Study of Magnetic Resonance Image and Computed Tomography-Guided Stereotactic Body Radiation Therapy for Abdominopelvic Sarcomas (MARS Trial)

Each patient will undergo radiation simulation and planning. A custom vac-lok bag, alpha cradle, or equivalent immobilization device will be used. Both CT and MRI simulation will be obtained, which is standard of care for any patient undergoing radiation therapy for soft tissue sarcomas.

The study investigator will be responsible for delineating the gross tumor volume (GTV) using the CT as well as MRI performed as part of staging. Guidelines for contouring will be as per the currently open NRG trial for sarcomas. In general, this may entail expansions by 5-15 mm isotropically, should include any suspicious areas be identified on T2 weighted MRI, and should be cropped to natural anatomic borders. This clinical target volume (CTV) will then be expanded to a planning treatment volume (PTV) using a 3-5 mm expansion.

A prescription dose of 5-6 Gy x 5 fractions (25-30 Gy) will be delivered to at least 95% of the PTV. Stereotactic body radiotherapy (SBRT) and/or intensity modulated radiotherapy (IMRT) planning techniques may be used to minimize radiation dose to nearby organs at risk (OAR) but is not required.

Delineation of normal structures will be performed and verified by the responsible study investigator. The radiation physicist or dosimetrist will optimize the treatment plan prior to approval for treatment. Dose volume histograms (DVH) and normal tissue constraint parameters specified below will be used to judge the plan quality and optimize PTV coverage with OAR sparing prior to approval.

Radiation will be delivered daily for 5 consecutive days with the exception of weekends and holidays. In instances where the radiation treatment week contains a holiday or scheduling availability is limited, two fractions of radiation may be given on the same day providing that the fractions are administered ≥ 6 hours apart (this is considered standard of care treatment).

Surgical resection of at least the primary tumor will follow within 12 weeks of completing radiation therapy. Surgical specimens will be sent to pathology for evaluation and for review by a multidisciplinary tumor board.

Inclusion criteria

• Histologically confirmed sarcoma
• Primary or recurrent disease involving the abdomen or pelvis
• Resectable primary lesion
• Age ≥ 12 years old
• Karnofsky performance status (KPS) ≥ 70 or Eastern Cooperative Oncology Group (ECOG) 0-2
• If a woman is of childbearing potential, a negative serum or urine pregnancy test must be documented

Exclusion criteria

• Active treatment of a separate malignancy
• History of prior irradiation to the area targeted for treatment