Enhancing targeted doses: Low-energy photon lipiodol-enhanced radiotherapy (LEPERT) for liver cancer patients.

Objectives: This study proposes a novel approach, "Low-energy photon Lipiodol-Enhanced Radiotherapy" (LEPERT), for patients with liver cancer. Moreover, we evaluate the dose difference of the conventional treatment planning with 10 MV X-ray beam (MV-plan) and LEPERT.

Methods: The computed tomography (CT) was modeled with the Monte Carlo simulation. For LEPERT, 120 kV X-ray beams collimated with CT were irradiated on a virtual tumor filled with Lipiodol at 10-50 mg/mL, which was inserted into a whole-body phantom. A prescribed dose of 40 Gy/4fr was irradiated to achieve D_95% of the target. The doses to the target and organs at risk (OARs), such as the bone, normal liver, spinal cord, and kidneys, were evaluated by comparison with conventional radiotherapy with a 10 MV VMAT plan (MV-plan).

Results: Differences in the effective energy and off-axis ratio between the measurements and simulations were within 2 keV and 3%, respectively. The D_2% of tumors exceeded 130% of the prescribed dose at 50 mg. The difference in the D_98% of the tumor between LEPERT and MV-plan was within 0.7 Gy. The V_5Gy of the normal liver (>40 mg/mL) was lower for LEPERT than for MV-plan. The V_20Gy of the normal liver (>10 mg/mL) for LEPERT was over 80% lower than that for MV-plan. Dose constraints for the OARs were satisfied.

Conclusion: The LEPERT can selectively enhanced only the tumor region with sparing the OAR dose. It could be a novel and effective treatment technique in the point that the treatment machine is a general CT device.