Long-Term Control of Giant Retroperitoneal Liposarcoma by Proton Beam Therapy Combined With Hyperthermia: A Case Report and Literature Review

Retroperitoneal liposarcoma is a rare malignancy that often grows to a large size and is difficult to manage because of frequent local recurrence and proximity to critical organs. Surgical resection remains the primary curative treatment, but complete resection is often not feasible in advanced cases. We report the case of a man in his thirties with a giant retroperitoneal liposarcoma arising near the pancreas. After multiple recurrences and surgical resections over eight years, the tumor progressed to extensive peritoneal dissemination, forming a single massive lesion (maximum diameter 19 cm) that was no longer amenable to surgery. The patient was treated with proton beam therapy (PBT) delivering 70 Gy(relative biological effectiveness (RBE)) in 35 fractions, combined with regional hyperthermia. Because the tumor exceeded the maximum field size of the PBT system, irradiation was performed using a "puzzle-field" technique with multiple stitched fields. The treated tumor showed marked shrinkage, which was maintained for four years, accompanied by improvement in performance status from 1 to 0. Acute toxicities were mild, and no symptomatic late adverse events were observed. Local control was achieved within the irradiated field, although disease progression later occurred outside the treated area. This case demonstrates the feasibility of combining proton beam therapy with hyperthermia to achieve durable local control in a giant, unresectable retroperitoneal liposarcoma. The "puzzle-field" irradiation strategy may offer a practical solution for overcoming field size limitations in particle therapy and represents a valuable treatment option in selected advanced cases.