Volume 42 Issue 6
Dec.  2018
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Value of 18F-FDG PET/CT for diagnosing and treating childhood and adolescent lymphoma

  • Childhood and adolescent lymphomas account for 10%-15% of all pediatric cancers. Most cases of pediatric lymphoma involve highly aggressive tumors and extranodal sites. As such, accurate staging and early assessment of therapeutic response are of great value for lymphoma in children and adolescents. Conventional imaging modalities (e.g., ultrasound, CT, MRI, and 67Ga) present some limitations in their diagnosis and treatment. 18F-FDG PET/CT is a new imaging technique that combines the functional data of PET with the morphological information of CT. This article reviews the current role of 18F-FDG PET/CT in the staging, efficacy evaluation, and follow-up of childhood and adolescent lymphoma and finds that 18F-FDG PET/CT is more sensitive than other imaging techniques in monitoring lymph nodes and the spleen. By imaging more lesions, the accuracy of 18F-FDG PET/CT for staging is better than that achieved by traditional imaging methods. At the same time, because of its metabolic changes earlier than the anatomical changes, assessing treatment efficacy promptly and accurately, as well as determining the nature of residual lesions, may be possible. Because of its lower recurrence rate, the trade-offs between monitoring recurrence and radiation exposure during the follow-up period must be weighed.
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  • [1] Ferrari C, Niccoli AA, Merenda N, et al. Pediatric Hodgkin Lymphoma: Predictive value of interim 18F-FDG PET/CT in therapy response assessment[J/OL]. Medicine (Baltimore), 2017, 96(5): e5973[2018-01-07]. https://www.ncbi.nlm.nih.gov/pubmed/28151888. DOI: 10.1097/MD.0000000000005973.
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    [9] Uslu L, Donig J, Link M, et al. Value of 18F-FDG PET and PET/CT for evaluation of pediatric malignancies[J]. J Nucl Med, 2015, 56(2):274-286. DOI:10.2967/jnumed.114.146290.
    [10] Bakhshi S, Bhethanabhotla S, Kumar R, et al. Posttreatment PET/CT rather than interim PET/CT using Deauville Criteria predicts outcome in pediatric Hodgkin lymphoma:a prospective study comparing PET/CT with conventionalImaging[J]. J Nucl Med, 2017, 58(4):577-583. DOI:10.2967/jnummed.116.176511.
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    [12] Zapata CP, Cuglievan B, Zapata CM, et al. PET/CT versus bone marrow biopsy in the initial evaluation of bone marrow infiltration in various pediatric malignancies[J/OL]. Pediatr Blood Cancer, 2018, 65(2)[2018-01-07]. https://www.ncbi.nlm.nih.gov/pubmed/28901637. DOI: 10.1002/pbc.26814.
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    [14] Kluge R, Kurch L, Montravers F, et al. FDG PET/CT in children and adolescents with lymphoma[J]. Pediatr Radiol, 2013, 43(4):406-417. DOI:10.1007/s00247-012-2559-z.
    [15] Cheng G, Chen W, Chamroonrat W, et al. Biopsy versus FDG PET/CT in the initial evaluation of bone marrow involvement in pediatric lymphoma patients[J]. Eur J Nucl Med Mol Imaging, 2011, 38(8):1469-1476. DOI:10.1007/s00259-011-1815-z.
    [16] Purz S, Mauz-Körholz C, Körholz D, et al.[18F]Fluorodeoxyglucose positron emission tomography for detection of bone marrow involvement in children and adolescents with Hodgkin's lymphoma[J]. J Clin Oncol, 2011, 29(26):3523-3528. DOI:10.1200/JCO.2010.32.4996.
    [17] Kluge R, Körholz D. Role of FDG-PET in Staging and Therapy of Children with Hodgkin Lymphoma[J]. Klin Padiatr, 2011, 223(6):315-319. DOI:10.1055/s-0031-1287834.
    [18] Cheng G, Servaes S, Zhuang H. Value of 18F-fluoro-2-deoxy-D-glucose positron emission tomography/computed tomography scan versus diagnostic contrast computed tomography in initial staging of pediatric patients with lymphoma[J]. Leuk Lymphoma, 2013, 54(4):737-742. DOI:10.3109/10428194.2012.727416.
    [19] Kiratli PÖ, Tuncel M, Bar-Sever Z. Nuclear Medicine in Pediatric and Adolescent Tumors[J]. Semin Nucl Med, 2016, 6(4):308-323. DOI:10.1053/j.semnuclmed.2016.01.004.
    [20] Seth R, Puri K, Singh P, et al. The role of fluorodeoxyglucose positron emission tomography-computerized tomography in resolving therapeutic dilemmas in pediatric Hodgkin lymphoma[J]. Indian J Nucl Med, 2012, 27(3):141-144. DOI:10.4103/0972-3919.112717.
