Abstract
Objective
PET/CT scan has been increasingly used in assessment of Head and Neck cancer prior to treatment for evaluation and for surveillance. In this study we aim to assess the utilization of PET/CT scan at a tertiary care hospital.
Methods
Retrospectively data was reviewed of all patients of Head and Neck cancer who underwent PET/CT scan for workup or for follow-up between July 2018 and December 2019. PET/CT scan done in the pre-treatment assessment and post-treatment surveillance were analyzed for its utility.
Results
A total of 145 patients were included. The main indication for pre-treatment PET/CT scan was loco-regionally advanced disease (62 of 90 patients, 68.8%). No specific indication was noted in 19 patients (21%). A significant change in treatment decision was seen in pre-treatment patients based on M stage following a PET/CT scan. However, no change was noted on the basis of T or N stage. In the post-treatment surveillance there was a significant correlation of type of recurrence with clinical assessment and indication for PET/CT scan. 37 out of 87 patients (42.5%) underwent PET/CT scan for no specific reason, of which, 07 patients (18.9%) were detected to have distant metastasis.
Conclusion
Role of PET/CT in the pre-treatment assessment is very limited and maybe confined to advanced local or regional disease. Post-treatment surveillance with PET/CT scan has a promising role and must be done as a baseline during 1st follow up at 03 months in all patients who have advanced disease and have undergone multi-modality treatment for the same.
Keywords: PET/CT, Head and neck cancer, Post-treatment surveillance
Introduction
Evaluation of Head and Neck carcinoma includes clinical assessment of primary and neck. In addition to clinical examination cross sectional imaging is essential for assessment of loco-regional disease as well as distant metastasis. Despite its cost, use of PET–CT scan has increased in the recent times for the assessment of the Head and Neck Cancers as it covers a larger area from the head to the thigh and also has an advantage of giving metabolic functional data which aids in better assessment of the cancer.
According to 2017 NCCN guidelines, indications for PET/CT in HNSCC include initial workup for stage III and IV disease, Nasopharyngeal cancer, Occult primary, Mucosal melanoma and post-treatment surveillance [1].
The assessment of head and neck cancers is focused on assessment of primary tumour, neck nodal status and distant metastasis. PET/CT scan performed in post-treatment surveillance can help differentiate between residual disease and treatment related changes [2]. In case of post surgical patients, additional value of PET CT Scan over clinical assessment and timing of PET/CT scan are uncertain [3].
In this study we aim to see the utilization of PET/CT scan in our hospital in patients with Head and Neck Cancer.
Objectives
(a)To study the various indications for ordering PET/CT Scan in patients with Head and Neck Cancers.
(b)To assess the implications of findings of pre-treatment PET/CT scan on staging and treatment planning in patients with Head and Neck Cancers.
(c) To assess the implications of findings of post-treatment scan on follow up.
Methodology
Data Source and Study Design
We retrospectively reviewed the data from Cancer registry of a tertiary care hospital of patients that were diagnosed with Head and Neck cancer between June 2018 and December 2019. PET/CT scan was done at our center with Siemens Biograph 2 integrated PET-CT scanner. The radiopharmaceutical 18-F FDG used in the procedure was produced in an in-house cyclotron Siemens RDS eclipse. Consultants of Nuclear Medicine of our hospital read the scans and based on this clinical staging was given. In our institution, all patients of Head and neck cancer are evaluated using conventional imaging like USG neck, CT Scan or MRI based on the site of the primary lesion. PET/CT scan is not performed in all patients of Head and neck cancer. It is reserved for patients with advanced loco-regional disease or in case of suspicion of distant metastasis. PET/CT scan is done in the post-treatment surveillance on the basis of pre-treatment staging of the disease, clinical assessment and any suspicion of residual/recurrent disease.
Study Population
All consecutive patients of Head and Neck Cancer who underwent PET/CT Scan either pre-treatment or post-treatment during the period were included in the study. The data of these patients were extracted. The clinical staging of patients included in the study was Tx, T1-T4b and N0–N3b. The clinical staging was done and pathological staging was not taken into account since the patients were a mix of surgical and non-surgical treatment modality.
Statistical Analysis
The demographics of patients with Age, Sex, Site, histopathology of tumour, ECOG status and cTNM staging were analyzed using descriptive statistics in SPSS 21.0. The descriptive statistics were represented as frequencies and mean with standard deviation.
