Liver Regeneration Following Radiation Therapy in Hepatocellular Carcinoma Patients: Insights from Functional Liver Imaging

PURPOSE/OBJECTIVE(S)

A critical need for hepatocellular carcinoma (HCC) patients is understanding how the liver recovers following radiation therapy (RT). While liver regeneration after hepatic resection has been well-studied, liver recovery following RT is less understood. We have previously studied 99mTc-sulphur colloid (SC) single photon emission tomography (SPECT)/CT to spatially and quantitatively analyze liver function. The purpose of this study was to assess both volumetric and functional liver changes following RT.

MATERIALS/METHODS

Patients with HCC had liver function assessed with SC SPECT/CT before and after definitive RT. Patients received 30-67.5 Gy in 4-15 fractions. Anatomic and functional liver metrics were assessed before and after treatment. The anatomic liver volume (ALV) was drawn on CT imaging. Liver function was measured as the functional volume encompassing 30% of maximum uptake (FLV) and mean liver-to-spleen uptake ratio (L/S). Changes in liver size and function were compared to clinical characteristics, including Child-Pugh (CP) score. Parametric t-tests were used to analyze the data.

RESULTS

Of 23 evaluable patients (proton RT, n = 16 or photon RT, n = 7), 15 patients had CP-A5/6, 7 had CP-B7/8, and 1 had CP-C10 scores. The mean interval of SC SPECT was 67 days following RT (range, 44 to 113 days). The mean PTV was 272 cc (range 22-802 cc). Regarding baseline liver status, mean pre-treatment ALV was 1584 cc (range 810-2749 cc) with no significant difference in ALV between CP-A and B/C patients (p = 0.285). Pre-treatment mean liver function as assessed with L/S was 1.06 ± 0.43 with significantly greater function in CP-A compared to CP-B/C patients (1.27 vs 0.66, respectively, p<0.001). Mean pre-treatment FLV was 1351 ± 430.8 cc with no significant difference in FLV between CP-A and B/C patients (1422 ± 441 cc vs 1220 ± 436 cc, respectively, p = 0.31). When evaluating change following RT, the mean change in ALV was 0.9% (range, -29% to 23%) with no significant difference between CP-A and CP-B/C patients (-1.5% vs 5.4%, respectively, p = 0.19). In contrast, change in liver function following RT was larger; mean change in FLV was -20% (range, -55% to 33%) and mean change in L/S was -16% (range, -66% to 105%). While change in FLV was not significantly different between CP-A and CP-B/C patients, CP-B/C patients had significantly greater decline in mean liver function (L/S) than CP-A patients (-40 ± 18% vs -3.6 ± 36%, respectively, p = 0.018). There was no association between change in liver volume and change in L/S, p = 0.543.

CONCLUSION

Functional liver imaging metrics reveal different information about the potential functional reserve of irradiated livers compared to anatomic measurements. These data imply that functional liver imaging may more accurately assess the regenerative potential of irradiated and non-irradiated volumes of liver, which may be useful in clinical scenarios where assessment of the function of future liver remnants become critical.

Imaging and dosimetric errors in 4D PET/CT-guided radiotherapy from patient-specific respiratory patterns: a dynamic motion phantom end-to-end study

