胰腺癌平扫或强化氟脱氧葡萄糖PET-CT图像靶区勾画研究

目的 探讨平扫或强化氟脱氧葡萄糖(FDG) PET-CT图像在胰腺癌靶区勾画中的作用。方法 回顾分析本院 2008—2009年间 21例局部晚期不可切除及术后复发胰腺癌患者资料,以相同固定体位分别行平扫CT、PET,其中 11例之后行强化CT。将扫描数据输入治疗计划系统,行平扫或强化CT、PET图像融合,分别依据强化CT、平扫CT、平扫PET及平扫或强化PET-CT融合图像勾画大体肿瘤体积(GTV),并用配对或成组t检验比较不同图像GTV大小。结果 21例患者平扫 GTV_CT、平扫 GTV_PET、平扫或强化 GTV_PET-CT平均值分别为76.9、47.0、44.5 cm³,平扫 GTV_PET-CT平均体积明显小于平扫GTV_CT (z=－3.91,P=0.000)。11例强化 GTV_CT、强化 GTV_PET、强化 GTV_PET-CT平均体积分别为64.1、45.1、49.3 cm³,强化 GTV_PET-CT平均体积明显小于强化GTV_CT (z=－2.13,P=0.033),强化 GTV_PET-CT平均体积与平扫 GTV_PET-CT相似(z=－0.80,P=0.424)。结论 PET和强化或平扫CT的融合图像能提高不可切除胰腺癌靶区勾画准确性,有望降低放疗不良反应。     

F-fluorocholine PET-guided target volume delineation techniques for partial prostate re-irradiation in local recurrent prostate cancer

Background and purpose

We evaluate the contribution of ¹⁸F-choline PET/CT in the delineation of gross tumour volume (GTV) in local recurrent prostate cancer after initial irradiation using various PET image segmentation techniques.

Materials and methods

Seventeen patients with local-only recurrent prostate cancer (median = 5.7 years) after initial irradiation were included in the study. Rebiopsies were performed in 10 patients that confirmed the local recurrence. Following injection of 300 MBq of ¹⁸F-fluorocholine, dynamic PET frames (3 min each) were reconstructed from the list-mode acquisition. Five PET image segmentation techniques were used to delineate the ¹⁸F-choline-based GTVs. These included manual delineation of contours (GTV_man) by two teams consisting of a radiation oncologist and a nuclear medicine physician each, a fixed threshold of 40% and 50% of the maximum signal intensity (GTV_40% and GTV_50%), signal-to-background ratio-based adaptive thresholding (GTV_SBR), and a region growing (GTV_RG) algorithm. Geographic mismatches between the GTVs were also assessed using overlap analysis.

Results

Inter-observer variability for manual delineation of GTVs was high but not statistically significant (p = 0.459). In addition, the volumes and shapes of GTVs delineated using semi-automated techniques were significantly higher than those of GTVs defined manually.

Conclusions

Semi-automated segmentation techniques for ¹⁸F-choline PET-guided GTV delineation resulted in substantially higher GTVs compared to manual delineation and might replace the latter for determination of recurrent prostate cancer for partial prostate re-irradiation. The selection of the most appropriate segmentation algorithm still needs to be determined.     

Current status of PSMA PET imaging in prostate cancer

The past decade has witnessed the rising popularity and acceptance of molecular definitions on disease management. Prostate‐specific membrane antigen (PSMA), in light of its molecular nature and cytokinetic properties, has rapidly become the target for development of a variety of functional tracers for PET/CT evaluation of prostate cancer. The most commonly used PSMA‐binding analog is ⁶⁸Ga‐labeled PSMA‐11, which is now widely applied in both research and clinical settings. Literature data in the recent years have been enriched by a number of meta‐analyses and systemic reviews on the evolving role of PSMA PET in primary diagnosis, staging, detection of biochemical recurrence after primary cancer treatment, identification, and significance of oligometastasis, as well as in restaging and treatment monitoring. Being a highly sensitive and reasonably specific molecular tracer, PSMA‐binding analogs have a high potential to possess the majority of imaging characteristics required for a variety of management decisions in prostate malignancy.     

68Ga-PSMA PET/CT Replacing Bone Scan in the Initial Staging of Skeletal Metastasis in Prostate Cancer: A Fait Accompli?

