TP3 FINAL EXAM REVIEW | QUESTIONS AND
ANSWERS | 2025/2026 UPDATE | RATED 100%
CORRECT
SBRT lung fractionation Answer - 6-30Gy in 1-5fx
5 Fx x 10 Gy
4 Fx x 12 Gy
3 Fx x 20 Gy
Dose heterogeneity Answer - 1. Overlapping beams with tight margin will put
high doses in the center of the target.
2. High Doses in Center may not help radiobiologically but there is no particular
disadvantage.
3. Higher dose of radiation administered anywhere within the tumor will
enhance the composite cytotoxic effect of and increase the TCP.
4. EUD (Equivalent Uniform Dose) is more robust for prospective description of
SBRT. EUD is less sensitive to estimates of surviving fractions and number of
tumor chologens.
Normalization for SBRT lung? Answer - 80-90%
SBRT lung constraint spinal cord? Answer - 18Gy
, SBRT lung constraint esophagus? Answer - 27Gy
SBRT lung constraint ipsilateral lung? Answer - 24Gy
SBRT lung constraint heart? Answer - 30Gy
SBRT lung constraint trachea? Answer - 30Gy
SBRT lung constraint ipsilateral bronchus? Answer - 30Gy
SBRT lung constraint whole lung? Answer - V20 <10%
SBRT target delineation? Answer - GTV, CTV, ITV, PTV?
GTV=CVT for SBRT
ITV: Margin added to CTV
PTV: 5mm all directions with exception 10mm Sup-Inf
1. Margins around targets can vary from -4mm to +4mm.
2. With negative margins, there will be a higher dose in the center.
3. With negative margins, there is a larger gradient created.
Why do we use 4D CT in lung treatments? Answer - It allows us to see the
movement of the tumor with the patients breathing cycle
If the tumor is moving too much and the PTV is not drawn to encompass this
movement then the tumor would not get the full dose.
ANSWERS | 2025/2026 UPDATE | RATED 100%
CORRECT
SBRT lung fractionation Answer - 6-30Gy in 1-5fx
5 Fx x 10 Gy
4 Fx x 12 Gy
3 Fx x 20 Gy
Dose heterogeneity Answer - 1. Overlapping beams with tight margin will put
high doses in the center of the target.
2. High Doses in Center may not help radiobiologically but there is no particular
disadvantage.
3. Higher dose of radiation administered anywhere within the tumor will
enhance the composite cytotoxic effect of and increase the TCP.
4. EUD (Equivalent Uniform Dose) is more robust for prospective description of
SBRT. EUD is less sensitive to estimates of surviving fractions and number of
tumor chologens.
Normalization for SBRT lung? Answer - 80-90%
SBRT lung constraint spinal cord? Answer - 18Gy
, SBRT lung constraint esophagus? Answer - 27Gy
SBRT lung constraint ipsilateral lung? Answer - 24Gy
SBRT lung constraint heart? Answer - 30Gy
SBRT lung constraint trachea? Answer - 30Gy
SBRT lung constraint ipsilateral bronchus? Answer - 30Gy
SBRT lung constraint whole lung? Answer - V20 <10%
SBRT target delineation? Answer - GTV, CTV, ITV, PTV?
GTV=CVT for SBRT
ITV: Margin added to CTV
PTV: 5mm all directions with exception 10mm Sup-Inf
1. Margins around targets can vary from -4mm to +4mm.
2. With negative margins, there will be a higher dose in the center.
3. With negative margins, there is a larger gradient created.
Why do we use 4D CT in lung treatments? Answer - It allows us to see the
movement of the tumor with the patients breathing cycle
If the tumor is moving too much and the PTV is not drawn to encompass this
movement then the tumor would not get the full dose.
