Radiation and Cancer Physics

SS 32 - Physics 10 - Imaging for Response Assessment II

237 - Metabolic Regression Velocity Post Lung SBRT - How Early Do We Get to See !

Wednesday, October 24
8:45 AM - 8:55 AM
Location: Room 217 A/B

Metabolic Regression Velocity Post Lung SBRT - How Early Do We Get to See !
S. Gawde1, V. Shankar1, C. Haritha2, S. Parekh1, V. N. Bhaskar1, A. Karuppusamy1, A. Bhange1, and B. ajai Kumar3; 1HCG Cancer Center, Mumbai, India, 2CR Reddy Cancer Center, Nellore, Andhra Pradesh, India, 3HCG Cancer Center, Bengaluru, India

Purpose/Objective(s): FDG PET-CT is a well established cancer imaging tool for diagnosis, staging and response assessment. It is also well known that, post chemotherapy or radiotherapy, metabolic response preceeds morphologic response based on size criteria.Normally PET-CT post SBRT is done at 3 months. However, earliest time needed when one would get maximum metabolic response following Lung SBRT was never known or assessed. Present study evaluates the metabolic regression velocity patterns post SBRT with serial FDG PET-CT scans in patients with oligo solitary lung metastases within first 3 months of the treatment.

Materials/Methods: 5 patients with oligometastatic lung tumors (Primaries: Colorectal cancer -2, Breast - 2 and Head and neck cancer- 1 ) were planned SBRT by Deep inspiratory breath hold technique using Active breath controller on 6 DOF C-arm Linac using body fix immobilisation. A risk adapted multi-fractionated regimen (3-5 fractions) was used and doses delivered were in the range of 110-118gy BED. All patients underwent diagnostic pre- and post-treatment PET-CT scans. Post SBRT PET-CTs scans were timed serially at 48hrs, 10 days, 30 days and 60 and 90 days post treatment. PET-CT reports were reviewed in order to determine the pre- and post- treatment maximum standardized uptake value (m-SUV) of the lesion, including “complete resolution” of FDG-avidity. Corresponding Morphologic variations of the target lesions were studied on the CT images during the evaluation period (first 3 months).

Results: All the 5 patients showed serial regression in metabolic activity, with maximum regression in metabolic activity occurring at 10 days post SBRT. The observed metabolic regression was between 40-54% ( median – 50%) at 48 hours and 67-82% ( median 80%) at 10 days post SBRT. 10 days after SBRT, there was no further decrease in metabolic activity. SUV thereupon remained constant ranging between 2.3 - 3.2 upto 3 months suggesting to fact that inflammation might have been initiated between 48hrs and 10 days.The earliest morphologic changes on CT in the form of ground glass appearance was detected at 60 days post SBRT scan uniformly in all patients. During the evaluation period (first 3 months) there was no significant change in size of the lesion.

Conclusion: In cases of solitary lung oligomets the metabolic response precedes morphologic response with 50% median metabolic regression within 48hrs and 80% median metabolic regression by 10th day post SBRT. To the best of our knowledge, this is the first study reported in literature which looked into the metabolic regression velocity patterns within the first 3 months post SBRT.

Author Disclosure: S. Gawde: None. V. Shankar: None. S. Parekh: None. V.N. Bhaskar: None. A. Karuppusamy: None. B. ajai Kumar: Partner; Health Care Global Enterprise. Stock; Health Care Global Enterprise. CEO; Health Care Global Enterprise.

Sachin Gawde, MBBS, DRM, DNB, FANMB

Disclosure:
No relationships to disclose.

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