Purpose

⁶⁸Ga ligands targeting prostate-specific membrane antigen (PSMA) are rapidly emerging as a significant step forward in the management of prostate cancer. PSMA is a type II transmembrane protein with high expression in prostate carcinoma cells. We prospectively evaluated the use of ⁶⁸Ga-PSMA positron emission tomography/computed tomography (PET/CT) in patients with prostate cancer and compared the results to those for technetium-99m (^99mTc)-10-metacyloyloxydecyl dihydrogen phosphate (MDP) bone scintigraphy (BS).

Functional imaging of neuroendocrine tumors with combined PET/CT using 68Ga-DOTATATE (DOTA-DPhe1,Tyr3-octreotate) and 18F-FDG

BACKGROUND.

The aim was to assess the relevant distribution of the novel PET tracer ⁶⁸Ga‐DOTATATE in neuroendocrine tumors (NETs) with combined positron emission tomography / computed tomography (PET/CT) and compare its performance with that of ¹⁸F‐FDG PET/CT.

METHODS.

The imaging findings with ⁶⁸Ga‐DOTATATE and ¹⁸F‐FDG on 38 consecutive patients with a diagnosis of primary or recurrent NET were compared and correlated with tumor grade on histology based on ki67 and mitotic index.

RESULTS.

The sensitivity of ⁶⁸Ga‐DOTATATE PET/CT was 82% (31 of 38) and that of ¹⁸F‐FDG PET/CT was 66% (25 of 38). The sensitivity of combined ⁶⁸Ga‐DOTATATE and ¹⁸F‐FDG PET/CT was 92% (35 of 38). There was greater uptake of ⁶⁸Ga‐DOTATATE than ¹⁸F‐FDG in low‐grade NET (median SUV 29 vs 2.9, P < .001). In high‐grade NET there was higher uptake of ¹⁸F‐FDG over ⁶⁸Ga‐DOTATATE (median SUV 11.7 vs 4.4, P = .03). There was a significant correlation with predominant tumor uptake of ⁶⁸Ga‐DOTATATE or ¹⁸F‐FDG and tumor grade on histology (P < .0001).

CONCLUSIONS.

⁶⁸Ga‐DOTATATE PET/CT is a useful novel imaging modality for NETs and is superior to ¹⁸F‐FDG for imaging well‐differentiated NET. Functional imaging with both ⁶⁸Ga‐DOTATATE and ¹⁸F‐FDG has potential for a more comprehensive tumor assessment in intermediate‐ and high‐grade tumors. Cancer 2008. ©2008 American Cancer Society.     

Flourodeoxyglucose positron emission tomography scan may be helpful in the case of ductal variant prostate cancer when prostate specific membrane antigen ligand positron emission tomography scan is negative

Gallium‐68 prostate specific membrane antigen ligand (Ga‐68 PSMA) positron emission tomography/computed tomography (PET/CT) scanning is emerging as a useful imaging modality for the staging of suspected and known recurrent or metastatic prostate cancer and in staging of newly diagnosed higher grade prostate cancer. However, we have observed at our institution that in some cases of the more aggressive ductal variant, Ga‐68 PSMA uptake has sometimes been poor compared with prominent 18‐flourodeoxyglucose (F‐18 FDG) avidity seen in F‐18 FDG PET/CT, which would suggest that FDG PET/CT scans are important in staging of ductal pattern prostate cancer.     

Gallium‐68 PSMA uptake in adrenal adenoma

Gallium‐68 (Ga‐68) labelled prostate‐specific membrane antigen (PSMA) imaging by positron emission tomography (PET) has emerged as a promising tool for staging of prostate cancer and restaging of disease in recurrence or biochemical failure after definitive treatment of prostate cancer. Ga‐68 PSMA PET produces high target‐to‐background images of prostate cancer and its metastases which are reflective of the significant overexpression of PSMA in these cells and greatly facilitates tumour detection. However, relatively little is known about the PSMA expression of benign neoplasms and non‐prostate epithelial malignancies. This is a case report of PSMA uptake in an adrenal adenoma incidentally discovered on PET performed for restaging of biochemically suspected prostate cancer recurrence. With the increasing use of PSMA PET in the management of prostate cancer – and the not infrequent occurrence of adrenal adenomas – the appearance of low‐ to moderate‐grade PSMA uptake in adrenal adenomas should be one with which reporting clinicians are familiar.     

