Body Surface Area (BSA)
Calculation of body surface area for precise chemotherapy dosage adjustment.
Why calculate Body Surface Area (BSA) in Oncology?
In medical practice, especially in oncology and hematology, dosing drugs with a narrow therapeutic index (such as cytotoxic chemotherapy) cannot be based on a single standard dose. Body Surface Area (BSA), measured in square meters (m²), is recognized as the most reliable biometric parameter for normalizing medication dosage.
BSA vs. Body Weight: The Superiority of Surface
Historically, many drugs were dosed based on weight (mg/kg). However, studies have shown that metabolic elimination, renal function, and hepatic blood flow are much better correlated with BSA than weight alone. Using weight alone poses major risks:
- Underdosing in Pediatrics: Children have a larger BSA relative to their weight. Weight-based dosing risks making chemotherapy ineffective.
- Overdosing in Obese Patients: Excess fat does not proportionally increase drug clearance capacity. Weight-based dosing in severe obesity can lead to fatal hematological toxicity.
ASCO Recommendations and "Capping"
ASCO recommends using actual body weight for chemotherapy. However, for highly toxic drugs (e.g., Vincristine), many institutions "cap" the BSA at 2.0 m² or 2.2 m² for safety.
Standard Calculation Formulas
MIDEX integrates the most validated formulas: Mosteller (Global Reference), DuBois & DuBois (Historical Standard), and Haycock (Preferred for Pediatrics).
- Formule de Mosteller (1987) : C\'est aujourd\'hui la référence mondiale. Recommandée pour sa simplicité mathématique :
√(Poids × Taille / 3600). - Formule de DuBois & DuBois (1916) : Historiquement la plus utilisée, elle reste très pertinente et est le standard de nombreuses publications scientifiques.
- Formule de Haycock (1978) : Particulièrement validée et précise pour la pédiatrie et les nourrissons.
Average BSA Reference Values
| Patient Category | Average BSA (m²) |
|---|---|
| Full-term Newborn | 0.25 m² |
| 2-year-old Child | 0.50 m² |
| 9-year-old Child | 1.07 m² |
| Average Adult Woman | 1.60 m² |
| Average Adult Man | 1.90 m² |
References:
1. Mosteller RD. Simplified calculation of body-surface area. N Engl J Med. 1987;317(17):1098.
[PubMed]
2. Griggs JJ, et al. Appropriate chemotherapy dosing for obese adult patients with cancer: American Society of Clinical Oncology (ASCO) clinical practice guideline. J Clin Oncol. 2012.
[PubMed]
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