    [21] Riad R, Omar W, Kotb M, et al. Role of PET/CT in malignant pediatric lymphoma[J]. Eur J Nucl Med Mol Imaging, 2010, 37(2):319-329. DOI:10.1007/s00259-009-1276-9.
    [22] Wahl RL, Jacene H, Kasamon Y, et al. From RECIST to PERCIST: Evolving Considerations for PET response criteria in solid tumors[J]. J Nucl Med, 2009, 50 Suppl 1: S122-150. DOI: 10.2967/jnumed.108.057307.
    [23] Cheson BD, Pfistner B, Juweid ME, et al. Revised response criteria for malignant lymphoma[J]. J Clin Oncol, 2007, 25(5):579-586. DOI:10.1200/JCO. 2006.09.2403.
    [24] 覃春霞, 兰晓莉. PET/CT在恶性淋巴瘤疗效评估中的应用[J].临床内科杂志, 2015, 32(3):166-169. DOI:10.3969/j.issn.1001-9057.2015.03.006.Qin CX, Lan XL. Application of PET/CT in the evaluation of malignant lymphoma[J]. J Clin Intern Med, 2015, 32(3):166-169. DOI:10.3969/j.issn.1001-9057.2015.03.006.
    [25] Bailly C, Eugène T, Couec ML, et al. Prognostic Value and Clinical Impact of 18FDG-PET in the Management of Children with Burkitt Lymphoma after Induction Chemotherapy[J/OL]. Front Med (Lausanne), 2014, 1: 54[2018-01-06]. https//www.ncbi.nlm.nih.gov/pmc/articles/PMC4292173. DOI: 10.3389/fmed.2014.00054.
    [26] Ilivitzki A, Radan L, Ben-Arush M, et al. Early interim FDG PET/CT prediction of treatment response and prognosis in pediatric Hodgkin disease-added value of low-dose CT[J]. Pediatr Radiol, 2013, 43(1):86-92. DOI:10.1007/s00247-012-2517-9.
    [27] Depas G, De Barsy C, Jerusalem G, et al. 18F-FDG PET in children with lymphomas[J]. Eur J Nucl Med Mol Imaging, 2005, 32(1):31-38. DOI:10.1007/s00259-004-1604-z.
    [28] Furth C, Steffen IG, Erdrich AS, et al. Explorative analyses on the value of interim PET for prediction of response in pediatric and adolescent non-Hodgkin lymphoma patients[J]. EJNMMI Res, 2013, 3(1):71. DOI:10.1186/2191-219X-3-71.
    [29] Hutchings M, Loft A, Hansen M, et al. FDG-PET after two cycles of chemotherapy predicts treatment failure and progression-free survival in Hodgkin lymphoma[J]. Blood, 2006, 107(1):52-59. DOI:10.1182/blood -2005-06-2252.
    [30] Bhojwani D, McCarville MB, Choi JK, et al. The role of FDG-PET/CT in the evaluation of residual disease in paediatric non-Hodgkin lymphoma[J]. Br J Haematol, 2015, 168(6):845-853. DOI:10.1111/bjh.13219.
    [31] Furth C, Steffen IG, Amthauer H, e t al. Early and late therapy response assessment with[18F]fluorodeoxyglucose positron emission tomography in pediatric Hodgkin's lymphoma:analysis of a prospective multicenter trial[J]. J Clin Oncol, 2009, 27(26):4385-4391. DOI:10.1200/JCO.2008.19.7814.
    [32] Levine JM, Weiner M, Kelly KM. Routine use of PET scans after completion of therapy in pediatric Hodgkin disease results in a high false positive rate[J]. J Pediatr Hematol Oncol, 2006, 28(11):711-714. DOI:10.1097/01.mph.0000243648.66734.eb.
    [33] Meany HJ, Gidvani VK, Minniti CP. Utility of PET scans to predict disease relapse in pediatric patients with Hodgkin lymphoma[J]. Pediatr Blood Cancer, 2007, 48(4):399-402. DOI:10.1002/pbc.20797.
    [34] Longo DL. Treatment of advanced Hodgkin lymphoma:the more things change, the more they stay the same[J]. J Clin Oncol, 2013, 31(6):660-662. DOI:10.1200/JCO.2012.44.7235.
    [35] Nievelstein RA, van Ufford HM Q, Kwee TC, et al. Radiation exposure and mortality risk from CT and PET imaging of patients with malignant lymphoma[J]. Eur Radiol, 2012, 22(9):1946-1954. DOI:10.1007/s00330-012-2447-9.
    [36] Voss SD, Chen L, Constine LS, et al. Surveillance computed tomography imaging and detection of relapse in intermediate- and advanced-stage pediatric Hodgkin's lymphoma:a report from the Children's Oncology Group[J]. J Clin Oncol, 2012, 30(21):2635-2640. DOI:10.1200/JCO.2011.40.7841.
    [37] Rathore N, Eissa HM, Margolin JF, et al. Pediatric Hodgkin lymphoma:are we over-scanning our patients[J]. Pediatr Hematol Oncol, 2012, 29(5):415-423. DOI:10.3109/08880018.2012.684198.
    [38] Eissa HM, Allen CE, Kamdar K, et al. Pediatric Burkitt's lymphoma and diffuse B-cell lymphoma:are surveillance scans required[J]. Pediatr Hematol Oncol, 2014, 31(3):253-257. DOI:10.3109/08880018.2013.834400.
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    [44] Daldrup-Link H. How PET/MR Can Add Value For Children With Cancer[J]. Curr Radiol Rep, 2017, 5(3):15. DOI:10.1007/s40134-017-0207-y.
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Value of 18F-FDG PET/CT for diagnosing and treating childhood and adolescent lymphoma

