Nuclear Medicine & Radiation Therapy

With the emerging multi-modality imaging performed at multiple time points for each patient, it becomes more important to analyze the serial images quantitatively, select and combine both complementary and contradictory information from various sources, for accurate and personalized evaluation of tumor response to therapy.

This paper reviews efforts of incorporating FDG based PET/CT data into target volume delineation for radiotherapy treatment planning. Relationship between PET-based and CT-based volumes generally suffer from poor correlation between the two image data sets, expressed in terms of large statistical variation in gross tumor volume ratios irrespective of the thresholding method used. Future of biologically tailored target volumes for radiotherapy treatment planning might not be the replacement of CT or MRI based anatomical gross tumor volumes by PET based volumes. Instead, the two target volumes should complement each other into a complex mosaic of biological target volumes.

Objective: In clinical practice, PET images are acquired during shallow breathing and CT images of the PET/ CT during shallow breathing or at near end-expiration. We determined the clinical significance of pulmonary nodules that were missed on PET/CT acquired during non-breath-hold (NBH) imaging in patients with proven non-thoracic solid malignancies. Methods: 200 consecutive cancer patients who underwent both PET/CT and diagnostic breath-hold (BH) chest CT within 30 days, and who had a follow-up with BH CT at least 2 years after these baseline studies, were evaluated. NBH CT of the PET/CT was analyzed first, followed by the baseline BH CT. Missed nodules were defined as nodules not detected on NBH PET/CT, but detected on BH CT. Missed nodules were then evaluated on BH CT performed at least 2 years later. A second radiologist was used to evaluate inter observer variability for a subset of 50 patients. Results: 343 nodules were identified in 121 patients. 166 nodules from 86 patients were classified as missed nodules. Seven of these 166 nodules were excluded due to interval surgery or development of consolidation. When a change in size was counted only if it was ≥2 mm, only 11 of the 159 nodules (6.9%) grew, 113 nodules (71.1%) did not change, and the remaining 35 nodules (22.0%) were not present at follow-up. Malignancy was deemed the most likely diagnosis in only 6 of the original 159 missed nodules. Conclusion: Although the incidence of pulmonary nodules missed on NBH PET/CT was high, most of these nodules did not show any growth on follow-up and few were proven to be metastatic. Current clinical practice of PET/CT, with acquisition during shallow breathing or at near end expiration is sufficient; performing additional deep inspiration BH CT does not appear warranted.

Radionuclide cisternography (RC) is an underutilized but sensitive modality used to differentiate between normal pressure and non-communicating hydrocephalus and can also detect cerebrospinal fluid (CSF) leakage. We present a case of intracranial tuberculous with severe headache and hydrocephalus. RC was performed with Tc-99m labeled DTPA showing communicating hydrocephalus with characteristics Christmas tree sign and early appearance of renal activity due to spinal CSF leak into systemic circulation. This patient responded well to ventriculo-peritoneal shunt (VP shunt).