Dosimetric comparison of volumetric‐arc therapy versus sliding window intensity‐modulated radiotherapy in postoperative treatment for primary soft tissue sarcoma of the thigh

Abstract

Intensity-modulated radiotherapy (IMRT) has demonstrated improved local control in extremity soft tissue sarcoma (STS) after limb-sparing surgery compared with three-dimensional conformal radiation therapy. Our purpose was to evaluate sliding-window IMRT (SW-IMRT) and volumetric arc therapy (VMAT) in planning target volume (PTV) coverage and dose to organs-at-risk (OAR). Sixteen patients undergoing postoperative RT for lower extremity STS were included. For each patient, one VMAT plan and one SW-IMRT plan were proposed. Both were evaluated using cumulative dose-volume histogram data for OAR and PTVs. Prescribed dose was 66Gy (2Gy/fraction) to PTV1 and 56Gy (1.69Gy/fraction) to PTV2. OARs contoured were femur, neurovascular bundle, minimum tissue corridor, normal tissue outside PTV2, joint and genitalia. T-Student test was performed. Eleven male (69%) and five female patients (31%) were analyzed. Mean age was 60 years. Both techniques showed optimal target coverage, conformity index (CI) and homogeneity index (HI). VMAT PTV2 CI was 1.13 (mean)±0.08 (standard deviation) versus 1.19±0.10 SW-IMRT PTV2 CI (P<0.05). VMAT PTV1 HI was 0.09±0.01 versus 0.08±0.01 SW-IMRT PTV1 HI (P<0.05). Regarding OARs, VMAT delivered lower dose to femur, genitalia, normal tissue outside PTV2 and joints. SW-IMRT spared tissue corridor mean dose (10.4Gy±6.8Gy) versus (14.7±6.5Gy) VMAT (P<0.05). Both techniques achieved great conformity, homogeneity and coverage of PTV. VMAT produced lower dose to OARS and SW-IMRT was superior in sparing dose to normal-tissue-corridor, which could reduce risk of lymphedema.