Plan 1: Create a field directly opposed to the original field (PA).

Assign equal (50/50) weighting

to each field.
• What shape does the dose distribution resemble?
When looking at the axial plane, the dose distribution resembles an hourglass with the
90% dose line (thick yellow line). When looking at the sagittal view at isocenter, the
90% IDL are relatively symmetrical, and the shape also resembles an hourglass. The
100% IDL (thick red line) are contained within the first few cm of tissue from the AP
and PA fields with some 100% within the PTV itself. The 95% IDL (thick orange line) is
connected from the PA field, but not the AP field. This is happening medially and
superiorly within the field as seen from the frontal view. The 50% IDL (thick light blue
line) is a rectangle through the axial and sagittal views. My hot spot is 115% and
located posteriorly and inferiorly in the patient’s tissue. It is located 1.59 cm into the
patient which is approximately dmax of a 6Mv beam. It is very small in size so I put on
the 114% line (thick green line) to make it easier to visualize. Even though the beams
are equally weighted, the AP does not have a hot spot mirroring this location. With
the knowledge I have, I surmise this is because of there being more dense tissue
(muscle and fat) that the beam is passing through before being attenuated by the
lower density lung tissue.
•
•
 • How much of the PTV is covered entirely by the 100% isodose line?
9.66929% of the PTV is covered by the 100% IDL.

• In your own words, summarize two advantages of using a parallel opposed plan?
(Review Khan, 5th ed., 11.5.A, Parallel Opposed Fields)
A single field may work when wanting to treat a superficial tumor; however, it is not
the best way when treating tumors that are deeper within the patient. Parallel
opposed beams help to cover our target volume with more homogeneity throughout
our tumor volume. Parallel opposed beams also make treatments simple and easy to
reproduce, which is what is a goal of radiation therapy: reproducibility. There is a
downside to using this method, we will be treating more normal tissue when using
parallel opposed beams.

Plan 2: Add a direct left lateral field to the plan and assign equal weighting to all fields. How
did this field addition change the isodose distribution?
The 80% IDL (thick light green) is in the shape of a box when looking at the axial plane and a
circle when looking at the frontal and sagittal planes. The 90% IDL (thick yellow line) is in
relatively the same shape as the 80% IDL; however, there is a little horn you can see on the
axial view that is located medially (yellow arrow). You can also see (when comparing to the
80% IDL in the sagittal view), that the 90% IDL shape is not as symmetric as the 80% and is
getting thinner inferiorly. When looking at the 80% (thick light green line), 95% (thick orange
line) and 100% IDL (thick red line), we can see that the 95% is asymmetrical. We also see the
100% IDL is located laterally and inferiorly within the PTV volume (outline is thin red). My
hot spot is a lot cooler: 103.6% of the total dose. This hot spot is located within the PTV
volume and is very small. 103% IDL is thick green line. This is to visualize the hotspot better
as it is not very big.
• How much of the PTV is covered entirely by the 100% isodose line?
21.7124% of the PTV is covered entirely by the 100% IDL.
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.
• What angles did you choose and why?
I chose an RAO and LPO with angles of 330 and 150 respectively. I tried steeper angles
of 315 and 135 degrees, but I realized that there was a lot more of the right lung in the
treatment field than if using angles that are 30 degrees off the AP/PA fields. The right
lung being treated is highlighted with red. As you can see, there is hardly any right
lung treated with the 330- and 150-degree obliques.
Also, there was not a lot of difference between coverage on PTV between the two
plans or lower doses with the OARs between the two angles, so my deciding factor
was keeping as much healthy lung tissue out of the treatment fields as possible.
Below there is a DVH to show the difference between the two plans. The plan I chose
has lines with squares and the comparison plan has the lines with triangles.
 • In your own words, summarize why beam energy is an important consideration for lung
treatments? (Review Khan, 5th ed., 12.5.B3, Lung Tissue)
When planning a lung treatment, the beam will be moving through different densities
(tissue, bone, lung) to treat our target volume. These different densities will impact
how the beam behaves; generally, changes in the absorption of the primary beam and
scattered electrons along with changes of the secondary electron fluence are seen at
different points throughout the inhomogeneity. Scattered electrons impact the dose
near the inhomogeneity, whereas secondary electron fluence impacts the dose within
tissues of the inhomogeneity and at the boundaries. With the low density of lung
tissue, researchers find that as beam energy increases, more electrons travel outside
the geometry of the beam itself, which can result in underdosing the outside of a lung
tumor. This impact on dose within the lung is seen more significantly with small field
sizes and energies greater than 6MV.

Plan 4: Alter the weights of the fields to achieve the best PTV coverage.
• How does field weight adjustment impact a plan?
When we utilize field weighting for an SAD treatment plan, we can adjust the dose
distribution from each beam angle to adjust for the distance between the beam and
the tumor. Not every angle is going to be the same in terms of distance from our
target and what kind of tissues and OARs are between the beam and the target.
When we manipulate our beam weighting, we are utilizing one of our tools to get an
ideal dose distribution for our plan.
 • List your final choice for field weighting on each field.

