Monte Carlo simulations used to calculate the energy deposited in the coronary artery lumen as a function of iodine concentration and photon energy.

PURPOSE: To better understand the risks of cumulative medical X-ray investigations and the possible causal role of contrast agent on the coronary artery wall, the correlation between iodinated contrast media and the increase of energy deposited in the coronary artery lumen as a function of iodine concentration and photon energy is investigated. MATERIALS AND METHODS: The calculations of energy deposition have been performed using Monte Carlo (MC) simulation codes, namely PENetration and Energy LOss of Positrons and Electrons (PENELOPE) and Monte Carlo N-Particle eXtended (MCNPX). Exposure of a cylinder phantom, artery and a metal stent (AISI 316L) to several X-ray photon beams were simulated. RESULTS AND DISCUSSION: For the energies used in cardiac imaging the energy deposited in the coronary artery lumen increases with the quantity of iodine. Monte Carlo calculations indicate a strong dependence of the energy enhancement factor (EEF) on photon energy and iodine concentration. The maximum value of EEF is equal to 25; this factor is showed for 83 keV and for 400 mg Iodine/mL. No significant impact of the stent is observed on the absorbed dose in the artery for incident X-ray beams with mean energies of 44, 48, 52 and 55 keV. CONCLUSION: A strong correlation was shown between the increase in the concentration of iodine and the energy deposited in the coronary artery lumen for the energies used in cardiac imaging and over the energy range between 44 and 55 keV. The data provided by this study could be useful for creating new medical imaging protocols to obtain better diagnostic information with a lower level of radiation exposure.

Metabolic tumour volumes measured at staging in lymphoma: methodological evaluation on phantom experiments and patients.

PURPOSE: The presence of a bulky tumour at staging on CT is an independent prognostic factor in malignant lymphomas. However, its prognostic value is limited in diffuse disease. Total metabolic tumour volume (TMTV) determined on (18)F-FDG PET/CT could give a better evaluation of the total tumour burden and may help patient stratification. Different methods of TMTV measurement established in phantoms simulating lymphoma tumours were investigated and validated in 40 patients with Hodgkin lymphoma and diffuse large B-cell lymphoma. METHODS: Data were processed by two nuclear medicine physicians in Reggio Emilia and Créteil. Nineteen phantoms filled with (18)F-saline were scanned; these comprised spherical or irregular volumes from 0.5 to 650 cm(3) with tumour-to-background ratios from 1.65 to 40. Volumes were measured with different SUVmax thresholds. In patients, TMTV was measured on PET at staging by two methods: volumes of individual lesions were measured using a fixed 41% SUVmax threshold (TMTV41) and a variable visually adjusted SUVmax threshold (TMTVvar). RESULTS: In phantoms, the 41% threshold gave the best concordance between measured and actual volumes. Interobserver agreement was almost perfect. In patients, the agreement between the reviewers for TMTV41 measurement was substantial (ρ c = 0.986, CI 0.97 - 0.99) and the difference between the means was not significant (212 ± 218 cm(3) for Créteil vs. 206 ± 219 cm(3) for Reggio Emilia, P = 0.65). By contrast the agreement was poor for TMTVvar. There was a significant direct correlation between TMTV41 and normalized LDH (r = 0.652, CI 0.42 - 0.8, P <0.001). Higher disease stages and bulky tumour were associated with higher TMTV41, but high TMTV41 could be found in patients with stage 1/2 or nonbulky tumour. CONCLUSION: Measurement of baseline TMTV in lymphoma using a fixed 41% SUVmax threshold is reproducible and correlates with the other parameters for tumour mass evaluation. It should be evaluated in prospective studies.