PMC6775241_01
Staging CT scans and PET imaging of the primary tumor and metastatic lesion prior to radiation therapy. (A) Coronal section of the initial CT of the abdomen/pelvis with contrast identifying a large soft-tissue mass in the right retroperitoneal space overlying the right psoas muscle with extension into the right hemi-pelvis. (B) Coronal section of a CT of the abdomen/pelvis approximately 2 months after the initial diagnosis demonstrating interval growth of the now inoperable retroperitoneal mass. (C) Coronal PET/CT maximum intensity projection (MIP) performed approximately 3 months after initial diagnosis, demonstrating the large FDG-avid mass in the right retroperitoneal space (blue arrow). FDG-avidity in the inferior aspect of the image in the figure corresponds to physiological uptake in the urinary bladder (yellow arrow). (D) Coronal PET/CT MIP from the same study as in C demonstrating a non-enlarged FDG-avid lymph node in the left supraclavicular nodal station. Blue arrows, primary mass; yellow arrow, physiologic FDG uptake.
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CT abdomen/pelvis identified a 17.5 x 8.8 x 5.2 cm lobulated retroperitoneal soft tissue mass extending into the right pelvis without evidence of metastases (Figure 1A). CT-guided core needle biopsy demonstrated a high-grade, poorly differentiated neoplasm (Supplemental Figure 1). CT chest/abdomen/pelvis identified primary mass progression to 20.5 x 10.3 x 7.1 cm and new right common iliac lymphadenopathy without metastases (Figure 1B). CT-guided re-biopsy and immunohistochemistry (IHC) demonstrated unclassified round cell sarcoma with INI1 loss (Supplemental Figures 1B-F). PET/CT identified a bulky centrally necrotic right retroperitoneal soft tissue mass (SUVmax 21.4; liver SUVmean 2.3) extending into the right hemipelvis, a soft tissue nodule medial to the right psoas muscle (SUVmax 16.4), several non-enlarged FDG-avid paracaval lymph nodes (SUVmax 13.5), and faintly metabolic right external iliac and inguinal lymph nodes (Figure 1C). A single FDG-avid, non-enlarged left supraclavicular lymph node (SUVmax 8.6) was identified but not amenable to biopsy (stage IV: cT4N1M1; Figure 1D).
PET/CT of the primary retroperitoneal sarcoma with palliative proton radiotherapy plan dose distribution. (A-C) Representative coronal, axial, and sagittal images from the CT simulation for radiation treatment planning fused to the staging PET scan showing the clinical target volume (CTV-orange) and planning target volume (PTV-aqua) encompassing the right retroperitoneal FDG-avid disease. The CTV encompassed the FDG-avid sites of disease with a 0.5 cm expansion to create the PTV. (D-F) Representative coronal, axial, and sagittal images from the radiation treatment plan showing the dose color wash from right anterior and right posterior oblique beams. Dose color wash ranges from 2 CGE (dark blue) to >50 CGE (red) without significant exit dose beyond the 2 CGE isodose. Treatment was delivered using right anterior oblique and right posterior oblique passively scattered proton beams from a MEVION S250 unit.
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Palliative proton radiotherapy was recommended to the primary mass and adjacent FDG-contiguous lymphadenopathy [50 Cobalt Gray Equivalents (CGE)/25 fractions, 2 CGE/fraction; Mevion S250, Mevion Medical Systems, Inc., Littleton, MA] due to the tumor location, size, and close proximity to the right kidney and small bowel (Figure 2). CT-guided needle biopsy of the left supraclavicular lymph node revealed metastatic disease from primary RPS (Supplemental Figure 2). CD4 and CD8 IHC on the pre-radiation RPS biopsy demonstrated TILs (CD4 10% positive, CD8 2% positive; 5:1 ratio) arranged in scattered nodules with patchy single-cell infiltration throughout, with similar results found for the non-irradiated left supraclavicular lymph node biopsied 1 month after completing radiation (CD4 10% positive, CD8 2% positive; 5:1 ratio; Supplemental Figures 2, 3).
Maximum Intensity Projections (MIP) from PET/CT scans performed 1 month before, 1, and 5 months after radiation treatment. (A) PET/CT prior to radiation treatment demonstrating a large primary retroperitoneal mass, lesion superior to the mass at approximately T12 and left supraclavicular mass that were not included in the radiation treatment plan (blue arrows). (B) PET/CT performed 1.5 months after completing radiation treatment to the primary retroperitoneal mass demonstrating disease progression at sites outside of the radiation treatment field (red arrows). (C) PET/CT performed 5 months after completing radiation treatment demonstrating regression of disease at non-irradiated sites. (D) Representative inverted coronal image from the patient's CT simulation for radiation treatment showing radiation dose color wash covering the primary mass. Note that disease superior to the mass adjacent to the right kidney and left supraclavicular region were not included in this plan. Dose range: blue >= 2 CGE, green >= 25 CGE, red >= 50 CGE. Yellow arrows indicate physiologic uptake in the urinary bladder as in Figure 1.
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T12-L1-adjacent retroperitoneal mass (1.4 cm; SUVmax 21.9, prior SUVmax 10.9), and new FDG-avid nodal metastases (RECIST 1.1; Figure 3B). The primary RPS decreased in size and FDG-avidity (20.5 x 10.3 cm to 8.7 x 4.5 cm; SUVmax 20 to 7.1; Figure 3B). The patient reported significant improvement in right lower extremity edema, pain, range of motion, and performance status. PET/CT performed 5 months after radiation demonstrated near complete metabolic response of the biopsy-proven left supraclavicular metastasis (SUVmax 3.2, previously 18.1; liver SUVmean 2.5), and size reduction to <10 mm, with residual focal FDG avidity in the right retroperitoneum (SUVmax 4.4, previously 6.5) consistent with post-radiation changes vs. residual disease without other abnormal metabolic activity (Figure 3C). CD4 and CD8 IHC on the pre-radiation RPS biopsy demonstrated TILs (CD4 10% positive, CD8 2% positive; 5:1 ratio) arranged in scattered nodules with patchy single-cell infiltration throughout, with similar results found for the non-irradiated left supraclavicular lymph node biopsied 1 month after completing radiation (CD4 10% positive, CD8 2% positive; 5:1 ratio; Supplemental Figures 2, 3).
CT chest/abdomen/pelvis scans from post-radiation disease progression through continued interval follow up to monitor late responses to radiation therapy and to assess for recurrence. Representative coronal images from interval CT scans of the pelvic mass (left column- blue arrow), para-esophageal (middle column- blue arrow), and left biopsy-proven supraclavicular lymph node (right column- blue arrow) across several interval CT scans. (A-C) 1 month post-radiation without contrast. (D-F) 5 months post-radiation with contrast, (G-I) 7 months post-radiation with contrast, (J-L) 17 months post-radiation with contrast. Note imaging appearance of a stable, regressed right retroperitoneal mass (D, blue arrow), regression of the enlarged para-esophageal lymph node (E, blue arrow), and regression of the left supraclavicular lymph node noted at 5 months post-radiation (F, blue arrow). A previously identified enlarged left thyroid nodule is also present across the scans (C,F,I,L, yellow arrow) and is not consistent with metastatic disease.
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The patient continued to improve, with interval imaging at 6, 10, 13, and 17 months post-radiotherapy demonstrating residual RPS/scar tissue and resolved metastases (Figure 4).