Decision On SBRT, regular Or Less Fractions RT with a Simple TCP and EQD2 Calculation
Presentations
PO-GePV-M-258 (Sunday, 7/25/2021) [Eastern Time (GMT-4)]
Purpose: The determination to use SBRT or fractionated RT for none-small lung cancer (NSCLC) are typically determined by tumor size and location without patient specific TCP and EQD2 calculations. A method is proposed here to quickly assess the patient cancer and tissue cell distributions, TCP and EQD2.
Methods: Physician-defined CTV (or GTV) is decomposed into small ROIs, that are defined by intersections of radiopacity on an average of 4DCT scans and SUV of FDG PET images for an apparent cancer cell density. Nearby OARs are prioritized according to the patient conditions. Clinical SBRT plans with GTV < 22 cc and IMRT plans with CTVs > 500 cc are retrospectively analyzed. A unified multi-activation (UMA) model for cell survival of squamous cell lung carcinoma (SW1573, n=12, Do=1.1-Gy), adenocarcinoma of Lung (HX144, n=4.0, Do=2.2-Gy), (normal epithelial cell lines, n = 9.0, Do=1.1-Gy) and tumor cell density of 10⁵/gram are used for TCP and EQD2 calculations.
Results: Plans of standard SBRT in five 10-Gy fractions have approximately 100%TCP for most density levels of the cancer cells. A low density volume at the periphery of an adenocarcinoma with a GTV of 10 cc has the lowest 98%TCP and a high but acceptable EQD2 of 90-Gy to a 25-cc of the surrounding lung. TCP and EQD2 to the treatment in options of: (1) 1.8-Gyx37, (2) 3-Gyx22, or (3) 13.2-Gyx5 of a 750-cc squamous cell lung cancer, 0.1-cc spinal cord, 25-cc lungs, 5-cc heart, and 2-cc esophagus are (1) 33%, 36, 65, 40, 58-Gy, (2) 98%, 37, 99, 43, 75-Gy, and (3) 100%, 46, 227,73, 248-Gy, respectively, favor of the option (2).
Conclusion: The new method can quickly calculate TCP and EQD2 with apparent cell density and dose distribution which may help clinicians make accurate treatment decisions.
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