Oropharyngeal Carcinoma: RTP and Follow-up

Radiation therapy planning and follow-up in head and neck cancer

Amish Shah, PhD

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

 |  Oct 15, 2012

History

A 57-year-old male was admitted in the emergency room with a neck mass and hoarseness of voice in April 2011. The patient noted right upper neck swelling along with hoarseness of voice and difficulty in swallowing for a couple of months prior. A contrast CT of the neck revealed a mass in the right neck involving the oropharynx, hypopharynx and larynx. Histopathology of the biopsy specimen revealed squamous cell carcinoma. Patient was treated with induction chemotherapy with Taxol®, Carboplatin and Erubtix®.

 

Diagnosis

Two weeks following completion of induction chemotherapy (July 2011), the patient was referred for Fludeoxyglucose F 18* (18F FDG) PET•CT for complete staging prior to radiation therapy decision. Clinically, the patient demonstrated a palpable mass in posterior right tonsillar fossa extending down to the pharyngeal wall along with a palpable right neck node. The study was performed on a Biograph™ 40 TruePoint PET•CT (Fig. 1)

 

*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.

 

 

Fig. 1: PET•CT demonstrated an 18F FDG-avid mass in the right tonsillar fossa (SUVmax 6.6) extending from the level of cricoid cartilage down to the right aryepiglottic fold involving the pyriform sinus and the right vocal cord. A large soft-tissue mass in the right neck also is noted, comprising matted level 3 nodes, but with increased metabolic activity in only a portion of the lymph node (SUVmax 7.4) mass suggesting necrotic changes within the malignant nodes with significant residual disease. Compared to previous CT scan performed prior to induction chemotherapy, there was slight decrease in size of the neck mass which suggests partial response to chemotherapy in spite of significant amount of residual malignant neck nodal tissue. No distant metastases were visualized. Tracheostomy tube shows mild increased uptake as expected.

 

The planned course of adjuvant radiation therapy was delayed because the patient developed severe sepsis requiring hospitalization in late July 2011. In August 2011, a PET•CT was repeated for radiation therapy treatment planning. This PET•CT (Fig. 2, 3) showed a dramatic increase in disease progression, with the primary mass doubling in size.

 

Fig. 2-3: The images represent post-chemotherapy July 2011 (bottom image) and pre-radiation therapy August 2011 (top image). The increase in size and intensity of glucose metabolism of the oropharyngeal tumor and adjacent neck nodal mass is clearly demonstrated using Siemens Biograph 40 TruePoint PET•CT.

 

Specifically, there was an increase in the size and metabolic activity of the right pharyngeal mass involving the right lower oropharynx, hypopharynx and larynx, extending from right cricoid cartilage to the inferior aspect of the right tonsillar fossa and laterally to the right submandibular space. The SUVmax of the pharyngeal tumor was 19.2, which was a three-fold increase from the previous value of 6.0. The hypermetabolic neck node residual metastatic disease also showed increased metabolic activity. No new metastatic disease or distant metastases was visualized. In view of the significant volume of primary tonsillar fossa tumor and residual neck node metastases, adjuvant radiation therapy was planned. The plan was to treat the oropharynx, larynx and hypopharynx to 70 Gy at 2 Gy per fraction. Due to the severe extent of the disease, accelerated fractionated treatment course was advocated with 6 fractions delivered each week. The involved gross disease in the oropharynx and neck nodes was planned to receive 70 Gy. The neck region at high risk could receive 63 Gy, while the neck region with low risk would receive 57 Gy.

   

Comments

The interval progression of tumor in this case was due to the delay in radiation therapy delivery because of ancillary medical problems. The repeat high-resolution Biograph PET•CT in August 2011was necessary to reassess the true extent of primary tumor and metabolically active lymph node metastases. In view of the significant necrosis in the neck nodal mass secondary to induction chemotherapy and the interval progression prior to radiation, CT-based radiation planning in this case was clearly inadequate since it is difficult to define the margins of active nodal metastases with CT alone in presence of so much necrosis. A radiation plan based on the initial PET•CT performed in July 2011 was also inadequate since there was a clear possibility of tumor progression in the one month interval during which the patient’s general condition was worsened due to sepsis and which may accelerate tumor progression due to low immunity status. The repeat PET•CT performed in August 2011 clearly delineated the expanded margins of the primary and neck nodes, which helped clearly define the gross tumor volume (GTV) and planning target volume (PTV) margins. The escalated dose to the metabolically active tumor also was based on the outstanding Biograph PET•CT delineation. PET•CT-based radiation therapy planning is being increasingly dopted for oropharyngeal carcinoma. High accuracy for definition of metabolically active primary tumor volume, definition of necrotic zones and ability to detect cervical lymph node metastases not enlarged on CT makes PET•CT-based planning useful (Fletcher et al. J Nucl Med. 2008;49:480–508). PET helps delineate tumor areas or lymph nodes missed by CT or MRI as well identify regions requiring additional radiation dose (Troost et al J Nucl Med 2010; 51:66–76). 18F FDG PET has been used to direct dose rescalation to 18F FDG-avid subvolumes of the tumor applying either uniform or voxel intensity-based dose escalation (Schwarz et al. Head Neck 2005;27:478– 87.). Madani et al. (Int J Radiat Oncol Biol Phys 2007;68:126–35.) achieved dose escalation of up to 77.5 Gy in 3 Gy fractions using intensity-modulated radiation therapy (IMRT) with simultaneous integrated boost in 41 head and neck cancer patients.Several studies also have used sequential 18F FDG PET•CT studies during the course of radiation therapy to modify GTV based on metabolic and morphological response of tumor to achieve tumor dose escalation and reduce toxicity. Geets et al. (Radiother Oncol 2007;85:105–15.) performed contrast-enhanced CT, MRI and PET before the start of treatment and then once weekly during week 2 to 5 in a series of head and neck cancer patients. The GTVs elineated from PET were at all times significantly smaller than those defined on CT and MRI. During the course of treatment, the CTVs and PTVs progressively decreased. At 45 Gy, the mean PTV decreased by 48%. Modifications of the GTV and high dose volumes based on intra-radiation therapy PET•CT studies achieved significantly smaller GTVs compared to the initial plan which led to improved dose distributions. 

 

Conclusion
All these studies highlight the increasing adoption of 18F FDG PET•CT as the basis for radiation therapy planning for head and neck cancers, with particular emphasis on dose escalation to tumor areas with highest metabolic activity as well as adaptive radiation planning based on sequential PET•CT imaging during the course of chemoradiation to achieve better target delineation and dose escalation which translates in improved local control. This case illustrates the routine use of PET•CT for radiation planning in oropharyngeal cancer, particularly for correct delineation of margins of metabolically active tumor to define the PT for highest 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.