CT & Radiotherapy Calculators
Dose and fractionation calculators for CT and radiotherapy
Estimation only. Effective dose from DLP is a population-averaged risk metric for a reference phantom. It is not a patient dose. Do not use it for individual risk counselling, and never use these outputs to plan a clinical exposure or a course of treatment.
Every coefficient below is a published value; sources are listed at the foot of the page. These are teaching and estimation tools, not a substitute for your department’s dosimetry or treatment-planning system.
CT dose
CT dose bench
Adult k-factors (AAPM Report 96, after Shrimpton 2004; ICRP 60 weighting). Paediatric k-factors are substantially higher and are not offered here.
Effective diameter = √(AP × LAT). Conversion factors are the AAPM Report 204 exponential fits.
DLP and effective dose
DLP = CTDIvol × scan length. E ≈ DLP × k, where k depends on the body region.
k-factors (DLP → effective dose): AAPM Report No. 96, The Measurement, Reporting and Management of Radiation Dose in CT (2008), after Shrimpton PC et al., NRPB-W67 (2004). ICRP 60 tissue weighting. Values recomputed with ICRP 103 weighting (Deak PD et al., Radiology 2010;257:158–166) differ by up to ~30% for some regions.
SSDE (size-specific dose estimate)
Scanner CTDIvol assumes a fixed phantom. SSDE corrects it for the patient’s actual size.
SSDE: AAPM Report No. 204, Size-Specific Dose Estimates (SSDE) in Pediatric and Adult Body CT Examinations (2011). Conversion factors use the published exponential fits: f32 = 3.704369·e−0.03671937·Deff, f16 = 1.874799·e−0.03871313·Deff.
Fractionation
BED and EQD2
Linear-quadratic model. BED = nd(1 + d/[α/β]); EQD2 = BED ÷ (1 + 2/[α/β]).
The LQ model is least reliable above roughly 8–10 Gy per fraction; SBRT comparisons made this way are indicative only.
Linear-quadratic model: Fowler JF, Br J Radiol 1989;62:679–694; Joiner MC & van der Kogel AJ, Basic Clinical Radiobiology, 5th ed. (2018).
Alternative fractionation
How many fractions of a new size deliver the same EQD2 as a reference schedule?
Iso-effective for the chosen α/β only. A schedule matched for tumour effect will not be matched for late normal tissue, and overall treatment time is ignored.
Linear-quadratic model: Fowler JF, Br J Radiol 1989;62:679–694; Joiner MC & van der Kogel AJ, Basic Clinical Radiobiology, 5th ed. (2018).
Contrast
Iodine delivery rate
IDR governs arterial enhancement far more than total contrast volume does.
Total iodine load = concentration × volume. Injection duration = volume ÷ flow rate.
Iodine delivery rate: Bae KT, Intravenous contrast medium administration and scan timing at CT, Radiology 2010;256:32–61.
Contrast dose by weight
Weight-based iodine load, the approach recommended for body CT.
0.4–0.6 g I/kg is a common range for routine portal-venous body CT; departments differ, and your protocol governs.
k-factors (DLP → effective dose): AAPM Report No. 96, The Measurement, Reporting and Management of Radiation Dose in CT (2008), after Shrimpton PC et al., NRPB-W67 (2004). ICRP 60 tissue weighting. Values recomputed with ICRP 103 weighting (Deak PD et al., Radiology 2010;257:158–166) differ by up to ~30% for some regions.
SSDE: AAPM Report No. 204, Size-Specific Dose Estimates (SSDE) in Pediatric and Adult Body CT Examinations (2011). Conversion factors use the published exponential fits: f32 = 3.704369·e−0.03671937·Deff, f16 = 1.874799·e−0.03871313·Deff.
Linear-quadratic model: Fowler JF, Br J Radiol 1989;62:679–694; Joiner MC & van der Kogel AJ, Basic Clinical Radiobiology, 5th ed. (2018).
Iodine delivery rate: Bae KT, Intravenous contrast medium administration and scan timing at CT, Radiology 2010;256:32–61.