2017 Section 7 Green Book

Clinical Review & Education Review

Use of FDG-PET/CT in Oropharyngeal Squamous Cell Carcinoma

Figure 3. Value of Positron Emission Tomography/Computed Tomography (PET/CT) in Radiation Therapy Planning for Oropharyngeal Squamous Cell Carcinoma (OPSCC)

A

B

C

70 Gy 60 Gy

70 Gy 60 Gy

Imaging of a man in his 50s who received a diagnosis of stage cT3N2cM0 human papillomavirus–negative OPSCC. A, Pretreatment PET/CT. B, Simulation CT. These were fused for radiation therapy planning, which aided in identifying gross tumor volumes (yellow), including posterior oropharyngeal primary, bulky adenopathy of the right side of the neck with central necrosis, and small left

neck nodes that did not meet CT size criteria but were FDG avid. Planning target volumes were prescribed 70 Gy (red) and 60 Gy (blue). C, The resulting intensity-modulated radiotherapy plan was conformal to the target contours, and the patient had a complete response to treatment.

diation therapy on the normal surrounding tissues and achieve the best treatment response, radiation dose and volume should be ad- justed according to the extent of primary and nodal disease and the risk of subclinical disease in each area ( Figure 3 ). 30 Modern radio- therapy technology and intensity-modulated radiotherapy allow for such dose adjustment. 31 Positron emission tomography in combi- nationwithCT orMRI can provide biological tumor information plus anatomicfeatures,whichcanchangeradiotherapytargetplanning. 32 Chatterjee et al 31 reported that PET/CT ismuchbetter than contrast- enhanced CT in radiotherapy planning for OPSCC because it pro- videsmore clinically relevant information anddecreases the chance of a geographical miss. Gross tumor volume (GTV) is an important factor for intensity- modulated radiotherapy planning. Computed tomography, with or without contrast, often cannot assess GTVprecisely in the orophar- ynx and neck as a result of lack of clear demarcation between tu- mor and normal surrounding tissues. 33 In addition, when using PET in preradiotherapy planning, the radiation field size and dose may increase as a result of identification of normal-size LNswith FDGup- take (Figure3). 34 Gross tumor volume attained fromPET/CT imaging was reported to be different from that of contrast CT in advanced stages of OPSCC, which changes the area and dosage of radiotherapy. 31 Paulino et al 35 showed that approximately 25% of patients did not receive the optimal radiation dosage by using CT GTV, and PET/CT not only changes the GTV for radiotherapy plan- ning but also defines the initial extent of disease more precisely. 36 On the other hand, PET may underestimate tumor volume defini- tionbecauseof tumor necrosis or lack ofmetabolic activity in an area of tumor, especially in HPV-related nodal metastases (Figure 3); so alongsidePET,othermodalitiessuchasclinicalexamination,contrast- enhanced CT, or MRI should be considered. 33 Not only is PET/CT highly accurate in detecting extent of tumor and nodal involve- ment for pretreatment radiotherapy planning, but it also provides associated staging and prognostic information for determination of whether to use concurrent chemotherapywith radiation therapy. 34

Using contrast-enhanced PET/CT leads to a combined anatomic, metabolic, and biologic approach to radiation therapy planning of head and neck cancers. 36

Value of PET in Evaluating Therapy Response of OPSCC Treatment of OPSCC with surgical or radiation strategies leads to tissue changes such as edema, hyperemia, and fibrosis, and these changes affect the accuracy of CT and MRI in detecting residual and/or recurrent lesions. Because fibrosis and/or scar tissue has no associated metabolic activity on PET, PET can better discrimi- nate between fibrosis and/or scarring vs recurrent and/or residual disease than the other imaging modalities. Some studies evalu- ated the ability of PET to detect residual tumor and therapy response. 33 Most of these studies reported that PET is more effective than CT and MRI for estimating the response to chemo- radiotherapy of OPSCC. 10 One of the most important factors in therapy assessment is using reliable, accurate, and valid interpre- tation criteria. Recently, Marcus et al 37 presented a standardized interpretation criterion for head and neck PET/CT (Hopkins crite- ria), which demonstrated excellent interreader reliability, accu- racy, and survival prediction. According to the Hopkins criteria, the activity in the internal jugular vein and liver were taken as a reference and the FDG uptake of the suspicious area was com- pared with the uptake of the internal jugular vein and liver (eTable 3 in the Supplement ). Studies showed that FDG-PET can assess volume changes dur- ing radiotherapy and is a good imaging modality to evaluate early therapy response. 32 This couldbe used tohelpphysicians assess the behavior of tumor during therapy and change the treatment strat- egies if needed. Other reports showed a significant association be- tween pretreatment value of SUV and response to chemotherapy. There was a reverse association between SUV and therapy re-

JAMA Otolaryngology–Head & Neck Surgery January 2016 Volume 142, Number 1 (Reprinted)

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