An efficient procedure for tomotherapy treatment plan verification using the on-board detector.

In this work, a fast and simple procedure for tomotherapy treatment plan verification using the on-board detector (OBD) has been developed. This procedure allows verification of plans with static and dynamic jaws (TomoEDGE). A convolution-based calculation model has been derived in order to link the leaf control sinogram from the treatment planning system to the data acquired by the OBD during a static couch procedure. The convolution kernel has been optimized using simple plans calculated in the Tomotherapy Cheese phantom. The optimal kernel has been found to be a lorentzian function, whose parameter Γ is 0.186 for the 1 cm jaw opening, 0.232 for the 2.5 cm jaw opening and 0.373 for the 5 cm jaw opening. The evaluation has been performed with a γ-index analysis. The dose criterion was 3% of the 95th percentile of the dose distribution and the distance-to-agreement criterion is 2 mm. In order to validate the procedure, it has been applied to around 50 clinical treatment plans, which had already been validated by the Delta4 phantom (Scandidos, Sweden). 96% of the tested plans have passed the criteria. Concerning the other 4%, significant discrepancies between the leaf pattern in the leaf control sinogram and the OBD data have been shown, which might be due to differences in the leaf open time. This corresponds also to a higher sensitivity of this method over the Delta4, adding the possibility of better monitoring the treatment delivery.

Comparison of organ doses and image quality between CT and flat panel XperCT scans in wrist and inner ear examinations.

The aim of this study was to evaluate and compare organ doses delivered to patients in wrist and petrous bone examinations using a multislice spiral computed tomography (CT) and a C-arm cone-beam CT equipped with a flat-panel detector (XperCT). For this purpose, doses to the target organ, i.e. wrist or petrous bone, together with those to the most radiosensitive nearby organs, i.e. thyroid and eye lens, were measured and compared. Furthermore, image quality was compared for both imaging systems and different acquisition modes using a Catphan phantom. Results show that both systems guarantee adequate accuracy for diagnostic purposes for wrist and petrous bone examinations. Compared with the CT scanner, the XperCT system slightly reduces the dose to target organs and shortens the overall duration of the wrist examination. In addition, using the XperCT enables a reduction of the dose to the eye lens during head scans (skull base and ear examinations).

Computed tomography commissioning programmes: how to obtain a reliable MTF with an automatic approach?

The purpose of this study was to assess the spatial resolution of a computed tomography (CT) scanner with an automatic approach developed for routine quality controls when varying CT parameters. The methods available to assess the modulation transfer functions (MTF) with the automatic approach were Droege's and the bead point source (BPS) methods. These MTFs were compared with presampled ones obtained using Boone's method. The results show that Droege's method is not accurate in the low-frequency range, whereas the BPS method is highly sensitive to image noise. While both methods are well adapted to routine stability controls, it was shown that they are not able to provide absolute measurements. On the other hand, Boone's method, which is robust with respect to aliasing, more resilient to noise and provides absolute measurements, satisfies the commissioning requirements perfectly. Thus, Boone's method combined with a modified Catphan 600 phantom could be a good solution to assess CT spatial resolution in the different CT planes.

Extent of transcription of the E strand of polyoma virus DNA during the early phase of productive infection.

Early polyoma virus-specific RNA, in nuclei and cytoplasm of cells labeled with [(3)H]uridine, was analyzed by hybridization with filter-bound Hpa II fragments of polyoma DNA. About 40% of labeled cytoplasmic virus-specific RNA hybridized with Hpa II fragment 2, which represents about 40% of the region coding for E-strand mRNA's; less than 5% hybridized with fragments 1 or 3, which lie outside this region. A somewhat lower proportion (about 30%) of labeled nuclear virus-specific RNA hybridized with fragment 2, and a small but significant fraction (7 to 14%) hybridized with fragments 1 and 3. About two-thirds of the nuclear RNA which hybridized to fragment 1 was complementary to the E strand, and one-third was complementary to the L strand. Results did not vary greatly in samples labeled for periods of from 15 min to 3 h. The major species of pulse-labeled nuclear polyoma-specific RNA sedimented at 22S and thus is slightly larger than the 19S cytoplasmic mRNA. These results show that most early nuclear RNA ( approximately 75%) is transcribed from the region of the E strand, which codes for early mRNA's, and that there is probably a site at which transcription is terminated at the end of this region. However, a small amount of early nuclear RNA ( approximately 15%) is transcribed from the remainder of the E strand, perhaps by readthrough of this termination signal. In addition, there is a small amount of transcription from the L strand, whose significance is unclear. Neither the L-strand transcripts nor the nonmessenger E-strand transcripts are transported to the cytoplasm.