176 - Does Dose Avoidance of Uninvolved Skin/Subcutaneous Tissues Reduce Morbidity in Preoperative Intensity-Modulated Radiation Therapy for Soft Tissue Sarcomas of the Lower Extremity?
Presenter(s)
S. Roohani1,2, A. Griffin3, A. Liu4, C. Catton5, D. Shultz6, P. Wong5, D. G. Kirsch3, P. Ferguson7, K. Tsoi7, J. Wunder7, and P. Chung5; 1Radiation Medicine Program, Princess Margaret Cancer Centre, Toronto, ON, Canada, Toronto, ON, Canada, 2Charité University Medicine Berlin, Berlin, Germany, 3University of Toronto, Toronto, ON, Canada, 4Department of Biostatistics, Princess Margaret Cancer Centre, University Health Network, Toronto, Ontario, Canada, Toronto, ON, Canada, 5Department of Radiation Oncology, University of Toronto, Toronto, ON, Canada, 6Radiation Medicine Program, Princess Margaret Cancer Centre, Toronto, ON, Canada, 7Division of Orthopaedic Surgery, University Musculoskeletal Oncology Unit, Mount Sinai Hospital, Toronto, ON, Canada
Purpose/Objective(s): To evaluate the impact of dosimetric sparing of uninvolved normal tissues including the skin/subcutaneous ‘flaps’ on acute and late toxicities in preoperative image-guided intensity modulated radiation therapy (IG-IMRT) for soft tissue sarcomas of the lower extremity (LE-STS).
Materials/Methods: Patients from a phase 2 preoperative IG-IMRT trial (flap-sparing) in LE-STS (2005–2009) were propensity-matched to patients from a prospectively maintained institutional database (non-flap sparing) who received preoperative IG-IMRT (2005–2020). Covariates included age, sex, tumor size, grade, and location. In the flap-sparing cohort, the future surgical skin/subcutaneous ‘flaps’ were delineated for dose avoidance at radiation treatment planning whereas in the non-flap-sparing cohort, there was no such specific attempt at dose avoidance to these uninvolved normal tissues. Priority was given to cover PTV where there was a conflict with dose avoidance of the normal tissue. Patients received 50 Gy in 25 daily fractions over 5 weeks followed by surgery 4-8 weeks after completion of IG-IMRT. Primary outcome was major wound healing complication rate (WC). Secondary outcomes were late RTOG toxicity (edema, skin, subcutaneous, joint, bone fracture) and oncological outcomes. Overall survival (OS), disease-free survival (DFS), local recurrence (LR) and distant metastasis (DM) were estimated using the Kaplan-Meier method. Cox regression analyses were used to examine WC, OS, DFS, LR, and DM between the two groups.
Results: The flap-sparing cohort of 54 patients was matched 1:5 with 270 non-flap-sparing patients. Median follow-up was 110 months and 67 months, respectively. WC rates were similar (27.8% vs. 27.4%), with flap-sparing not significantly associated with WC (HR: 1.0, 95% CI: 0.58–1.75, p=0.991). Late =G2 toxicities were comparable: fibrosis (7.4% vs. 11.9%), joint stiffness (1.9% vs. 3.3%), and edema (11.1% vs. 10.0%). Bone fracture was 3.7% vs. 1.5%, respectively. At 5 years, OS was 81.5% vs. 79.1%, DFS was 66.4% vs. 67.5%, LR was 7.4% vs. 5.0%, and DM was 29.6% vs. 29.6%; all p >0.1.
Conclusion: Dosimetric avoidance of uninvolved normal tissue, especially skin/subcutaneous ‘flaps’, appeared to have minimal impact on WCs and late toxicity in LE-STS patients treated with preoperative IG-IMRT. Our findings reinforce the benefits of preoperative IG-IMRT in improving acute and late toxicity profiles. A more detailed dosimetric analysis may uncover subtle differences between the plans that have yet to translate into clinical outcomes in the overall population and warrant further investigation in future studies.