Dosimetric comparison of axilla and groin radiotherapy techniques for high-risk and locally advanced skin cancer

ABSTRACT

PURPOSE: Radiation therapy targeting axilla and groin lymph nodes improves regional disease control in locally advanced and high-risk skin cancers. However, trials generally used conventional two-dimensional radiotherapy (2D-RT), contributing towards relatively high rates of side effects from treatment. The goal of this study is to determine if three-dimensional conformal radiation therapy (3D-CRT), intensity-modulated radiation therapy (IMRT), or volumetric-modulated arc therapy (VMAT) may improve radiation delivery to the target while avoiding organs at risk in the clinical context of skin cancer regional nodal irradiation. MATERIALS AND METHODS: Twenty patients with locally advanced/high-risk skin cancers underwent computed tomography simulation. The relevant axilla or groin planning target volumes and organs at risk were delineated using standard definitions. Paired t-tests were used to compare the mean values of several dose-volumetric parameters for each of the 4 techniques. RESULTS: In the axilla, the largest improvement for 3D-CRT compared to 2D-RT was for homogeneity index (13.9 vs. 54.3), at the expense of higher lung V₂₀ (28.0% vs. 12.6%). In the groin, the largest improvements for 3D-CRT compared to 2D-RT were for anorectum Dmax (13.6 vs. 38.9 Gy), bowel D200cc (7.3 vs. 23.1 Gy), femur D₅₀ (34.6 vs. 57.2 Gy), and genitalia Dmax (37.6 vs. 51.1 Gy). IMRT had further improvements compared to 3D-CRT for humerus Dmean (16.9 vs. 22.4 Gy), brachial plexus D₅ (57.4 vs. 61.3 Gy), bladder D₅ (26.8 vs. 36.5 Gy), and femur D₅₀ (18.7 vs. 34.6 Gy). Fewer differences were observed between IMRT and VMAT. CONCLUSION: Compared to 2D-RT and 3D-CRT, IMRT and VMAT had dosimetric advantages in the treatment of nodal regions of skin cancer patients.