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SIRT MAA Mapping — SCE Medical Oncology MCQ

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ModerateGI CancersSIRT MAA MappingSCE Medical Oncology

A 60-year-old woman with CRC liver metastases is being assessed for selective internal radiation therapy (SIRT). Before treatment, she requires a mapping angiogram with Tc-99m MAA (macroaggregated albumin). What is the purpose?

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Correct answer: D — To assess the hepatopulmonary shunt fraction — if >20% of injected microspheres bypass the liver to the lungs, SIRT is contraindicated due to radiation pneumonitis risk; the mapping also identifies aberrant vessels feeding the GI tract

Pre-SIRT mapping angiography with Tc-99m MAA simulates microsphere distribution: (1) assesses hepatopulmonary shunt fraction — if >20%, significant lung irradiation would occur (contraindication); 10-20% requires dose reduction. (2) Identifies aberrant vessels from the hepatic artery to GI organs (stomach, duodenum, gallbladder) that could cause non-target radiation damage (requires coil embolisation before SIRT). (3) Confirms adequate tumour targeting. This is a mandatory safety assessment before every SIRT procedure.

Reference: NICE IPG401; ESMO mCRC; Comprehensive SIRT guidelines