APBI in patients with pacemakers or AICDs who desire breast preservation seems to be a technically safe and reasonable application of targeted radiation therapy.

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222 Background: We report on outcomes and toxicity of liver SRT/SBRT based on 3D-CT/SPECT treatment planning with conformal avoidance of well perfused functional normal liver volumes (FNLV). Methods: 51 patients with unresectable metastatic (36) or primary (15) hepatic tumors (65 targets) completed SRT planning with 99mTc sulfur colloid 3D-SPECT/CT to define FNLVs. Various degrees of FNLV retraction as a result of hepatic cirrhosis or systemic or intrahepatic chemotherapy were observed. For conformal avoidance of the residual FNLV, total dose and fractionation were adapted to FNLV constraints. 4D-CT and SPECT-based dosimetry were compared and treatment outcomes and toxicity were analyzed with medium followup 14.5 months (3-36months). Results: The in-field local control rate was 95%, hepatic failure free survival - 88%, hepatic progression free survival - 78% and overall survival - 70%. 25% patients developed Grade ≤ 2 elevation of liver enzymes with no incidence of “classic” radiation-induced liver disease. No patients with hepatic cirrhosis had Child-Pugh score progression. The most common toxicity was Grade ≤ 2 fatigue. For the group, FNLVs were significantly reduced compared to CT-derived NLV (p<0.01) with marked FNLV contraction in patients with Child-Pugh ≥ B cirrhosis, those who completed hepatic resections or received TACE within 2 months prior to SRT. Treatment planning with incorporated SPECT/CT helps to reduce volumes of functionally active liver parenchyma receiving doses above prescription threshold in patients with HCC compared to conventional 4D-CT treatment planning (p<0.01). There was no such correlation for non-HCC patients. Conclusions: 3D-SPECT/CT treatment planning allows identification and conformal avoidance of FNLV from high radiation doses facilitating safety of liver SRT in patients with preexisting liver disease. Outcomes are favorable, however participation in prospective Phase III trial would estimate true value of this method.

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