Clinical utility of integrated positron emission tomography/computed tomography imaging in the clinical management and radiation treatment planning of locally advanced rectal cancer

PurposeThe role of 18F-fluorodeoxyglucose positron emission tomography-computed tomography (FDG-PET/CT) in the staging and radiation treatment planning of locally advanced rectal cancer is ill defined. We studied the role of integrated PET/CT in the staging, radiation treatment planning, and use as an imaging biomarker in rectal cancer patients undergoing multimodality treatment.Methods and materialsThirty-four consecutive patients with T3-4N0-2M0-1 rectal adenocarcinoma underwent FDG-PET/CT scanning for staging and radiation treatment planning. Planned clinical management was compared before and after the addition of PET/CT information. Three radiation oncologists independently delineated CT-based gross tumor volumes (GTVCT) using clinical information and CT imaging data, as well as gradient autosegmented PET/CT-based GTVs (GTV_PETCT). The mean GTV, interobserver concordance index (CCI), and proximal and distal margins were compared. The maximal standardized uptake value (SUVmax), metabolic tumor volume (MTV), and dual-time point PET parameters were correlated with clinicopathologic endpoints.ResultsClinical management was altered by PET/CT in 18% (n = 6) of patients with clinical upstaging in 6 patients and radiation treatment planning altered in 5 patients. Of the 30 evaluable preoperative patients, the mean GTV_PETCT was significantly smaller than the mean GTV_CT volumes: 88.1 versus 102.8 cc (P = .03). PET/CT significantly increased interobserver CCI in contouring GTV compared with CT only-based contouring: 0.56 versus 0.38 (P < .001). The proximal and distal margins were altered by a mean of 0.4 ± 0.24 cm and −0.25 ± 0.18 cm, respectively. MTV was inversely associated with 2-year progression-free survival (PFS) and overall survival (OS): smaller MTVs (< 33 cc) had superior 2-year PFS (86% vs 60%, P = .04) and OS (100% vs 45%, P < .01) compared with larger MTVs (> 33 cc). SUVmax and dual-time point PET parameters did not correlate with any endpoints.ConclusionsFDG-PET/CT imaging impacts overall clinical management and is useful in the radiation treatment planning of rectal cancer patients by decreasing interobserver variability in contouring target boost volumes. Pretreatment MTV may provide useful prognostic information and requires further study.     

Small Molecule,Multimodal, [18F]-PET and Fluorescence Imaging Agent Targeting Prostate-Specific Membrane Antigen: First-in-Human Study

BackgroundA first-in-human study of [¹⁸F]-BF3-Cy3-ACUPA, a small-molecule imaging agent that can be unimolecularly both positron emitting and fluorescent, is conducted to determine its safety, biodistribution, radiation dosimetry, feasibility in tumor detection by preoperative positron emission tomography (PET), as well as its intraoperative fluorescence imaging utility in patients with prostate-specific membrane antigen positive (PSMA⁺) tumors.MethodsTen patients aged 66 ± 7 years received a 6.5 ± 3.2 mCi intravenous injection of [¹⁸F]-BF3-Cy3-ACUPA and underwent PET/computed tomography (CT) imaging. Radiation dosimetry of [¹⁸F]-BF3-Cy3-ACUPA, normal organ biodistribution, and tumor uptakes were examined. Two patients were prescheduled for radical prostatectomy (RP) with extended pelvic lymphadenectomy approximately 24 hours following [¹⁸F]-BF3-Cy3-ACUPA injection and imaging. Without reinjection, intraoperative fluorescence imaging was performed on freshly excised tissue during RP. Frozen sections of excised tissue during RP were submitted for confirmatory histopathology and multiphoton fluorescence and brightfield microscopy.ResultsAbsorbed doses by organs including the kidneys and salivary glands were similar to 68Ga-PSMA-11 imaging. [¹⁸F]-BF3-Cy3-ACUPA physiologic radiotracer accumulation and urinary/biliary excretion closely resembled the distribution of other published PSMA tracers including [¹⁸F]-JK-PSMA-7, [¹⁸F]-PSMA-1007, [¹⁸F]-DCFPyL, and [¹⁸F]-DCFBC. ¹⁹F-BF3-Cy3-ACUPA was retained in PSMA⁺ cancer tissues in patients for at least 24 hours, allowing for intraoperative fluorescence assessment of the prostate and of the embedded prostate cancer without contrast reinjection. After 24 hours, the imaging agent mostly decayed or cleared from the blood pool. Preoperative PET and fluorescence imaging findings were confirmed with final histopathology and multiphoton microscopy.ConclusionOur first-in-human results demonstrate that [¹⁸F]-BF3-Cy3-ACUPA is safe and feasible in humans. Larger trials with this PET tracer are expected to further define its capabilities and its clinical role in the management of PSMA⁺ tumors, especially in prostate cancer.     

