Dosimetry: Module 5 (in entirety) questions with
verified answers
% cold (under rx dose) = Ans✓✓✓ Minimum Target Dose/Prescribed
Dose
% hot (over rx dose) = Ans✓✓✓ Maximum Target Dose/Prescribed
Dose
As field size gets bigger, dmax shifts (towards/away) the skin surface.
Ans✓✓✓ Towards - why? Scatter
Beam Related Factors Effecting the Deposition of Dose Ans✓✓✓
Inverse Square
Attenuation (ie. flattening filter)
CI = Ans✓✓✓ External getting Rx. Dose (cc's)/PTV volume (cc's)
implying
CTV + IM + SM Ans✓✓✓ define the Planning Target Volume (PTV) on
which the selection of beam size and arrangement is based.
CTV Ans✓✓✓ Clinical Target Volume
, Contains a GTV and/or microscopic disease - must receive the
prescribed dose to effect cure or palliation.
CTV = GTV + a margin to cover potential "subclinical" invasion.
Defining Normal Tissues (OAR) Ans✓✓✓ •After the radiation
oncologist defines the volume to be treated, the structures that will
also be affected by the radiation must be defined so that dose to the
structure can be tracked for toxicity. These are sometimes referred to
as organs at risk or normal tissues.
These structures can be defined by the radiation oncologist OR the
dosimetrist.
Defining Normal Tissues Ans✓✓✓ The compromise to be accepted
when delineating the PTV is due to the presence of Organs at Risk
(OAR). Such OAR are normal tissues whose sensitivity and location in
the vicinity of the CTV may significantly influence treatment planning
and/or absorbed dose level
OAR are defined as Serial or Parallel structures
dmax - 10MV Ans✓✓✓ 2.5cm
dmax - 18MV Ans✓✓✓ 3.2cm
verified answers
% cold (under rx dose) = Ans✓✓✓ Minimum Target Dose/Prescribed
Dose
% hot (over rx dose) = Ans✓✓✓ Maximum Target Dose/Prescribed
Dose
As field size gets bigger, dmax shifts (towards/away) the skin surface.
Ans✓✓✓ Towards - why? Scatter
Beam Related Factors Effecting the Deposition of Dose Ans✓✓✓
Inverse Square
Attenuation (ie. flattening filter)
CI = Ans✓✓✓ External getting Rx. Dose (cc's)/PTV volume (cc's)
implying
CTV + IM + SM Ans✓✓✓ define the Planning Target Volume (PTV) on
which the selection of beam size and arrangement is based.
CTV Ans✓✓✓ Clinical Target Volume
, Contains a GTV and/or microscopic disease - must receive the
prescribed dose to effect cure or palliation.
CTV = GTV + a margin to cover potential "subclinical" invasion.
Defining Normal Tissues (OAR) Ans✓✓✓ •After the radiation
oncologist defines the volume to be treated, the structures that will
also be affected by the radiation must be defined so that dose to the
structure can be tracked for toxicity. These are sometimes referred to
as organs at risk or normal tissues.
These structures can be defined by the radiation oncologist OR the
dosimetrist.
Defining Normal Tissues Ans✓✓✓ The compromise to be accepted
when delineating the PTV is due to the presence of Organs at Risk
(OAR). Such OAR are normal tissues whose sensitivity and location in
the vicinity of the CTV may significantly influence treatment planning
and/or absorbed dose level
OAR are defined as Serial or Parallel structures
dmax - 10MV Ans✓✓✓ 2.5cm
dmax - 18MV Ans✓✓✓ 3.2cm
