WE-G-217BCD-07: Implementation and Evaluation of Helical On-Board CBCT and Exact Image Reconstruction

PURPOSE

Longitudinal coverage of CBCT, which is 17 cm for head scan and 15.5 cm for body scan, is not enough to cover the entire PTV for over 90% of head/neck and gastrointestinal/genitourinary/gynecologic patients if lymph nodes are involved. Helical CBCT, which was accomplished using external beam LINAC in its research mode, is one promising way to extend the CBCT longitudinal coverage. Aim of this study is to compare Katsevich's exact algorithm with traditional FDK algorithm for helical CBCT image reconstruction.

METHODS

CBCT projection raw data were acquired on a TrueBeam LINAC machine (Varian Medical Systems) in the research mode in helical trajectories that encompass a 360 degree rotation, 25 cm pitch, 100 kVp, 80 mA, and 25 ms, with a Catphan 600. Reconstruction was done with Katsevich's exact and FDK approximate algorithms. Scatter correction, beam-hardening correction, and non-uniform gantry angle correction, are performed on projection data to reduce artifacts and noise. Image qualities (CT number accuracy, uniformity, SNR) were evaluated and compared between the reconstruction algorithms.

RESULTS

Images reconstructed by Katsevich's algorithm show better qualities, compared to ones by FDK algorithm and HU numbers have higher uniformity and accuracy. The HU-density calibration curve closely conforms to the manufacturer recommended values. The level of noise computed as the standard deviation in the phantom uniform region is 28.07 for the Katsevich algorithm, compared to 44.64 for the FDK algorithm.

CONCLUSIONS

Katsevich's exact reconstruction algorithm provided better image qualities than FDK for helical CBCT scans. This result will very useful for our ongoing investigation of helical CBCT, which would lead to improvement of CBCT longitudinal coverage of PTV and would be essential for future image-guided adaptive radiation therapy applications. Varian Research Agreement with Washington University in St. Louis.

WE-G-213CD-04: A Triggering System to Guide 4DMRI Image Acquisition

PURPOSE

To develop a practical triggering system based on pre-selected respiratory amplitudes to guide prospectively the image acquisition of 4DMRI to track abdominal tumor motion for radiotherapy treatment planning.

METHODS

The proposed triggering scheme consists of a preparation stage and an acquisition stage. Immediately prior to MRI acquisition, the preparation stage monitors the respiration via an external respiratory belt. Based on the respiratory amplitude and status (i.e., inhalation↑ or exhalation↓), the respiration cycle is equally divided into N respiratory states. For example, in the 4-state case, the 4 respiratory states are 5%↓″, 50%↑, 95%↑ and 50%↓. The 5%↓ and 95%↑ are used instead of 0% and 100% to improve the robustness of the triggering system. Each state is associated with a trigger which starts image acquisition for one and only one slice. A complete 4DMRI imageset requires N dynamic scans. In each dynamic scan, all slices are acquired once and each is in a specific respiratory state. In different dynamic scans, each slice is associated with different respiratory states to form a 4D dataset. For proof-of-principle, the triggering system was integrated into a T2-weighted turbo spin echo sequence (TE=100ms, TR=7122ms) on a clinical 1.5T MRI (Philips Achieva) scanner. The 4-state case was tested on a healthy subject.

RESULTS

Plots of the physiology data recorded and exported from the scanner clearly verified that triggers occurred at the expected locations. Four T2-weighted images from a representative slice recorded the liver motion corresponding to the 4 respiratory states.

CONCLUSIONS

Our results confirmed that the newly-developed system could trigger prospectively to guide 4DMRI image acquisition to achieve T2 weighting, which has a better tumor-tissue contrast than those offered by previous 4DMRI techniques with T1 or T2/T1 weighting. This is a first report of a pure T2-weighted 4DMRI to track respiration induced abdominal motion.

Is carbon dioxide a safe and good alternative for diatrizoate meglumine as a contrast in digital subtraction angiography?

Contrast-induced nephropathy is well-known sequelae of iodinated contrast (diatrizoate meglumine). Carbon dioxide (CO(2)) can be used as an alternative contrast agent. The aim of this study was to compare the renal injury and the quality of images of aortogram using iodinated contrast versus CO(2) using digital subtraction angiography (DSA). This prospective randomized study was done in 29 healthy dogs using DSA aortogram. Dogs were randomly assigned to receive iodinated contrast or CO(2). 6-F pigtail catheter was introduced via femoral artery approach to perform aortogram under general anesthesia. Serum creatinine (S.Cr.) and urinary enzymes, namely: N-acetyl D-glucosaminidase (NAG), alanine aminopeptidase (AAP), and gamma glutamyl transferase (GGT), were measured before and 48 hours after aortogram. There was no change in S.Cr. in both the groups. Significantly more enzymuria was seen following iodinated contrast than CO(2). Enzymuria pre and postaortogram following the iodinated contrast was GGT: 14.9 +/- 5.92 vs. 26.2 +/- 15.1 (P = 0.001), NAG: 1.63 +/- 0.90 vs. 3.6 +/- 2.14 (P = 0.0001), and AAP: 1.51 +/- 0.75 vs. 3.38 2.41 (P = 0.001), and in the CO(2) group was GGT: 15.5 +/- 4.9 vs. 21.1 +/- 9.04 (P = 0.02), NAG: 2.12 +/- 1.06 vs. 3.82 3.27 (P = 0.08), and AAP: 1.28 +/- 0.76 vs. 2.51 +/- 1.72 (P = 0.03). More than 50% increase over the preprocedural value was significantly less following CO(2). Images obtained with iodinated contrast were superior to those with CO(2,) however, the quality of image with CO(2) was adequate for delineation of the renal artery and major branches. Both iodinated contrast and CO(2) cause significant enzymuria. More severe enzymuria (>50% increase) was seen significantly less with the use of CO(2). Quality of images is better with iodinated contrast.

