The goal of this interventional study is to compare sensitivity of regular chest x-ray to ultra-low-dose computed tomography to find pulmonary relapse in follow-up of soft tissue sarcoma. The main question[s] it aims to answer are:

• Is ultra-low-dose computed tomography more sensitive than regular chest x-ray to find pulmonary relapse?
• Does ultra-low-dose computed tomography detect the most fast-growing pulmonary metastases earlier than regular chest x-ray?

Participants will have seven ultra-low-dose computed tomography imagings in addition to simultaneous routine protocol of chest x-rays. Participants therefore work as their own controls.

After primary treatment with curative intent for soft tissue sarcoma, patients fulfilling the inclusion criteria and giving informed consent are enrolled. In study protocol patients have their regular chest x-ray once in two months plus ultra-low-dose computed tomography imaging is repeated seven times during the first two years of follow-up. After two years patients without detectable metastases continue in regular follow-up program. The aims of this prospective comparative study are to investigate whether ultra-low-dose computed tomography is more accurate than chest x-ray in soft tissue sarcoma and especially whether the most fast-growing pulmonary metastases could be detected earlier.

Inclusion Criteria:

• primary high grade soft tissue sarcoma with no metastases at diagnoses or during treatment and treatment with curative intent.

Exclusion Criteria:

• metastases at diagnoses or during treatment