Mono iso-centric VMAT planning for SBRT of multiple liver metastasis- A case report.

Introduction: Hepatocellular carcinoma (HCC) is the second most common cause of cancer mortality worldwide. The risk factors associated with the development of HCC are chronic Hepatitis B, Hepatitis C, and alcoholic cirrhosis. The standard care for HCC is surgical resection but the scope is limited for some patients. Continuous advancement of radiation therapy enabled the technique of stereotactic body radiotherapy (SBRT) as an option for the treatment of those cases for which surgery cannot be done. According to recent literature and meta-analysis, SBRT is an optimum treatment method with high local control with low toxicity. In SBRT, radiation is delivered with a smaller number of fractions than conventional radiation and employs high-precision delivery and accuracy with the help of image guidance. From a series of retrospective and prospective studies, it has been confirmed that SBRT achieves excellent local control in patients with early-stage inoperable, intermediate-stage, and advanced diseases.

Background: A 42-year-old male patient related to HBeAg infection and high AFP levels developed HCC BCLC Stage A was admitted to our department. There were two lesions with PTV volumes of 41.07 cc and 9.573 cc with a distance between them of 3.51 cm. These two lesions were treated with a mono-isocentric VMAT planning with SBRT technique. In this case, we present an unusual clinical practice of mono-isocentric treatment planning for treating multiple liver lesions. Since radiation therapy was viewed as the primary form of treatment because the patient wasn't an ideal candidate for surgery, SBRT was selected as the patient's primary modality of treatment because of the tiny volume of the two lesions and the normal liver volume (>700cc). Triple-phase 4DCT was performed for simulation to account for the motion of target volume and normal structures. After delineating the target volume and other normal structures, treatment planning was done with a dose of 45 Gray which was to be delivered in 5 fractions. Two PTVs were created with a margin of 3.0 mm to IGTV. Considering the positions of the lesions, a single isocentre plan was created using a 6MV FFF photon beam for both the PTVs with the VMAT technique. The treatment was carried through with 3 arcs, one coplanar, and the other 2 non-coplanar. At the time of treatment, after the proper positioning of the patient, one CBCT image was taken to match with the planned CT image acquired at the time of the simulation. After applying the translational and rotational errors, the patient was treated.

Results: The patient was treated successfully. After treatment, the condition of the patient was normal, and no toxicities have been observed in follow-up.

Conclusion: Mono isocentric VMAT planning can be used for closely spaced lesions considering the position of lesions and other normal structures in the vicinity.