Whole-liver Palliative Radiotherapy Using SIB for Diffuse Liver Metastases: 3D-CRT versus ^99mTc-GSA SPECT Image-guided VMAT

Background/Aim: This study aimed to compare the dosimetric parameters of the simultaneous integrated boost (SIB) technique using volumetric modulated arc therapy (VMAT) guided by ^99mTc-labeled diethylenetriamine pentaacetate-galactosyl human serum albumin (^99mTc-GSA) single-photon emission computed tomography (SPECT) image with those of conventional three-dimensional conformal radiotherapy (3D-CRT).

Patients and Methods: Five patients with diffuse liver metastases underwent ^99mTc-GSA SPECT and computed tomography (CT) imaging before RT planning. A SPECT threshold was used for determining the functional liver structure (FLS). The 3D-CRT plan included anterior–posterior opposed beams. The prescribed dose was 8 Gy in one fraction, with a goal of 95% of the planning target volume (PTV), D₉₅, receiving at least 95% of the prescribed dose. The absorbed dose received by 2 cm³ of organ at risk (OAR) volume (D_2cc) was below 10 Gy. The VMAT plan comprised two or three arcs. The goals for the PTV and OARs matched those of 3D-CRT. The PTV dose in SIB (PTV_boost) defined according to FLS was optimized at an isodose line [~80% of the maximum dose (D_max)] received at D₉₅ of PTV_boost. Two plans were compared using the dose–volume histogram parameters of PTV, PTV_boost, FLS, and OARs.

Results: Dosimetric parameters including D_mean, D_max, V_110%, and V_120% for PTV were significantly higher in the VMAT plan than in the 3D-CRT plan. Likewise, for PTV_boost, the VMAT plan had significantly higher values of dosimetric parameters (D₉₅, D_mean, D_max, V_110%, and V_120%) than the 3D-CRT plan. The FLS and OAR parameters did not significantly differ between the two plans, except for the spinal cord.

Conclusion: ^99mTc-GSA SPECT image-guided VMAT planning using SIB allows selective target dose increase in palliative radiotherapy for diffuse liver metastases.