Pre-simulation
Supine Breast cases are most commonly seen with a prescription of 50 Gy in 25 fx (conventional) or 42.56 Gy in 16 fx (hypofractionation), optionally followed by a boost of 10 Gy in 5 fx.
You will not need to import any ancillary images for this plan, though, on rare occasions, a PET scan may be requested by the physician.
Simulation
Patients are simulated in the supine position while lying on a breast board. The breast board holds the patient’s ipsilateral arm above the head, and the patient will turn their head away from the treated breast. For left-sided breast cases, the physician may opt for a deep inspiration breath hold (DIBH) simulation in which the patient will take a deep breath and hold it for the full duration of the CT scan. The lungs expand upon taking a breath and push the heart inward and away from the left breast. The lungs in an expanded state have a greater volume, and with the heart also now further away from the treatment area, the dose to both of these OARs will receive significantly less (compared to non-DIBH).
The therapists will align the CT machine laser indicators with the patient’s body to place radiopaque BBs on the patient anteriorly and ipsilaterally in the same axial plane. A radiopaque adhesive wire may also be placed over the lumpectomy scar for only the scan, which is typically performed by the physician. The CT scan will then take place using a slice thickness of 2.5 mm, and the images will then be pushed to the treatment planning system (TPS). After the simulation, the BBs will be removed and markings (tattoos) will be made in their places for which the therapists will align the lasers to during treatment setup.
Contouring
Create a structure set that includes the following structures:
- Two unique structures: Laterality + Breast or Chest Wall
- e.g. LT Chest Wall and RT Breast
- Chest wall should be a High Resolution Structure
- PTV Laterality + Breast/Chest Wall
- e.g. PTV LT Breast or PTV LT Chest Wall
- Chest wall should be a High Resolution Structure
- Axillary Node
- IMC Node
- S_CLAV Node
- Two unique structures: “Lung LT” and “Lung RT”
- Heart
- Esophagus
- Spinal Cord
- Liver
- LT or RT Humeral Head (Ipsilateral)
- Mandible
- Brachial Plexus (Optional)
- BBs
- Body
- S_CLAV Wire
- Scar Wire or Lumpectomy Wire (Depending on Mastectomy or Intact breast)
- CTV Lumpectomy (If breast is still intact)
- PTV Lumpectomy (If breast is still intact)
If there is a DIBH scan, keep in mind that the primary treatment will be planned on the DIBH scan and the boost/CD will be planned on the Free Breathing (FB) scan. Therefore, if there is a lumpectomy, the physician will need to contour on the FB scan.
Before contouring the BB and the scar wire structures, make sure to convert them to High Resolution Structures which will allow you to define the wire location more precisely. Using the adaptive brush in combination with adjusting the contrast level can help with contouring wire/BB structures. When these contours are complete, you may crop the scar wire and BBs outside of the body contour since these markings were only used for the CT scan and will not be present at the time of treatment. Furthermore, go into the properties of these structures and set the HU = 0. This is a second precautionary measure taken to tell the TPS that there should not be such a high density structure in that place at the time of treatment.
The physician will contour the “RT/LT (Ipsilateral) Breast”, “RT/LT (ipsilateral) Chest wall”, “CTV Lumpectomy”, and/or nodal structures depending on the patient. Do NOT modify physician drawn contours.
The physician drawn contours are used as a reference, and you will instead work with the “PTV Breast” or “PTV Chest wall” structure.
- For the “PTV Breast”: Crop the physician drawn “RT/LT Breast” outside the body contour by an additional 5 mm. This will bring the PTV volume inside the body and remove the 5 mm of skin.
- For the “PTV Chest wall”: Crop the physician drawn “RT/LT Chest wall” that extends outside the body with no additional margin. A bolus will be used to deliver superficial dose. For patients with an expander, the physician may ask to crop the volume by an additional 3 mm which extends outside the body and treat without a bolus.
- For the physician drawn “CTV Lumpectomy”, add a 7 mm outer expansion to create a “PTV Lumpectomy” volume.
- If the “PTV Lumpectomy” now extends outside the “PTV Breast”, crop the “PTV Lumpectomy” inside the “PTV Breast”.
- If the original “CTV Lumpectomy” is EXCLUDED from the newly cropped “PTV Lumpectomy” on any slice, boolean the “CTV Lumpectomy” into the “PTV Lumpectomy”. A bolus may be used in such a case as the “CTV Lumpectomy” is most likely superficial, and it is up to the physician’s discretion.
- To summarize, the “PTV Lumpectomy” starts as a 7 mm margin around “CTV Lumpectomy”, but it should not extend outside the “PTV Breast”. If the “PTV Lumpectomy” is missing a part of the original “CTV Lumpectomy”, then the “CTV Lumpectomy” will be booleaned back into “PTV Lumpectomy”. At this point, the “PTV Lumpectomy” will extend outside “PTV Breast” in order to include the original “CTV Lumpectomy”.
- If the scar wire is being treated for the boost/CD (Generally indicated by an absence of a lumpectomy volume), no additional contouring modifications are required.
