RPR-15

Patient-scatter dose rate

Ḣ_s = a W (F/400) / d². Scatter from the patient toward a secondary wall.

Reading speed

ScatterNCRP 151 patient scatter

Governing equation

\dot H_s=a W (F/400)/d^{2}

where

a: Scatter fraction a (1 m) (—)
W: Workload (Gy/wk)
F: Field area at iso (cm²)
d: Distance from patient (m)
H_s: Weekly scatter dose (mSv/wk)

Lecture brief

Historical brief

Inverse-square, half-value layer, ICRP weighting and ALARA are the protection craft since the 1920s commissions. The lab computes transmission, equivalent dose and a shielding snapshot. This sheet (RPR-15 — Patient-scatter dose rate) is the form associated with NCRP 151 patient scatter. Working symbols: $a$ , $W$ , $F$ , $d$ $\rightarrow$ $H_s$ . a is the scatter fraction at 1 m for a 400 cm² field. For 6 MV at 90° a ≈ 1.5×10^{−4}. Field area scales almost linearly.

Purpose

Purpose: compute

H_s

from

a

W

F

d

in Radiation protection via

\dot H_s=a W (F/400)/d^{2}

Ḣ_s = a W (F/400) / d². Scatter from the patient toward a secondary wall. Use it when a real radiation protection question must be answered in SI before a code check.

Live realistic example

In symbols

Live case. Given

a = 1.500e-4\,\mathrm{—}

W = 250.000\,\mathrm{Gy/wk}

F = 400.000\,\mathrm{cm^{2}}

d = 4.000\,\mathrm{m}

, the governing relation

\dot H_s=a W (F/400)/d^{2}

yields

H_s = 2.344\,\mathrm{mSv/wk}

. A patient as a scatterer, a side wall, a 1/d² fall-off. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

Scatter fraction a (1 m) a0.00015 —Workload W250 Gy/wkField area at iso F400 cm²Distance from patient d4 m

Outputs

Weekly scatter dose H_s2.344 mSv/wk

Reading speed

Watch on YouTube

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Narration of this film

A patient as a scatterer, a side wall, a 1/d² fall-off.

a is the scatter fraction at 1 m for a 400 cm² field. For 6 MV at 90° a ≈ 1.5×10^{−4}. Field area scales almost linearly.

Reading speed

Watch on YouTube