Biomedical subjects

Eric C Ford

Publications and source records attributed to Eric C Ford.

7 recordsLinked to original sources

PubMed2006

Tumor delineation using PET in head and neck cancers: threshold contouring and lesion volumes.

Tumor boundary delineation using positron emission tomography (PET) is a promising tool for radiation therapy applications. In this study we quantify the uncertainties in tumor boundary delineation as a function of the reconstruction method, smoothing, and lesion size in head and neck cancer patients using FDG-PET images and evaluate the dosimetric impact on radiotherapy plans. FDG-PET images were acquired for eight patients with a GE Advance PET scanner. In addition, a 20 cm diameter cylindrical phantom with six FDG-filled spheres with volumes of 1.2 to 26.5 cm3 was imaged. PET emission scans were reconstructed with the OSEM and FBP algorithms with different smoothing parameters. PET-based tumor regions were delineated using an automatic contouring function set at progressively higher threshold contour levels and the resulting volumes were calculated. CT-based tumor volumes were also contoured by a physician on coregistered PET/CT patient images. The intensity value of the threshold contour level that returns 100% of the actual volume, I(V100), was measured. We generated intensity-modulated radiotherapy (IMRT) plans for an example head and neck patient, treating 66 Gy to CT-based gross disease and 54 Gy to nodal regions at risk, followed by a boost to the FDG-PET-based tumor. The volumes of PET-based tumors are a sensitive function of threshold contour level for all patients and phantom datasets. A 5% change in threshold contour level can translate into a 200% increase in volume. Phantom data indicate that I(V100) can be set as a fraction, f, of the maximum measured uptake. Fractional threshold values in the cylindrical water phantom range from 0.23 to 0.51. Both the fractional threshold and the threshold-volume curve are dependent on lesion size, with lesions smaller than approximately 5 cm3 displaying a more pronounced sensitivity and larger fractional threshold values. The threshold-volume curves and fractional threshold values also depend on the reconstruction algorithm and smoothing filter with more smoothing requiring a higher fractional threshold contour level. The threshold contour level affects the tumor size, and therefore the ultimate boost dose that is achievable with IMRT. In an example head and neck IMRT plan, the D95 of the planning target volume decreased from 7770 to 7230 cGy for 42% vs. 55% contour threshold levels. PET-based tumor volumes are strongly affected by the choice of threshold level. This can have a significant dosimetric impact. The appropriate threshold level depends on lesion size and image reconstruction parameters. These effects should be carefully considered when using PET contour and/or volume information for radiotherapy applications.

Head and Neck Neoplasms↗

PubMed2005

Reduction of organ motion in lung tumors with respiratory gating.

We evaluated the ability of a commercial respiratory gating system to assure the reproducibility of internal anatomy in respiration synchronized CT (RS-CT) scans. This passive system uses an infrared sensitive camera to track the motion of reflective markers mounted on the abdomen. Eighteen patients, nine with lung tumors and nine with liver tumors, were selected for evaluation of the Varian Real-Time Position Monitor respiratory gating system. Liver tumors were chosen as surrogate for lower lobe tumors. Each patient underwent at least two identical RS-CT scans, at end-inspiration (EI) or end-expiration (EE), to assess intra-fraction reproducibility. Twelve patients also underwent a free breathing scan and an opposed-respiration phase synchronized scan (EI if the two first were an EE and vice versa). On each CT, a physician contoured the liver, the kidneys, the spleen, and the diaphragms for the liver patients; and similarly, the lungs, the gross tumor volume (GTV), the trachea, the heart and the diaphragms for the lung patients. After registering the different CT images using bony anatomy, the changes of each structure between the respective data sets were quantified in terms of its volume, the displacement of its center of mass (COM), and an "index" coefficient of reproducibility. An analysis of the CT scans obtained at EI and EE phases yielded an average superior-inferior (SI) difference of the diaphragm position of 14.4 mm (range: 45.9-0.9). A similar analysis of CT scans acquired at the same breathing phase yielded 0.7 mm (range: 3.1-0, p=0.0001). Similar conclusions were derived in analysis of COM positions of the following structures: lungs, heart, lung's GTV, liver, spleen and kidneys. Evaluation of volume changes for lungs, liver, and spleen confirmed reproducibility of RS-CT while the "index" coefficient confirmed reproducibility of RS-CT of all organs. A commercial gating system using external markers for RS-CT significantly improves the positional reproducibility of thoracic and upper abdominal structures. This reproducible decrease in organ motion will allow a reduction of the margin of expansion facilitating increase in target dose beyond that allowed by conventional radiation treatments.

Adult↗

PubMed2005

Intraoperative fluoroscopic dose assessment in prostate brachytherapy patients.

