Comparison of CT and integrated PET-CT based radiation therapy planning in patients with malignant pleural mesothelioma

Our plain-English summary of Comparison of CT and integrated PET-CT based radiation therapy planning in patients with malignant pleural mesothelioma, by B. Pehlivan, E. Topkan, C. Onal, et al (Radiation Oncology, 2009).

The study

• Authors: B. Pehlivan, E. Topkan, C. Onal, G.N. Nursal, O. Yuksel, Y. Dolek, M.N. Yavuz, A.A. Yavuz
• Journal: Radiation Oncology
• Published: 2009;4:35
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: When combined with adequate tumoricidal doses, accurate target volume delineation remains to be the one of the most important predictive factors for radiotherapy (RT) success in locally advanced or medically inoperable malignant pleural mesothelioma (MPM) patients. Recently, 18-fluorodeoxyglucose positron emission tomography (PET) has demonstrated significant improvements in diagnosis and accurate staging of MPM. However, role of additional PET data has not been studied in RT planning (RTP) of patients with inoperable MPM or in those who refuse surgery. Therefore, we planned to compare CT with co-registered PET-CT as the basis for delineating target volumes in these patients group.

Methods: Retrospectively, the CT and co-registered PET-CT data of 13 patients with histologically proven MPM were utilized to delineate target volumes separately. For each patient, target volumes (gross tumor volume [GTV], clinical target volume [CTV], and planning target volume [PTV]) were defined using the CT and PET-CT fusion data sets. The PTV was measured in two ways: PTV1 was CTV plus a 1-cm margin, and PTV2 was GTV plus a 1-cm margin. We analyzed differences in target volumes.

Results: In 12 of 13 patients, compared to CT-based delineation, PET-CT-based delineation resulted in a statistically significant decrease in the mean GTV, CTV, PTV1, and PTV2. In these 12 patients, mean GTV decreased by 47.1% +/- 28.4%, mean CTV decreased by 38.7% +/- 24.7%, mean PTV1 decreased by 31.1% +/- 23.1%, and mean PTV2 decreased by 40.0% +/- 24.0%. In 4 of 13 patients, hilar lymph nodes were identified by PET-CT that was not identified by CT alone, changing the nodal status of tumor staging in those patients.

Conclusion: This study demonstrated the usefulness of PET-CT-based target volume delineation in patients with MPM. Co-registration of PET and CT information reduces the likelihood of geographic misses, and additionally, significant reductions observed in target volumes may potentially allow escalation of RT dose beyond conventional limits potential clinical benefits in tumor control rates, which needs to be tested in future studies.

In plain English

This retrospective planning study did not examine asbestos exposure. The authors used scans from 13 patients with malignant pleural mesothelioma who were not candidates for curative surgery, either for medical reasons or because they refused it, and who had received chest radiation with palliative intent. For each patient, the tumor and treatment areas were outlined twice, once on CT alone and once on combined PET-CT, and the resulting volumes were compared. In 12 of the 13 patients, the PET-CT outlines were significantly smaller. In those 12 patients, the mean gross tumor volume fell by 47.1%, with a standard deviation of 28.4%. In one patient the volumes grew, because PET detected an involved lymph node that was not visible on CT. PET-CT showed hilar lymph nodes missed by CT in 4 of 13 patients, which changed their lymph node stage. In 3 patients, PET-CT also showed spread below the diaphragm that CT did not show. The authors concluded that PET-CT-based outlining was useful, but said more clinical studies are needed before firmer conclusions can be drawn.

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: Retrospective treatment-planning (target volume delineation) comparison study
• Who was studied: 13 patients with histologically diagnosed malignant pleural mesothelioma (MPM) at Baskent University, Adana, Turkey. They were not candidates for curative resection because of medical reasons or their own refusal, and had been treated with chest irradiation with palliative intent. 4 of the 13 were women. Median age was 50 years (range 38 to 74). Study dates were not given.
• Exposure: No asbestos or fiber exposure was studied. The study compared radiotherapy target volumes outlined on CT alone with those outlined on combined PET-CT.
• Main results:
  • In 12 of 13 patients, PET-CT-based outlining gave statistically significantly smaller volumes than CT. In these 12 patients, the mean decreases (mean plus or minus standard deviation) were: gross tumor volume (GTV) 47.1% plus or minus 28.4%; clinical target volume (CTV) 38.7% plus or minus 24.7%; planning target volume 1 (PTV1) 31.1% plus or minus 23.1%; and PTV2 40.0% plus or minus 24.0%.
  • Across all 13 patients (Table 2), mean GTV was 788.9 cc on CT, with a standard deviation of 845.1 cc. On PET-CT it was 441.4 cc, with a standard deviation of 420.0 cc (P = 0.01).
  • In the 12 patients, the reductions were due solely to smaller primary tumor volumes on PET-CT. PET data did not lead to any lymph nodes being excluded.
  • In one patient, PET-CT volumes were larger than CT volumes: by 19% (GTV), 2% (CTV), 10% (PTV1) and 15% (PTV2). The increase was due to an additional involved lymph node detected by PET that was not apparent on CT.
  • In 4 of 13 patients (31%), PET-CT showed increased uptake in hilar lymph nodes that did not appear on CT, which changed the N (lymph node) stage in those 4 patients.
  • In 3 patients (23%), PET-CT showed spread of disease below the diaphragm that CT did not show.
• The authors' conclusion: The authors concluded that PET-CT-based target volume outlining was useful in patients with MPM. They said its largest potential benefit may be fewer geographic misses than with CT-based planning, but that more clinical studies are required.
• Limitations the authors state:
  • The clinic had no helical tomotherapy unit or similar volumetric arc technology. This limited the authors' ability to create clinically relevant and acceptable treatment plans, so they compared only the outlined target volumes.
  • The authors said the study should be regarded as baseline data for further clinical and dosimetric studies, not as a guide.
  • The authors said more clinical studies are required before more definite conclusions can be reached.

Topics

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

Medical terms in this study, explained in our Lexicon: PET-CT, Pleural Mesothelioma, Staging, Hilar Lymph Nodes.

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