2847 - Impact of Bolus on Clinical Outcomes in Patients Treated with Radiation Therapy for Vulvar Squamous Cell Carcinoma
Presenter(s)
J. M. Stark1, N. S. McCall2, A. McCook-Veal3, J. Switchenko4, K. A. Ward5, N. Ali6, A. B. Patel Jr7, J. W. Shelton8, T. Y. Eng9, and J. S. Remick9; 1Emory University, Atlanta, GA, 2Department of Radiation Oncology, UPMC Hillman Cancer Center, Pittsburgh, PA, 3Winship Cancer Institute of Emory University, Atlanta, GA, 4Department of Biostatistics & Bioinformatics, Rollins School of Public Health, and Winship Cancer Institute of Emory University, Atlanta, GA, 5Department of Radiation Oncology, University of Virginia, Charlottesville, VA, 6University of Rochester School of Medicine and Dentistry, Rochester, NY, 7Winship Cancer Institute at Emory University, Atlanta, GA, 8Department of Radiation Oncology, Winship Cancer Institute, Emory University, Atlanta, GA, 9Department of Radiation Oncology, Winship Cancer Institute of Emory University, Atlanta, GA
Purpose/Objective(s): Radiation therapy (RT) for vulvar squamous cell carcinoma (VSCC) is associated with significant skin toxicity. Bolus is advised to increase surface dose; however, it is unknown whether bolus is necessary with modern RT techniques due to greater number of beam angles resulting in higher surface dose. The purpose of this study was to evaluate our institutional experience in treating VSCC with bolus and without bolus and assess impact on local control (LC) and radiation dermatitis (RD).
Materials/Methods: Patients with VSCC treated with RT for curative intent from 2009-2024 were retrospectively analyzed. Sociodemographic, clinicopathologic and treatment related factors were recorded from the medical record. Radiation-induced acute and late (=3 months after RT) grade 3 or higher RD was assessed by CTCAE version 5.0. Kaplan-Meier model was used to estimate LC between bolus versus non-bolus using the log-rank test. Cox-regression univariate analysis (UVA) was performed to assess factors associated with LC and G3 or higher RD. P-value of < 0.05 was considered statistically significant.
Results: A total of 57 patients with VSCC were included; 33 were treated with and 24 were treated without super flab bolus. All patients received IMRT/VMAT except for 2 patients treated with bolus and 1 patient treated without bolus who received 3D conformal radiation (3DCRT); 1 patient in each group received a combined IMRT/VMAT and 3DCRT. EBRT plus brachytherapy boost was delivered to 4 and 3 patients in the bolus and non-bolus groups, respectively. Bolus thickness was 0.5cm (n=29) or 1cm (n=4). Median number of fractions with bolus was 10 days (range 10-39). Adjuvant RT was delivered in 9 (27%) and 12 (50%) (p=0.08) and concurrent chemotherapy was given to 21 (64%) and 12 (50%) (p=0.30) of patients treated with and without bolus, respectively. The median dose in the definitive and adjuvant treatment setting was 62Gy (range 50-74Gy) and 57.6Gy (Range 45-64.8Gy), respectively. There was no difference between groups in terms of age, race, smoking status, BMI, history of diabetes or HIV, p16 status or FIGO stage. After mean follow up of 27.5 months (Interquartile range: 4.6-39.4), local recurrence occurred in 19% versus 17% of patients and 1-year LC was 81.7% versus 90.5% (p=0.52) for patients treated with and without bolus, respectively. Acute Grade 3 or higher RD occurred in 10 (30%) and 9 (37.5%) (p=0.569) and late grade 3 or higher RD occurred in 5 (15%) and 5 (20.8%) (p=0.73) patients treated with and without bolus, respectively. On UVA, there were no factors associated with acute or late grade 3 or higher RD.
Conclusion: Local control was not different among patients with VSCC receiving RT with or without bolus. Larger studies are necessary to validate these findings to optimize the therapeutic ratio for this rare and difficult to treat disease.