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

Early Experience Using Proton Beam Therapy for Extremity Soft Tissue Sarcoma: A Multicenter Study

Purpose

Proton beam therapy (PBT) may provide an advantage when planning well-selected patients with extremity soft tissue sarcoma (eSTS), specifically for large, anatomically challenging cases. We analyzed our early experience with PBT on toxicity and outcomes.

Materials and Methods

A retrospective study was performed for eSTS treated between June 2016 and October 2020 with pencil beam scanning PBT at 2 institutions. Diagnostic, treatment, and toxicity characteristics were gathered from baseline to last follow-up or death. Wound complications were defined as secondary operations for wound repair (debridement, drainage, skin graft, and muscle flap) or nonoperative management requiring hospitalization. Statistical analysis was performed with R software.

Results

Twenty consecutive patients with a median age 51.5 years (range, 19–78 years) were included. Median follow-up was 13.7 months (range, 1.7–48.1 months). Tumor presentation was primary (n = 17) or recurrent after prior combined modality therapy (n = 3). Tumor location was either lower extremity (n = 16) or upper extremity (n = 4). Radiation was delivered preoperatively in most patients (n = 18). Median pretreatment tumor size was 7.9 cm (range, 1.3 –30.0 cm). The 1-year locoregional control was 100%. Four patients (20%) had developed metastatic disease by end of follow-up. Maximum toxicity for acute dermatitis was grade 2 in 8 patients (40%) and grade 3 in 3 patients (15%). After preoperative radiation and surgical resection, acute wound complications occurred in 6 patients (35%). Tumor size was larger in patients with acute wound complications compared with those without (medians 16 cm, range [12–30.0 cm] vs 6.3 cm, [1.3–14.4 cm], P = .003).

Conclusion

PBT for well selected eSTS cases demonstrated excellent local control and similar acute wound complication rate comparable to historic controls. Long-term follow-up and further dosimetric analyses will provide further insight into potential advantages of PBT in this patient population.

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.