Program Information
Tumor Control Probability Increase Using SBRT Boost for PET Positive Lymph Nodes for Cervical Cancer
J Snyder*, W Sun , A Willett , Y Kim , University Of Iowa Hospitals and Clincs, Department of Radiation Oncology, Iowa City, IA
Presentations
WE-G-FS1-8 (Wednesday, August 2, 2017) 4:30 PM - 6:00 PM Room: Four Seasons 1
Purpose: This study examines the use of an SBRT boost to PET positive lymph nodes (PET (+) LN) metastases from locally advanced cervical cancer and evaluates overall tumor control probability (TCP) and OAR doses.
Methods: 10 patients with cervical cancer and PET (+) LN metastasis who received EBRT (45Gy in 25 fractions) followed by an EBRT boost (5.4-9 Gy in 3-5 fractions) and HDR BT (16-30Gy in 3-5 fractions) were retrospectively analyzed. Three of these patients experienced locoregional recurrence. SBRT boost plans (24Gy in 3 fractions) were generated as a replacement for the clinical boost doses. All physical dose maps were converted into equivalent 2Gy dose per fraction (EQD2) dose maps using a α/β value of 10 for PET (+) LN and 3 for all other tissue. Logistic TCP models were modeled based upon 1) institutional and 2) SBRT clinical outcome data. The rectum (V50), bladder (V65), and bowel (V45) doses were assessed by the QUANTEC dose constraints.
Results: The average D90 and mean EQD2 doses to the PET (+) LN for the SBRT technique were 37.4Gy10 and 41.2Gy10 greater than those of the clinical approach. The EQD2 D90 and mean doses were 88.5±7.5Gy and 96.2±9.5Gy for the SBRT plan versus 51.1±4.1Gy and 54.9±4.0Gy for the clinical plan. The TCP values of the SBRT technique were on average 41±14% and 71±10% higher than that of the clinical technique when TCP was modeled using institutional and SBRT clinical outcome data, respectively. All OAR doses for both the SBRT and clinical techniques were less than the QUANTEC dose limits.
Conclusion: The use of SBRT yielded significantly higher EQD2 doses to PET positive lymph node metastases while remaining within the QUANTEC dose limits for all OAR’s. This dose escalation results in a higher TCP value when institutional and clinical SBRT outcomes are modeled.
Funding Support, Disclosures, and Conflict of Interest: Dr. Kim reports grants from NIH/NIBIB 1R01EB020665-01, grants from NIH/NIBIB R01EB020665-02, grants from NIH 1R21CA209874-01, grants from NIH STTR Phase I, outside the submitted work; .
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