    Corresponding author: Yiwei Wu, wuyiwei3988@gmail.com
  • Department of Nuclear Medicine, the First Affiliated Hospital of Soochow University, Suzhou 215000, China

Abstract: Childhood and adolescent lymphomas account for 10%-15% of all pediatric cancers. Most cases of pediatric lymphoma involve highly aggressive tumors and extranodal sites. As such, accurate staging and early assessment of therapeutic response are of great value for lymphoma in children and adolescents. Conventional imaging modalities (e.g., ultrasound, CT, MRI, and 67Ga) present some limitations in their diagnosis and treatment. 18F-FDG PET/CT is a new imaging technique that combines the functional data of PET with the morphological information of CT. This article reviews the current role of 18F-FDG PET/CT in the staging, efficacy evaluation, and follow-up of childhood and adolescent lymphoma and finds that 18F-FDG PET/CT is more sensitive than other imaging techniques in monitoring lymph nodes and the spleen. By imaging more lesions, the accuracy of 18F-FDG PET/CT for staging is better than that achieved by traditional imaging methods. At the same time, because of its metabolic changes earlier than the anatomical changes, assessing treatment efficacy promptly and accurately, as well as determining the nature of residual lesions, may be possible. Because of its lower recurrence rate, the trade-offs between monitoring recurrence and radiation exposure during the follow-up period must be weighed.

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  • 淋巴瘤是儿童及青少年中除白血病、脑和中枢神经系统以外的第三大恶性肿瘤,约占所有儿科恶性肿瘤的10%~15%,其中非霍奇金淋巴瘤(Non-Hodgkins lymphoma,NHL)占60%,霍奇金淋巴瘤(Hodgkins lymphoma,HL)占40%[1]。HL更多侵犯淋巴结和脾脏,多表现为无痛性淋巴结肿大,其中多达80%的病例涉及颈部淋巴结。儿童及青少年淋巴瘤与成人淋巴瘤在多个方面有着明显的不同,混合细胞型和结节硬化型是青春期前期HL的两种主要组织病理学亚型,而青少年HL主要以结节硬化型为主[2];小儿NHL多为高度侵袭性淋巴瘤,较成人NHL更易侵犯结外组织,如骨髓和中枢神经系统[3]。儿童及青少年淋巴瘤的预后也优于成人,HL和NHL的五年生存率分别为95%和78%[4]。及时地诊断、准确的分期和疗效评价对儿童及青少年淋巴瘤预后有重要的价值。这其中,影像学评价在儿童及青少年淋巴瘤的诊疗中起着重要的作用。