CD26 expression in donor stem cell harvest and its correlation with engraftment in human haematopoietic stem cell transplantation: potential predictor of early engraftment

BACKGROUND

The efficiency of haematopoietic stem and progenitor cells (HSPCs) is important when donor cell numbers are limiting. Stable white blood cell (WBC) and platelet engraftment is crucial for the outcome of haematopoietic stem cell transplantation (HSCT).

DESIGN

This article evaluates CD26/dipeptidyl peptidase-IV expression on mobilised peripheral blood stem cell (PBSC) harvest of donors and its correlation with engraftment in HSCT. We have analysed CD26 expression on cells in various gates, that is, lymphocytes, monocytes, neutrophils and all populations using flow cytometry tool.

RESULTS

Ours is the first study on human mobilised PBSC harvest from cancer patients or allogeneic related donors (n = 28) to demonstrate that increased CD26 expression leads to early engraftment in transplanted cancer patients. Correlation of CD26 expression with WBC engraftment was statistically significant (lymphocyte gate: P < 0.00001; monocyte gate: P < 0.00001; neutrophil gate: P < 0.00001; all populations: P < 0.00001). CD34 expression is a known predictor of engraftment. Nevertheless, there was no correlation between CD34 and CD26 expression in these cases.

CONCLUSIONS

This study has given important leads indicating that CD26 expression may be an independent predictor of engraftment. Further study with large number of patients as well as study on circulatory CD26 may add valuable information towards improving current knowledge on CD26.

Spatiotemporal effects of sonoporation measured by real-time calcium imaging

To investigate the effects of sonoporation, spatiotemporal evolution of ultrasound-induced changes in intracellular calcium ion concentration ([Ca(2+)](i)) was determined using real-time fura-2AM fluorescence imaging. Monolayers of Chinese hamster ovary (CHO) cells were exposed to a 1-MHz ultrasound tone burst (0.2 s, 0.45 MPa) in the presence of Optison microbubbles. At extracellular [Ca(2+)](o) of 0.9 mM, ultrasound application generated both nonoscillating and oscillating (periods 12 to 30 s) transients (changes of [Ca(2+)](i) in time) with durations of 100-180 s. Immediate [Ca(2+)](i) transients after ultrasound application were induced by ultrasound-mediated microbubble-cell interactions. In some cases, the immediately affected cells did not return to pre-ultrasound equilibrium [Ca(2+)](i) levels, thereby indicating irreversible membrane damage. Spatial evolution of [Ca(2+)](i) in different cells formed a calcium wave that was observed to propagate outward from the immediately affected cells at 7-20 microm/s over a distance >200 microm, causing delayed transients in cells to occur sometimes 60 s or more after ultrasound application. In calcium-free solution, ultrasound-affected cells did not recover, consistent with the requirement of extracellular Ca(2+) for cell membrane recovery subsequent to sonoporation. In summary, ultrasound application in the presence of Optison microbubbles can generate transient [Ca(2+)](i) changes and oscillations at a focal site and in surrounding cells via calcium waves that last longer than the ultrasound duration and spread beyond the focal site. These results demonstrate the complexity of downstream effects of sonoporation beyond the initial pore formation and subsequent diffusion-related transport through the cellular membrane.

Analysis and comparison of clinicohematological parameters and molecular and cytogenetic response of two Bcr/Abl fusion transcripts

Different forms of p210 are produced by alternative splicing, namely b2a2 and b3a2. There have been many contrasting data establishing a relationship between the two Bcr/Abl transcripts and platelet counts and also response to treatment. However, the data published to date have been on a small group of patients. The aim of the present study was to determine whether there was any difference between clinical and hematological parameters at diagnosis between the two Bcr/Abl fusion transcripts in our population, and whether the two transcripts responded differently or similarly to imatinib treatment. RT-PCR was performed in 202 cases for detection of Bcr/Abl transcripts in newly diagnosed chronic myelogenous leukemia cases in one year. The two transcripts were compared and correlated with clinical, hematological and FISH data and with response to treatment. A total of 138 cases were of b3a2 and 64 were of b2a2 transcript. There was no correlation between the hematological parameters and the type of transcript. There was a significant association of blast crisis with b2a2, especially with myeloid blast crisis. When compared to FISH results, 10% of b3a2 were found to have a significant association with 5'Abl deletion as compared to 3% of b2a2. On analyzing the therapeutic response, we did not find any difference between the two transcripts. In conclusion, our findings confirm that the b3a2 type transcript is not significantly associated with thrombocytosis, that the short transcript, b2a2, occurs with acute phase, i.e., blast crisis, and that there is no difference in treatment response between the two transcripts. However, further studies are required to understand the molecular pathways involved in the Bcr/Abl mechanism.