Adaptive Dose Escalation using Serial Four-dimensional Positron Emission Tomography/Computed Tomography Scans during Radiotherapy for Locally Advanced Non-small Cell Lung Cancer.

AIMS: Computed tomography (CT)-based radiotherapy dose escalation for locally advanced non-small cell lung cancer (LA-NSCLC) has had limited success. In this planning study, we investigated the potential for adaptive dose escalation using respiratory-gated 18F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography scans (4DPET/4DCT) acquired before and during a course of chemoradiotherapy (CRT). MATERIALS AND METHODS: We prospectively enrolled patients with LA-NSCLC receiving curative intent CRT. Radiotherapy was delivered using intensity-modulated radiotherapy (IMRT) using the week 0 4DCT scan. Three alternative, dose-escalated IMRT plans were developed offline based on the week 0, 2 and 4 4DPET/4DCT scans. The FDG-avid primary (PET-T) and nodal disease (PET-N) volumes defined by the 50% of maximum standard uptake value threshold were dose escalated to as high as possible while respecting organ at risk constraints. RESULTS: Thirty-two patients were recruited, 27 completing all scans. Twenty-five patients (93%) were boosted successfully above the clinical plan doses at week 0, 23 (85%) at week 2 and 20 (74%) at week 4. The median dose received by 95% of the planning target volume (D95) at week 0, 2 and 4 to PET-T were 74.4 Gy, 75.3 Gy and 74.1 Gy and to PET-N were 74.3 Gy, 71.0 Gy and 69.5 Gy. CONCLUSIONS: Using 18F-FDG-4DPET/4DCT, it is feasible to dose escalate both primary and nodal disease in most patients. Choosing week 0 images to plan a course with an integrated boost to PET-avid disease allows for more patients to be successfully dose escalated with the highest boost dose.

Evaluation of differential magnification during brain SPECT acquisition.

OBJECTIVE: We developed a modification of the acquisition zoom technique, referred to as differential magnification (DM), to improve the pixel resolution with fanbeam collimators. This study evaluated the effects of DM on brain SPECT image quality. METHODS: SPECT imaging was performed using a triple-head camera with and without DM for a line source in air, Jaszczak and Hoffman phantoms, and 15 clinical patients having regional cerebral blood-flow scans with 99mTc ECD. Full width at half maximum (FWHM) and contrast ratios were measured on the line source and Jaszczak phantom data, respectively. Visual image evaluation was performed by 2 independent, blinded observers for the Hoffman brain phantom images and clinical patient studies. RESULTS: FWHM improved on the fanned axis (transverse plane) by 0.05 mm (P < 0.001), and the unfanned axis (longitudinal plane) by 0.66 mm (P < 10(-6)), when DM was used. The mean improvement of contrast ratios for the spheres on the Jaszczak phantom with DM was 11.4% (P < 0.004). The images with DM were rated superior to those without, for the Hoffman brain phantom and the clinical patients. CONCLUSION: This study has demonstrated that SPECT acquisition with fanbeam collimators and DM significantly improves both FWHM and image contrast, resulting in superior image quality. DM techniques may be useful in improving clinical brain SPECT images.

External radioactive reference markers in SPECT imaging of the dopamine system.

OBJECTIVE: External radioactive reference markers have been used to localize the canthomeatal (CM) line and correct for head rotation in perfusion brain SPECT. This ensures that regardless of the subject's head position or rotation under the SPECT camera, reconstructed transaxial slices are reoriented parallel to the CM line. This study was undertaken to demonstrate the value of external radioactive reference markers in dopamine SPECT imaging. METHODS: We compared visual and marker methods of reorienting the transaxial slices between dopamine and perfusion brain SPECT studies, respectively. These consisted of imaging normal controls and patients with Alzheimer's or Parkinson's disease using a triple-head camera. Intra- and interoperator variability of the visual and marker methods of reorientation was determined for both perfusion and dopamine studies. RESULTS: In both intra- and interoperator studies, the variability of image reorientation was significantly reduced (P = 0.0066 and 0.014, respectively) by using the marker method on dopamine images. The variability of reorientation using the marker method for a single operator with dopamine images was 3.0% coefficient of variation (CV), and for the interoperator study (5 different operators) this was 7.0% CV. CONCLUSION: This study demonstrated that SPECT imaging of the dopamine system with external radioactive reference markers significantly reduced the variability of determining the angle of reorientation. This resulted in a standardized and consistent method of reorienting transaxial slices, allowing comparison within and between subjects of pre- and postsynaptic dopamine SPECT studies.

Neuroanatomical localization for clinical SPECT perfusion brain imaging: a practical proportional grid method.

For the purpose of facilitating anatomical localization in interpretation of 99Tcm-hexamethylpropyleneamine oxime (HMPAO) brain single photon emission tomographic (SPECT) scans, a stereotaxic proportional grid system was applied in the form of an interactive computer program. This method takes advantage of a rotating gamma camera system which permits planar scout imaging for the determination of anatomical reference lines, and standardization of tomographic slices for brain size. Using measurements made on a lateral planar HMPAO image, proportional grids were constructed onto standardized transaxial images. This method was implemented for 33 clinical HMPAO SPECT studies. It required less than 15 min of an operator's time. This simple and practical neuroanatomical localization technique can be instrumental as an aid to the interpretation of routine clinical HMPAO SPECT images.