    18F-FDG PET/CT是利用18F标记的FDG作为示踪记,以图像方式从分子水平显示机体及病灶组织的代谢状况,从而进行疾病的诊断。实现了PET的功能代谢显像与CT解剖结构显像相融合,不仅可以获得功能和代谢等分子信息,还具有较高的空间分辨力和准确性。除此之外,18F-FDG PET/CT可以根据SUV对治疗后的疗效进行半定量分析。在最常见的侵袭性小儿NHL中,超过97%的患者具有18F-FDG的摄取[5],HL患者100%具有18F-FDG的摄取[6]。近年的研究显示,18F-FDG PET/CT在儿童及青少年淋巴瘤中的分期、疗效监测、随访方面具有重要的价值,同时一次显像可以全身评估是否需要进一步的化疗及外放射治疗,以避免不必要的与治疗有关的并发症及提高生存率。

1.   18F-FDG PET/CT在儿童及青少年淋巴瘤分期中的作用

    1.1.   分期价值

  • 儿童及青少年在HL分期体系中最常用的标准为Ann Arbor改良分期,在NHL中最常用的标准为St Jude分期[1]。多项研究表明,18F-FDG PET/CT较传统影像学方法在淋巴瘤的分期中具有更高的价值,18F-FDG PET/CT可以发现更多的淋巴结和结外病灶,如脾脏、骨髓等[2, 7-8]18F-FDG PET/CT在恶性淋巴瘤分期中的灵敏度和特异度分别为96%~99%和95%~100%[9]。同时,18F-FDG PET/CT可以改变1/3淋巴瘤患儿的分期,其中大多数为分期上调[8]。Bakhshi等[10]对57例淋巴瘤患儿(≤18岁)进行18F-FDG PET/CT与传统影像学方法在分期中的比较,结果发现,18F-FDG PET/CT使40.3%患儿的分期上调,7.0%患儿的分期下调,分期上调中39%的患儿发生治疗方案的改变。Bakhshi等[7]对34例NHL患儿(≤18岁)进行前瞻性研究,结果发现,18F-FDG PET/CT改变了5例(14.7%)患儿的分期,18F-FDG PET/CT较对比增强CT额外发现18处病灶。Paulino等[11]比较了18F-FDG PET/CT与传统影像学方法对接受化疗和累及区域放疗的HL患者(6~21岁)的影响,53例病例中,19例患者(35.8%)的18F-FDG PET/CT与CT结果表现不一致,18F-FDG PET/CT改变了9.4%患者的分期,使17.0%患者的累及区域放疗计划发生改变。18F-FDG PET/CT提高了小儿淋巴瘤分期的准确率,从而制定适当的治疗方案,提高治愈率,减少不必要的与治疗相关的不良反应。

    18F-FDG PET/CT较骨髓活检发现骨髓浸润具有更高的灵敏度。HL具有骨髓浸润时即临床诊断为Ⅳ期,其治疗和预后方案均发生改变。NHL具有骨髓浸润时,与疾病的进展、高的国际预后指数具有一定的关联。目前,诊断骨髓浸润的“金标准”是骨髓活检(bone marrow biopsy,BMB)[12],常选择的活检部位为单侧或双侧髂骨。但BMB是一种侵入性的检查方法,灵敏度低,具有一定程度的并发症(出血、感染等),且部分局灶性骨髓浸润患者可能会被漏诊,导致假阴性的结果。Hassan等[13]对784例HL患儿(2~18岁)行BMB及18F-FDG PET/CT检查,18F-FDG PET/CT的灵敏度、特异度、阳性预测值(positive predictive value,PPV)、阴性预测值(negative predictive value,NPV)分别为93.6%、94.0%、53.0%和99.4%。有研究发现,NHL中常见的淋巴母细胞性淋巴瘤常表现为弥漫性骨髓浸润,18F-FDG PET/CT可能导致一定的假阴性结果[14]。Cheng等[15]评估了18F-FDG PET/CT对31例HL和23例NHL患者的初始评估骨髓浸润的作用,结果发现,18F-FDG PET/CT在淋巴瘤的初始诊断中具有较高的灵敏度和准确率,并且对BMB具有实质性的补充作用,应该被用作一线诊断方法。Purz等[16]对175例新诊断HL(<18岁)患儿进行BMB与18F-FDG PET/CT的比较,结果11.0%患儿的分期发生改变,5.7%患儿的治疗方案发生改变,因此,他们认为18F-FDG PET/CT在小儿HL分期中可以取代BMB。18F-FDG PET/CT检测骨髓浸润较BMB具有更高的灵敏度,并可对骨髓穿刺的部位进行指导。另有多项研究[2, 16-17]发现,18F-FDG PET/CT在诊断HL浸润时可以取代BMB。