Special issue “The advance of solid tumor research in China”: 68Ga-PSMA-11 PET/CT for evaluating primary and metastatic lesions in different histological subtypes of renal cell carcinoma

Conventional imaging examinations are not sensitive enough for the early detection of recurrent or metastatic lesions in renal cell carcinoma (RCC) patients. We aimed to explore the role of ⁶⁸Ga-prostate specific membrane antigen (PSMA)-11 positron emission tomography (PET)/computed tomography (CT) in the detection of primary and metastatic lesions in such patients. We retrospectively analyzed 50 RCC patients who underwent ⁶⁸Ga-PSMA-11 PET/CT from November 2017 to December 2020. We observed a higher median accuracy and tumor-to-background maximum standard uptake value (SUV_max) ratio (TBR) of ⁶⁸Ga-PSMA-11 PET/CT in clear cell RCC (ccRCC; 96.57% and 6.00, respectively) than in non-clear cell RCC (ncRCC; 82.05% and 2.99, respectively). The accuracies in detecting lesions in the renal region, bone, lymph nodes and lungs in ccRCC were 100.00%, 95.00%, 98.08% and 75.00%, respectively, and those in the renal region, bone and lymph nodes in ncRCC were 100.00%, 86.67% and 36.36%, respectively. The median TBRs of the lesions from the above locations were 0.38, 10.96, 6.69 and 13.71, respectively, in ccRCC and 0.13, 4.02 and 0.73, respectively, in ncRCC. The PSMA score evaluated with immunohistochemistry was correlated with the SUV_max (P = .046) in RCC. Higher PSMA scores were observed in ccRCC than in ncRCC (P = .031). ⁶⁸Ga-PSMA-11 PET/CT resulted in changes in clinical management in 12.9% (4/31) of cases because of the discovery of new metastases not detected with conventional imaging. These results indicate that ⁶⁸Ga-PSMA-11 PET/CT is a promising method for the detection of metastatic lesions in ccRCC, especially for those in the bone and lymph nodes.     

68Ga-PSMA PET/CT在前列腺癌复发中的应用进展

 前列腺癌（prostate cancer, PCa）发病率高,根治性治疗后,复发病灶的早期诊断对患者的预后至关重要。前列腺特异性膜抗原（prostate specific membrane antigen,PSMA）是一种在PCa中高表达的跨膜糖蛋白,利用核素⁶⁸Ga标记其小分子抑制剂作为显像剂,进行PET/CT显像,可以得到反映PCa病灶在体内分布的影像。欧美很多国家已经将68Ga-PSMA PET/CT应用于寻找PCa患者复发病灶,并取得了很好的效果,该技术在我国还处于起步阶段。本文综述了多个有关⁶⁸Ga-PSMA PET/CT在前列腺癌复发中的研究进展,旨在提高我们对该项新技术的认识水平。     

Metastasis-directed Therapy (SBRT) Guided by PET-CT 18F-CHOLINE Versus PET-CT 68Ga-PSMA in Castration-sensitive Oligorecurrent Prostate Cancer: A Comparative Analysis of Effectiveness

