I am concerned about radiation risk from spect scan, how much radiation and risk is there from it?

SPECT OR PET?? Do you mean spect or pet? Two are different. Spect means single photon emission computerized tomography and pet means positron emission tomography. Spect provides blood flow information and pet provides metabolic information. In either case, the radiation is less than the one received with conventional x-ray ct scan.
Low radiation risk. SPECT stands for single photon emission computed tomography. The isotope used is usually low energy such as technetium. SPECT produces sagittal coronal, and transaxial thin slices of organ investigated. SPECT does not contribute] to radiation burden. SPECT technique is used for brain, heart, skeleton, etc.
See answer. The dose from a single SPECT exam is small. The risk is related to dose. You should check with the facility for the exact dose. You should look at the following links:
https://www.radiologyinfo.org/en/submenu.cfm?pg=safety
https://www.radiologyinfo.org/en/pdf/safety-xray.pdf

The second one lists relative doses to put things in perspective.
SPECT. Do you mean technetium cardiac spect? Total effective dose is 9.4 mSv. Estimated increased cancer risk over baseline is 0.0661%.
SPECT. Spect (single-photon emission computed tomography) is a method of image acquisition. There are many different nuclear medicine radiotracers which can be used for spect. Each tracer has its own half life and own specific energy/radiation emissions. The radiation risk depends on which tracer is used for the spect scan. What are you having the scan for?
Minimal. Singlepositronemissiontomography uses radioactive materials to determine their metabolism in various organs. There is less risk to these injected materials than there is in spending a day at the beach.