  • 1.2.   18F-FDG PET/CT在儿童及青少年淋巴瘤分期中的局限性

  • 受到空间分辨率和呼吸运动的影响,18F-FDG PET/CT在评估肺内浸润(<5 mm)的灵敏度上不如胸部CT(100% vs.70%)[2]。Cheng等[18]发现18F-FDG PET/CT在评估肺内小结节时,得到的是假阴性结果。同时,在审阅小儿淋巴瘤图像时,应注意棕色脂肪以及胸腺、肌肉、扁桃体和生长发育引起的骨骼等生理性摄取[19]

2.   18F-FDG PET/CT在儿童及青少年淋巴瘤疗效评价中的作用
  • 早期观察患者对治疗的反应非常重要,对治疗效果差的患者及时更换或加强治疗方案,对于治疗效果佳的患者避免过度治疗。在治疗效果佳的患者中,细胞代谢和趋化因子的合成机制关闭,但肿瘤消失需要一定的时间[20],因而在影像学上表现为残留病灶的存在。在治疗结束后,30%~60%的患者会持续性出现异常残留病灶,而其中只有10%~20%的残留病灶经病理证实为阳性[21]

    在1999年之前各个研究组间尚无统一的淋巴瘤评估标准,对于淋巴瘤的评估主要依据实体肿瘤评估标准,包括1979年的世界卫生组织(world health organization,WHO)标准、2000年实体瘤疗效评价标准(response evaluation criteria in solid tumors,RECIST)以及2009年RECIST1.1版。WHO、RECIST均是从解剖形态学变化对疗效进行评估,存在一定的局限性。为此,Wahl等[22]于2009年提出依据18F-FDG摄取的PET实体瘤疗效标准(PET response criteria in solid tumors,PERCIST),在分子影像学的基础上对治疗疗效进行评估。但淋巴瘤的治疗反应与实体肿瘤之间存在一定的差异,1999年国际工作组首次提出淋巴瘤疗效评估标准[23],使不同的淋巴瘤研究之间可进行比较,但其具有一定的局限性,如可能会受到不同观察者及同一观察者多次观察之间差异的影响等。近些年,Deauvill标准是中期PET评估常用的视觉标准,其具有简便、可重复测量的优点,根据淋巴瘤对18F-FDG的摄取程度不同分为5分,大量研究证明,在淋巴瘤(如HL、弥漫大B细胞淋巴瘤、滤泡性淋巴瘤)的疗效评价中应用Deauvill标准,不同观察者之间具有良好的一致性[24]。但由于背景亮度的程度不同、残余病灶的大小及与纵隔和肝脏之间的距离不等,都会引起一定的错误判断。除上述研究方法外,半定量分析法也经常应用在淋巴瘤的疗效评价中,其主要依据病灶治疗前后的SUVmax的变化来评估治疗疗效。半定量分析法可以客观地对疗效进行评估,但其必须保持前后扫描的方案和匹配条件一致。

