BME 704 Radiation Therapy Lecture 1-3
Exam Study Guide
Radiation becomes less efficient beyond approximately what point? Why? - ANSWER
100 keV/µm. This is where overkill is, which is when max potential damage has been
reached, and an increase in LET beyond this point results in wasted dose.
Ex: @ 500 keV/µm many of the cells may have three or more ionizing events when only
two are required to kill the cell.
Direct action - ANSWER Radiation (electron) interacts directly with the target (DNA).
Atom in DNA may get excited, initiating a chain of events that leads to biological
changes
1/3 of dmg to DNA
Indirect action - ANSWER Radiation (electron) gets knocked off (esp water bc its 80% of
a cell) and makes free radicals (OH) that are able to interact with target ie. damage DNA
causes 2/3 of damage to DNA
Linear Energy Transfer (LET) - ANSWER amount of energy deposited by radiation per
unit length of medium (tissue) keV/um
Low LEt --> Zig zag
High LET -> straight
Stopping Power - ANSWER amount of energy lost by radiation per unit path length,
proportional to Z^2, increases rapidly at low energies, and reaches a maximum then
decreases as increasing the energy
Relative Biological Effectiveness (RBE) - ANSWER measure of the ability to damage
biomaterial
higher LET particles do more dmg compared to low ones
Optimal RBE - ANSWER a double strand break is highly effective, there is less chance of
repair compared to single strand break
RBE depends on (RRNDTB) - ANSWER • Radiation quality (LET)
• Radiation dose (energy) ie # of particles
• Number of dose fractions
, • Dose rate
• Type of biological cell or tissue (white blood cells are super sensitive to rad dmg)
• Biologic endpoint
What is the relationship between LET and RBE? - ANSWER High-LET (more radiation
depositing in a material) generally harms cells more, so it has a higher RBE (ability to
damage cells)
Equivalent Dose - ANSWER equal to the effective dose multiplied by the radiation
weighting factor, W_R
Equivalent dose is calculated for individual organs.It is based on the absorbed dose to
an organ, adjusted to account for the effectiveness of the type of radiation.Equivalent
dose is expressed in milliSieverts (mSv) to an organ.
Units of Equivalent Dose - ANSWER Rem (rad equivalent) and Sievert (gray equivalent)
1 Sv = ___ Rem - ANSWER 100 Rem
Cell Cycle - ANSWER G1 (growth)
S (DNA synthesis)
G2 (prep for mitosis)
M (mitosis/cell division)
radiation can effect the G1 and G2 phases
Double Strand Break - ANSWER most important problem produced in chromosomes,
leads to cell death
2 dsb may result in cell death, mutation to carcinogenesis
Chromosome Aberration - ANSWER occurs in G1 phase (pre-DNA synthesis &
chromosome duplication), ring and dicentric
not lethal, but can create cancer cells from small deletion and symmetrical
translocation
Exam Study Guide
Radiation becomes less efficient beyond approximately what point? Why? - ANSWER
100 keV/µm. This is where overkill is, which is when max potential damage has been
reached, and an increase in LET beyond this point results in wasted dose.
Ex: @ 500 keV/µm many of the cells may have three or more ionizing events when only
two are required to kill the cell.
Direct action - ANSWER Radiation (electron) interacts directly with the target (DNA).
Atom in DNA may get excited, initiating a chain of events that leads to biological
changes
1/3 of dmg to DNA
Indirect action - ANSWER Radiation (electron) gets knocked off (esp water bc its 80% of
a cell) and makes free radicals (OH) that are able to interact with target ie. damage DNA
causes 2/3 of damage to DNA
Linear Energy Transfer (LET) - ANSWER amount of energy deposited by radiation per
unit length of medium (tissue) keV/um
Low LEt --> Zig zag
High LET -> straight
Stopping Power - ANSWER amount of energy lost by radiation per unit path length,
proportional to Z^2, increases rapidly at low energies, and reaches a maximum then
decreases as increasing the energy
Relative Biological Effectiveness (RBE) - ANSWER measure of the ability to damage
biomaterial
higher LET particles do more dmg compared to low ones
Optimal RBE - ANSWER a double strand break is highly effective, there is less chance of
repair compared to single strand break
RBE depends on (RRNDTB) - ANSWER • Radiation quality (LET)
• Radiation dose (energy) ie # of particles
• Number of dose fractions
, • Dose rate
• Type of biological cell or tissue (white blood cells are super sensitive to rad dmg)
• Biologic endpoint
What is the relationship between LET and RBE? - ANSWER High-LET (more radiation
depositing in a material) generally harms cells more, so it has a higher RBE (ability to
damage cells)
Equivalent Dose - ANSWER equal to the effective dose multiplied by the radiation
weighting factor, W_R
Equivalent dose is calculated for individual organs.It is based on the absorbed dose to
an organ, adjusted to account for the effectiveness of the type of radiation.Equivalent
dose is expressed in milliSieverts (mSv) to an organ.
Units of Equivalent Dose - ANSWER Rem (rad equivalent) and Sievert (gray equivalent)
1 Sv = ___ Rem - ANSWER 100 Rem
Cell Cycle - ANSWER G1 (growth)
S (DNA synthesis)
G2 (prep for mitosis)
M (mitosis/cell division)
radiation can effect the G1 and G2 phases
Double Strand Break - ANSWER most important problem produced in chromosomes,
leads to cell death
2 dsb may result in cell death, mutation to carcinogenesis
Chromosome Aberration - ANSWER occurs in G1 phase (pre-DNA synthesis &
chromosome duplication), ring and dicentric
not lethal, but can create cancer cells from small deletion and symmetrical
translocation
