Biomedical subjects

Andrew Wu

Publications and source records attributed to Andrew Wu.

8 recordsLinked to original sources

PubMed2006

Abdominal organ motion measured using 4D CT.

PURPOSE: To measure respiration-induced abdominal organ motion using four-dimensional computed tomography (4D CT) scanning and to examine the organ paths. METHODS AND MATERIALS: During 4D CT scanning, consecutive CT images are acquired of the patient at each couch position. Simultaneously, the patient's respiratory pattern is recorded using an external marker block taped to the patient's abdomen. This pattern is used to retrospectively organize the CT images into multiple three-dimensional images, each representing one breathing phase. These images are analyzed to measure organ motion between each phase. The displacement from end expiration is compared to a displacement limit that represents acceptable dosimetric results (5 mm). RESULTS: The organs measured in 13 patients were the liver, spleen, and left and right kidneys. Their average superior to inferior absolute displacements were 1.3 cm for the liver, 1.3 cm for the spleen, 1.1 cm for the left kidney, and 1.3 cm for the right kidney. Although the organ paths varied among patients, 5 mm of superior to inferior displacement from end expiration resulted in less than 5 mm of displacement in the other directions for 41 of 43 organs measured. CONCLUSIONS: Four-dimensional CT scanning can accurately measure abdominal organ motion throughout respiration. This information may result in greater organ sparing and planning target volume coverage.

Abdomen↗

PubMed2006

Localizing moving targets and organs using motion-managed CTs.

Respiration-induced target and organ motion impacts the radiotherapy strategies of some cancers. Various methods and techniques have been used to investigate motion-related radiotherapy issues, including retrospective 4-dimensional (4D) computed tomography (CT), prospective gated CT, and breath-hold CT scans. This paper reviews these methods and, particularly, the method using retrospective 4D CT scans, which has been developed at our institution. Some motion studies based on retrospective 4D CT images of patients are also examined. These studies have led to reduced planning target volume (PTV) margins for a number of patients, because the respiratory motion was observed to be minimal or gated radiotherapy was used. Respiratory motion managed CTs and, particularly, retrospective 4D CTs are proving to be useful for measuring soft tissue motion, identifying patients who could benefit from gated radiotherapy, and evaluating the effects of respiratory motion during radiotherapy.

Humans↗

PubMed2006

Does breast size affect the scatter dose to the ipsilateral lung, heart, or contralateral breast in primary breast irradiation using intensity-modulated radiation therapy (IMRT)?

PURPOSE: To evaluate the relationship between the primary breast volume and dose received by the ipsilateral lung, heart (for left-breast cancers), and contralateral breast during primary breast irradiation using intensity-modulated radiation therapy (IMRT). METHODS AND MATERIALS: Sixty-five patients with breast carcinoma were treated using 6-MV photons with IMRT technique using the Eclipse Planning System following breast conserving surgery. All patients had a treatment planning CT scan. The primary breast, ipsilateral lung, and heart were contoured on the axial CT slices. The primary breast volume was calculated using the Eclipse Planning System. The mean ipsilateral lung and heart doses were obtained from the dose-volume histogram. The contralateral breast dose was measured using paired thermoluminescent dosimeters (TLDs) placed on the patient's contralateral breast, 4 cm from the center of the medial border of the primary breast irradiation field. RESULTS: The mean dose delivered with photons to the primary breast for all patients was 49.97 Gy. The mean volume of the primary irradiated breast was 1167.9 cc. As a percentage, the mean ipsilateral lung, heart, and contralateral breast doses were 11.2%, 6.1%, and 7.2%, respectively. The primary breast volume positively correlated with the contralateral breast dose (P < 0.0005). There was no significant correlation between the breast volume and the ipsilateral lung or heart dose (P = 0.463 and 0.943, respectively). CONCLUSION: This study suggests that the primary breast size significantly affects the scatter dose to the contralateral breast but not the ipsilateral lung or heart dose when using IMRT for breast irradiation.

Breast↗

PubMed2005

Intensity modulated radiation therapy (IMRT) reduces the dose to the contralateral breast when compared to conventional tangential fields for primary breast irradiation.

PURPOSE: To determine the dose received by the contralateral breast during primary breast irradiation using IMRT compared to conventional tangential field techniques. METHODS AND MATERIALS: Between March 2003 and March 2004, 83 patients with breast carcinoma were treated using 6, 10, or mixed 6/18 MV photons (65 with tangential IMRT technique and 18 with 3-dimensional technique using tangential fields with wedges) for primary breast irradiation following breast-conserving surgery. Paired thermoluminescent dosimeters (TLDs) were placed on each patient's contralateral breast, 4 and 8 cm from the center of the medial border of the tangential field. The TLDs were left on the patient during a single fraction and then measured 24 h afterwards. RESULTS: The mean dose delivered with photons to the primary breast for all patients was 4999 cGy (SD = 52) with a mean single fraction dose of 199 cGy (SD = 8). The mean percent of the prescribed dose to the contralateral breast measured at the 4- and 8-cm positions were 7.19% (SD = 2.28) and 4.63% (SD = 2.12), respectively, for patients treated with IMRT compared to 11.22% (SD = 2.73) and 10.70% (SD = 3.44), respectively, for the patients treated with conventional tangential field techniques. This represented a 36% and 57% reduction at the 4 and 8-cm contralateral positions, respectively, in the mean dose to the contralateral breast using IMRT compared to 3-D technique which was statistically significant (p < 0.0005, <0.0005, respectively). CONCLUSION: Primary breast irradiation with tangential IMRT technique significantly reduces the dose to the contralateral breast compared to conventional tangential field techniques.

