The role of radiation in retroperitoneal sarcomas

Abstract

Retroperitoneal sarcomas form a group of rare malignancies that require expertise in every aspect of management. Patients benefit from referral to cancer centers that can provide comprehensive, multidisciplinary, oncologic management. The role of radiation in retroperitoneal sarcoma management is, appropriately, the subject of considerable controversy due to the absence of high-level evidence proving its efficacy. Nonetheless, the preponderance of available data suggests that radiation therapy likely improves local control and, in some settings, may favorably impact resectability and survival. These outcome observations coupled with the lower doses (45-54 Gy) and normal tissue displacement characteristic of preoperative radiation therapy leads us to favor preoperative radiotherapy followed by oncologic resection for most retroperitoneal sarcomas. This strategy appears to provide the highest chance of safe and successful delivery of multimodal therapy, which can otherwise be hindered by postoperative complications as a result of technically challenging surgery and normal tissue radiation dose tolerances. Dose-escalation and selective integrative boosts to "at-risk" margins are attractive strategies that merit, and arguably require, further clinical evaluation. We believe that postoperative radiotherapy should be reserved for very high-risk cases and should be treated to a dose of ≥60 Gy respecting normal tissue dose tolerances. An additional approach that we consider in the postoperative setting is close surveillance with consideration of preoperative radiotherapy at recurrence before repeat surgical resection. Highly conformal radiotherapy techniques, such as IMRT with image guidance, should be employed to minimize dose to normal tissues and thereby allow delivery of efficacious radiation doses. If feasible, referral to a treatment facility with proton beam therapy should be discussed with the patient, especially if normal tissue dose constraints cannot be met using IMRT/IGRT. Participation in prospective studies should be highly encouraged.

FIGURE 1

A case demonstrating highly conformal radiotherapy dose-distributions achieved with intensity modulated radiotherapy (IMRT) as displayed in axial, sagittal and coronal images. A 79-year old woman presented with deep abdominal discomfort and lower limb edema leading to a diagnosis of intermediate grade leiomyosarcoma of the inferior vena cava. After multidisciplinary assessment, preoperative radiotherapy using TomoTherapy-based IMRT was offered. A differential dose of 50 Gy to the surgeon-defined, at-risk margin (red contour) and 45 Gy to the entire GTV plus PTV margin (yellow contour) was delivered sparing contralateral kidney (green contour), bowel/peritoneal cavity (black contour), liver and spinal cord. Ipsilateral kidney (light blue) was sacrificed as part of the planned surgical resection. 50 Gy, 40 Gy and 15 Gy isodose lines are shown in green, blue and pink, respectively. The patient remains disease- and toxicity-free two and half years after treatment.