BackgroundThe present analysis aims to compare the impact of 18F-fluorocholine (¹⁸F-choline) and gallium-68 prostate-specific membrane antigen (⁶⁸Ga-PSMA) positron emission tomography (PET)-computed tomography (CT)–guided metastases-directed therapies (MDTs) in patients with castration-sensitive oligorecurrent prostate cancer (PC).Materials and MethodsInclusion criteria were: (1) histologically proven prostate adenocarcinoma; (2) evidence of biochemical relapse after primary tumor treatment; (3) ≤ 3 hypermetabolic oligorecurrent lesions detected by ¹⁸F-choline or ⁶⁸Ga-PSMA PET-CT; (4) PET-CT imaging performed in a single nuclear medicine department; (5) patients treated with upfront stereotactic body radiotherapy (SBRT) without hormone therapy; and (6) SBRT delivered with a dose per fraction ≥ 5 Gy. In the case of oligoprogression (≤ 3 lesions outside the previous RT field) after MTD, a further course of SBRT was proposed; otherwise, androgen deprivation therapy (ADT) was administered.ResultsA total of 118 lesions in 88 patients were analyzed. Forty-four (50%) patients underwent ⁶⁸Ga-PSMA PET-guided SBRT, and the remaining underwent choline PET-based SBRT. The median follow-up was 25 months (range, 5-87 months) for the entire cohort. Overall survival and local control were both 100%. Distant progression occurred in 48 (54.5%) patients, for a median distant progression-free survival of 22.8 months (range, 14.4-28.8 months). The median pre-SBRT prostate-specific antigen was 2.04 ng/mL in the choline PET cohort and 0.58 ng/mL in the PSMA-PET arm. Disease-free survival rates were 63.6% and 34%, respectively, in the ⁶⁸Ga-PSMA and choline PET group (P = .06). The ADT administration rate was higher after choline-PET–guided SBRT (P = .00) owing to the higher incidence of polymetastatic disease after first-course SBRT compared with ⁶⁸Ga-PSMA-based SBRT.ConclusionIn the setting of oligorecurrent castration-sensitive PC, PSMA-PET-guided SBRT produced a higher rate of ADT-free patients when compared with the ¹⁸F-choline-PET cohort. Randomized trials are advocated.     

Volumetric and dosimetric impact of MRI in delineation of gross tumor volume of non-spinal vertebral metastases treated with stereotactic ablative radiation therapy

PurposeTo investigate the Gross Tumor Volumes (GTV) and its dosimetric impact of magnetic resonance imaging (MRI) assisted contouring for non-spinal metastasis treated with stereotactic ablative body radiotherapy (SABR).Material and methodsFive observer contours on CT (GTV_CT) and CT + MR (GTV_CT+MR) were evaluated against expert team contours (GTV_EC) for 14 selected cases. Dice Similarity Index (DSC) and Geographical Miss Index (GMI) quantify observer variation. We also analyze the maximum dose (D_max) and dose received by 0.35cc (D_0.35cc) of the spinal cord (SC) for GTV_CT and GTV_CT+MR, where optimization parameters and priorities were unchanged. Percent rank function is also evaluated for SC doses.ResultsThe mean DSC and GMI scores for the CT-only dataset are 0.6974 and 0.2851 and for CT + MR dataset is 0.7764 and 0.1907 respectively. Statistically, significant results were found for mean GTV volumes between GTV_EC versus GTV_CT and GTV_CT versus GTV_CT+MR (P < 0.001). Dosimetric analysis of D_max and D_0.35cc exceeded 84.2% and 88.5% of times its respective threshold doses for CT-only dataset, whereas for the CT + MR dataset, it exceeded only by 18% and 15.7% times. ‘Percent rank’ function analysis for SC doses also indicates the same.ConclusionThis study supports MRI fusion for GTV and OAR delineation for non-spinal metastasis. Our study showed that the dosimetric analysis is vital for observer variation studies and the addition of the MR data set is significant to improve the confidence of Stereotactic treatments.     

Comparison of CT and PET-CT based planning of radiation therapy in locally advanced pancreatic carcinoma

Background

To compare computed tomography (CT) with co-registered positron emission tomography-computed tomography (PET-CT) as the basis for delineating gross tumor volume (GTV) in unresectable, locally advanced pancreatic carcinoma (LAPC).

Methods

Fourteen patients with unresectable LAPC had both CT and PET images acquired. For each patient, two three-dimensional conformal plans were made using the CT and PET-CT fusion data sets. We analyzed differences in treatment plans and doses of radiation to primary tumors and critical organs.

