Concept Architecture
Concept
Theoretically, Relative Dose Intensity (RDI) is a quantitative measure of the extent to which the delivered dose intensity of a therapeutic regimen matches the dose intensity specified in the planned treatment protocol. It is founded on the principle that reductions in dose or delays in treatment administration may influence treatment effectiveness, particularly in oncology. The concept exists to standardise the assessment of treatment delivery and facilitate comparisons across patients, clinical trials and health economic evaluations.
Mathematically, Relative Dose Intensity is expressed as the ratio of the actual dose intensity administered to the planned dose intensity. Dose intensity itself is defined as the amount of drug administered per unit time. The resulting ratio is commonly expressed as a proportion or percentage, with values below 100% indicating reductions resulting from dose reductions, treatment delays or missed cycles.
In practice, Relative Dose Intensity is calculated from chemotherapy administration records by comparing cumulative doses and treatment duration with the planned regimen. It is widely used in oncology clinical trials, observational studies and routine practice to assess protocol adherence and examine associations between treatment delivery, survival, toxicity and healthcare resource utilisation. In health economics, RDI informs estimates of treatment effectiveness, adverse event management, medicine utilisation and costs within pharmacoeconomic models.
Purpose
Used to quantify the extent to which patients receive the intended treatment intensity, supporting evaluation of treatment adherence, clinical effectiveness and economic consequences of dose modifications.
Mathematical Formulae
Primary Formula
RDI = (Actual dose intensity � Planned dose intensity) ? 100%
Supporting Formulae
Dose intensity:
DI = Total dose administered � Treatment duration
Relative dose intensity as a proportion:
RDI = Actual dose intensity � Planned dose intensity
Related Mathematical Methods
- Dose Intensity
- Medication Adherence Measurement
- Survival Analysis
- Regression Analysis
- Pharmacy Utilisation Analysis
Example
A chemotherapy protocol specifies 600 mg administered every three weeks for six cycles over 18 weeks.
Planned dose intensity:
DI = 3,600 mg � 18 weeks = 200 mg/week
The patient receives a total of 3,060 mg over the same period.
Actual dose intensity:
DI = 3,060 mg � 18 weeks = 170 mg/week
Relative dose intensity:
RDI = (170 � 200) ? 100% = 85%
The patient received 85% of the planned treatment intensity.
Excel Implementation
| Function | Example Formula | Health Economics Application |
|---|---|---|
| SUM | =SUM(DoseRange) | Calculates the cumulative dose administered. |
| DATEDIF | =DATEDIF(StartDate,EndDate,"d")/7 | Calculates treatment duration in weeks. |
| IF | =IF(ActualDI/PlannedDI>=0.85,"Maintained","Reduced") | Classifies treatment intensity according to predefined thresholds. |
| AVERAGE | =AVERAGE(RDIRange) | Calculates mean RDI across a patient cohort. |
| COUNTIFS | =COUNTIFS(RDIRange,">=0.85") | Counts patients maintaining target dose intensity. |
VBA (Optional)
VBA can automate calculation of Relative Dose Intensity across chemotherapy regimens and generate reports identifying patients with clinically significant dose reductions or treatment delays.
Sources
- Hryniuk WM, Bush H. The importance of dose intensity in chemotherapy of metastatic breast cancer. Journal of Clinical Oncology.
- Hryniuk WM. Average relative dose intensity and the impact of chemotherapy dose reductions. Seminars in Oncology.
- Lyman GH, Dale DC, Crawford J. Incidence and predictors of reduced relative dose intensity in cancer chemotherapy.
- Drummond MF, Sculpher MJ, Claxton K, Stoddart GL, Torrance GW. Methods for the Economic Evaluation of Health Care Programmes.
- Briggs A, Claxton K, Sculpher M. Decision Modelling for Health Economic Evaluation.
- ISPOR Good Practice Reports.
Related Concepts (2)
Library
Publications
1
Pharmacoeconomics: From Theory to Practice — Renee J. G. Arnold (ed.), 2nd Edition ed., 2021 (CRC Press (Routledge))
An applied, practitioner-oriented pharmacoeconomics reference covering decision modelling, cost of illness, Markov modelling, retrospective database analysis, budget impact, multi-criteria decision analysis, value-based pricing of pharmaceuticals, and reimbursement, with real-world examples.
BookView source →
Frequently Asked Questions (6)
What is relative dose intensity?
A measure comparing the dose intensity a patient actually received to the originally planned, full dose intensity, expressed as a percentage.
Source: DeVita, Lawrence & Rosenberg 2019
What comparison does relative dose intensity express?
Relative dose intensity expresses, as a percentage, how much of the planned dose intensity a patient actually received, comparing the drug delivered against the full amount originally intended. A figure near one hundred per cent means the patient got close to the planned treatment, while a lower value means dose reductions or delays cut into it. This matters because, for some cancers, falling below a threshold of relative dose intensity is linked to worse outcomes. How much of the intended dose was actually given is what it captures. DeVita and colleagues (2019) describe this.
Source: DeVita et al. 2019
How is relative dose intensity calculated?
Relative dose intensity is calculated by comparing the dose intensity actually received, the amount of drug delivered per unit of time, with the originally planned full dose intensity, expressed as a percentage of the planned intensity. So relative dose intensity is the received intensity as a percentage of the planned intensity, which is why it reflects delivery against plan, since it relates what was actually given to what was intended, and factors such as dose reductions and delays that lower the delivered intensity reduce the relative dose intensity below the full planned level, providing a measure of how much of the intended treatment intensity the patient actually received.
Source: DeVita, Lawrence & Rosenberg 2019
Why does relative dose intensity matter?
Relative dose intensity matters because, for some treatments, delivering close to the planned intensity may be important for effectiveness, so a reduced relative dose intensity, from reductions or delays, could indicate that less than the intended treatment was given, potentially affecting the outcome. So relative dose intensity matters for treatment delivery and outcome, which is why it is monitored, since falling below the planned intensity may weaken the treatment in regimens where intensity is important, and tracking relative dose intensity shows how much of the intended treatment was delivered, helping to identify when reductions or delays have substantially lowered the intensity, which could affect the effectiveness of the regimen.
Source: DeVita, Lawrence & Rosenberg 2019
How do dose reductions and delays affect relative dose intensity?
Dose reductions and dose delays affect relative dose intensity by lowering the dose intensity actually delivered relative to the plan: reductions decrease the amount given and delays spread doses further apart, both reducing the relative dose intensity below the full planned level. So dose reductions and delays lower relative dose intensity, which is why they reduce the percentage delivered, since both decrease the intensity of treatment actually received compared with the plan, and their effect on relative dose intensity shows how much the delivered treatment has fallen below the intended intensity, making relative dose intensity a way of capturing the combined impact of reductions and delays on treatment delivery.
Source: DeVita, Lawrence & Rosenberg 2019
How does relative dose intensity relate to dose intensity?
Relative dose intensity relates to dose intensity in that dose intensity is the amount of drug delivered per unit of time, and relative dose intensity expresses the delivered dose intensity as a percentage of the planned full dose intensity. So relative dose intensity is derived from dose intensity relative to the plan, which is why the two are connected, since dose intensity measures the treatment delivered over time and relative dose intensity compares this with what was intended, and while dose intensity describes the intensity itself, relative dose intensity shows how closely the delivered intensity matched the planned intensity, providing a measure of adherence to the intended treatment intensity.
Source: DeVita, Lawrence & Rosenberg 2019
Trust Record
Verified by Dr Darrin Baines
British health economist
Professional identity: darrinbaines.org
Verification date: 28 Apr 2026
Content version: 1.0.0
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