Joseph Rajendran

Hypoxia Imaging with [F-18] FMISO-PET in Head and Neck Cancer: Potential for Guiding Intensity Modulated Radiation Therapy in Overcoming Hypoxia-Induced Treatment Resistance

BACKGROUND AND PURPOSEnPositron emission tomography (PET) imaging with [F-18] fluoromisonidazole (FMISO) has been validated as a hypoxic tracer. Head and neck cancer exhibits hypoxia, inducing aggressive biologic traits that impart resistance to treatment. Delivery of modestly higher radiation doses to tumors with stable areas of chronic hypoxia can improve tumor control. Advanced radiation treatment planning (RTP) and delivery techniques such as intensity modulated radiation therapy (IMRT) can deliver higher doses to a small volume without increasing morbidity. We investigated the utility of co-registered FMISO-PET and CT images to develop clinically feasible RTPs with higher tumor control probabilities (TCP).nnnMATERIALS AND METHODSnFMISO-PET images were used to determine hypoxic sub-volumes for boost planning. Example plans were generated for 10 of the patients in the study who exhibited significant hypoxia. We created an IMRT plan for each patient with a simultaneous integrated boost (SIB) to the hypoxic sub-volumes. We also varied the boost for two patients.nnnRESULTnA significant (mean 17%, median 15%) improvement in TCP is predicted when the modest additional boost dose to the hypoxic sub-volume is included.nnnCONCLUSIONnCombined FMISO-PET imaging and IMRT planning permit delivery of higher doses to hypoxic regions, increasing the predicted TCP (mean 17%) without increasing expected complications.

SU‐FF‐J‐106: FMISO‐PET Hypoxia Imaging: A Novel Method to Plan IMRT‐Based Boost Radiation to Hypoxic Subvolumes

Purpose: To investigate the use of [F‐18] fluoromisonidazole (FMISO) PET and intensity modulated radiation treatment(IMRT) planning to escalate the dose to hypoxic subvolumes in patients with advanced head and neck tumors.Method and Materials: Seventy‐three patients with head and neck cancer underwent FMISO‐PET scans, with fifty‐three of them also undergoing FDG‐PET scans as part of ongoing research studies. An initial treatment plan used a PTV defined with a 0.5‐cm margin around physician‐defined primary GTVs and affected nodal systems. The prescription dose is 70 Gy to the PTV and 50 Gy to the affected nodes, while sparing the spinal cord, mandible, and parotid glands. Physician‐defined regions of enhanced FMISO signal were used to define boost volumes on coregistered FMISO‐PET/CT images. The boost plan prescription dose to the hypoxic subvolumes is an additional 10 Gy. Results: Initial results from example treatment plans for two head and neck cancer patients are as follows (average over patients): to the PTV V100 = 87.2%, Dmin = 6081 cGy, D10 = 7303 cGy and to the nodal system V100 = 95.9%, Dmin = 4764 cGy, D10 = 5280 cGy. The IMRT boost plan yields V100 = 95.1%, Dmin = 979 cGy, D10 = 1012 cGy to the hypoxic PTV. The critical structures of interest received the following dose distributions from the composite IMRT plans: cord D1 = 3890 cGy, left (contralateral) parotid gland D1 = 1965 cGy, right parotid gland D1 = 4907 cGy (same side as primary tumor), and mandible D5 = 6220 cGy. Conclusion: We demonstrate the feasibility of directing dose‐escalatedIMRT to hypoxic subvolumes in head and neck cancer using coregistered FMISO‐PET and CTimages. Ongoing research and patient studies are expected to provide conclusive information on the clinical role of this procedure.