    多项研究表明,依据功能成像的18F-FDG PET/CT对于淋巴瘤患儿的预后评估价值优于依据形态学变化的传统影像学方法[25-26]。Bailly等[25]对19例治疗后的伯基特淋巴瘤患儿(2~17岁)进行研究,18F-FDG PET/CT表现为阴性者共15例,其中有9例与传统影像学方法检查结果一致,6例不一致后经病理证实为阴性,18F-FDG PET/CT与传统影像学检查方法的NPV分别为93%和73%。Depas等[27]报道,18F-FDG PET/CT评估治疗结束后残留病灶的特异度为94%,而传统影像学检查方法的特异度仅为54%。Ilivitzki等[26]对34例HL患儿(3~17岁)进行前瞻性研究,治疗中期18F-FDG PET/CT的NPV为96%。Furth等[28]研究了16例NHL患儿,在化疗2个疗程后,18F-FDG PET/CT与传统影像学检查方法的NPV分别为85.7%和76.9%。

    由于HL中恶性细胞仅占一小部分[29],其余细胞为炎性反应性细胞,所以在PET中观察到的18F-FDG摄取可能是由炎性细胞而非残余肿瘤细胞引起,导致假阳性出现。除此之外,坏死、胸腺反应性增生、心脏的生理性摄取、儿童颈部肌肉或Waldeyer淋巴环也可引起假阳性结果。Bhojwani等[30]对化疗后的18例NHL患者进行回顾性分析,结果发现,表现为18F-FDG PET/CT阳性的8例患者,后经病理证实仅有2例为残余病灶,其PPV为25%。Furth等[28]报道HL患儿经过2个疗程化疗后,18F-FDG PET/CT的PPV为33.3%。因此,有研究者[27, 30]建议,在小儿淋巴瘤中,若18F-FDG PET/CT为阳性结果,则需结合活检结果来决定是否改变治疗方案。另一方面,除了Depas等[27]报道的3例假阴性结果外,多数研究结果提示18F-FDG PET/CT具有较高的NPV[2, 28, 30],因此有理由认为,18F-FDG PET/CT阴性结果的患者具有较长的无进展生存期。

    18F-FDG PET/CT评价疗效存在的一个重要问题是在治疗间期何时行18F-FDG PET/CT检查,目前尚无定论。研究者化疗一个周期后行18F-FDG PET/CT的结果与3次或多次化疗周期后产生的结果是否相似?有研究发现,PET-2(化疗2个疗程后PET显像)阳性的HL患者比PET-2阴性的HL患者显示出更低的2年无进展生存期[1]。因此许多学者提倡在治疗中期行18F-FDG PET/CT显像对预后进行判断[31-33]。也有研究结果[10]显示,中期PET结果为阴性或阳性的HL患者,其无事件生存率和总体生存率没有显著差异,而治疗结束后,18F-FDG PET/CT结果阴性者具有较高的总体生存率和无事件生存率。因此部分学者推荐在治疗中后期行18F-FDG PET/CT显像[10, 34]

3.   18F-FDG PET/CT在儿童及青少年淋巴瘤随访中的作用
  • 18F-FDG PET/CT在淋巴瘤随访中的价值存在一定的争议。一方面,部分研究者认为,18F-FDG PET/CT是淋巴瘤患者随访中监测复发的有效方式,具有较高的灵敏度和特异度[35]。Depas等[27]对患者进行了长期随访,在59次影像学检查结果中,PET检查结果56次为阴性,而传统影像学检查结果39次为阴性,在长期随访监测中,PET和传统影像学检查方法的特异度分别为100%和66%。另一方面,Voss等[36]对来自儿童肿瘤组织机构的216例HL患儿进行研究,结果发现,在随访患儿的常规监测中,仅11.6%(25/216)的患儿复发,且对总体生存率没有产生影响。Rathore等[37]在对99例HL患者的1358次常规监测扫描研究中发现,仅13%的患者复发。在他们的结果中,超过一半的患者通过临床症状、实验室检查或体格检查发现复发。同样,Eissa等[38]在对44例B细胞NHL患儿(3~16岁)进行的研究中发现,仅有6.8%的患儿复发。