PURPOSE: To evaluate a fluoroscopy-based intraoperative dosimetry system to guide placement of additional sources to underdosed areas, and perform computed tomography (CT) verification. METHODS AND MATERIALS: Twenty-six patients with prostate carcinoma treated with either I-125 or Pd-103 brachytherapy at the Puget Sound VA using intraoperative postimplant dosimetry were analyzed. Implants were performed by standard techniques. After completion of the initial planned brachytherapy procedure, the initial fluoroscopic intraoperative dose reconstruction analysis (I-FL) was performed with three fluoroscopic images acquired at 0 (AP), +15, and -15 degrees. Automatic seed identification was performed and the three-dimensional (3D) seed coordinates were computed and imported into VariSeed for dose visualization. Based on a 3D assessment of the isodose patterns additional seeds were implanted, and the final fluoroscopic intraoperative dose reconstruction was performed (FL). A postimplant computed tomography (CT) scan was obtained after the procedure and dosimetric parameters and isodose patterns were analyzed and compared. RESULTS: An average of 4.7 additional seeds were implanted after intraoperative analysis of the dose coverage (I-FL), and a median of 5 seeds. After implantation of additional seeds the mean V100 increased from 89% (I-FL) to 92% (FL) (p < 0.001). In I-125 patients an improvement from 91% to 94% (p = 0.01), and 87% to 93% (p = 0.001) was seen for Pd-103. The D90 increased from 105% (I-FL) to 122% (FL) (p < 0.001) for I-125, and 92% (I-FL) to 102% (FL) (p = 0.008) for Pd-103. A minimal change occurred in the R100 from a mean of 0.32 mL (I-FL) to 0.6 mL (FL) (p = 0.19). No statistical difference was noted in the R100 (rectal volume receiving 100% of the prescribed dose) between the two techniques. The rate of adverse isodose patterns decreased between I-FL and FL from 42% to 8%, respectively. The I-125 patients demonstrated a complete resolution of adverse isodose patterns after the initial isodose reconstruction (I-FL). The Pd-103 patients demonstrated a final rate of 8% gaps, 0% islands, and 0% holes on corrected isodose reconstruction. CONCLUSION: The use of intraoperative fluoroscopy-based dose assessment can accurately guide in the implantation of additional sources to supplement inadequately dosed areas within the prostate gland. Additionally, guided implantation of additional source, can significantly improve V100s and D90s, without significantly increasing rectal doses.

Brachytherapy↗

PubMed2005

FDG-PET/CT-guided intensity modulated head and neck radiotherapy: a pilot investigation.

BACKGROUND: 2-deoxy-2[(18)F]fluoro-D-glucose-positron emission tomography (FDG-PET) imaging can be registered with CT images and can potentially improve neck staging sensitivity and specificity in patients with head and neck squamous cell cancer. The intent of this study was to examine the use of registered FDG-PET/CT imaging to guide head and neck intensity modulated radiotherapy (IMRT) planning. METHODS: Twenty patients with squamous cell carcinoma of the oral cavity, oropharynx, larynx, or hypopharynx underwent FDG-PET and contrast-enhanced CT imaging of the head and neck before neck dissection surgery. Combined FDG-PET/CT images were created by use of a nonrigid image registration algorithm. All IMRT plans were theoretical and were not used for treatment. We prescribed 66 Gy in 30 fractions to FDG-avid CT abnormalities and nodal zones directly involved with disease, without prophylactic coverage of uninvolved neck levels. Matched CT-guided IMRT plans designed according to the specifications of Radiation Therapy Oncology Group (RTOG) H-0022 were available for comparison. We investigated the feasibility of FDG-PET/CT-directed IMRT dose escalation in five patients with FDG-avid disease located away from critical normal structures. After 66 Gy, FDG-avid disease with 0.5-cm margins was boosted in 220 cGy increments until dose-limiting criteria were reached. RESULTS: Elimination of prophylactic coverage to FDG-PET/CT-negative neck levels markedly reduced mean dose (Dmean) to the contralateral parotid gland (p < .001) and Dmean to the laryngeal cartilage (p = .001). No FDG-PET/CT-directed plan missed pathologically verified nodal disease. During the dose escalation exercise, we successfully increased the dose to 95% of the planning target volume (PTV95%) to a mean of 7490 cGy (range, 7153-8098 cGy). CONCLUSIONS: We demonstrate early proof of the principle that FDG-PET/CT-guided IMRT planning can selectively target and intensify treatment of head and neck disease while reducing critical normal tissue doses. Routine clinical use of such planning should not be engaged until the accuracy of FDG-PET/CT is fully validated. Future directions, including refinement of treatment to gross disease and radiologically uninvolved neck nodal levels, are discussed.

Adult↗

PubMed2004

Measurement of lung tumor motion using respiration-correlated CT.

