Optimal treatment of retroperitoneal sarcoma (RPS) remains undefined. Here, we report the feasibility of using high-dose boost radiation (3 to 4 Gy) to the central part of the tumor in patients with unresectable RPS. Five patients with unresectable RPS were treated with radiation therapy using a central boost technique with intensity modulated radiation therapy (IMRT). On average, doses of 25 Gy – 45 Gy were delivered to the outer part of the tumor (PTV1), while the central part of the tumor (PTV2) received 56 Gy – 75 Gy physical dose, which translates to 62.67 Gy – 87.5 Gy equivalent dose in 2 Gy fractions (EQD2). To minimize radiation toxicity to the adjacent bowel and other organs, we used sequential, interdigitated, or simultaneous integrated boost (SIB) techniques. In this case series of variable RPS histology, the median survival post radiation therapy was 30 months. Three of the five patients had clinically stable local disease on follow up scans and none of the patients experienced clinically significant toxicity. In summary, in this small case series of 5 patients, treatment was tolerated well, and excellent local responses were observed regardless of the timing of central boost. Given the high rates of metastatic disease that developed in responding patients, effective systemic therapy will likely be needed for unresectable RPS treated with aggressive radiation therapy to the central part of the tumor.
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