A Prospective Study of 18FDG-PET With CT Coregistration for Radiation Treatment Planning of Lymphomas and Other Hematologic Malignancies

Abstract

Purpose This prospective single-institution study examines the impact of positron emission-tomography (PET) using 2-[18F] fluoro-2-deoxyglucose and CT scan radiation treatment planning (TP) on target volume definition in lymphoma. Methods and Materials 118 patients underwent PET/CT TP during 6/2007-5/2009. Gross tumor volume (GTV) was contoured on CT-only and PET/CT studies by radiation oncology (RO) and nuclear medicine (NM) for 95 patients with positive PET scans. Treatment plans and dose-volume histograms were generated for CT-only and PET/CT for 95 evaluable sites. Paired t-test statistics and Pearson correlation coefficients were used for analysis. Results 70 (74%) patients had non-Hodgkin lymphoma, 10 (11%) had Hodgkin lymphoma, 12 (10%) plasma-cell neoplasm, and 3 (3%) other hematologic malignancies. Forty-three (45%) presented with relapsed/refractory disease. Forty-five (47%) received no prior chemotherapy. The addition of PET increased GTV as defined by RO in 38 patients (median, 27%; range, 5-70%) and decreased GTV in 41 (median, 39.5%; range, 5-80%). The addition of PET increased GTV as defined by NM in 27 patients (median, 26.5%; range, 5-95%) and decreased GTV in 52 (median, 70%; range, 5-99%). Intra-observer correlation between CT-GTV and PET-GTV was higher for RO than for NM (0.94, P < .01 vs. 0.89, P < .01). Based on Bland-Altman plots, the PET-GTVs defined by RO were larger than NM. On evaluating clinical TPs, only four (4%) patients had inadequate target coverage (D95<95%) of the PET-GTV defined by NM. Conclusions Significant differences between RO and NM volumes were identified when PET was co-registered to CT for radiation planning. Despite this, the PET-GTV defined by RO and NM received acceptable prescription dose in nearly all patients. However, given the potential for a marginal miss, consultation with an experienced PET reader is highly encouraged when delineating PET/CT volumes, particularly for questionable lesions and to assure complete and accurate target volume coverage.

Dosimetric impact of amino acid positron emission tomography imaging for target delineation in radiation treatment planning for high-grade gliomas

“…From a clinical toxicity standpoint, reporting of differences in PTV instead of GTV is a more clinically meaningful interpretation of observed differences. This was consistent with prior reports of similar studies utilizing 18 F-Fluoro-ethyl-tyrosine (FET) based RT contouring [13] , [14] , [15] .…”

Involved Site Radiation Therapy in Adult Lymphomas: An Overview of International Lymphoma Radiation Oncology Group Guidelines

“…5,16 18-Fluorodeoxyglucose (FDG) positron emission tomography (PET) is critical for accurate staging and may modify RT volumes. [17][18][19][20][21][22][23][24][25] PET does not obviate the need for contrast CT to delineate (for example) mediastinal lymphadenopathy, or magnetic resonance imaging (MRI) to define head and neck involvement. Smallvolume disease not evident on PET may be visible on CT or MRI.…”

The Optimal Use of Imaging in Radiation Therapy for Lymphoma: Guidelines from the International Lymphoma Radiation Oncology Group (ILROG)

“…47 Another study evaluated 95 treatment sites in both HL and non-Hodgkin lymphoma and found similar results. 40 In summary, these studies concluded that the incorporation of FDG-PET has a significant impact on target definition in ISRT and INRT volumes for both HL and non-HL.…”

“…As discussed earlier, extranodal marginal zone lymphomas, small lymphocytic lymphoma, and cutaneous T cell lymphomas have variable FDG uptakes, 3 and FDG-PET/CT might underestimate the extent of disease or miss it altogether. [40][41][42][43][44] Some anatomic sites have high level of physiologic FDG uptake, making visualization of lymphoma more difficult, such as primary central nervous system lymphoma (FDG uptake in normal brain tissue) and bowel lymphoma 45 (FDG uptake in normal bowel). Alternative imaging modalities are discussed later.…”