RTOG Sarcoma Radiation Oncologists Reach Consensus on Gross Tumor Volume and Clinical Target Volume on Computed Tomographic Images for Preoperative Radiotherapy of Primary Soft Tissue Sarcoma of Extremity in Radiation Therapy Oncology Group Studies

Abstract

Objective To develop an Radiation Therapy Oncology Group (RTOG) atlas delineating gross tumor volume (GTV), and clinical target volume (CTV) to be used for preoperative radiotherapy of primary extremity soft tissue sarcoma (STS). Methods A consensus meeting was held during the RTOG meeting in January 2010 to reach agreement about GTV and CTV delineation on CT images for preoperative radiotherapy of high-grade large extremity STS. Data were presented to address the local extension of STS. Extensive discussion ensued to develop optimal criteria for GTV and CTV delineation on CT images. Results A consensus was reached on appropriate CT-based GTV and CTV. GTV is gross tumor defined by T1 contrast-enhanced MRI images. Fusion of MRI and CT is recommended to delineate the GTV. CTV for high-grade large STS typically includes GTV plus 3 cm margins in the longitudinal directions. If this causes the field to extend beyond the compartment, the field can be shortened to include the end of a compartment. The radial margin from the lesion should be 1.5 cm including any portion of the tumor not confined by an intact fascial barrier, bone or skin surface. Conclusion The consensus on GTV and CTV for preoperative radiotherapy of high-grade large extremity STS is available as web-based images as well as descriptive format through the RTOG. This is expected to improve target volume consistency and allow for rigorous evaluation of the benefits and risks of such treatment.

Agreement Among RTOG Sarcoma Radiation Oncologists in Contouring Suspicious Peritumoral Edema for Preoperative Radiation Therapy of Soft Tissue Sarcoma of the Extremity

“…In the meantime, the extent of edema inclusion within the radiation treatment volume should be carefully evaluated, weighing the risk of missing tumor cells against risk of causing important toxicities translating into decreased limb function and quality of life. RTOG sarcoma panel currently agrees that the CTV should be manually contoured to encompass any suspicious peritumoral edema that is not already included in this margin (7) but the extent of inclusion remains subject to clinical judgment. Edema will typically already be included when 3 cm longitudinal margins are used and the benefit of including edema more than 4 cm from the GTV is unclear.…”

“…In a recent study from the RTOG group evaluating the variability in definition of GTV and CTV as delineated by sarcoma radiation oncologists, substantial to almost perfect agreement was found between physicians when specific instructions were provided (16). An RTOG atlas for GTV and CTV definition aiming at improving target volume consistency was subsequently developed and the current consensus is to combine the edema volume (in this case, the STAPLE95) and the anatomical expansion (in this case the CTV2cm or CTV3cm) to form the clinical target volume (to which a PTV margin would be added) (7). Clinical judgment is required to decide how much of the T2 edema is suspicious.…”

“…For the purpose of analysis, two CTV contours were delineated by a single observer per RTOG 0630 guidelines (7). A CTV3cm was created using a 3 cm proximal and distal expansion with a 1.5 cm radial margin, and a CTV2cm was created using a 2 cm proximal and distal margin and a 1 cm radial margin (Figures 1 and 2).…”

Significant Reduction of Late Toxicities in Patients With Extremity Sarcoma Treated With Image-Guided Radiation Therapy to a Reduced Target Volume: Results of Radiation Therapy Oncology Group RTOG-0630 Trial

“…Details of GTV and CTV definitions were described in a recent consensus report. 5 PTV included CTV plus 5 mm for all patients.…”

Sarcomas

“…Inclusion of suspicious edema defi ned on MRI T2 images beyond the margins mentioned above was left to the clinical judgement of the radiation oncologist. It could be excluded from the CTV in case the risk of tumor cell occurrence seemed to be low or the irradiation caused excessive toxicity (Wang et al 2011 ).…”