Breast↗

PubMed2005

Not all 2 Gray radiation prescriptions are equivalent: Cytotoxic effect depends on delivery sequences of partial fractionated doses.

PURPOSE: To test whether or not the commonly prescribed daily dose of 2 Gy (whole fraction), when delivered as various partial fraction (PF) dose sequences simulating clinical treatment fields, produces equal biologic effects. METHODS AND MATERIALS: Eleven actively proliferating cell lines derived from human and animal tissues were used in this study. 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide (MTT) and clonogenic assays were used to determine the radiation effects on cell proliferation and survival, respectively. The 2 Gy dose was divided into 2 or more PFs for delivery to simulate the delivery of clinical treatment fields. Most irradiation sequences contained two parts consisting of at least 1 small PF, denoted by S which was 0.5 Gy or less, and a large PF, denoted by L which was 1 Gy or more. Irradiation schemes were designed to include the following conditions: (a) the 2 Gy dose divided into combinations of an L-dose and one or more S-doses; (b) the L-dose given either before or after the S-doses; and (c) delivery of all partial fractions within a fixed total time. RESULTS: Significant differences in biologic effect were observed between sequences in which the L-dose was given before or after the S-doses in both the MTT and clonogenic assays. Nearly all the latter schemes, that is S-L, produced greater cytotoxic effects than the L-S schemes. CONCLUSIONS: These data demonstrate that the biologic effects of 2 Gy may differ in different clinical settings depending on the size and sequence of the partial fractions. The variation between cytotoxic effects is likely a result of the combination of low-dose hyper-radiosensitivity (HRS) and higher-dose increased radioresistance (IRR) effects established recently. We suggest that to ensure the optimal biologic effect of a prescribed dose of 2 Gy clinically, it is critical to consider the sequence in which the treatment fields are delivered when partial fractions of different sizes are used.

Animals↗

PubMed2004

Hybrid PET-CT simulation for radiation treatment planning in head-and-neck cancers: a brief technical report.

PURPOSE: To prospectively study the impact on tumor and normal tissue delineation for RT planning by use of hybrid PET-CT simulation for patients with head-and-neck cancer. METHODS AND MATERIALS: Twenty-one patients were simulated in treatment position on a hybrid PET-CT scanner. Images were transferred to the Varian Eclipse planning system. Abnormal areas of fluorodeoxyglucose (FDG) uptake were contoured on PET for the gross tumor volume of primaries (GTVp) and abnormal nodal region of primaries (ABNp) then compared with the same CT gross tumor volumes (GTVc) and abnormal nodal region (ABNc). A statistical analysis was performed to evaluate the correlation of PET and CT volumes. RESULTS: Positron emission tomography demonstrated the primary in all cases, whereas CT did not find the primary in 3 cases. In 8 patients, additional areas of disease were seen only in PET. The average ratio of GTVc/GTVp was 3.1 (range, 0.3-23.6), whereas for ABNc/ABNp was 0.7 (range, 0-4). Volumes for the primaries were significantly larger on CT than on PET (p = 0.002) but not for nodal regions (p = 0.5). CONCLUSIONS: Hybrid PET-CT simulation is feasible and provides valuable information that results in greater delineation of normal tissues from tumor bearing areas at high risk for recurrence. This finding may further improve therapeutic window for IMRT for head-and-neck cancers.

Adult↗

PubMed2004

Virtual three-dimensional blackboard: three-dimensional finger tracking with a single camera.

We present a method for three-dimensional (3D) tracking of a human finger from a monocular sequence of images. To recover the third dimension from the two-dimensional images, we use the fact that the motion of the human arm is highly constrained owing to the dependencies between elbow and forearm and the physical constraints on joint angles. We use these anthropometric constraints to derive a 3D trajectory of a gesticulating arm. The system is fully automated and does not require human intervention. The system presented can be used as a visualization tool, as a user-input interface, or as part of some gesture-analysis system in which 3D information is important.

Journal Article↗

PubMedDate not supplied

Intensity-modulated radiation therapy (IMRT) reduces the dose to the contralateral breast when compared to conventional tangential fields for primary breast irradiation: initial report.

PURPOSE: This study was designed to compare the dose received by the contralateral breast during primary breast irradiation using intensity-modulated radiotherapy with the dose received via conventional tangential field techniques. METHODS/MATERIALS: Between March 2003 and March 2004, 44 patients with breast carcinoma were treated using 6-, 10-, or mixed 6/18-MV photons(36 with tangential intensity-modulated radiotherapy technique and eight with three-dimensional technique using tangential fields with wedges) for primary breast irradiation after breast-conserving surgery. Paired thermoluminescent dosimeters were placed on each patient's contralateral breast, 4 cm from the center of the medial border of the tangential field. The thermoluminescent dosimeters were left on the patient during a single fraction and then measured 24 hours later. RESULTS: The mean dose delivered with photons to the primary breast for all patients was 4998 cGy [SD = 52], and the mean single fraction dose was 200 cGy [SD = 9]. The mean percent of the prescribed dose to the contralateral breast was 7.74% (SD = 2.35) for patients treated with intensity-modulated radiotherapy, compared with 9.74% [SD = 2.04] for the patients treated with conventional tangential field techniques. This represented a 20% reduction in the mean dose to the contralateral breast with the use of intensity-modulated radiotherapy when compared with the dose received via the three-dimensional technique, a result that was statistically significant. CONCLUSION: Primary breast irradiation with tangential intensity-modulated radiotherapy technique significantly reduces the dose to the contralateral breast when compared with conventional tangential techniques.

Breast Neoplasms↗