Results

Changes in GTV delineation were necessary in 5 patients based on PET-CT information. In these patients, the average increase in GTV was 29.7%, due to the incorporation of additional lymph node metastases and extension of the primary tumor beyond that defined by CT. For all patients, the GTV_CT versus GTV_PET-CT was 92.5 ± 32.3 cm³ versus 104.5 ± 32.6 cm³ (p = 0.009). Toxicity analysis revealed no clinically significant differences between two plans with regard to doses to critical organs.

Conclusion

Co-registration of PET and CT information in unresectable LAPC may improve the delineation of GTV and theoretically reduce the likelihood of geographic misses.     

Reproducibility of rectal tumor volume delineation using diffusion-weighted MRI: Agreement on volumes between observers

PurposeTo retrospectively evaluate the inter-observer agreement between a radiologist and a radiation oncologist and volume differences, in T2 and diffusion-weighted (DWI) MRI of gross tumor volume (GTV) delineation, in rectal cancer patients.Materials and methodsTwo observers, a radiologist and a radiation oncologist, delineated GTVs of 50 patients on T2-weighted MRI (T2_GTV) and echo planar DWI (DWI_GTV). Observers agreement was assessed using DICE index, Bland-Altman analysis and intra-class correlation coefficient (ICC). Student's t-test was used for GTV comparison.ResultsMedian T2_GTV and DWI_GTV were 17.09 ± 14.12 cm³ (1.92–62.03) and 12.79 ± 12.31 cm³ (1.23–62.25) for radiologist, and 16.82 ± 13.66 cm³ (1.78–65.9) and 13.72 ± 12.77 cm³ (1.29–69.75) for radiation oncologist. T2_GTV were significantly larger compared to DWI_GTV (P < 0.001 and P < 0.001, for both observers). Mean DICE index for T2_GTV and DWI_GTV were 0.80 ± 0.07 and 0.77 ± 0.06. The mean difference between the two observers were 0.26 cm³ (95% CI: ?5.36 to 5.88) and ?1.13 cm³ (95% CI: ?5.70 to 3.44) for T2 and DWI volumes. The ICC for T2 volumes was 0.989 (95% CI: 0.981–0.994) (P < 0.001) and 0.992 (95% CI: 0.986–0.996) (P < 0.001) for DWI volumes.ConclusionDWI resulted in smaller volumes delineation compared to T2-weighted MRI. Substantial and almost perfect agreements were reported for DWI_GTV and T2_GTV between radiologist and radiation oncologist. Due to the fact that DWI could be considered a simple technique for volume delineation for radiation oncologist, DWI could be used to improve quality in radiation planning for an accurate boost volume delineation when a dose escalation is investigated.     

The feasibility of prostate-specific membrane antigen positron emission tomography(PSMA PET/CT)-guided radiotherapy in oligometastatic prostate cancer patients

Background

To investigate the efficacy and toxicity of 68Ga-PSMA-HBED-CC (⁶⁸Ga-PSMA) PET-CT-guided RT in the treatment of oligometastatic prostate cancer retrospectively.

Methods

A total of 23 prostate cancer patients with biochemical relapse, of which 13 were castration sensitive (CS) and 10 castration resistant (CR), were treated with intensity-modulated and image-guided RT (IMRT-IGRT) on ≤3 metastases detected by ⁶⁸Ga PSMA PET-CT. Androgen deprivation therapy was continued in CR patients.

Results

A total of 38 metastases were treated. The involved sites were pelvic bone (n = 16), pelvic lymph nodes (n = 11), paraaortic lymph nodes (n = 6), ribs (n = 3) and vertebral body (n = 2). The median PSA prior to RT was 1.1 ng/mL (range 0.1–29.0 ng/mL). A median dose of 43.5 Gy (range 30–64 Gy) was delivered by IMRT-IGRT in 12–27 fractions. At a median follow-up of 7 months (range 2–17 months), 19 patients (83%) were in remission. Four patients (17%) developed distant recurrences. The actuarial 1-year LC, PFS and OS rates were 100, 51 (95% CI 8–83%) and 100%. Univariate analysis demonstrated a statistically significantly better PFS in CS patients as compared to CR patients (1-year PFS 67 vs. 0%, p < 0.01). One patient experienced grade 2 acute gastrointestinal toxicity. Grade 3 or more toxicity events were not observed.

