How much energy is imparted to one cell during one day's treatment? Assume that the specific gra

How much energy is imparted to one cell during one day's...

Key Concepts

Energy Conversion Between Joules and Electron Volts

This concept involves converting energy from SI units (Joules) to electron volts (eV), a unit frequently used in atomic and molecular physics and radiation physics. Understanding that 1 Joule is equivalent to 6 x 10^18 eV is crucial for dealing with energy scales relevant to biological interactions and the effects of radiation at the cellular level.

Absorbed Dose in Radiobiology

Absorbed dose refers to the amount of energy deposited per unit mass of tissue by ionizing radiation. It is a fundamental concept in radiation therapy and health physics, indicating how much energy a cell or tissue absorbs during treatment. This concept underpins the calculations for energy imparted to cells, guiding the dosage needed to achieve a therapeutic effect while minimizing harm to surrounding healthy tissue.

Specific Gravity in Tissue Dose Calculations

Specific gravity, the ratio of the density of a substance to the density of a reference substance (typically water in biological contexts), is essential in dosimetry calculations when tissue densities are assumed. In the context of radiation treatment, assuming a specific gravity of 1 allows for simplification of dose calculations by equating the tissue's density to that of water, which is a standard reference in radiological physics.

Energy Deposition at the Cellular Level

This concept focuses on how the radiation dose delivered to a biological tissue translates into energy deposition in individual cells. It involves considering the mass and size of cells as well as the distribution of the absorbed energy. This understanding is critical in estimating the microscopic effects of radiation, such as potential DNA damage, and forms the basis for evaluating the biological outcome of radiotherapy treatments.

Transcript

00:01 Here we're going to think through some quantitative things about treating a cell, a cancerous cell, and trying to kill those cells with high -energy photons coming from some x -ray device.

00:18 And so the specifics of the tumor are we're going to assume a density 10 to the 8 cells per cubic centimeter in the tumor.

00:29 And we are going to assume that the patient is going to be exposed to 70 units of dosage called the gray extended over 35 days, so two grays a day.

00:47 And the question is how much energy is going to be needed per cell? that's the question.

01:04 And why that would be useful is then we could think through how many m .e.

01:09 V photons need to be bombarded into the cell.

01:16 Okay, so first of all, it's good to know what a gray is.

01:19 So we'll start there.

01:20 That one gray is the same as one jewel of energy deposited per kilogram of material.

01:29 And we see that our dosage is going to be two grays per day.

01:35 And this is per day per exposure slash day.

01:47 Okay, and we're using two grays a day.

01:48 So we'll go ahead and multiply our mungray, which is two joules per kilogram.

02:02 And so we're going to set up a ratio to figure out our unknown jewels if we knew the mass of one cell.

02:21 Okay, so they give us the cell density.

02:24 And if we knew the mass density, we would be very close to figuring out the mass of one cell.

02:33 So one thing that's usually safe to assume about living tissue is the density is going to be close to water or one gram per cubic centimeter.

02:49 And so we know that one cell can be figured out using the density of cells times.

03:01 The inverse 1 cubic centimeter over 10 to the minus 8.

03:07 Sorry, 10 to the 8th.

03:11 I'm already trying to divide that through in my head.

03:17 So basically, that density is the same as 1 gram over 10 to the 8th cells.

03:32 And we can work that out that give myself some room.

03:39 I'm running out of room.

03:40 Is equal to x grams over one cell.

03:53 And so we can solve that for x, and we'll have the mass of one cell...

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