Enzymatic activity mediated by recombinant human DNA ligase I (hLI), in conjunction with tannin removal procedures, has been applied to a natural-product screen involving approximately 1000 plant extracts and various pure compounds. The primary hLI activity assay involved the measurement of the amount of radiolabelled phosphate in a synthetic nucleic acid hybrid that becomes resistant to alkaline phosphatase as a result of ligation. A bioactivity-guided fractionation scheme resulted in the isolation of ursolic [IC50=100 micrograms/ml (216 microM)] and oleanolic [IC50=100 micrograms/ml (216 microM)] acids from Tricalysia niamniamensis Hiern (Rubiaceae), which demonstrated similar DNA ligase inhibition profiles to other triterpenes such as aleuritolic acid. Protolichesterinic acid [IC50=6 micrograms/ml (20 microM)], swertifrancheside [IC50 = 8 micrograms/ml(11)microM)] and fulvoplumierin [IC50=87 micrograms/ml (357 microM)] represent three additional natural-product structural classes that inhibit hLI. Fagaronine chloride [IC50=10 micrograms/ml (27 micronM] and certain flavonoids are also among the pure natural products that were found to disrupt the activity of the enzyme, consistent with their nucleic acid intercalative properties. Further analyses revealed that some of the hLI-inhibitory compounds interfered with the initial adenylation step of the ligation reaction, indicating a direct interaction with the enzyme protein. However, in all cases, this enzyme-inhibitor interaction did not disrupt the DNA relaxation activity mediated by hLI. These results indicate that, although the same enzyme active site may be involved in both enzyme adenylation and DNA relaxation, inhibitors may exert allosteric effects by inducing conformational changes that disrupt only one of these activities. Studies with inhibitors are important for the assignment of specific cellular functions to these enzymes, as well as for their development into clinically useful antitumour agents.

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Purpose: To verify the necessity of 6D localization detection and correction in radiation therapy. Methods: An anthropomorphic head and neck phantom was used to test the BrainLab ExacTrac x‐ray imaging system. After initial positioning, both ExacTrac and the on‐board kV CBCT were used to detect the offset at the same position, using both manual and automatic registration algorithms. Then 6D offset including rotational errors up to 5 degree were introduced. Both ExacTrac and CBCT were used to correct the offsets and the residual errors were evaluated. Finally, 6D offset detected by ExacTrac for a C‐Spine patient was reported. Results: The differences in 3D offset detected by ExacTrac and CBCT were 1.5 ± 1.2(Lateral), 2.7 ± 2.7(Vertical), and 4.0 ± 6.3(longitudinal) mm with manual registration while the corresponding differences decreased to 0.6 ± 0.3, 1.0 ± 0.3, and 0.3 ± 0.3 when automatic registration were used. CBCT corrected the translational offset to within 0.5 mm but the rotational errors remained and detected by the ExacTrac system (Yaw=2.1, Roll=1.1, Pitch=1.4 degree). When similar offset was introduced and corrected using ExacTrac, the residual error detected by both CBCT and ExacTrac were within 0.5 mm / 0.5 degree. The average offset from the 112 ExacTrac x‐ray corrections for the C‐Spine patient was 0.6 ± 1.6 (lateral), 5.4 ± 8(vertical), 1.6±1.1(longitudinal) mm, and 0.7 ± 0.6 (pitch), 0.7 ± 0.4(roll), 1.2 ± 0.7 (yaw) degree. Larger rotational errors, with a maximum of 2.7 degree (corresponds to about 1.5 to 4.5 mm offset for a POI 10 to 30 cm away from the isocenter), were observed when couch rotational were involved. Conclusion: Rotational errors are common in patient localization, especially when couch rotation is involved. Both appropriate imaging system and 6D robotic couch are necessary to detect and correct the rotational localization errors.

Purpose: TomoTherapy IMRT plans for various anatomical sites were analyzed in order to obtain dosimetric characteristics, and to determine plan quality and deliverability.Methods: Treatment plans for thirty patients treated with TomoTherapy were reviewed and analyzed. The distribution of treatment sites was: abdomen (n=4), brain (n=4), head and neck (H&N; n=6), lung (n=6), pelvis (n=5) and prostate (n=5). Prescription dose (PD), D90%, PTV, max, mean and min doses of PTV were extracted from the plans and DVH data. Metrics calculated include: homogeneity index (H.I.=max dose in PTV/ PD), mean dose of PTV over PD, max dose of PTV over min dose in PTV, and D90%/PD were calculated for the different treatment sites. In order to verify plan delivery, absolute and relative dose measurements were performed and analyzed using an ion chamber and GafChromic films. Results: Mean prescription isodose lines were 95.7% (n=30). The PTV ranged from 11.7 to 982.2 cc. For H.I. the prostate site yielded the smallest H.I. of 0.99 while the pelvis site yielded the greatest H.I. of 1.14. The prostate site produced the smallest mean dose over PD (0.97) and H&N produced the greatest (1.03). The overall H.I. was 1.06 and the overall ratio of mean dose over PD was 1.02. The overall max dose over min dose was 1.18. The mean difference for absolute point dose measurements was −0.9%. Measured film profiles demonstrated excellent agreement with calculated profiles in plan delivery QA Conclusions: For the treatment sites reviewed prostate had the most homogeneous plans, while lung had the most inhomogeneous plans in this study. The overall mean dose over PD and QA results were excellent in TomoTherapy. TomoTherapy is capable of planning and delivering high quality IMRT treatments for a wide variety of treatment sites