ensure accuracy of delivered dose during total body irradiation (TBI). We present an analysis of semiconductor diode dosimetry, constituting seven years of dosimetry data from eighty-six patients who underwent total body irradiation. For lateral field irradiation, the mean exit dose, averaged over five anatomical sites (head, sternal notch, chest, abdomen and pelvis) and as a percentage of the planned dose was 95.7% (SD 7.8%). For AP/PA irradiation, the mean exit dose averaged over five anatomical sites and as a percentage of the planned dose was 95.5% (SD 9.8%). We propose a number of possible reasons for these differences, including patient setup variations, movement of the patient and diodes during treatment, imprecise placement of planned bolus material, inaccurate inhomogeneity corrections and modelling by the treatment planning system.

Aging in the AXC/SSh rat: diminished prostate L-ornithine decarboxylase (ODC) activity reflects diminished prostate ODC protein and transcript content.

Immunotitration of L-ornithine decarboxylase (ODC) activity in ventral prostates of young mature (6-month-old) and aged (26-month-old) AXC/SSh rats established that the relation between enzyme activity and prostate ODC mass content was age invariant, demonstrating that the 4-fold diminution in prostate ODC activity in aged subjects represents decreased ODC protein content. Testosterone treatment of aged rats increased prostate ODC activity 2-fold and did not affect prostate ODC half-life. These latter findings and the preceding observation established that the testosterone-mediated increase in prostate ODC activity in aged individuals reflected increased ODC mass content. The half-life of prostate S-adenosyl-L-methionine decarboxylase, another prominent enzyme of polyamine biosynthesis, also was not altered by testosterone treatment of 26-month-old animals. The age-related diminution and testosterone-mediated increase in ventral prostate ODC activity occurred in concert with comparable quantitative changes in ventral prostate ODC transcript content. Because plasma testosterone content was age invariant between 3 and 18 months, the age span during which much of the reduction in prostate ODC activity occurs, and then declined by 50% at 26 months, our studies suggest that age-related diminutions in prostate ODC activity and transcript content reflect altered prostate sensitivity to androgen rather than response to diminished plasma testosterone content. Our data imply that age-related alterations in androgen regulation of androgen-responsive genes may be characteristic of the prostate during aging.

Altered androgen regulation of differentiated ventral prostate function during aging of the AXC rat.

We have examined testosterone regulation of differentiated androgen responsive ventral prostate function in aging AXC rats as a possible means of identifying age-related changes in prostate gene function. Concerning cellular content of functional macromolecules, we identified three categories of age-related change in ventral prostate: (1) diminutions completely reversible by short-term chronic testosterone treatment, as exemplified by androgen receptor content; (2) diminutions partially reversible by testosterone treatment, as exemplified by prolactin receptor content and L-ornithine-decarboxylase (ODC) activity; and (3) diminutions not reversed by exogenous testosterone treatment, as exemplified by S-adenosyl-L-methionine decarboxylase (AMDC) activity. A fourth category of alteration revealed apparent age-related changes in polyamine homeostasis. The anabolic products of ODC and AMDC activities, putrescine, spermidine and spermine, showed an age-related diminished dependence between the activities of ODC and AMDC and ventral prostate polyamine content. The possibility that these changes reflect age-related alterations in ventral prostate gene activity is under investigation.

Creatine kinase and lactate dehydrogenase: stability of isoenzymes and their activity in stored human plasma and prostatic tissue extracts and effect of sample dilution.

We examined the effect of storing human plasma or extracts of prostate at -90 degrees C on the activity of creatine kinase and lactate dehydrogenase and isoenzyme distribution. Enzyme activities were unaltered during storage for as long as six weeks. If these preparations were thawed only once at 2 to 4 degrees C, they could be stored for as long as 165 days at -90 degrees C with no change in isoenzyme distribution. Inexplicably, apparent isoenzyme distribution of prostatic lactate dehydrogenase was sensitive to sample dilution, whereas the isoenzyme distribution of lactate dehydrogenase in plasma was not. Our observations emphasize the importance of validating details of analytical protocols that are to be used for quantification of new types of specimens.