The IMRiS Trial: A Phase 2 Study of Intensity Modulated Radiation Therapy in Extremity Soft Tissue Sarcoma

Area of Science:

• Radiation Oncology
• Surgical Oncology
• Medical Physics

Background:

• Primary soft tissue sarcoma (STS) is rare, often affecting extremities.
• Limb-sparing surgery combined with radiation therapy (RT) is standard for high-risk cases.
• Late normal tissue toxicity and limb function after RT require thorough investigation.

Purpose of the Study:

• To prospectively evaluate late normal tissue toxicity and limb function after intensity modulated radiation therapy (IMRT) in extremity STS.
• To determine the rate of grade ≥2 late soft tissue fibrosis at 24 months post-IMRT.
• To compare outcomes between preoperative and postoperative RT cohorts.

Main Methods:

• Prospective study of patients (age ≥16 years) with extremity STS receiving IMRT.
• Two cohorts: preoperative IMRT (50 Gy) or postoperative IMRT (60/66 Gy).
• Primary endpoint: grade ≥2 late subcutaneous fibrosis at 24 months using Radiation Therapy Oncology Group (RTOG) criteria.

Main Results:

• 159 patients received IMRT; median follow-up 35.2 months.
• 10.8% (95% CI, 5.7%-18.1%) experienced grade ≥2 subcutaneous fibrosis at 24 months.
• Lower rates of skin, bone, and joint toxicity were observed; preoperative RT had more wound complications (29.2% vs 3.8%).

Conclusions:

• The 10.8% rate of grade ≥2 subcutaneous fibrosis is consistent with other IMRT trials and lower than historical 3D-CRT rates.
• IMRT demonstrates benefits for extremity STS patients regarding late toxicity.
• This study supports the use of IMRT in managing extremity STS.