Adjuvant therapy varies according to the status of surgical margins, which, in turn, depends on expert processing of the resection specimen and careful examination of the specimen margins. Before margins can be proclaimed negative, it is necessary to ensure that the margins have been evaluated appropriately and adequately. In patients with very small tumors and negative margins, no adjuvant therapy is required. These patients can simply be followed according to the surveillance schedule outlined in the algorithm (see ). If the margins are close to vital structures or if a local recurrence would lead to major dysfunction, adjuvant RT can be used when the expected risk of radiation complications is low. If the surgical margins are positive (as often occurs when patients are referred to sarcoma centers after an attempted resection of a tumor that was not initially suspected to be a sarcoma), repeat resection should be strongly considered. Note that RT does not substitute for suboptimal surgical resection. If the patient has not previously received RT, one could attempt to control microscopic residual disease with RT if surgery is not feasible.

The usual dose of RT is 50 Gy when used preoperatively as an adjuvant modality; an intraoperative boost or a postoperative boost with brachytherapy or an external-beam RT is recommended  for positive or close margins. Preoperative RT has several advantages. First, the treatment volume is smaller because the need to cover the operative field is not present. Second, preoperative radiation may reduce seeding during surgical manipulation of the tumor. The tumor may or may not regress with preoperative RT, but the pseudocapsule may thicken and become acellular, easing resection and decreasing the risk of recurrence. However, the main disadvantage of preoperative RT is its effect on wound healing. A higher complication rate has been observed when primary closure is used. Therefore, involvement of a plastic surgeon in the team may be necessary to reduce wound complications when preoperative radiation is contemplated. If wide margins are obtained, additional radiation may not be needed. Often, margins are close because of the proximity of many of these tumors to major neurovascular bundles or bone. At the time of resection, surgical clips should outline the area of recurrence risk. Brachytherapy boosts should be delivered several days after surgery, through catheters placed at operation, with doses of 12 to 20 Gy based on margin status. Alternatively, a single intraoperative dose to the tumor bed of 12 to 16 Gy, based on margin status, can be delivered immediately after resection with exposure of the area at risk, avoiding uninvolved organs. External-beam RT may be an alternative to brachytherapy or intraoperative radiation: recommended doses are 10-14 Gy for close margins, 16- 20 Gy for microscopically positive margins, and 20-26 Gy for grossly positive margins. After preoperative radiation, a 3- to 6-week interval before resection is necessary to decrease the risk of wound complications. Very long intervals between resection and postoperative radiation are not recommended. Many institutions are no longer giving a boost after preoperative radiation to patients who have widely negative margins, based on local control rates that approach 95% with preoperative radiation at 50 Gy and negative margins.

When surgical resection is the initial therapy, postoperative RT choices include brachytherapy or external-beam RT, or a combination. Brachytherapy alone has been used as an adjuvant in patients with negative margins: 45 to 50 Gy to the tumor bed has been shown to reduce recurrence without a significant effect on wound healing. However, brachytherapy-alone techniques require special expertise and significant experience. If brachytherapy is used as a boost, doses of 10 to 20 Gy based on margin are recommended; a boost dose of 10 to 16 Gy for close margins or 20 Gy for positive margins is recommended. Generally, external-beam RT is delivered to large fields after surgical healing is complete (at 3-8 weeks) to doses of 50 Gy. Most institutions include the entire operative bed within that radiation field. If no intraoperative radiation or brachytherapy was used in the immediate operative or postoperative period, an external-beam RT boost should be added. For negative margins, an additional 10 to 16 Gy is recommended to a reduced field that includes the original tumor bed, based on grade and width of margins. For microscopically positive margins, an additional 16 to 20 Gy is recommended for grossly positive margins, an additional 20 to 26 Gy is suggested.