PET•CT RTP and Follow-up in a Case of Lung Carcinoma

PET•CT during follow-up of radiation therapy for lung cancer

Amish Shah, PhD

Case study data provided by MD Anderson Cancer Center, Orlando, Fla., USA

 |  2012-10-25

History
A 64-year-old female presented with leftsided chest pain, cough and fever. Initial CT of the chest demonstrated postobstructive pneumonia in the left upper lobe of the lung and left hilar lymphadenopathy. In view of the CT findings being suspicious of malignancy, a bronchoscopy with biopsy of the left upper lobe mass was performed. Histopathology confirmed the lesion to be poorly differentiated non-small cell lung carcinoma. For comprehensive staging, the patient was referred for fludeoxyglucose F 18* (18F FDG) PET•CT. The 40-slice PET•CT study was performed on a Biograph™ TruePoint system (Fig. 2).

 

*Siemens’ PETNET Solutions is a manufacturer of fludeoxyglucose F 18 injection (18F FDG). Indication and important safety information as approved by the US Food and Drug Administration can be found at the bottom of the page for 18F FDG, adult dose 5-10 mCi, administered by intravenous injection.

Diagnosis
Since the patient had advanced locoregional disease (T2,N3,M0), she was subjected to definitive concurrent chemoradiation therapy, which offered the best opportunity for local control. Patient was treated on the TomoTherapy platform using intensity-modulated radiation therapy (IMRT) and 6 MV photons. The patient received a total dose of 66 Gy in 2 Gy daily fractions to areas of gross disease. During the course of therapy, the patient was noted to have a favorable response to treatment at which point a re-plan became necessary. The final eight fractions of radiation therapy were delivered according to a modified IMRT treatment plan. Following concurrent chemoradiation therapy with Carboplatin/Cisplatin and Etoposide, the patient was clinically reviewed and referred for follow up PET•CT, which was performed 11 weeks after completion of the last fraction of radiation. Although the restaging PET•CT showed dramatic  response to chemoradiation (Fig. 1), there were areas of persistent disease both within the primary tumor and mediastinal lymph nodes. In view of presence of residual disease, the patient was advised to undergo two additional cycles of chemotherapy for consolidation purposes. 

 

Fig. 2
Scan shows large irregular hypermetabolic left upper lobe mass with associated obstructive lobar collapse along with large hypermetabolic lymph node metastases in the left hilar, paratracheal and left supraclavicular region. The primary tumor showed a SUVmax of 26.2. The lymph node lesions were 2 to 3.5 mm in size with SUVmax of 33.2. There was, however, no evidence of distant metastases. Examination Protocol: 10 mCi 18F FDG 60-minute post-injection delay. Two minute per bed PET acquisition.

 

Fig. 3
The image demonstrates 3D tumor region of interest (ROI) generated from the fused PET•CT using a threshold of 13% of the SUVmax, which covered the visually apparent primary tumor and nodal metastases. Planning target volume for the primary tumor and adjacent hilar and paratracheal, as well as the supraclavicular nodes planned on the PET•CT data also are shown in the bottom row defined using Pinnacle treatment planning software. PET•CT helped to clearly delineation the primary tumor margin from the adjacent atelectatic lung for tumor gross tumor volume delineation, as well as assisting to define the true extent of lymph node involvement.


 

Comments
PET•CT is increasingly being used for radiation therapy planning for lung cancer. The high sensitivity of Biograph PET•CT scanners for detection of early lymph node metastases as shown in this case demonstrating high glucose avidity even when normal in size on CT helps accurate staging of lung carcinoma and to define the involved lymph nodal groups to include in the radiation therapy portal.

 

Conclusion
The use of 18F FDG PET•CT during follow-up of radiation therapy for lung cancer is complicated by 18F FDG uptake in post-radiation inflammation. This is why an interval of 8 to 12 weeks is recommended for a follow-up 18F FDG PET•CT after radiation therapy completion to minimize this effect. In the present study, this interval was maintained and substantial decrease in SUV was demonstrated, which underlined the efficacy of the radiation plan and dose prescription. It is interesting to note that the areas of residual tumor visualized in the posttherapy PET correspond to regions of highest 18F FDG uptake in the pre-therapy scans, clearly supporting the hypothesis that lung tumor areas with the highest metabolically activity are at highest risk of local failure and need dose escalation. 


*Fludeoxyglucose F 18 Injection
INDICATIONS AND USAGE

Fludeoxyglucose F 18 injection (18F FDG) is indicated for positron emission tomography (PET) imaging in the following setting:
Oncology: For assessment of abnormal glucose metabolism to assist in the evaluation of malignancy in patients with known or suspected abnormalities found by other testing modalities, or in patients with an existing diagnosis of cancer.
 

IMPORTANT SAFETY INFORMATION
Radiation Risks

Radiation-emitting products, including fludeoxyglucose F 18 injection, may increase the risk for cancer, especially in pediatric patients. Use the smallest dose necessary for imaging and ensure safe handling to protect the patient and health care worker.
 

Blood Glucose Abnormalities
In the oncology and neurology setting, suboptimal imaging may occur in patients with inadequately regulated blood glucose levels. In these patients, consider medical therapy and laboratory testing to assure at least two days of normoglycemia prior to fludeoxyglucose F18 injection administration.
 

Adverse Reactions
Hypersensitivity reactions with pruritus, edema and rash have been reported; have emergency resuscitation equipment and personnel immediately available.


Full Prescribing Information for Fludeoxyglucose F 18 Injection


Fludeoxyglucose F 18 injection is manufactured by Siemens' PETNET Solutions, 810 Innovation Drive, Knoxville, TN 39732
 

The statements by Siemens customers described herein are based on results that were achieved in the customer's unique setting. Since there is no "typical" hospital and many variables exist (e.g., hospital size, case mix, level of IT adoption) there can be no guarantee that other customers will achieve the same results.