If the patient has artifact caused from the expander, you should contour out the artifact region in a separate structure. Then, assign it HU equal to 0 so that this region is equivalent to tissue as the artifact will not be present during the time of treatment. Be sure not to include the metallic or artifact causing structure itself within this structure.
If the patient has a pacemaker, it should be contoured as well. Pacemakers can receive no more than a max point dose of 2 Gy.
Planning Setup
Refer to the link below for a broad setup overview:
3D supine breast plans are generally treated using two opposing tangent fields (medial & lateral) of the same isocenter. If there is nodal involvement, a third field, called the supraclavicular (SCLAV) field, is used and created in a separate plan (Requiring a Plan Sum). It will be an en face 15X beam to cover the nodes with a slight gantry rotation (About 350° or 10°) to avoid the spinal cord. More specific details will be discussed further down.
In the event of a superficial lumpectomy volume or scar wire, the physician will typically approve of a 0.5 CM thick bolus over the superficial treatment area. Insert a bolus which covers the entirety of the superficial treatment area with a slight extra margin to take setup error into account.
Most supine breast tangents are treated using an energy of 6X, but large breasts in particular may be treated using higher energies if it is dosimetrically advantageous. Some patients are treated with mixed energies, such as 6X and 18X together on each side. This may occur in patients with a large breast separation (>23 CM breast separation).
3D Breast/Chest Wall Planning
Modify the gantry angles of both fields to deliver adequate dose to the “PTV Breast” or “PTV Chest wall” while minimizing OAR overlap and also matching the posterior borders of the medial and lateral fields. Matching the posterior field borders will prevent the overlap of beam divergence in the body, thereby minimizing the spread and buildup of low dose beyond the field edge.
Once the fields are setup, starting with one field, create MLC leaves and use the ‘fit to structure’ function. Input the following parameters and press ok:
- Select the target structure to be the PTV.
- Select elliptical margin, collimator coordinate system, leaf edge-contour meet point = outside, closed leaf meeting position = center, and only check “optimize collimator jaws.
- Give a 3 CM anterior margin and a 0 CM margin elsewhere. This 3 CM margin will be the “flash” that accounts for breast swelling.
After using this tool, you should see that the field size, on the axial view and the BEV, have been adjusted to include the entirety of the PTV. Verify that the contours for the contralateral breast, heart, and ipsilateral lung have minimal overlap as possible with this field in the BEV. If there is an unsatisfactory overlap:
- Rotate the gantry and re-fit to structure until an acceptable angle is achieved.
- Possibly rotate the collimator by 5° to 15° such that the posterior field edge becomes near parallel to the chest wall seen through the DRR to keep an OAR out of the field.
- Include more of the ipsilateral lung and/or the heart (if the previously mentioned suggestions did not work). Sometimes, simply the positioning of the patient from simulation or the patient anatomy may not be ideal to minimally involve all the OARs, and so including more of the ipsilateral lung and/or the heart in the field in this scenario would be acceptable. It is best to consult with the physician on his/her preference.
Remember that in making these field adjustments, the opposing field may no longer be tangential and will require further adjustment of the gantry angle afterwards.
When you are satisfied with the field, manually create a 1.5 CM superior (as there is no nodal involvement) and inferior margin on the PTV by adding 1.5 to the appropriate X/Y field size (depending on collimator rotation). Furthermore, the MLC leaves need to be manually adjusted as well:
- All the MLC leaves which enter anteriorly will need to be dragged out manually to match the new anterior field border. The MLC leaves will only be kept in the field if it is to block part of the raised ipsilateral arm.
- The posterior MLC leaves will generally match the outline of the PTV contour (as there is no nodal involvement). These leaves are adjusted in rare cases such as to give more coverage to posterior regions of the breast.
You can then repeat the method above to create a flash and add margins on the second opposing tangent field.
Place your reference point near the breast-lung interface and calculate.
Refer to the link below for more information on 3D breast field-in-field planning:
Refer to the link below for more information on breast electronic (irregular surface) compensator planning:
In general, a supine breast plan WITHOUT nodal involvement must meet the following constraints:
- At least 95% of the prescription dose covers at least 95% of the PTV.
- The maximum hot spot or “3D Dose Max” cannot exceed 110% prescription dose (108% for hypofractionated cases).
- 108% of the prescription dose cannot be delivered to more than 5% of the irradiated breast volume.
- The volume of the ipsilateral lung that receives 20 Gy cannot exceed 20% (preferably 15%).
- The mean dose to the heart cannot exceed 4 Gy.
- The contralateral breast cannot exceed a max point dose of 3-4 Gy.
- Additionally, the following constraints are recommended:
- 105% of the prescription dose should not be delivered to more than 15-20% of the irradiated breast volume.
- No hot spots in the inframammary fold or close to the skin.
3D Breast/Chest Wall Planning with Nodal Involvement
This guide will be discussing the monoisocentric treatment method. This method consists of a medial, lateral, and SCLAV field that are all set to the same isocenter. The isocenter will typically be placed at the junction of the clavicular head and the first rib. The field opening of the medial and lateral fields superior to the isocenter will be closed, and the field opening of the SCLAV field inferior to the isocenter will be closed. In otherwords, the medial and lateral fields will only be open to treat inferior to the isocenter, and the SCLAV field will only be open to treat superior to the isocenter. The SCLAV field may involve parts of the Breast/Chest Wall volume and will not always be restricted to treating only the nodes.
