Residency · Residency · Radiation Oncology
Vulvar Cancer: Adjuvant and Definitive Radiation Approaches
Introduction
Vulvar cancer is an uncommon gynecologic malignancy, representing about 5% of all female genital tract cancers. The vast majority of cases, over 90%, are squamous cell carcinoma. Effective treatment necessitates a multidisciplinary strategy that combines surgery with radiation therapy. This lecture focuses on the indications for adjuvant and definitive radiation, principles of treatment planning, and strategies for managing treatment-related toxicities.
Surgical Management and Staging
Standard Surgical Approach
The standard surgical management of vulvar cancer involves either a radical vulvectomy or a wide local excision with a minimum gross margin of 1 cm. Lymph node assessment is critical and can be performed via sentinel lymph node biopsy or inguinofemoral lymph node dissection. Pathologic examination revealing surgical margins less than 8 mm is associated with a higher risk of local recurrence, underscoring the importance of achieving adequate margins during surgery.
FIGO Staging Highlights
The FIGO staging system classifies vulvar cancer based on the extent of local and nodal involvement. Stage I disease is confined to the vulva without nodal involvement. Stage III includes cases with inguinofemoral lymph node involvement. Stage IVA denotes invasion into adjacent structures such as the upper urethra, bladder, or rectum, or the presence of bilateral fixed or ulcerated lymph nodes. Among these factors, nodal status remains the single most important prognostic indicator.
Adjuvant Radiation Indications
Post-Operative Vulvar Bed Radiation
Adjuvant radiation to the vulvar bed is indicated in cases with close or positive surgical margins, defined as less than 8 mm, as well as when the depth of invasion exceeds 5 mm or when lymphovascular space invasion is present. The typical radiation dose delivered to the vulvar bed ranges from 45 to 50.4 Gy, with a boost dose of 54 to 60 Gy administered for positive margins to improve local control.
Adjuvant Inguinal and Pelvic Radiation
Adjuvant radiation to the inguinal and pelvic lymph nodes is recommended for patients with two or more positive inguinal lymph nodes, as demonstrated by the GOG-37 trial. Additional indications include extracapsular extension in any node or a single positive node with macroscopic involvement greater than 2 mm. The GOG-37 trial showed superior survival outcomes with adjuvant inguinal and pelvic radiation compared to pelvic node dissection alone.
GOG-37 Trial
In the GOG-37 trial, patients with positive inguinal lymph nodes were randomized to either pelvic node dissection or inguinal/pelvic radiation. The two-year overall survival was 68% in the radiation group compared to 54% in the surgery group. This landmark study established adjuvant groin and pelvic radiation as the standard of care for node-positive vulvar cancer.
Definitive Chemoradiation
Indications
Definitive chemoradiation is indicated for locally advanced vulvar cancer (T3-T4) that is not amenable to primary surgical resection. It is also considered in cases where exenteration would be required but organ preservation is preferred, as well as for unresectable inguinal lymphadenopathy.
GOG-101 and GOG-205
The GOG-101 trial evaluated preoperative chemoradiation using 5-fluorouracil and cisplatin with split-course radiation therapy, resulting in 47% of patients achieving freedom from residual disease. The GOG-205 trial used weekly cisplatin at 40 mg/m² concurrently with radiation totaling 57.6 Gy, achieving a clinical complete response rate of 64%. Patients with residual disease after chemoradiation typically require surgical resection.
Dose and Fractionation
The initial radiation fields encompass the vulva, inguinal, and pelvic lymph nodes, delivering 45 to 50.4 Gy in 1.8 Gy fractions. A sequential boost to gross disease is administered to reach a total dose of 60 to 70 Gy, depending on tumor response. Minimizing treatment breaks is essential to maintain therapeutic efficacy.
Radiation Treatment Planning
Target Volumes
The clinical target volumes (CTVs) include the vulvar CTV, which covers the residual or preoperative gross tumor volume with appropriate margins. The inguinal CTV encompasses the bilateral inguinofemoral nodal basins, while the pelvic CTV includes the external iliac, internal iliac, and obturator nodal chains. Para-aortic nodes are included only if pelvic nodes are positive.
IMRT Advantages
Intensity-modulated radiation therapy (IMRT) offers significant advantages by reducing acute skin and gastrointestinal toxicities. It allows precise dose sculpting to spare critical structures such as the femoral heads, small bowel, and bladder. The feasibility of IMRT for vulvar cancer was demonstrated in the RTOG 0418 trial.
Patient Positioning
Patients are positioned in the frog-leg position to optimally expose the inguinal and vulvar regions. Custom immobilization devices, such as vacuum cushions, are used to ensure reproducibility. Daily image guidance is recommended to enhance treatment accuracy.
Management of Treatment Toxicity
Acute Effects
Moist desquamation of the vulvar and inguinal skin is an almost universal acute side effect of radiation therapy. Management includes sitz baths, application of barrier creams, and adequate pain control. Although treatment breaks may be necessary to manage toxicity, they should be limited to less than one week to avoid compromising treatment outcomes.
Late Effects
Late toxicities include vulvar fibrosis and stenosis, which can impact function and quality of life. Lymphedema of the lower extremities is common, especially when surgery and radiation are combined. Sexual dysfunction and psychosocial effects are also important considerations in survivorship care.
Key Clinical Pearls
Nodal status remains the most critical prognostic factor in vulvar cancer, with two or more positive nodes mandating adjuvant inguinal and pelvic radiation, as established by the GOG-37 trial. Definitive chemoradiation with concurrent cisplatin is effective for organ preservation in locally advanced disease. The use of IMRT is strongly recommended to reduce the significant acute toxicity associated with vulvar and groin irradiation. Close surgical margins under 8 mm necessitate adjuvant radiation to the vulvar bed to reduce recurrence risk. Finally, minimizing treatment breaks is crucial because prolonged overall treatment time can compromise local control.
References
- Homesley HD, Bundy BN, Sedlis A, et al. Radiation therapy versus pelvic node resection for carcinoma of the vulva with positive groin nodes. Obstet Gynecol. 1986;68(6):733-740.
- Moore DH, Ali S, Koh WJ, et al. A phase II trial of radiation therapy and weekly cisplatin chemotherapy for the treatment of locally-advanced squamous cell carcinoma of the vulva: a Gynecologic Oncology Group study. Gynecol Oncol. 2012;124(3):529-533.
- Beriwal S, Coon D, Heron DE, et al. Preoperative intensity-modulated radiotherapy and chemotherapy for locally advanced vulvar carcinoma. Gynecol Oncol. 2008;109(2):291-295.
- Rao YJ, Chin RI, Hui C, et al. Improved survival with definitive chemoradiation compared to definitive radiation alone in squamous cell carcinoma of the vulva: a review of the National Cancer Database. Gynecol Oncol. 2017;147(3):572-579.