18F-FDG PET Assessment of Malignant Pleural Mesothelioma: Total Lesion Volume and Total Lesion Glycolysis-The Central Role of Volume

Our plain-English summary of 18F-FDG PET Assessment of Malignant Pleural Mesothelioma: Total Lesion Volume and Total Lesion Glycolysis-The Central Role of Volume, by J.C. Reynolds, R. Maass-Moreno, A. Thomas, et al (Journal of Nuclear Medicine, 2020).

The study

• Authors: J.C. Reynolds, R. Maass-Moreno, A. Thomas, A. Ling, E.B. Padiernos, S.M. Steinberg, R. Hassan
• Journal: Journal of Nuclear Medicine
• Published: 2020;61(11):1570-1575
• Cited by: 7 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Cancer survival is related to tumor volume. 18F-FDG PET measurement of tumor volume holds promise but is not yet a clinical tool. Measurements come in 2 forms: the first is total lesion volume (TLV) based on the number of voxels in the tumor, and the second is total lesion glycolysis (TLG), which is the TLV multiplied by the average SUL (i.e., SUV normalized for lean mass) of the tumor (SULaverage). In this study, we measured tumor volume in patients with malignant pleural mesothelioma (MPM). Methods: A threshold-based program in Interactive Data Language was developed to measure tumor volume in 18F-FDG PET images. Nineteen patients with MPM were studied before and after 2 cycles (6 wk) of chemoimmunotherapy. Measurements included TLV, TLG, the sum of the SULs in the tumor (SULtotal, a measure of total 18F-FDG uptake), and SULaverageResults: Baseline TLV ranged from 11 to 2,610 cm3 TLG ranged from 32 to 8,552 cm3 g/mL and correlated strongly with TLV. Although tumor volumes ranged over 3 orders of magnitude, SULaverage stayed within a narrow range of 2.4-5.3 units. Thus, TLV was the major component of TLG, whereas SULaverage was a minor component and was essentially constant. Further evaluation of SULaverage showed that in this cohort its 2 components, SULtotal and TLV, changed in parallel and were strongly correlated (r = 0.99, P < 0.01). Thus, whether the tumors were large or small, 18F-FDG uptake as measured by SULtotal was proportional to the TLV. Conclusion: TLG equals TLV multiplied by SULaverage, essentially TLV multiplied by a constant. Thus TLG, commonly considered a measure of metabolic activity in tumors, is also in this cohort a measure of tumor volume. The constancy of SULaverage is due to the fact that 18F-FDG uptake is proportional to tumor volume. Thus, in this study, 18F-FDG uptake was also a measure of volume.

© 2020 by the Society of Nuclear Medicine and Molecular Imaging.

In plain English

This study examined how PET scans using a radioactive sugar tracer (18F-FDG) measure malignant pleural mesothelioma. It used scans from 19 patients with stage III or IV disease in a phase 1 trial of the immunotoxin SS1P given with pemetrexed and cisplatin. Patients were scanned before treatment and after 6 weeks. A computer program measured tumor volume (total lesion volume, TLV) and total lesion glycolysis (TLG). TLG is commonly considered a measure of a tumor's metabolic activity. Before treatment, TLV ranged from 11 to 2610 cm3 and TLG from 32 to 8552 cm3-SUL, and the two were strongly correlated. Tumor sizes varied widely, but the average tracer uptake per image unit (voxel) stayed between 2.4 and 5.3. Total tracer uptake was linearly related to tumor volume. After 6 weeks of therapy, TLV and TLG each fell by a median of 75%. The authors concluded that in this group, TLG was also a measure of tumor volume. They noted that the data came from a single study with a small number of patients and that the findings should be tested in other cancers.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Exploratory imaging analysis of 18F-FDG PET scans from patients enrolled in a phase 1 treatment trial, with a separate accuracy check of the measuring program on 35 tumor nodules
• Who was studied: 19 patients (84% male, median age 67, range 52 to 76) with histologically confirmed malignant pleural mesothelioma, measurable stage III and IV disease, enrolled in a phase 1 study approved by the National Cancer Institute Institutional Review Board; dates not given
• Exposure: Asbestos exposure was not studied. Patients received the antimesothelin immunotoxin SS1P with pemetrexed and cisplatin and had 18F-FDG PET/CT scans at baseline and at 6 weeks.
• Main results:
  • Before treatment, total lesion volume (TLV) ranged from 11 to 2610 cm3, and total lesion glycolysis (TLG) ranged from 32 to 8552 cm3-SUL
  • After 6 weeks of therapy, TLV and TLG each fell by a median of 75%. TLV then ranged from 0 to 1460 cc and TLG from 0 to 4470 cm3-SUL.
  • TLG and TLV were strongly correlated at baseline and at 6 weeks, and so were their percent changes with therapy (Table 1 lists Spearman r of 0.99 at baseline, 0.99 at 6 weeks and 0.95 for change)
  • Average SUL per voxel (SUL-average) ranged only from 2.4 to 5.3. It averaged 3.64 (plus or minus 0.16) at baseline and 3.61 (plus or minus 0.16) at 6 weeks, p=0.87.
  • Total tracer uptake (SUL-total) was linearly related to tumor volume (regression on all baseline and 6-week values: r2 = 0.9575, p < .0001)
  • PET-measured TLV was correlated with modified RECIST CT measurements: r = 0.67 at baseline and r = 0.63 at 6 weeks (both p less than .01)
  • SUL-average values were not related to overall survival
• The authors' conclusion: The authors concluded that TLG and TLV were highly correlated and both measure tumor volume. In this mesothelioma study they found a cause-and-effect relationship between tumor volume and TLG. Whether these results hold in other tumors needs further study.
• Limitations the authors state:
  • The data came from a single study involving a small number of patients
  • Mesothelioma spreads over surfaces rather than forming a localized mass; whether this affected the results is unknown, and the findings should be tested with other cancers
  • Tumor types with higher metabolic activity may behave differently
  • The volume method used a liver-based background threshold, modified to use standard errors instead of standard deviations, which lowered the threshold

Topics

The National Library of Medicine indexes this study under subjects our site covers: Mesothelioma.

Medical terms in this study, explained in our Lexicon: Pleural Mesothelioma.

Related studies

• Volume-based parameter of 18)F-FDG PET/CT in malignant pleural mesothelioma: prediction of therapeutic response and prognostic implications — H.Y. Lee, S.H. Hyun, et al. (2010)
• Central photopenic lesions on FDG-PET scan in a patient with peripheral T cell lymphoma — A. Mavi, T. Dhuriraj, et al. (2008)
• The role of fluorodeoxyglucose-positron emission tomography/computed tomography in differentiating between benign and malignant adrenal lesions — P. Ozcan Kara, T. Kara, et al. (2011)
• Clinical value of fluorodeoxyglucose-positron emission tomography/computed tomography in differentiation of malignant mesothelioma from asbestos-related benign pleural disease: an observational pilot study — H. Yildirim, M. Metintas, et al. (2009)
• The association of 18F-FDG PET/CT parameters with survival in malignant pleural mesothelioma — A. Klabatsa, S. Chicklore, et al. (2014)
• Relationship between 18F-FDG uptake on positron emission tomography and molecular biology in malignant pleural mesothelioma — K. Kaira, M. Serizawa, et al. (2012)

Browse more research in Journal of Nuclear Medicine, or return to medical research.