treatment planning: ICRU 50

Question 1

ICRU Report No.29

Answer 1

dose specification for reporting external beam therapy for photons and electrons

Question 2

ICRU report NO.50

Answer 2

prescribing, recording and reporting photon beam therapy

Question 3

ICRU 50 enables

Answer 3

compare results of tx w departmental collegues
radiation oncologist to benefit from departments experience
results being compared w other centres

Question 4

GTV consists of:

Answer 4

GTV primary (primary tumour)
GTV nodal (metastatic lymphadenopathy)

where tumour cells density is the highest

Question 5

Reasons to identify GTV

Answer 5

adequate dose must be delivered to all of GTV for tumour control in radical treatments

allows recording for tumour response in relation to dose

Question 6

PTV takes into account

Answer 6

anatomical and biological factors
treatment reproducibilty

Question 7

PTV is the volume used

Answer 7

for dose calculation and specification of target dose

Question 8

PTV considerations

Answer 8

anatomical location
immobilisation
mechanical and dosimetric considerations of treatment unit

Question 9

Treated Volume

Answer 9

volume enclosed by isodose surface

Question 10

reasons to identify treated volume:

Answer 10

shape and size relative to PTV is important optimisation parameter

recurrence within treatment volume but outside PTV may be considered a true in feild recurrence due to :
inadequate dose and NOT a marginal recurrence due to inadequate volume

Question 11

Irradiated Volume

Answer 11

tissue volume which receives a dose that is considered significant in related to normal tissue tolerance

Question 12

Organs at risk

Answer 12

normal tissues whose radiation sensitivity significantly influences treatment planning and /or prescribed dose

Question 13

Organs at Risk can be divided into classes

Answer 13

class I -severe morbidity or fatal effect
class II-moderate to mild morbidity
class III-mild and reversible morbidity

Question 14

Dose variation in the PTV

Answer 14

heterogeneity in a given volume has to be accepted due to technical reasons

tf, heterogeneity should be keep within +7% to -5% of prescribed dose

Question 15

Maximum dose

Answer 15

one inside PTV and outside PTV

max dose to normal tissues is important for limiting and evaluating the side effects of treatment

Question 16

Minimum dose

Answer 16

lowest dose is PTV
no volume limit recommended when reporting min dose

Question 17

average dose

Answer 17

based on calculation of dose at each number of a large number of discrete points

Question 18

Median dose

Answer 18

the central value of doses at all lattice points, when arranged according to magnitude

Question 19

Modal dose

Answer 19

the dose that occurs most frequently at all lattice points , when arranged according to magnitude

Question 20

Hot Spots

Answer 20

represents a volume outside the PTV that recieves a dose more than 100% of specified PTV dose

Question 21

Recommendations for Reporting

Answer 21

-report the dose near to the centre of the PTV and also the max and min dose to PTV

-mean dose and DVH analysis if available

-

Question 22

ICRU reference point selecting criteria:

Answer 22

dose to the point should be clinically relevant and representative of the dose throughout the PTV

point should be easy to define in a clear way

point should be selected in area where the dose can be accurately determined

point should be selected in area w no steep dose gradient

Question 23

to fulfil these criteria, point should be selected

Answer 23

at central part of CTV
on or near central axis of beam