    相对成人来说,儿童和青少年对辐射更加敏感,具有更长的时间发生继发性肿瘤。有研究报道,儿童和青少年患者中,平均约0.4%的男性和0.7%的女性最终因医疗辐射暴露导致死亡[35]。在对淋巴瘤患儿的随访中发现,18F-FDG PET/CT检查增加了额外的辐射暴露和经济负担[38-39]。有学者认为,对分期低和化疗效果好的患者,可减少监测扫描的次数或无需扫描[36, 39];对没有临床表现或复发征象的HL和B-NHL,则可不必进行常规监测扫描[38]。大多数HL的复发发生在完成治疗后的1年内[40],而成熟B细胞NHL淋巴瘤复发的时间通常在治疗结束后的半年内[41]。因此,尚需大量的前瞻性研究来确定在淋巴瘤的随访过程中是否使用了监测手段、使用了何种类型的监测手段以及确定随访的时间。

4.   18F-FDG PET/CT与其他影像学技术的比较
  • 传统影像学方法如超声、CT、MRI也常用来评估小儿淋巴瘤,除此之外,还有67Ga肿瘤显像和PET/MRI。这些影像学方法也都存在着优势和局限性。

    超声在浅表淋巴结受累的初期评估及随访过程中具有重要的作用,同时其是检测睾丸浸润的最佳检查方法,但超声检查明显受到疾病部位的限制。

    CT具有较高的密度分辨率,可以更好地显示由软组织构成的器官。其检查时间短,对儿童也不需要进行镇静。CT诊断标准主要依靠淋巴结的大小,但CT不能辨别正常大小的恶性淋巴结,也不能区别由其他原因所导致的淋巴结肿大,同时对于肝脏和脾脏的浸润,CT诊断具有一定的局限性。由于儿童后腹膜缺乏脂肪,因此在判断儿童腹腔疾病中存在一定的困难。尽管存在一些局限性,CT仍然是淋巴瘤患者分期和治疗后评估的最常用方式。

    MRI具有T1加权像、T2加权像、质子密度等多个成像参数,可分别获得同一解剖部位或层面的多种图像。同时MRI可获得人体轴位、冠状位、矢状位及任意倾斜层面的多平面图像,并且具有较高的软组织分辨率,是诊断骨髓和中枢神经系统浸润的首选方法。但是带有心脏起搏器或体内有铁磁性物质的患者不能进行检查且其常规扫描的时间较长。

    67Ga是亲肿瘤显像剂,与肿瘤的组织数量有关,而与肿瘤的大小无关,在诊断、监测及预测长期的临床结果中具有重要的价值。然而对于初期的淋巴瘤,67Ga具有较低的灵敏度和特异度,同时由于肠道的生理性摄取,对于腹部和盆腔疾病检测的特异度和灵敏度较低[42]

    PET/MRI是将PET与MRI相结合的一种新的“一站式”成像技术,即能在一次成像时对全身情况进行综合评估,避免重复麻醉。在探测骨髓浸润方面具有较高的灵敏度、优越的软组织分辨率[43]以及可提供更多的病理生理信息,且无辐射危害。研究表明,与PET/CT相比,PET/MRI在显著降低辐射暴露的同时具有较高的病灶检出率[44]。因此,PET/MRI的初步应用是有意义的,但仍需要更多的前瞻性研究来证实PET/MRI在小儿淋巴瘤中的应用价值。

5.   总结
  • 综上所述,18F-FDG PET/CT已经成为评估儿童及青少年淋巴瘤的重要显像技术。作为功能显像技术,在探测淋巴结、脾脏方面较依据解剖形态改变的传统影像学检查方法具有更高的灵敏度,可通过一次显像发现更多病灶,在分期方面具有更高的准确性。同时,对治疗反应的早期评估、残存病灶性质的判定具有重要价值。然而由于儿童及青少年的特殊性,较低的复发率以及18F-FDG PET/CT检查不可避免的辐射问题,应权衡随访过程中监测复发和辐射暴露之间的利弊关系。同时18F-FDG PET/CT也存在一些局限,例如:18F-FDG PET/CT在检测肺内浸润(尤其是直径<5 mm)时具有较低的灵敏度,因此应结合胸部CT以提高其在检测肺内小结节上的准确性;在对患者的疗效评价中,可使用半定量分析法提高Deauville标准在中期18F-FDG PET/CT评估的准确性;患者进行多次影像检查会导致辐射剂量的积累,多项研究提出使用低剂量CT代替诊断性CT,用于PET显像中的衰减校正,从而减少扫描时间;此外,一些生理性情况可能导致假阳性。

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