The indications for ordering PET-CT scan in the pre or post treatment settings were noted.
Non-parametric Tests were used for analysis. In the pre-treatment PET/CT scan patients pre vs post PET/CT Scan T and N stage were compared using the Wilcoxon signed rank tests and M stage were compared using Chi-Square test. The pre vs post PET/CT scan group staging was compared using Spearman’s Rank Test. Pre vs post PET/CT scan treatment decision was compared using Chi Square test. The relation of T and N Stage with Post PET/CT scan Distant Metastasis was analyzed using Mann Whitney Test.
Post-treatment Indication for PET/CT Scan was compared to type of recurrence and treatment of recurrence using Chi Square–Fisher’s Exact Test. Post treatment clinical status on examination was compared to type of recurrence on PET/CT Scan using Chi Square–Fisher’s Exact Test.
Results
Descriptive Statistics
145 patients were included in the study, of which, 90 patients underwent a pre-treatment PET/CT scan and 90 patients underwent post-treatment PET/CT Scan. A total of 35 patients underwent PET/CT scan in both pre-treatment and post-treatment stage. 130 patients (89.7%) were males and 15 patients (10.3%) were females with a mean age of 57 years ± 10 yrs. 102 patients (70.3%) were ECOG 0 and 43 patients (29.7%) were ECOG 1. Site wise distribution of patients is shown in graph. 1 (original).
Graph. 1.
Site-wise distribution of patients
The most common histology was moderately differentiated squamous cell carcinoma (MDSCC) that comprised 78/145 (53.8%) followed by WDSCC 39/145 (26.9%), PDSCC 21/145 (14.5%), Well-differentiated thyroid Cancer 3/145 (2.1%), Adenocarcinoma 3/145 (2.1%) and Carcinoma in-situ 1/145 (0.7%).
Various indications for PET/CT scan in the pre-treatment group are as shown in Table 1 (original). Various indications for post-treatment PET/CT scan are as shown in Table 2 (original).
Table 1.
Indications for PET/CT scan in the pre-treatment patients (N = 90)
| S No | Indications for PET/CT Scan | n (%) |
|---|---|---|
|
1 2 3 4 5 6 7 |
No specific indication Locally advanced disease Extensive nodal burden Suspicious distant metastasis Contralateral neck nodes in small primary Suspicious primary with negative histology Unknown primary |
19 (21%) 46 (51%) 16 (17.8%) 4 (4.4%) 1 (1.1%) 2 (2.2%) 2 (2.2%) |
Table 2.
Indications for PET/CT Scan in the post-treatment surveillance (N = 90)
| S No | Indication for PET/CT Scan | n (%) |
|---|---|---|
|
1 2 3 4 5 6 |
Suspicious local disease Suspicious regional disease Suspicious distant metastasis Response assessment to NACT No specific indication To rule out distant metastasis for surgery workup |
36 (40%) 4 (4.4%) 7 (7.8%) 1 (1.1%) 40 (44.4%) 2 (2.2%) |
Pre-Treatment PET/CT Scan
There was no significant change in Pre vs post PET/CT scan T stage (p > 0.05). There was a significant change in pre vs post PET/CT scan N stage (p < 0.001) and M stage (p < 0.05). The overall TNM group staging following PET/CT scan showed a strongly significant change compared to clinical workup staging using conventional imaging (p < 0.001). A total of 4 of the 90 patients (4.44%) were detected to have synchronous primary.
There was no significant correlation between T stage and Post PET/CT scan distant metastasis (p > 0.05). There was no significant correlation between N stage and Post PET/CT scan distant metastasis (p > 0.05). However, on cases to case assessment it was observed that on subgrouping the patients based on T and N stage out of 12 cases with distant metastasis 6 (50%) had advanced local disease (T3-T4b), 03 (25%) had loco-regional advanced disease (T3-T4b, N2a-N3b), 02 (16.67%) had advanced nodal disease (N2a-N3b) and 01 (8%) had small primary and nodal disease (T0-T2, N0-N1).
There was a strongly significant difference in treatment decision before and after PET/CT scans (p < 0.001).
Post Treatment PET/CT Scan
It was observed that 53/90 (58.9%) of the post-treatment PET/CT scans were done on 1st follow up, 17/90 (18.9%) during 2nd follow up, 10/90 (11.1%) during 3rd follow up and rest during subsequent 2–3 follow ups.
