99mTechnetium SPECT–guided functional liver–sparing radiotherapy planning for recurrent hepatocellular carcinoma: a dosimetric comparison

The aim of this study was to establish an optimal treatment strategy for functional liver–sparing radiotherapy by incorporating technetium-99 m galactosyl human serum albumin ( 99m Tc-GSA) single-photon emission computed tomography (SPECT) into radiotherapy planning for recurrent hepatocellular carcinoma (rHCC). Three irradiation techniques—volumetric-modulated arc therapy (VMAT), intensity-modulated radiotherapy (IMRT), and three-dimensional conformal radiotherapy (3D-CRT)—were systematically compared. Six patients with rHCC who underwent stereotactic body radiotherapy (SBRT) were included. Eligible patients had previously received SBRT to a different hepatic segment and had undergone 99m Tc-GSA SPECT before the current course of radiotherapy. For treatment planning, planning computed tomography (CT) images were rigidly registered with 99m Tc-GSA SPECT images, and functional liver regions were manually contoured by radiation oncologists. Using identical functional liver contours, three treatment plans—VMAT, IMRT, and 3D-CRT—were independently generated by medical physicists. The prescribed dose was 40 Gy, delivered in four fractions. These treatment plans were retrospectively created for research purposes and were separate from actual clinical treatments. Under identical planning target volume dose-coverage conditions, the dose–volume histogram indices (V2–V40) of the functional liver were compared among the three techniques. VMAT consistently demonstrated the best preservation of functional liver regions, particularly in the low-dose range, followed by IMRT and 3D-CRT. These findings demonstrate the feasibility of 99m Tc-GSA SPECT-guided function-avoidance radiotherapy planning for the re-irradiation of rHCC and suggest that VMAT provides an optimal balance between target coverage and functional liver preservation.