Evaluation of Healthy Tissue Dose at Different Regions between Volumetric-Modulated Arc Therapy and Intensity-Modulated Radiation Therapy Plans in the Treatment of Various Cancers

Dosimetric Comparison of VMAT and IMRT Pre-Operative Radiotherapy for Soft Tissue Sarcoma of the Extremities

PURPOSE

Radiotherapy is a standard part of limb conserving therapy for extremity soft tissue sarcoma (STS) at high risk of recurrence. Toxicities increase with radiation dose and volume of normal tissue irradiated. This study sought to compare dosimetry of volumetric modulated arc radiotherapy (VMAT), with intensity modulated radiotherapy (IMRT) and to investigate the optimal planning technique.

METHODS AND MATERIALS

Twenty patients with extremity STS who underwent preoperative radiotherapy (50 Gy in 25 fractions) between 2016 and 2020 at a sarcoma specialist centre were included. The original treatment techniques were sliding window IMRT or 3D conformal. VMAT plans were retrospectively generated according to the original tumour and organ at risk constraints. Quality assurance was performed as per departmental protocol. Wilcoxon signed-rank test was used to compare dosimetric parameters (for planning target volume, in-field bone, and soft tissue structures), monitor units (MU) and treatment time.

RESULTS

Median patient age was 65 years and majority were male (n=14, 70%). Commonest subtype was undifferentiated pleomorphic sarcoma (n=14, 70%) and most tumours were located on the thigh (n=12, 60%). Median PTV volume was 1110 cm³ and median volume of in-field bone 236 cm³. VMAT plans had significantly lower average MU (480 vs 862 MU, p<0.001) and overall treatment time (300 vs 153 seconds, p<0.001). PTV coverage favoured VMAT, with marginally higher mean, minimum, and maximum doses, and higher Conformity Index. However, differences were not statistically significant. Dose to infield bone and soft tissue structures were similar or slightly lower with VMAT.

CONCLUSIONS

In extremity soft tissue sarcoma, VMAT plans demonstrated a favourable trend toward tumour coverage and dose conformity compared to IMRT along with significantly lower monitor units and half the overall treatment time.