There was a significant correlation on comparison of post treatment clinical assessment of patients with post PET/CT Scan type of recurrence p < 0.001 on Fisher’s exact test and p < 0.05 on linear-by-linear association. There was also a significant correlation noted on comparing the indications for PET/CT scan in post treatment patients with type of recurrence (p < 0.001 on Fisher’s exact test) and (linear-by-linear association showing p < 0.05).
Out of 36 patients with suspicious local disease 29 (81%) were detected to have local residual disease or recurrence. 5 out of 5 patients with suspicious nodal disease were confirmed to have residual or recurrence in nodes. In addition 5 patients out of 36 who had suspicious local disease were detected to have nodal metastasis.
Total 40 post treatment PET/CT scans were done with no specific indication of which, 07 patients (17.5%) were detected to have distant metastasis.
A significant correlation was noted between indications for post treatment PET/CT scans with post scan treatment offered for the recurrence or residual disease (p < 0.001). However, on Linear-by-Linear association the correlation was non significant (p > 0.05).
Discussion
The role of PET/CT scan for the assessment of primary tumour is very limited in the pre-treatment imaging with no significant change noted in treatment planning based on increase or decrease of T-stage. The primary tumour assessment is of paramount importance in cases of unknown primary and in post-treatment surveillance and in some cases for assessment of synchronous primary. Jorgensen et al. in their study showed that PET/CT altered the overall T stage in 0% of their patients, 23.1% of N Stage and 3.8% of M Stage. Overall stage was not significantly altered and no significant change in the treatment offered [4]. In our study it was noted that 19 patients (21%) in the pre-treatment group underwent a PET/CT scan for no specific indications. This was possibly due to the tests ordered at other hospitals during the workup prior to referral or due to individual clinician or resident’s choice. 2/90 (2.2%) patients had an altered T stage after PET/CT scan which was not statistically significant (p = 1.000) and this did not change the treatment plan.
PET/CT scan can detect unto 30% of primary tumours in patients presenting with cervical lymph nodes from unknown primary [5, 6]. A study by Zhu et al. showed primary tumour detection rate of 44% sensitivity and 97% specificity [7]. In our study only two patients were cases of Unknown primary and following PET/CT scan primary site could be detected in both the patients.
It was noted in our group that 4 of 90 patients (4.44%) were detected to have synchronous primary, which was not detected on conventional workup. FDG PET/CT scan detects a considerable number of synchronous primaries with a prevalence of 8% [8].
Neck nodal metastasis is known to be an independent factor for poor prognosis with a drop in survival by 50% in N + disease. Use of pre-treatment PET/CT scan to assess the nodal stage may not change the actual treatment in most of HNSCC; however, it may alter the treatment planning for radiation. Kyzas et al. in their meta-analysis showed that PET/CT sensitivity was 79% and specificity was 86%. However, for cN0 it was only 50% and 87% respectively [9]. In our study in the pre-treatment group of patients there was a change in N stage in 18 out of 90 patients (20%) which was significant (p < 0.001), however, treatment modality did not significantly change due to the N stage. It had an impact on treatment planning for radiation.
Role of PET/CT scan in evaluation of HNSCC is of utmost importance to detect distant metastasis, presence or absence of which determines the management protocols and the prognosis of the disease. The common high risk factors for distant metastasis are ≥ 3 nodes, extra nodal spread, N3 nodes, Low jugular lymph nodes, bilateral cervical lymph nodes, second primary, poorly differentiated carcinoma, local recurrence and regional recurrence [10–13].
In a study by de Bree R et al. the sensitivity of FDG PET/CT in detecting distant metastasis was 46.2%, specificity of 96.4% and PPV and NPV of 82.8% and 82.6% respectively [11]. In our study, 12 out of 90 patients with pre-treatment PET/CT Scan were detected to have distant metastasis of which, 06 (50%) patients had locally advanced disease (T3-T4b), 03 (25%) had loco-regionally advanced disease (T3-T4b/N2-N3), 01 had Unknown Primary and 02 had Early local disease/Unknown primary with advanced regional disease. Pre vs post PET/CT scan M stage showed a significant change (p = 0.016).
