Lung Clinical Lab Assignment

Use the Lung CT data set provided to complete the following assignment:

Prescription: 60 Gy in 30 fractions to the PTV

Planning Directions: Place the isocenter in the center of the designated PTV (make sure it isn’t
in air). Create a single AP field using the lowest photon energy in your clinic. Create an MLC
block on the AP beam with a uniform 1 cm margin around the PTV. Apply the following
changes (one at a time) as listed in each plan exercise below. After making the adjustments
requested for each plan, answer the provided questions. Tip: Copy and paste each plan after
making the requested changes so you can compare all of them as needed.

Plan 1: Create a field directly opposed to the original field (PA). Assign equal (50/50) weighting
to each field. Embed an axial screen capture of your isodose distribution.
 What shape does the dose distribution resemble?
The shape of this field resembles an hourglass shape.
 How much of the PTV is covered entirely by the 100% isodose line?
20.97%
 What are two advantages of a parallel opposed plan? (Review Kahn, 5th ed., 11.5.A,
Parallel Opposed Fields)
According to Khan, advantages of the parallel opposed fields are the simplicity and
reproducibility of the setup, homogeneous dose to the tumor and less chance of a
geometric miss.
Plan 2: Add a direct left lateral field to the plan and assign equal weighting to all fields. Embed
an axial screen capture of your isodose distribution.
 How did this field addition change the isodose distribution?
The field addition eliminated the hotspots anterior and posterior. It also no longer
resembles the hourglass shape but is much more conformal around the tumor.
 How much of the PTV is covered entirely by the 100% isodose line?
35.99%
Plan 3: Add 2 oblique fields on the affected side—1 on the anterior portion and 1 on the
posterior portion of the patient. Assign equal weighting to all fields. Embed an axial screen
capture of your isodose distribution.
 What angles did you choose and why?
I chose 45 and 135 because I wanted equal spacing between the beams. This tumor is
located right in the center of the patient so I thought that this beam arrangement made
the most sense and would give the best coverage.
 Why is beam energy an important consideration for lung treatments? (Review Kahn,
5th ed., 12.5.B3, Lung Tissue)
According to Kahn, “when treating a tumor in the lung there is a possibility of
underdosage in the periphery of the tumor if small fields and high energy beams are
used”. This is because lung tissue has a much lower density, and if higher energy beams
are used not as many electrons are scattered and it won’t give good coverage.
Plan 4: Alter the weights of the fields to achieve the best PTV coverage. Embed an axial screen
capture of your isodose distribution.
 How does field weight adjustment impact a plan?
The field weight helps to increase coverage to the tumor. I was able to increase
coverage of the PTV from 33.82% to 43% with adjusting field weighting.
 List your final choice for field weighting on each field.
Final choice for weighting was:
AP: 25%
PA: 14%
LLAT: 36%
LPO: 10%
LAO: 15%
Plan 5: Try inserting wedges for at least one or more fields to improve PTV coverage. Embed a
screen capture of the beams-eye view (BEV) for each field that you used a wedge.
 List the wedge(s) used and the orientation in relation to the patient and describe its
purpose. (ie. Did it push dose where it was lacking or move a hotspot?)

AP: 30 degree
PA: 30 degree
Left Lat: 25 degrees

 Describe how your PTV coverage changed (relating to the 100% isodose line) with your
final wedge choice(s).
Coverage only increased slightly to 43.88% from 43.04%
Plan 6: Normalize your plan so that 95% of the PTV is receiving 100% of the prescription dose.
Embed an axial screen capture of your isodose distribution.
 Define normalization.
Normalization can either heat up or cool down a plan to help with dose distribution.
Normalization changes the percent of an isodose line, for example if you normalize to
95%, this means that anywhere that the tumor was receiving 95% of the dose, it will
now receive 100% of the dose. This also means that all the isodose lines will be
increased 5%.
 What impact did normalization have on your final plan?
Normalized to 90.5%
 What is your final hotspot and where is it?
Final hotspot is 116%, is located near the central axis inside the PTV.
 Are you satisfied with the location of the hotspot?
Yes, it is important to have the hotspot inside the tumor.
Plan 7: There are many ways to approach a treatment plan and what you just designed was just
one idea. Using the tools of your TPS, your current knowledge of planning, and the help of your
preceptor, adjust or design your own ideal 3D lung treatment plan. Get creative! You may
adjust the beam energy, beam weighting, wedges, add field-in-field, etc. Normalize your final
plan so that 95% of the PTV is receiving 100% of the dose.
 What energy(ies) did you use and why?
6x, this is the lowest beam energy available which works best for lung plans because of
the tissue density of lung. Because the tissue density is low, there is another buildup of
dose once the beam hits the tumor, therefore using the lowest energy, with the lowest
dmax will give the best coverage to the tumor.
 What is the final weighting of each field in the plan?
AP: 35%
LAO: 5%
LLAT: 20%
LPO: 5%
PA: 35%
 Where is the region of maximum dose (“hot spot”), what is it, and is this outcome
clinically acceptable?
The max dose point is receiving 6869 cGy which is a 114% hot spot. It is located in the
center of the PTV, this outcome is clinically acceptable, at my clinical site we will give
6000 cGy to the PTV and 7000 to the ITV. The hotspot is covering the ITV fairly well. At
my clinical site we would most likely try to make this even hotter so this outcome is very
acceptable.
 Embed a screen cap of your final plan’s isodose distribution in the axial, sagittal and
coronal views.

 Include a final screen capture of your DVH and embed it within this assignment. Make
it big enough to see (use a full page if needed). Be sure to provide clear labels on the
DVH of each structure versus including a legend. *Tip: Import the screen capture into
the Paint program and add labels. See example in Canvas.
 Use the table below to list typical OAR, critical planning objectives, and the achieved
outcome. Please provide a reference for your planning objectives.

Organ at Risk (OAR) Desired Planning Planning

Objective Objective
Outcome
Esophagus (RTOG 0920) V45<33%, V54< 15%, V45=0% V54=
Mean 34 Gy 0% Mean=3.4
Gy
Heart (RTOG 0623) V45<67%, V60<33% V45=0%
V60=0%
Combined Lung-ITV (Quantec) Mean <20-23 Gy 10Gy
V20<30-35% V20=17.78%
Spinal Cord (Quantec) Max dose 50 Gy 4.52 Gy
Trachea (Beaumont Health Systems) 84 Gy < 0.1 cc 12.3 Gy = 0.1
cc
Bronchus (Beaumont Health Systems) 84 Gy < 0.1 cc 65.6 cGy = 01.
cc