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 (D2cc) 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 (PTVboost) defined according to FLS was optimized at an isodose line ~80% of the maximum dose (Dmax) received at D95 of PTVboost. Two plans were compared using the dose–volume histogram parameters of PTV, PTVboost, FLS, and OARs. Results: Dosimetric parameters including Dmean, Dmax, V110%, and V120% for PTV were significantly higher in the VMAT plan than in the 3D-CRT plan. Likewise, for PTVboost, the VMAT plan had significantly higher values of dosimetric parameters (D95, Dmean, Dmax, V110%, and V120%) 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.
Shimohigashi et al. (2026) studied this question.