The contribution of integrated PET/CT to the evolving definition of treatment volumes in radiation treatment planning in lung cancer
ABSTRACT Positron emission tomography (PET) with the glucose analog [18F]fluro-2-deoxy-D-glucose (FDG) has been accepted as a valuable tool for the staging of lung cancer, but the use of PET/CT in radiation treatment planning is still not yet clearly defined. By the use of (PET/computed tomography (CT) images in treatment planning, we were able to define a new gross treatment volume using anatomic biologic contour (ABC), delineated directly on PET/CT images. We prospectively addressed three issues in this study: (1) How to contour treatment volumes on PET/CT images, (2) Assessment of the degree of correlation between CT-based gross tumor volume/planning target volume (GTV/PTV) (GTV-CT and PTV-CT) and the corresponding PET/CT-based ABC treatment volumes (GTV-ABC and PTV-ABC), (3) Magnitude of interobserver (radiation oncologist planner) variability in the delineation of ABC treatment volumes (using our contouring method).
Nineteen patients with Stages II-IIIB non-small-cell lung cancer were planned for radiation treatments using a fully integrated PET/CT device. Median patient age was 74 years (range: 52-82 years), and median Karnofsky performance status was 70. Thermoplastic or vacuum-molded immobilization devices required for conformal radiation therapy were custom fabricated for the patient before the injection of f-FDG. Integrated, coregistered PET/CT images were obtained and transferred to the radiation planning workstation (Xeleris). While the PET data remained obscured, a CT-based gross tumor volume (GTV-CT) was delineated by two independent observers. The PTV was obtained by adding a 1.5-cm margin around the GTV. The same volumes were recontoured using PET/CT data and termed GTV-ABC and PTV-ABC, correspondingly.
We observed a distinct "halo" around areas of maximal standardized uptake value (SUV). The halo was identified by its distinct color at the periphery of all areas of maximal SUV uptake, independent of PET/CT gain ratio; the halo had an SUV of 2 +/- 0.4 and thickness of 2 mm +/- 0.5 mm. Whereas the center of our contoured treatment volume expressed the maximum SUV level, a steady decline of SUV was noted peripherally until SUV levels of 2 +/- 0.4 were reached at the peripheral edge of our contoured volume, coinciding with the observed halo region. This halo was always included in the contoured GTV-ABC. Because of the contribution of PET/CT to treatment planning, a clinically significant (> or =25%) treatment volume modification was observed between the GTV-CT and GTV-ABC in 10/19 (52%) cases, 5 of which resulted in an increase in GTV-ABC volume vs. GTV-CT. The modification of GTV between CT-based and PET/CT-based treatment planning resulted in an alteration of PTV exceeding 20% in 8 out of 19 patients (42%). Interobserver GTV variability decreased from a mean volume difference of 28.3 cm3 (in CT-based planning) to 9.12 cm3 (in PET/CT-based planning) with a respective decrease in standard deviation (SD) from 20.99 to 6.47. Interobserver PTV variability also decreased from 69.8 cm3 (SD +/- 82.76) in CT-based planning to 23.9 cm3 (SD +/- 15.31) with the use of PET/CT in planning. The concordance in treatment planning between observers was increased by the use of PET/CT; 16 (84%) had < or =10% difference from mean of GTVs using PET/CT compared to 7 cases (37%) using CT alone (p = 0.0035). Conclusion: Position emission tomography/CT-based radiation treatment planning is a useful tool resulting in modification of GTV in 52% and improvement of interobserver variability up to 84%. The use of PET/CT-based ABC can potentially replace the use of GTV. The anatomic biologic halo can be used for delineation of volumes.
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ABSTRACT: In the thorax, the extent of tumor may be more accurately defined with the addition of (18)F-fluorodeoxyglucose (FDG) positron emission tomography (PET) to computed tomography (CT). This led to the increased utility of FDG-PET or PET/CT in the treatment planning of radiotherapy for non-small cell lung cancer (NSCLC). The inclusion of FDG-PET information in target volume delineation not only improves tumor localization but also decreases the amount of normal tissue included in the planning target volume (PTV) in selected patients. Therefore, it has a critical role in image-guided radiotherapy (IGRT) for NSCLC. In this review, the impact of FDG-PET on target volume delineation in radiotherapy for NSCLC, which may increase the possibility of safe dose escalation with IGRT, the commonly used methods for tumor target volume delineation FDG-PET for NSCLC, and its impact on clinical outcome will be discussed.Frontiers in Oncology 10/2014; 4:273. DOI:10.3389/fonc.2014.00273
British Journal of Radiology 11/2005; Supplement_28(1):18-32. DOI:10.1259/bjr/72059318 · 1.53 Impact Factor
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ABSTRACT: Radiotherapy is used for inoperable lung cancers, sometimes in association with chemotherapy. Outcomes of conventional radiotherapy are disappointing. New techniques improve adaptation to tumour volume, decrease normal tissue irradiation and lead to increasing tumour dose with the opportunity for improved survival. With intensity-modulated radiation therapy, isodoses can conform to complex volumes. It is widely used and seems to be indicated in locally advanced stages. Its dosimetric improvements have been demonstrated but outcomes are still heterogeneous. Stereotactic radiotherapy allows treatment of small volumes with many narrow beams. Dedicated devices or appropriate equipment on classical devices are needed. In early stages, its efficacy is comparable to surgery with an acceptable toxicity. Endobronchial brachytherapy could be used for early stages with specific criteria. Hadrontherapy is still experimental regarding lung cancer. Hadrons have physical properties leading to very accurate dose distribution. In the rare published studies, toxicities are roughly lower than others techniques but for early stages its effectiveness is not better than stereotactic radiotherapy. These techniques are optimized by metabolic imaging which precisely defines the target volume and assesses the therapeutic response; image-guided radiation therapy which allows a more accurate patient set up and by respiratory tracking or gating which takes account of tumour respiratory motions.Cancer/Radiothérapie 10/2014; DOI:10.1016/j.canrad.2014.06.017 · 1.11 Impact Factor