Abstract. Background/Aim: We evaluated the influence of previous treatments on the parametric discrepancies between dose-volume histograms (DVHs) and dose-function histograms (DFHs) generated based on 99m Tc-GSA SPECT images of hepatocellular carcinoma (HCC) patients treated with stereotactic body radiation therapy (SBRTPrimary liver cancer is the third most common cause of cancer death worldwide. Hepatocellular carcinoma (HCC) accounts for 85%-90% of primary liver cancers (1). Stereotactic body radiation therapy (SBRT) for HCC has been introduced as an alternative to standard treatments such as surgical resection and radiofrequency ablation (RFA) (1). SBRT delivers a highly conformal, potent dose of radiation to the tumor in some fractions, while minimizing radiation damage to organs at risk. SBRT provides excellent local control for HCC with a reported control rate of 80-90% (2-4).HCC response to radiation therapy (RT) exhibits a doseresponse relationship (5), but a fine balance is required between delivering a sufficient RT dose to control the HCC and avoiding radiation-induced liver toxicity. Radiationinduced liver injury (RILD), which occurs in 10-20% of HCC patients undergoing SBRT, remains a problematic adverse effect, because of pre-existing liver dysfunctions occurring secondary to comorbid conditions such as hepatitis B/C infection and cirrhosis (3, 4). The percentage of normal liver volume receiving a dose over the threshold dose calculated based on a dose-volume histogram (DVH) is commonly used for determining dose constraints and predicting radiation-induced liver toxicity; however, it has limited predictive ability (6, 7).A drawback of using DVH for SBRT planning in HCC is the lack of functional information because DVHs are generated based on computed tomography (CT) images, which provide only morphological information. A dosefunction histogram (DFH) generated based on single photon emission computed tomography (SPECT) images may facilitate the assessment of the functional status of organs at risk. For treatment planning in lung cancers, Marks et al. (8) performed DFH calculation using 99m Tc-labeled macroaggregated albumin and observed decreases in lung perfusion at, adjacent to, and separate from tumor in 94%, 74%, and 42% of patients, respectively. 99m Tc-labeled diethylene triamine pentaacetate-galactosyl human serum albumin 1511