Effective positron emission tomography / computed tomography (PET/CT) guidance in radiotherapy of lung cancer requires estimation and mitigation of errors due to respiratory motion. An end-to-end workflow was developed to measure patient-specific motion-induced uncertainties in imaging, treatment planning, and radiation delivery with respiratory motion phantoms and dosimeters. A custom torso phantom with inserts mimicking normal lung tissue and lung lesion was filled with [(18)F]FDG. The lung lesion insert was driven by six different patient-specific respiratory patterns or kept stationary. PET/CT images were acquired under motionless ground truth, tidal breathing motion-averaged (3D), and respiratory phase-correlated (4D) conditions. Target volumes were estimated by standardized uptake value (SUV) thresholds that accurately defined the ground-truth lesion volume. Non-uniform dose-painting plans using volumetrically modulated arc therapy were optimized for fixed normal lung and spinal cord objectives and variable PET-based target objectives. Resulting plans were delivered to a cylindrical diode array at rest, in motion on a platform driven by the same respiratory patterns (3D), or motion-compensated by a robotic couch with an infrared camera tracking system (4D). Errors were estimated relative to the static ground truth condition for mean target-to-background (T/Bmean) ratios, target volumes, planned equivalent uniform target doses, and 2%-2 mm gamma delivery passing rates. Relative to motionless ground truth conditions, PET/CT imaging errors were on the order of 10-20%, treatment planning errors were 5-10%, and treatment delivery errors were 5-30% without motion compensation. Errors from residual motion following compensation methods were reduced to 5-10% in PET/CT imaging, <5% in treatment planning, and <2% in treatment delivery. We have demonstrated that estimation of respiratory motion uncertainty and its propagation from PET/CT imaging to RT planning, and RT delivery under a dose painting paradigm is feasible within an integrated respiratory motion phantom workflow. For a limited set of cases, the magnitude of errors was comparable during PET/CT imaging and treatment delivery without motion compensation. Errors were moderately mitigated during PET/CT imaging and significantly mitigated during RT delivery with motion compensation. This dynamic motion phantom end-to-end workflow provides a method for quality assurance of 4D PET/CT-guided radiotherapy, including evaluation of respiratory motion compensation methods during imaging and treatment delivery.

Ventilatory depression in naive and tolerant rats in relation to plasma morphine concentration

1 The disappearance of morphine from specially formulated pellets containing 75 mg morphine base was measured for 10 days after they were implanted into adult rats; the morphine content decreased at a rate of 5 mg pellet daily.2 From the 2nd to the 6th day of implantation the plasma morphine concentration increased but by the 10th day had declined to only one half the concentration found on day 6.3 Six and 24 h after the pellets were removed from 6 day implanted animals the plasma concentration of morphine amounted to only one quarter to one sixth of the amount in the plasma, respectively, of animals with pellets intact.4 The pulmonary minute volume of naive and implanted rats was depressed by morphine in proportion to the plasma morphine concentration. Less depression was produced by intravenous morphine in the implanted rats than in the naive animals; the greater morphine tolerance displayed by the implanted animals could be shown by the third day of implantation and appeared to be maintained to the 10th day.5 The pulmonary minute volume of implanted rats on the 6th day was much less than the pulmonary minute volume of naive rats. Six and 24 h after the pellets were removed the pulmonary minute volume increased as the plasma morphine concentration decreased.6 The effects on the pulmonary minute volume produced by the slow release of morphine from the implanted pellets was not changed by the development of tolerance while the effects of morphine produced by rapid injection were diminished by the development of tolerance; the different effects of morphine are accordingly linked to the mode of administration.7 We conclude that the action of morphine on the pulmonary minute volume in tolerant rats following rapid injection is fundamentally different from its action following its slow release from implanted pellets, possibly due to differences in access to an undefined neuronal site.

Morphine depression and tolerance of nerve-induced parotid secretion

1 The nerve-induced secretion produced by the rat parotid gland is proportional to the frequency of stimulation. Morphine decreased the flow rate during stimulation at 2.5 and 5 Hz, but not at 20 Hz. This frequency-dependent action of morphine and was partially reversed by naloxone. 2 The secretion produced by the rat parotid gland during an intravenous infusion of acetylcholine was not diminished by morphine. Therefore, the action of morphine on nerve-induced secretion is most probably on the motor nerve terminals, which release acetylcholine. 3 Animals that had been implanted with morphine base pellets tolerated 4 times as much morphine as controls; after 6 days the minute ventilation was less depressed by graded doses of morphine than non-implanted controls. 4 Nerve-induced secretion in morphine-implanted animals was less depressed by morphine than control animals 6 and 24 h after the pellets were removed. The flow rates in the 6 h group treated with morphine were greater after naloxone than control (precipitated withdrawal) but at 24 h when withdrawal symptoms were no longer evident, naloxone produced only a slight reversal.