Sarcoma and Cutaneous Tumors

SS 20 - Sarcoma and Cutaneous Tumors

152 - Significant Reduction in Post-Operative Wound Complications With Dosimetric Skin Constraints in Patients Receiving Pre-Operative Radiation Therapy for Soft Tissue Sarcomas of the Extremity

Tuesday, October 23
7:45 AM - 7:55 AM
Location: Room 007 A/B

Significant Reduction in Post-Operative Wound Complications With Dosimetric Skin Constraints in Patients Receiving Pre-Operative Radiation Therapy for Soft Tissue Sarcomas of the Extremity
L. Gilbride1, D. E. Prah2, C. Johnstone2, and M. Bedi2; 1Medical College of Wisconsin Affiliated Hospitals, Milwaukee, WI, 2Medical College of Wisconsin, Milwaukee, WI

Purpose/Objective(s): Pre-operative radiation (RT) followed by limb-sparing surgery is accepted as management for soft tissue sarcomas (STS) of the extremity. Although there are advantages with pre-operative RT, one disadvantage is risk of post-operative wound complications (WC). There are several risk factors for WC, however, there is sparse data on dosimetry parameters that are associated with a higher risk of developing WC. In this study, we sought to develop normal tissue structures whose dosimetry parameters predicted for acute WC in patients receiving pre-operative RT in STSs of the extremity.

Materials/Methods: From 2000-2016, we retrospectively reviewed patients treated with pre-operative RT ± chemotherapy. WC were defined per the NCIC Trial. Contours were generated on CT from which prior delivered treatment plans were generated. Superficial tissue as a function of depth (STd) contours were generated using a Boolean function: [[GTV + 2cmsuperior +2cminferior] + 12cmaxial expansion] ∩ [PT - [PT-d]], where GTV was the gross tumor volume defined at the time of treatment, PT was the external contour of the patient, and d was the skin depth (1, 3, 5, and 10 mm). Contours were edited to remove contralateral limb. Dosimetric data for V10, V20, V50, and Dmax of the structures were analyzed as continuous variables using logistic regression in their ability to predict for acute WC. Receiver-operating curve (ROC) analysis was performed to assess the best cut-off that predicted for WC in those variables that were significant on logistic regression and Fisher exact was used to assess variation in WC amongst the ROC cut-off.

Results: Dosimetric data of 56 patients were analyzed. Median dose was 50 Gy. 65% had lower extremity tumors. 50 patients were treated using 3D RT and 6 were treated with IMRT. 41% of patients received chemotherapy. All patients had limb-sparing surgery. Dosimetric parameters ST3mmV10 (p=0.02, OR 1.063), ST3mmV20 (p=0.03, OR 1.051) and ST5mmDmax (p=0.03, OR 1.01) were associated increased WC. ROC curves showed that for the above parameters, ST3mmV10 < 85.6% (p=0.0019), ST3mmV20 < 65.3% (p=0.013), and ST5mmDmax < 53.3 cGy (p=0.0038) were associated with increased WC. In patients with ST3mmV10 ≥ 85.6%, 43% had WC vs 7% with ST3mmV10 < 85.6% (p=0.004). In patients with ST3mm20 ≥ 65.3 %, 57% had WC vs 24% with ST3mmV20 < 65.3% (p=0.02). In patients with ST5mmDmax ≥ 53.3 cGy, 93% had WCs vs 50% with ST5mmDmax < 53.3 cGy (p=0.005).

Conclusion: Although there are several risk factors for post-operative WC in patients with STS, there are no established dosimetric constraints that may be associated with WC. In this study, ST3mmV10, ST3mmV20, and ST5mmDmax were each associated with the development WC in STS of the extremity treated with pre-operative RT. Further studies with a larger sample size are needed to corroborate these findings.

Author Disclosure: L. Gilbride: None. D.E. Prah: Honoraria; Elekta. Travel Expenses; Elekta. C. Johnstone: Employee; Medical College of WI. M. Bedi: None.

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