In a study by Rohde et al., they observed that based on CXR/MRI, 99% of patients were recommended curative treatment and 1% for palliative treatment. The same patients were recommended 9% palliative treatment based on PET/CT. The absolute difference of 8% was statistically significant [14]. In another study by Sun Ryu et al. PET/CT staging led to management changes in 15.7% of which 4.8% had a high impact due to distant metastasis. Other 10.9% had a moderate impact with change in treatment planning due to upstaging of nodal disease [15]. In our study there was a change in treatment decision following PET/CT scan in 11 out of 90 patients (12.2%), which was statistically significant (p < 0.001). The change in decision was noted primarily because of change in M stage following a PET/CT scan. There was no change in treatment decision due to T or N Stage. However, treatment planning for Radiation was modified based on change in N stage following PET/CT scan.
PET/CT scan has an important role in post-treatment surveillance of patients with Head and Neck Cancer. Of which most important role is in surveillance for nodes. In a meta-analysis by Gupta et al. analysis for identifying neck recurrence gave a mean sensitivity of 74% (95% CI 50–89%) and mean specificity of 88% (95% CI 74–95%). The pooled mean PPV and NPV for detection of recurrent disease in the neck was 49% (95% CI 29–70%) and 96% (95% CI 84–99%) respectively [16]. In our study we noted that in post-treatment surveillance 05 patients had suspicious nodal residual / recurrence clinically, of which, all 05 were proven to have disease with PET/CT scan and histopathology. Also 05 out of the 36 patients with suspicious local residual/recurrence were detected to have nodal disease in addition. The sensitivity, specificity, PPV and NPV of PET/CT scan for N staging in our study was 67%, 96%, 73% and 95% respectively.
Gupta et al. in the meta-analysis showed a pooled sensitivity and specificity for detecting residual disease at the primary site to be 94% (95% CI 87–97%) and 82% (95% CI 76–86%), respectively. The pooled mean PPV and NPV was 75% (95% CI 68–82%) and 95% (95% CI 92–97%), respectively. In our study it was noted that the sensitivity, specificity, PPV and NPV for detecting residual disease at primary site was 85%, 96%, 93% and 91% respectively [16].
In our study the main indications for PET/CT scans in the post treatment surveillance were as enumerated in Table 2. Of the 40 PET/CT scans ordered for no specific indication, 07 (17.5%) were detected to have distant metastasis.
The timing of PET/CT scan is an important factor. Some studies have concluded that PET/CT scan be done as early as 2 months after therapy [17, 18]. Nelissen et al. in their study found that the test conducted before 3 months had higher false negative and false positive rates [19]. The best clinical approach is to perform a base line scan after treatment at 4–6 months and subsequent PET/CT to be performed in case of clinical suspicion for recurrence [20]. In our study, majority of patients (53/90, 58.9%) who underwent post treatment PET/CT scan were during the 1st follow up at around 03 months. 17 of 90 (18.9%) patients underwent follow up scan at around 06 months. 10/90 (11.1%) at 3rd follow up and the remaining 10 patients in the 4th or subsequent follow up.
Limitations of the Study
1. Statistical analysis based on sites/sub-sites was not done because of small number of patients in each.
2.Number of patients who underwent both pre and post treatment PET/CT scan were very few to draw any conclusions.
Conclusion
Assessment of Head and Neck cancer is best performed with cross-sectional imaging like CT Scan and MRI. PET/CT scans has a limited role in pre-treatment workup of Head & Neck Cancer and should be limited to loco-regionally advanced disease. PET/CT scan in post-treatment surveillance has a very significant role and must be performed in all advanced head and neck cancers that have undergone multi-modality treatment as a baseline during 1st follow-up at around 03 months and during subsequent follow-up if clinically indicated.
Author’s Contribution
Rajeev Chugh Conceptualization, methodology, Formal analysis, Investigation, Data curation, writing original draft, review and editing, Supervision, Visualization. DK Gupta Methodology, Validation, Formal analysis, Review and Editing. Bhaumik Patel Investigation, Resources, Data curation. Rekha Vashisth Validation, Methodology, Review and Editing. Arun Ravi John Methodology, Data curation, Resources, Review and Editing. Sunil Goyal Methodology, Review and Editing.
Funding
The study was retrospective and data was collected from the registry of the hospital. No funding was obtained from by any person/agency.
Data Availability
All the relevant data and material used for the study are available with the corresponding author in case needed for the purpose of reference.
Compliance with Ethical Standards
Conflict of interest
The authors declare that there is no conflict of Interest.
Ethics Approval
This is an observational study and the Institutional Ethics committee has confirmed that no ethical approval is required.
