Background
Retrospective analysis (MD Anderson Cancer Center) evaluating the impact of fractionation schedule on outcomes in melanoma treated with palliative or adjuvant RT. Compared hypofractionated RT (typically 30 Gy in 5 fractions = 6 Gy/fx) vs. conventional fractionation (1.8–2 Gy/fx) for melanoma at various sites. Assessed the radiobiological rationale and clinical outcomes by fractionation schedule.
Interventions and follow up
Arm A: Hypofractionated RT (6 Gy/fx or 3–5 Gy/fx schedules)
Arm B: Conventional fractionation (1.8–2 Gy/fx); retrospective comparison within cohort
Primary endpoint: Local control, toxicity by fractionation schedule
mFollow up: Not specified
Arm B: Conventional fractionation (1.8–2 Gy/fx); retrospective comparison within cohort
Primary endpoint: Local control, toxicity by fractionation schedule
mFollow up: Not specified
Results
Local Control (hypofractionation): Equivalent or superior to conventional fractionation
Radiobiological rationale: Melanoma alpha/beta ratio ~0.6 Gy (low) — favors hypofractionation
Hypofractionation outcomes: Comparable LC with fewer fractions; preferred for most melanoma RT
Radiobiological rationale: Melanoma alpha/beta ratio ~0.6 Gy (low) — favors hypofractionation
Hypofractionation outcomes: Comparable LC with fewer fractions; preferred for most melanoma RT
Adverse events
Toxicity: Acceptable with 6 Gy/fx for lymph node fields; caution needed near bowel/CNS
Main adverse events: Higher dose per fraction (≥6 Gy) at sites near critical structures (bowel, bladder, spinal cord, optic structures) requires careful planning. Skin reactions may be more acute with hypofractionation. Late fibrosis comparable between schedules for nodal fields.
Main adverse events: Higher dose per fraction (≥6 Gy) at sites near critical structures (bowel, bladder, spinal cord, optic structures) requires careful planning. Skin reactions may be more acute with hypofractionation. Late fibrosis comparable between schedules for nodal fields.
Conclusions
Melanoma has a low alpha/beta ratio (~0.6 Gy) based on clinical data, supporting hypofractionated RT as biologically equivalent or superior to conventional fractionation for local control. Hypofractionated schedules (6 Gy × 5 = 30 Gy; 4 Gy × 5 = 20 Gy) are preferred for most melanoma RT, providing equivalent or better efficacy with fewer fractions.
Key Limitations
Key Limitations: Retrospective; alpha/beta ratio estimates vary across studies (0.6–2.5 Gy); limited prospective validation of specific fractionation schedules for all melanoma sites; site-specific constraints may override optimal fractionation for immunostimulation.
Clinical Context
This MDACC analysis established the radiobiological basis for hypofractionation in melanoma. The 30 Gy/5 fx schedule is now standard for adjuvant nodal RT. Stereotactic approaches (SBRT 12–20 Gy × 1–3 fractions) are increasingly used for oligometastatic melanoma, especially in the immunotherapy era where local ablation + immunotherapy may enhance systemic response.
References