Conclusions

By providing optimal LC, low toxicity and a promising PFS in CS patients, the current retrospective study illustrated that ⁶⁸Ga PSMA PET-CT-guided RT may be an attractive treatment strategy in patients with oligometastatic prostate cancer. Validation by randomized trials is eagerly awaited.

     

Tumor volume delineation in head and neck cancer with 18-fluor-fluorodeoxiglucose positron emission tomography: adaptive thresholding method applied to primary tumors and metastatic lymph nodes

Purpose

There are several potential advantages of using 18-fluor-fluorodeoxiglucose (18F-FDG) PET for target volume contouring, but before PET-based gross tumor volumes (GTVs) can reliably and reproducibly be incorporated into high-precision radiotherapy planning, operator-independent segmentation tools have to be developed and validated. The purpose of the present work was to apply the adaptive to the signal/background ratio (R_S/B) thresholding method for head and neck tumor delineation, and compare these GTV_PET to reference GTV_CT volumes in order to assess discrepancies.

Materials and methods

A cohort of 19 patients (39 lesions) with a histological diagnosis of head and neck cancer who would undergo definitive concurrent radiochemotherapy or radical radiotherapy with intensity-modulated radiotherapy technique (IMRT), were enrolled in this prospective study. Contouring on PET images was accomplished through standardized uptake value (SUV)-threshold definition. The threshold value was adapted to R_S/B. To determine the relationship between the threshold and the R_S/B, we performed a phantom study. A discrepancy index (DI) between both imaging modalities, overlap fraction (OF) and mismatch fraction (MF) were calculated for each lesion and imaging modality.

Results

The median DI value for lymph nodes was 2.67 and 1.76 for primary lesions. The OF values were larger for CT volumes than for PET volumes (p < 0.001), for both types of lesions. The MF values were smaller for CT volumes than for PET volumes (p < 0.001), for both types of lesions. The GTV_PET coverage (OF_PET) was strongly correlated with the lesion volume (GTV_CT) for metastatic lymph nodes (Pearson correlation = 0.665; p < 0.01). For smaller lesions, despite the GTV volumes were relatively larger on PET than in CT contours, the coverage was poorer. Accordingly, the MF_PET/CT was negatively correlated with the lesion volume for metastatic lymph nodes.

Conclusions

The present study highlights the considerable challenges involved in using FDG PET imaging for the delineation of GTV in head and neck neoplasms. The methods that rely mainly on SUV_max for thresholding, as the R_S/B method, are very sensitive to partial volume effects and may provide unreliable results when applied on small lesions.     

COVID-19 vaccine related hypermetabolic lymph nodes on PET/CT: Implications of inflammatory findings in cancer imaging

We observed several patients presenting 2-[¹⁸F]FDG uptake in the reactive axillary lymph node at PET/CT imaging, ipsilateral to the site of the COVID-19 vaccine injection. Analog finding was documented at [¹⁸F]Choline PET/CT. The aim of our study was to describe this source of false positive cases. All patients examined by PET/CT were included in the study. Data concerning patient anamnesis, laterality, and time interval from recent COVID-19 vaccination were recorded. SUVmax was measured in all lymph nodes expressing tracer uptake after vaccination. Among 712 PET/CT scans with 2-[¹⁸F]FDG, 104 were submitted to vaccination; 89/104 patients (85%) presented axillary and/or deltoid tracer uptake, related to recent COVID-19 vaccine administration (median from injection: 11 days). The mean SUVmax of these findings was 2.1 (range 1.6–3.3). Among 89 patients with false positive axillary uptake, 36 subjects had received chemotherapy due to lymph node metastases from somatic cancer or lymphomas, prior to the scan: 6/36 patients with lymph node metastases showed no response to therapy or progression disease. The mean SUVmax value of lymph nodal localizations of somatic cancers/lymphomas after chemotherapy was 7.8. Only 1/31 prostate cancer patients examined by [¹⁸F]Choline PET/CT showed post-vaccine axillary lymph node uptake. These findings were not recorded at PET/CT scans with [¹⁸F]-6-FDOPA, [⁶⁸Ga]Ga-DOTATOC, and [¹⁸F]-fluoride. Following COVID-19 mass vaccination, a significant percentage of patients examined by 2-[¹⁸F]FDG PET/CT presents axillary, reactive lymph node uptake. Anamnesis, low-dose CT, and ultrasonography facilitated correct diagnosis. Semi-quantitative assessment supported the visual analysis of PET/CT data; SUVmax values of metastatic lymph nodes were considerably higher than post-vaccine lymph nodes. [¹⁸F]Choline uptake in reactive lymph node after vaccination was confirmed. After the COVID-19 pandemic, nuclear physicians need to take these potential false positive cases into account in daily clinical practice.     