Consent for publication
The authors’ consent for the publication of the article if accepted by the journal. Being an observational study and data collected from the registry, the same was not obtained from the patients.
Footnotes
Publisher's Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Contributor Information
Rajeev Chugh, Email: drrajeevchugh@ahrr.org.
D. K. Gupta, Email: docdk2000@yahoo.com
Bhaumik Patel, Email: patel_bhaumik@hotmail.com.
Arun Ravi John, Email: arun_medico2003@yahoo.co.in.
Rekha Vashisth, Email: rekhasomvashisth@gmail.com.
Sunil Goyal, Email: drsunilgoyal@yahoo.co.in.
References
- 1.National Comprehensive Cancer Network. NCCN guidelines insights: head and neck cancers, version 2.2017 [DOI] [PubMed]
- 2.Kitagawa Y, Nishizawa S, Sano K, Ogasawara T, Nakamura M, Sadato N, Yoshida M, Yonekura Y. Prospective comparison of 18F-FDG PET with conventional imaging modalities (MRI, CT, and 67Ga scintigraphy) in assessment of combined intraarterial chemotherapy and radiotherapy for head and neck carcinoma. J Nucl Med. 2003;44(2):198–206. [PubMed] [Google Scholar]
- 3.Shintani SA, Foote RL, Lowe VJ, Brown PD, Garces YI, Kasperbauer JL. Utility of PET/CT imaging performed early after surgical resection in the adjuvant treatment planning for head and neck cancer. Int J Radiat Oncol Biol Phys. 2008;70(2):322–329. doi: 10.1016/j.ijrobp.2007.06.038. [DOI] [PubMed] [Google Scholar]
- 4.Jorgensen JB, Smith RB, Coughlin A, Spanos WC, Lohr MM, Sperry SM, Militsakh O, Zitsch RP, III, Yueh B, Dooley LM, Panwar A. Impact of PET/CT on staging and treatment of advanced head and neck squamous cell carcinoma. Otolaryngol Head Neck Surg. 2019;160(2):261–266. doi: 10.1177/0194599818794479. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 5.Regelink G, Brouwer J, de Bree R, Pruim J, van der Laan BF, Vaalburg W, Hoekstra OS, Comans EF, Vissink A, Leemans RC, Roodenburg JL. Detection of unknown primary tumours and distant metastases in patients with cervical metastases: value of FDG-PET versus conventional modalities. Eur J Nucl Med Mol Imaging. 2002;29(8):1024–1030. doi: 10.1007/s00259-002-0819-0. [DOI] [PubMed] [Google Scholar]
- 6.Stoeckli SJ, Mosna-Firlejczyk K, Goerres GW. Lymph node metastasis of squamous cell carcinoma from an unknown primary: impact of positron emission tomography. Eur J Nucl Med Mol Imaging. 2003;30(3):411–416. doi: 10.1007/s00259-002-1078-9. [DOI] [PubMed] [Google Scholar]
- 7.Zhu L, Wang N. 18F-fluorodeoxyglucose positron emission tomography-computed tomography as a diagnostic tool in patients with cervical nodal metastases of unknown primary site: a meta-analysis. Surg Oncol. 2013;22(3):190–194. doi: 10.1016/j.suronc.2013.06.002. [DOI] [PubMed] [Google Scholar]
- 8.Strobel K, Haerle SK, Stoeckli SJ, Schrank M, Soyka JD, Veit-Haibach P, Hany TF. Head and neck squamous cell carcinoma (HNSCC)–detection of synchronous primaries with 18 F-FDG-PET/CT. Eur J Nucl Med Mol Imaging. 2009;36(6):919–927. doi: 10.1007/s00259-009-1064-6. [DOI] [PubMed] [Google Scholar]
- 9.Kyzas PA, Evangelou E, Denaxa-Kyza D, Ioannidis JP. 18F-fluorodeoxyglucose positron emission tomography to evaluate cervical node metastases in patients with head and neck squamous cell carcinoma: a meta-analysis. J Natl Cancer Inst. 2008;100(10):712–720. doi: 10.1093/jnci/djn125. [DOI] [PubMed] [Google Scholar]
- 10.Deurvorst SE, Hoekstra OS, Castelijns JA, Witte BI, Leemans CR, de Bree R. Clinical value of 18 FDG PET/CT in screening for distant metastases in head and neck squamous cell carcinoma. Clin Otolaryngol. 2018;43(3):875–881. doi: 10.1111/coa.13074. [DOI] [PubMed] [Google Scholar]