PURPOSE: We investigate the characteristics of lung tumor motion measured with respiration-correlated computed tomography (RCCT) and examine the method's applicability to radiotherapy planning and treatment. METHODS AND MATERIALS: Six patients treated for non-small-cell lung carcinoma received a helical single-slice computed tomography (CT) scan with a slow couch movement (1 mm/s), while simultaneously respiration is recorded with an external position-sensitive monitor. Another 6 patients receive a 4-slice CT scan in a cine mode, in which sequential images are acquired for a complete respiratory cycle at each couch position while respiration is recorded. The images are retrospectively resorted into different respiration phases as measured with the external monitor (4-slice data) or patient surface displacement observed in the images (single-slice data). The gross tumor volume (GTV) in lung is delineated at one phase and serves as a visual guide for delineation at other phases. Interfractional GTV variation is estimated by scaling diaphragm position variations measured in gated radiographs at treatment with the ratio of GTV:diaphragm displacement observed in the RCCT data. RESULTS: Seven out of 12 patients show GTV displacement with respiration of more than 1 cm, primarily in the superior-inferior (SI) direction; 2 patients show anterior-posterior displacement of more than 1 cm. In all cases, extremes in GTV position in the SI direction are consistent with externally measured extremes in respiration. Three patients show evidence of hysteresis in GTV motion, in which the tumor trajectory is displaced 0.2 to 0.5 cm anteriorly during expiration relative to inspiration. Significant (>1 cm) expansion of the GTV in the SI direction with respiration is observed in 1 patient. Estimated intrafractional GTV motion for gated treatment at end expiration is 0.6 cm or less in all cases; however; interfraction variation estimates (systematic plus random) are more than 1 cm in 3/9 patients. CONCLUSION: Respiration-correlated CT can be performed with currently available CT equipment and acquisition settings. RCCT provides not only three-dimensional information on intrafractional tumor motion and deformation, but also allows estimates of interfractional tumor variation when combined with radiographic measurements of diaphragm position variation during treatment.

Carcinoma, Non-Small-Cell Lung↗

PubMed2004

A block design for split-field tests of accelerator alignment.

We present a block design that facilitates split-field tests, a technique frequently employed to assess several potential misalignments in linear accelerators. Two tests are possible with this device using: (1) opposed collimator angles and (2) opposed gantry angles. The first test is sensitive to jaw symmetry only. In the second test, the alignment of one field edge indicates gantry sag, while the other field edge is sensitive to the combined effects of jaw asymmetry, misalignment of the beam spot, and misalignment of the gantry and collimator rotation axes. The block arrangement consists of a pattern of three polygons cast in lead or Cerrobend. The assembly mounts in the accessory tray of the accelerator and allows all necessary exposures to be taken in a single room entry. Any field size up to 24 cm can be tested with the assembly constructed here. A simultaneous test of light field-radiation field coincidence can also be accommodated. Exposed films with a prototype device show that offsets of +/-1 mm are readily visible. The block design facilitates the required measurements for split-field tests and makes this a practical technique for routine quality assurance on a linear accelerator.

Calibration↗

PubMed2003

Optimization of conformal thoracic radiotherapy using cone-beam CT imaging for treatment verification.

PURPOSE: Megavoltage cone-beam computed tomography (MVCBCT) has been proposed for treatment verification in conformal radiotherapy. However, the doses required for such imaging may compromise the quality of the delivered dose distribution. The present paper explores the effect of cone-beam imaging on dose homogeneity and critical organ dose and the use of our new tool, adapted intensity-modulated radiation therapy (AIMRT). METHODS AND MATERIALS: Three types of treatment plans were devised (3D-CRT [three-dimensional conformal radiotherapy], IMRT [intensity-modulated radiotherapy], and AIMRT) based on 4 patients with thoracic malignancies. MVCBCT fields were then integrated into the plans. The MVCBCT technique used 21 imaging portals at 10 degrees intervals. The MVCBCT apertures were shaped to conform to the planning target volume with a 6-mm margin. In a second set of plans, the field size was expanded by a further 2 cm. The unoptimized MVCBCT dose distribution was incorporated into the IMRT plan using AIMRT. RESULTS: Normal-tissue complication probability with MVCBCT is acceptable for all plans at the 66.6 Gy level, but exceeds tolerance for both 3D-CRT alone and 3D-CRT with MVCBCT at higher doses. In contrast, the use of AIMRT planning with MVCBCT allowed safe dose escalation to 85 Gy. Expanding the MVCBCT aperture provided better anatomic visibility with an acceptable lung dose. The results using IMRT with MVCBCT fell between the values measured for 3D-CRT and AIMRT with MVCBCT. CONCLUSION: The present study is the first to demonstrate that MVCBCT can be incorporated into 3D-CRT and IMRT planning with minimal effect on planning target volume homogeneity and dose to critical structures. This paves the way for highly conformal radiotherapy at greater doses delivered with increased confidence and safety.

Computer Graphics↗