Variation in background intensity affects PET-based gross tumor volume delineation in non-small-cell lung cancer: The need for individualized information

Purpose

Efficient tumor volume delineation by the combined use of PET/CT scanning is necessary for the proper treatment of non-small cell lung cancer (NSCLC). To understand the effect of variation in background intensity on PET-based gross tumor volume (GTV) delineation, we determined the background standard uptake values (SUVs) in normal lung, aorta (blood pool), and liver tissues and determined GTVs using different methods.

Methods

Thirty-seven previously untreated patients with pathologically confirmed NSCLC underwent PET/CT scanning with ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG). To obtain ¹⁸F-FDG uptake values in normal tissues, regions of interest in the lung lobes (left upper, left lower, right upper, right middle, and right lower), aorta, and liver zones (left, intermediate, and right) were measured. The coefficient of variation (CV) of the SUV was measured for each normal structure. The CT-based GTV (GTV_CT) was considered as the standard to which all PET-based GTVs were compared, and the correlation coefficient was analyzed to compare GTV obtained by the various delineation methods. Linear and logarithmic regression analyses were used to determine the relationship between GTV_CT and GTV_PET.

Results

Normal lung tissue showed a significantly lower SUV and less stability than tissue of the aorta or liver. For the lung, aorta, and liver, the maximum SUV (SUV_max) was 0.82 ± 0.32, 2.35 ± 0.37, and 3.24 ± 0.50 (CV: 38.79%, 15.82%, and 15.30%) and average SUV (SUV_ave) was 0.49 ± 0.18, 1.68 ± 0.32, and 2.34 ± 0.36 (CV: 36.38%, 18.92%, and 15.44%), respectively. The SUVs of the lung varied from lobe to lobe. The GTV delineation method using the SUV_ave of the lung lobe in which the tumor was found as background in the source-to-background ratio (SBR) method showed the best correlation with the volume of CT-based GTV (r = 0.81).

Conclusions

Our results show vast variation in the SUV among normal tissues, as well as in the different lung lobes. The tumor volume delineated using the SBR method correlated well with the CT-based tumor volume. We conclude that it is reasonable and precise to contour GTV in patients with NSCLC after taking into account the background intensity of the lung lobe in which the tumor is found.     

FDG PET-CT与MRI在鼻咽癌原发灶靶区勾画中的对比研究

目的 对比研究FDG PET-CT不同勾画方法间及与MRI显示鼻咽原发灶靶区差异,探讨FDG PET-CT勾画鼻咽原发灶大体肿瘤体积(GTV)生物靶区的可行性。方法 50例初治鼻咽癌患者治疗前均行FDG PET-CT和MRI检查,先在MRI图像上勾画GTV得到GTV-MRI,然后在FDG PET-CT上分别用目测法或不同阈值法(30%、40%、50%SUV_max)勾画GTV得到GTV-PET_vis、GTV-PET₃₀、GTV-PET₄₀、GTV-PET₅₀。采用Wilcoxon检验GTV-PET不同方法间和GTV-MRI差异,以及不同T分期中不同勾画方法间差异。结果 全组GTV-MRI、GTV-PET_vis、GTV-PET₃₀、GTV-PET₄₀、GTV-PET₅₀分别为27.8、22.2、22.7、14.4、9.0 cm³,除GTV-PET_vis与GTV-PET₃₀间(Z=－0.05,P=0.958)以及T_1~2期(25例) GTV-MRI与GTV-PET_vis和GTV-PET₃₀相似外(Z=－0.93、－0.93,P=0.353、0.353),其余均不同(Z=－5.74~－2.09,P=0.000~0.037)。结论 应用FDG PET-CT不同方法勾画的GTV-PET均max为阈值自动勾画鼻咽原发灶GTV可实现生物代谢肿瘤体积范围勾画。