Plan 5: Try inserting wedges for at least one or more fields to improve PTV coverage. You may
also adjust field weighting if you feel it’s necessary.
• 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?)
The 100% IDL (thick red line) was located more lateral and inferiorly within the ITV
(thin blue line and first screen shot below). There was also a gap between the 90%
(thick yellow line) and 95% (thick orange line) IDL posteriorly and lateral (see second
screen shot below).
I put a 20 In wedge on the AP. This was to act as a compensator for the slope of the
chest. The heel was lateral with the toe pointing towards midline of the patient.
There is also a 30 in wedge on the lateral beam. The heel was inferior with the toe
pointing toward the head of the patient. This was to help spread the hotspot towards
the head of the patient. As you can see, the AP wedge helped to even out the IDL.
There is still a gap between the 90 and 95% IDL, but it isn’t as prominent (first screen
shot below). You can also see that my 100% IDL is more spread out over the ITV (thin
aqua line and second screen shot below).
• Describe how your PTV coverage changed (relating to the 100% isodose line) with your
final wedge choice(s).
You can visually see how my 100% IDL changed with the above screen shots. With
plan 5 (wedges), 17.2% of the total volume of the PTV is covered with 100%. With
plan 4, 18.1% (no wedges) of the total volume of the PTV is covered with 100%. Even
though coverage dropped a little at 100%, we can see in the DVH comparison below
that Plan5 (Red line with triangles), has better coverage at 90% and 95% and a steeper
drop off. I left the cross hair at 95% for Plan 5 (With wedges) to show the slightly
better coverage at this point vs 69.4% for Plan 4 (no wedges). At 90% dose, Plan 5
covers 98.8% of PTV volume vs 96.9% for Plan 4. Visually above you can see how the
dose is more homogeneous throughout our target volume.
Plan 6: Normalize your plan so that 95% of the PTV is receiving 100% of the prescription dose.
• What impact did normalization have on your final plan?
When I normalized my plan, it made my plan hotter, which was needed as my PTV was
not receiving enough dose. You can see in the screen shot below that there is a better
homogeneous dose distribution between the 95%(thick orange line), 100% (thick red
line) and 105% (thick white line). The thin red line is the PTV volume. 99.9% of my
PTV volume (red line) is receiving 95% of the dose which is great. 100% of the ITV
(aqua line) is receiving 100% of the dose (see DVH below screen shots of dose
distributions).
 • What is your final hotspot and where is it?
111.2% of the presciption is my hotspot and it is located within my PTV.

• Are you satisfied with the location of the hotspot?

I am satisfied with this location because it is where I am trying to get the most dose
and not spare OARs. It is also not too hot, as I can use planning techniques (such as
field in field), to lower it to a more acceptable hot spot <110% according to my clinic’s
lung dose tolerance sheeting (located at the end of this paper).

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?
I used 6 MV. I played around with all the energies, including 6FFF and 10 FFF, but 6
MV seemed the most suitable for this tumor. Also learning about how lung tissue
impacts the beam as energies increase beyond 6 MV helped in this decision.
• What is the final weighting of each field in the plan?

• Where is the region of maximum dose (“hot spot”), what is it, and is this outcome
clinically acceptable?
The hot spot is small and is at exactly 110%. It’s location is inside the ITV volume at
the inferior tip of the drawn ITV. This is clinically acceptable as you can see in the DVH
in the below window, 0.03% of my total PTV (thin red line) volume has a maximum
dose of 109.4% which is acceptable in my clinic.
• Embed a screen cap of your final plan’s isodose distribution in the axial, sagittal and
coronal views.
108% is thick green line; 105% is white thick line; 100% is red thick line; 95% is orange
thick line; 80% is thick light green line; 50% is thick aqua line. The first three screen
shots are of the 95% and 105% IDL with the PTV (thin red line) and IVT (thin aqua line)
turned on to show the dose within the PTV/ITV volume. The last three screen shots
are of the isodose distribution of the plan without the PTV turned on.
• 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.
The references for my treatment objectives at Inova are below this table. I have
added other OARs that were contoured in the table below, but that Inova does not
 take into consideration. For the Primary Bronchus, the resource used for planning
objectives is in parentheses.
Organ at Risk (OAR) Desired Planning Objective Planning Objective Outcome

Heart Dmean(Gy) ≤ 20 1.9 Gy

V30Gy(%) ≤ 50 0.1 %

Esophagus Dmax(Gy) ≤ 63 20.0 Gy

Dmean(Gy) ≤ 34 4.5 Gy

Lung - CTV Dmean(Gy) ≤ 20 15.7 Gy

V20Gy(%) ≤ 37 35.5%
V5Gy(%) ≤ 65 47.9%

Spinal Cord Dmax(Gy) ≤ 45 1.2 Gy

Primary Bronchus Dmax(Gy) ≤ 80 64 Gy

(QUANTEC – Bronchial Tree)