K. Nakajima1, S. Sudo Sr1,2, H. Ogino1, Y. Yokoyama3, M. Sunagawa3, H. Iwata1, Y. Hattori1, K. Nomura1, Y. Tsuzuki1,2, K. Hayashi4, T. Toshito5, and A. Hiwatashi2; 1Department of Radiation Oncology, Nagoya Proton Therapy Center, Nagoya City University West Medical Center, Nagoya, Japan, 2Department of Radiology, Nagoya City University Graduate School of Medical Sciences, Nagoya, Japan, 3Division of Surgical Oncology, Department of Surgery, Nagoya University Graduate School of Medicine, Nagoya, Japan, 4Department of Proton Therapy Technology, Nagoya Proton Therapy Center, Nagoya City University West Medical Center, Nagoya, Japan, 5Department of Proton Therapy Physics, Nagoya Proton Therapy Center, Nagoya City University West Medical Center, Nagoya, Japan
Purpose/Objective(s): Surgical resection is the standard treatment for soft-tissue sarcomas (STS). However, trunk STS is often unresectable due to its large size and proximity to vital structures. There is limited evidence regarding proton therapy (PT) for trunk STS with definitive intent. We hypothesize that image-guided PT (IGPT) will provide long-term local control and improve survival for patients with unresectable trunk STS. Materials/
Methods: A single institutional retrospective study was conducted on patients who underwent IGPT with definitive intent for unresectable trunk STS from December 2013 to September 2022. In this study, the "trunk" was defined as regions excluding the extremities and head and neck areas. Patients under 18 years old and those with gynecological sarcomas were excluded. PT treatment employed either the passive scattering technique or spot scanning technique. Overall survival (OS), local control (LC), and progression-free survival (PFS) were analyzed using Kaplan-Meier estimates, and radiation-related adverse events were assessed using CTCAE version 5.0. Univariate analysis (UVA) was conducted to assess the association with OS. Results: Thirty-three patients were analyzed. The median age was 61 years (range: 19-85), and the median gross tumor volume (GTV) was 266 cc (range: 10-3017). The most common histological type was dedifferentiated liposarcoma (n=14; 42%), followed by leiomyosarcoma (n=6; 18%). The most frequent irradiation site was the retroperitoneum (n=22; 67%), followed by the gluteal region (n=5; 15%). The dose fractionation ranged from 57.2 to 70.2 Gy (RBE) in 13 to 33 fractions, with the most common being 70.2 Gy (RBE) in 26 fractions (n=19; 58%). Spot scanning technique was used in 26 patients (79%). The target was the primary tumor with no prior surgery in 16 patients (48%) and recurrent or metastatic tumor after surgery in 17 patients (52%). Two patients (6%) had previous radiotherapy. Seven patients (21%) had surgical absorbable spacer placement. The median follow-up duration was 21 months (range: 3-106). The 3-year OS, LC, and PFS were 53% (95% CI: 31-70%), 81% (60-92%), and 39% (23-55%), respectively. The most common initial recurrence pattern was distant metastasis. In UVA, GTV exceeding 300cc was identified as a poor prognostic factor for OS. No grade 3 or higher radiation-related adverse events were observed. Conclusion: This study explored the effectiveness of IGPT for unresectable trunk STS, particularly retroperitoneal sarcomas. IGPT demonstrated favorable LC, showing promise as a safe and effective treatment for this challenging condition.
