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Most chemotherapy doses are worked out from your height and weight. Both are measured in metric units and checked by two people before a new treatment starts, and your weight is rechecked during treatment. If you are a larger person, the American guideline says you should get the full dose for your actual size, not a reduced or 'capped' one.
Most cytotoxic doses are expressed per square metre of body surface area (BSA), calculated from height and weight (DuBois or Mosteller), or per kilogram. Errors start at the scales: ASCO-ONS (2024) cites a study of 10,000 records in which 20% held height or weight errors, and now requires height and weight in metric units, measured and documented and verified by two people, one licensed, before a new treatment plan is prepared. The order must state the calculation method, the variables, how often they are re-evaluated and what change prompts recalculation. BOPA (2025) requires an up-to-date height, weight and BSA on the first prescription and a local policy on when weight change triggers a new dose; it bands adult doses where national bands exist and asks that any BSA capping be documented.
For people with obesity, ASCO (2012, updated 2021) recommends full weight-based cytotoxic doses, especially when the aim is cure, and the 2021 update adds full approved doses of immunotherapy and targeted therapy; toxicity is handled the same way as in anyone else. The 2012 guideline found that up to 40% of obese patients received limited doses and that fears of toxicity were unfounded. Capping persists: in a German cohort of 730 women with early breast cancer capped at BSA 2.0 m2, those above 2.1 m2 had lower dose intensity and worse survival, with obesity a possible confounder. How often to re-weigh is unsettled; a 2,276-patient study found a 10% BSA change in at most 7.6% of patients and suggested three- to six-monthly weighing for most.
Why: Mistyped numbers, decimal slips and pounds written as kilograms are common, and each one changes the dose.
“Weight and height are measured and documented in the medical record in metric units (eg, kg and cm). Both the measurement and documentation are verified by two individuals, one of whom is a licensed clinician, prior to preparation and administration of a newly prescribed antineoplastic treatment plan.”
Why: Anyone checking the dose later can repeat the sum and see when it should change.
“The dose calculation, including: 3.9.8.1. The calculation methodology 3.9.8.2. The variables used to calculate the dose 3.9.8.3. The frequency at which variables are re-evaluated, such as weight or laboratory data 3.9.8.4. The changes in the values that prompt confirmation or recalculation of doses”
Why: The pharmacist needs the same numbers the prescriber used to check the dose independently.
“Ensure an up-to-date height, weight and BSA (where relevant) is calculated and documented on the prescription.”
Why: Reducing doses for larger people lowers the chance the treatment works, and full doses are not more toxic for them.
“The Panel continues to recommend that full, weight-based cytotoxic chemotherapy doses be used to treat obese adults with cancer.”
American Society of Clinical Oncology (Journal of Clinical Oncology, Griggs et al.) 2021
Why: There is no evidence that these drugs need reducing for body size, and the 2021 guideline extended full dosing to them.
“New to this version of the guideline, the Panel also recommends that full, approved doses of immunotherapy and targeted therapies be offered to obese adults with cancer.”
American Society of Clinical Oncology (Journal of Clinical Oncology, Griggs et al.) 2021
Why: Toxicity, not body size, is the reason to change a dose.
“In the event of toxicity, the consensus of the Panel is that dose modifications of systemic antineoplastic therapies should be handled similarly for obese and nonobese patients.”
American Society of Clinical Oncology (Journal of Clinical Oncology, Griggs et al.) 2021
Why: Weight loss or gain during treatment can make the original dose too high or too low.
“There must be a local policy in place which determines when treatment doses should be recalculated if the patients’ weight changes during the course of treatment.”
Why: A second, independent calculation catches arithmetic and unit errors before the drug is prepared.
“Check drug dose calculations (Flat, BSA, weight, AUC) and units are appropriate.”
How care is usually carried out, read from the guidelines and standards cited. Your own team's protocol and their judgement come first; this page is for understanding it, not for doing it yourself.
Metric height and weight, measured and verified by two people before a new plan (ASCO-ONS 2024); the calculation method, variables and recalculation triggers written on the order (ASCO-ONS 2024); an independent pharmacist check of every calculation (BOPA 2025); and full doses for actual body size in obesity, for cytotoxics and, since 2021, immunotherapy and targeted therapy (ASCO 2021). The sources do not set a re-weighing interval or a weight-change threshold; both are left to local policy, and BOPA tolerates documented BSA capping as individual practice, which ASCO recommends against routinely.
ASCO and ONS (JCO Oncology Practice) 2024 · British Oncology Pharmacy Association 2025 · American Society of Clinical Oncology (Journal of Clinical Oncology, Griggs et al.) 2021 · American Society of Clinical Oncology (Journal of Clinical Oncology, Griggs et al.) 2012
Where it differs: Doses are calculated from a maximum BSA, commonly 2.0 m2, for larger patients. BOPA allows it as individual or local practice if documented in the treatment plan.
Evidence: ASCO 2012 found up to 40% of obese patients received limited doses and recommended against it. In 730 women with early breast cancer at Tübingen, capping at 2.0 m2 meant those above 2.1 m2 received median relative dose intensity of 83.9% against 92.6%, and had worse 5-year overall survival (85.5% against 94.3%); the authors could not separate obesity itself from underdosing.
British Oncology Pharmacy Association 2025 · American Society of Clinical Oncology (Journal of Clinical Oncology, Griggs et al.) 2012 · Archives of Gynecology and Obstetrics 2026
Where it differs: Weighs every three months for acute leukaemia, lymphoma, pancreatic cancer and people under 20, and every six months for others, rather than monthly or every cycle.
Evidence: In 2,276 adults, a BSA change of 10% or more occurred in at most 7.6% and after a median of 84 days (Kemps 2024, Dutch hospital data). ASCO-ONS cites the same study and leaves the interval to the organisation.
European Journal of Hospital Pharmacy (Kemps et al.) 2024 · ASCO and ONS (JCO Oncology Practice) 2024
Where it differs: Patients are grouped into BSA bands and given a standard prepared dose per band, so doses can be made in advance.
Evidence: Using clearance data from 1,012 patients and six drugs, banding changed individual doses by minus 14% to plus 22% with no significant loss of precision in reaching the target exposure, except for paclitaxel (Chatelut 2012). BOPA asks for adult doses to be banded where national tables exist.
British Journal of Cancer (Chatelut et al.) 2012 · British Oncology Pharmacy Association 2025
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