What is the preferred device to physically level the slope of the chest and maximize reproducibility when treating a lung cancer patient with ionizing radiation?
Vac-loc with or without a wing board
A vac-loc and wing board are probably the best choice depending on where the lung tumor is located. Arms are highly movable and can be difficult to reproduce, especially if their position can affect treatment image alignment. A vac-loc would give the most consistency in reproducibility. Just be sure to keep the vac-loc out of the treatment field.
A vac-loc offers consistent reproducibility and can accommodate arm positioning without entering the field.
What is another choice to compensate for the slope of the chest, without tilting the patient’s body, when treating lung cancer?
A manual wedge
Layering bolus could work, but many lung patients cannot breath well. Thus, the extra weight would be problematic. In addition, reproducibility, day to day, would be difficult. I raised headrest might help, if the patient has hyperkyphosis, but would be uncomfortable and increase breathing difficulty for many. A physical, manual wedge would work. Modern treatment would likely use the MLC’s to create a virtual wedge.
Manual wedge is practical and reproducible; layering bolus or using elevated headrests is discouraged due to breathing concerns.
In lung cancer treatment with curative intent, field borders are often determined based on what?
Staging
The stage of a cancer describes the size of a tumour and how far it has spread from where it originated. The grade describes the appearance of the cancerous cells. Imaging does not always detect microscopic invasion, so is not the best choice for determining borders. And finally, metastasis is also not a good indicator. If the cancer has already spread, the treatment borders may simply be set for palliation.
Staging describes tumor size and spread, which is critical for defining field borders.
How would you determine the treatment field size from an x-ray for a lung cancer patient without a computer calculated treatment plan?
1)Count the distance on the x-rays fiducial markers and mark the patient based on 1 cm separations
2)Measure the distance of the fiducial markers and make the patient using the same measurements
3)Measure the fiducial markers and create a proportion based on 1 cm to mark the patient
None of the other answer options work perfectly because you need to remember that the field size is inside the patient and requires additional adjustments
You must account for the depth of the tumor and divergence — surface measurements are not enough.
What treatment field configuration would you likely choose for a single tumor in a lung cancer patient without a computer calculated treatment plan?
AP/PA Parallel Opposed
A single AP field would work, but it is a lot of dose to the anterior healthy tissue. If you used a lateral x-ray to determine the depth, you could set this up iso-centrically. Thus, rotating the gantry to the parallel position would be simple.
A simple and effective approach to treat central lung lesions with balanced dose distribution.
According to “Portal Design in Radiation Therapy,” what is the TD 5/5 for whole lung?
14 to 17.5 Gy
What should be prepared on the treatment table before the lung cancer patient enters the room?
Wing board with headrest, sheet or paper, knee sponge, optional vac-loc or slant board. Also gather tape, ruler, marker, and calipers.
What should be considered when setting up the table for tumors near the lung apex?
Use a slant board or vac-loc to flatten the chest and improve dose distribution due to the chest’s natural slope.
What special consideration must the therapist accommodate when setting up some lung patients?
An oxygen tank or concentrator, ideally placed between the patient’s legs.
What should be confirmed before starting treatment?
Patient identity (time-out), signed consent form, and patient understanding of the procedure.
What is the basic patient positioning for lung cancer treatment?
Supine, straight, arms raised above head, chest exposed.
What anatomical landmarks can help ensure the patient is straight using the anterior laser?
- Nose
- Mental protuberance
- Cricoid cartilage
- Sternal notch
- Xiphoid tip
- Umbilicus
What gantry angle should be used to begin setup?
0 degrees.
How is patient midline determined?
Use lateral lasers and visual judgment to set depth to midline.
How is the initial field size determined in a lung manual setup?
Open the field large; tumor size and margins determine actual size. At least a 2 cm margin is required; 3 cm is common without onboard imaging.
Why are 3 cm margins often used in manual setups for lung tumors?
To account for tumor movement with respiration and ensure full coverage during inhalation and exhalation.
How do you calculate magnification from an X-ray using fiducial markers?
MF = Image Size / Object Size. If markers are 1.5 cm apart on image but should be 1 cm, MF = 1.5.
How do you find the actual tumor size from an X-ray?
Divide image tumor size by MF. (e.g., 7 cm / 1.5 MF = 4.7 cm actual size).
What are the two setup options after determining tumor size and location on X-ray?
- Set to midline, apply MF-corrected measurements, draw field.
- Set to 100 SSD, draw field, then raise to midline and confirm.
How do you localize the tumor iso-center using the sternal notch?
Measure longitudinally from the notch to the iso-center, mark, then measure laterally and draw crosshairs.
How is midline depth confirmed?
Use calipers at AP field iso-center to measure separation. Subtract half from 100 cm, confirm match with ODI. Adjust field if needed.
What must be done after setup and before treatment?
Document setup, get necessary approvals, and proceed with treatment.
What radiation field setups are common for lung cancer?
- AP only
- AP/PA
- 3D CRT
- IMRT (step-and-shoot or arc)
- SBRT
A 4-field box is uncommon.
Why is a 4-field box uncommon in lung cancer radiation therapy?
It can result in high doses to the heart and healthy lung tissue.