- 11.de Bree R, Deurloo EE, Snow GB, Leemans CR. Screening for distant metastases in patients with head and neck cancer. Laryngoscope. 2000;110(3 Pt 1):397–401. doi: 10.1097/00005537-200003000-00012. [DOI] [PubMed] [Google Scholar]
- 12.Kuperman DI, Auethavekiat V, Adkins DR, Nussenbaum B, Collins S, Boonchalermvichian C, Trinkaus K, Chen L, Morgensztern D. Squamous cell cancer of the head and neck with distant metastasis at presentation. Head Neck. 2011;33(5):714–718. doi: 10.1002/hed.21529. [DOI] [PubMed] [Google Scholar]
- 13.Senft A, de Bree R, Hoekstra OS, Kuik DJ, Golding RP, Oyen WJ, Pruim J, van den Hoogen FJ, Roodenburg JL, Leemans CR. Screening for distant metastases in head and neck cancer patients by chest CT or whole body FDG-PET: a prospective multicenter trial. Radiother Oncol. 2008;87(2):221–229. doi: 10.1016/j.radonc.2008.03.008. [DOI] [PubMed] [Google Scholar]
- 14.Rohde M, Nielsen AL, Johansen J, Sørensen JA, Diaz A, Asmussen JT, Gerke O, Thomassen A, Gyldenkerne N, Døssing H, Bjørndal K. Up-front PET/CT changes treatment intent in patients with head and neck squamous cell carcinoma. Eur J Nucl Medi Mol Imaging. 2018;45(4):613–621. doi: 10.1007/s00259-017-3873-3. [DOI] [PubMed] [Google Scholar]
- 15.Ryu IS, Roh JL, Kim JS, Lee JH, Cho KJ, Choi SH, Nam SY, Kim SY. Impact of 18F-FDG PET/CT staging on management and prognostic stratification in head and neck squamous cell carcinoma: a prospective observational study. Eur J Cancer. 2016;1(63):88–96. doi: 10.1016/j.ejca.2016.05.002. [DOI] [PubMed] [Google Scholar]
- 16.Gupta T, Master Z, Kannan S, Agarwal JP, Ghsoh-Laskar S, Rangarajan V, Murthy V, Budrukkar A. Diagnostic performance of post-treatment FDG PET or FDG PET/CT imaging in head and neck cancer: a systematic review and meta-analysis. Eur J Nucl Medi Mol Imaging. 2011;38(11):2083. doi: 10.1007/s00259-011-1893-y. [DOI] [PubMed] [Google Scholar]
- 17.Leung AS, Rath TJ, Hughes MA, Kim S, Branstetter BF., IV Optimal timing of first posttreatment FDG PET/CT in head and neck squamous cell carcinoma. Head Neck. 2016;38(S1):E853–E858. doi: 10.1002/hed.24112. [DOI] [PubMed] [Google Scholar]
- 18.Moeller BJ, Rana V, Cannon BA, Williams MD, Sturgis EM, Ginsberg LE, Macapinlac HA, Lee JJ, Ang KK, Chao KC, Chronowski GM. Prospective risk-adjusted [18F] fluorodeoxyglucose positron emission tomography and computed tomography assessment of radiation response in head and neck cancer. J Clin Oncol. 2009;27(15):2509. doi: 10.1200/JCO.2008.19.3300. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 19.Nelissen C, Sherriff J, Jones T, Guest P, Colley S, Sanghera P, Hartley A. The role of positron emission tomography/computed tomography imaging in head and neck cancer after radical chemoradiotherapy: a single institution experience. Clin Oncol. 2017;29(11):753–759. doi: 10.1016/j.clon.2017.07.010. [DOI] [PubMed] [Google Scholar]
- 20.Ho AS, Tsao GJ, Chen FW, Shen T, Kaplan MJ, Colevas AD, Fischbein NJ, Quon A, Le QT, Pinto HA, Fee WE., Jr Impact of positron emission tomography/computed tomography surveillance at 12 and 24 months for detecting head and neck cancer recurrence. Cancer. 2013;119(7):1349–1356. doi: 10.1002/cncr.27892. [DOI] [PubMed] [Google Scholar]
Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
All the relevant data and material used for the study are available with the corresponding author in case needed for the purpose of reference.