Modify the gantry angles of the medial and lateral fields to deliver adequate dose to the “PTV Breast” or “PTV Chest wall” while minimizing OAR overlap and also matching the posterior borders of the medial and lateral fields. Matching the posterior field borders will prevent the overlap of beam divergence in the body, thereby minimizing the spread and buildup of low dose beyond the field edge.
Modify the gantry angle of the SCLAV field (generally between 345° and 15°) so that field excludes the spinal cord as much as possible while delivering adequate dose to the nodal structures.
Once the fields are setup, starting with one field, create MLC leaves and use the fit to structure function. Input the following parameters and press ok:
- Select the target structure to be the “PTV Breast” or “PTV Chest wall”.
- Select the elliptical margin, collimator coordinate system, leaf edge-contour meet point = outside, closed leaf meeting position = center, and only check “optimize collimator jaws.
- Give a 3 CM anterior margin and a 0 margin elsewhere. This 3 CM margin will be the “flash” that accounts for breast swelling.
After using this tool, you should see that the field size, on the axial view and the BEV, have been adjusted to include the entirety of the “PTV Breast” or PTV Chest wall”. Verify that the contours for the contralateral breast, heart, and ipsilateral lung have minimal overlap as possible with this field in the BEV. If there is an unsatisfactory overlap:
- Rotate the gantry and re-fit to structure until an acceptable angle is achieved.
- Include more of the ipsilateral lung and/or the heart (if the previously mentioned suggestions did not work). Sometimes, simply the positioning of the patient from simulation or the patient anatomy may not be ideal to minimally involve all the OARs, and so including more of the ipsilateral lung and/or the heart in the field in this scenario would be acceptable. It is best to consult with the physician on his/her preference.
Remember that in making these field adjustments, the opposing field may no longer be tangential and will require further adjustment of the gantry angle afterwards.
When you are satisfied with the field, manually create a 1.5 CM inferior margin on the PTV by adding 1.5 to the appropriate X/Y field size (depending on collimator rotation). As there is nodal involvement, there will be no superior margin added. The field opening superior to the isocenter (Y2 with no collimation) will be set to 0 CM in order to create the half-field block effect. Furthermore, the MLC leaves need to be manually adjusted as well:
- All the MLC leaves which enter anteriorly will need to be dragged out manually to match to new anterior field border. The MLC leaves will only be kept in the field if it’s to block the fat of an arm.
- The posterior MLC leaves and field border will be adjusted to allow for adequate coverage of the nodes. Do not extend the superior border of the field to cover the nodes as that will be the role of the SCLAV field.
You can then repeat the method above to create a flash and add margins on the second opposing tangent field.
Place your reference point near the breast-lung/breast-chest wall interface and calculate.
For the SCLAV field, the gantry angle will be at an angle that will provide adequate nodal coverage while also keeping off the spinal cord.
- Move the SCLAV field to its own unique plan and reference point.
- Verify that the energy is set to 15X.
- A physician will normally create the aperture/MLC pattern for the SCLAV field. However, you can prepare it yourself by giving a 0.7 CM – 1 CM margin around the nodes to be covered, and blocking the ipsilateral humeral head and spinal cord.
- Keep in mind that the inferior border (Y1 with no collimation) will always be set to 0 CM, as this creates the half-field block effect.
Place your reference point in the posterior/superior region of the supraclavicular nodes and calculate.
Create a plan sum with the tangential fields and the supraclavicular field to evaluate the DVH. Sometimes, MLC leaf adjustment of your field-in-fields and field weighting may need to be performed in the Plan Sum as the maximum hotspot may be a direct result of the scatter overlap at the junction.
Reduce the maximum hot spot, V108%, and V105%.
A supine breast plan WITH nodal involvement must meet the following constraints:
- At least 95% of the prescription dose covers at least 95% of the PTV.
- At least 95% of the prescription dose covers at least 90% of each nodal volume.
- The maximum hot spot or “3D Dose Max” generally cannot exceed 110% prescription dose, but hot spots in the nodal structures can be up to 115%.
- 108% of the prescription dose cannot be delivered to more than 5% of the irradiated breast volume.
- The volume of the ipsilateral lung that receives 20 Gy cannot exceed 32%.
- The volume of the contralateral lung that receives 5 Gy cannot exceed 15% (preferably 10%).
- The mean dose to the heart cannot exceed 4 Gy.
- The contralateral breast cannot exceed a max point dose of 3-4 Gy.
- The spinal cord max dose cannot exceed 45 Gy.
- The volume of the esophagus that receives 45 Gy cannot exceed 33%.
Additionally, the following constraints are recommended:
- 105% of the prescription dose should not be delivered to more than 15-20% of the irradiated PTV breast/chest wall volume.
- No hot spots in the inframammary fold or close to the skin.
Refer to the link below for a 3D supine boost planning tutorial:
