Planning for a Lumpectomy Boost
A Lumpectomy Boost can be treated with photons or electrons.
A boost plan with photons will be treated using four fields: medial, lateral, anterior superior-inferior oblique (ASIO), and anterior inferior-superior oblique (AISO). The isocenter of the fields for the boost do not need to change unless doing so provides a significant dosimetric advantage. Remember to name/number the fields appropriately.
Starting with either the medial or lateral field, use the fit to structure function. Input the following parameters and press ok:
- Select the target structure to be the “PTV Lumpectomy”.
- Select the circular margin, collimator coordinate system, leaf edge-contour meet point = outside, closed leaf meeting position = center, and only check “optimize collimator jaws”.
- Give a 0.7 CM circular margin.
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 Lumpectomy”. Repeat the method above on the second opposing field. The opposing field may no longer remain tangential after fitting the MLC leaves to the “PTV Lumpectomy” and will require a gantry rotation.
Moving on to the oblique fields, copy and paste the second field. The definition of the ASIO and AISO fields are defined in their names. ASIO indicates that an oblique beam will enter anteriorly from the superior to inferior direction (AISO is from the inferior to superior direction). Thus, rotate the couch to 90 degrees and rotate the gantry to 330 degrees. The sagittal viewing plane will demonstrate a beam as how ASIO had just been defined.
Use the fit to structure function. Input the following parameters and press ok:
- Select the target structure to be the “PTV Lumpectomy”.
- Select the circular margin, collimator coordinate system, leaf edge-contour meet point = outside, closed leaf meeting position = center, and only check “optimize collimator jaws”.
- Give a 0.7 CM circular margin.
Copy and paste the ASIO field, and change the gantry to 30 degrees. View the sagittal viewing plane to confirm the geometric parameters and then repeat the method mentioned above.
Place your reference point in the “PTV Lumpectomy” and calculate.
Refer to Basic Wedge Guide in order to reduce the hotspot.
In general, a photon boost plan must meet the following constraints:
- At least 95% of the prescription dose covers at least 95% of the PTV Lumpectomy.
- The maximum hot spot or “3D Dose Max” cannot exceed 110% prescription dose.
- No OAR should receive significant dose in the CD plan.
- 100% of the prescription dose from the Lumpectomy CD plan should not irradiate more than 33% of the original “PTV Breast”.
A boost plan with electrons will treated using one anterior oblique field which is en face to the “PTV Lumpectomy” at a minimum of 100 CM SSD. The SSD can be increased in increments of 5 CM (105 CM, 110 CM, etc.), and doing so can help the therapists set the patient up easier without significant dosimetric consequences. In the prescription tab, the prescribed dose (%) will be changed to 90%, meaning that the intended prescription dose will be prescribed to the 90% isodose line.
The energy chosen will depend on the depth of which the prescription dose is to be delivered. Physicians look to see that the “PTV Lumpectomy” is covered by the 90% isodose line (ocassionally the 80% isodose line). A rough rule of thumb to find which energy to use is by the following equation:
- E/3.2 = depth of the 90% isodose line
- E/2.8 = depth of the 80% isodose line
A cone size will be chosen that will cover the “PTV Lumpectomy” with a 1.5 CM margin and more room to spare around the margin. Collimation may sometimes be used to prevent the cone from colliding with the patient’s raised arm.
A block, and sometimes a bolus, will be attached to this field. The parameters of the block will be set to aperture and given a 1.5 CM margin around the “PTV Lumpectomy”. If a bolus is used, it needs to encompass the exposed field.
Place the reference point in the “PTV Lumpectomy” and calculate.
The reference point is to be placed in the location of dmax. Begin by moving the viewing planes to isocenter. By using the dose profile tool, drag the cursor along the central axis of the field, starting from a few CM outside the body and ending it a few CM past the scar wire. A dose profile will appear on the screen, and by moving the cursor to the peak of the curve, a blue line seen on the axial view will indicate the location where the reference point will be moved.
If the secondary check (e.g. RadCalc) dose not pass, move the reference point to the dmax of a different slice. You may also move the reference point transversely to the central axis at dmax.
The constraints for an electron lumpectomy boost follow the guideline of ALARA (as low as reasonably achievable). It is recommended to use the lowest electron energy possible that provides adequate coverage to the target so that the ipsilateral lung does not receive significant dose.
Planning for a Scar Boost
A Scar Boost plan will be treated using one anterior oblique electron field which is en face to the scar wire at a minimum of 100 CM SSD. The SSD can be increased in increments of 5 CM (105 CM, 110 CM, etc.), and doing so can help the therapists set the patient up easier without destructive dosimetric consequences. In the prescription tab, the prescribed dose (%) will be changed to 90%, meaning that the intended prescription dose will be prescribed to the 90% isodose line.
The energy chosen will depend on the depth of which the prescription dose is to be delivered (9E is commonly used). Physicians look to see that the scar wire is covered by the 90% isodose line (ocassionally the 80% isodose line). A rough rule of thumb to find which energy to use is by the following equation:
- E/3.2 = depth of the 90% isodose line
- E/2.8 = depth of the 80% isodose line
A cone size will be chosen that will cover the scar wire with a 1-1.5 CM margin and more room to spare around the margin. Collimation may sometimes be used for clearance to prevent the cone from colliding with the patient’s raised arm.
A block, and sometimes a bolus, will be attached to this field. The parameters of the block will be set to aperture and given a 1.5 CM margin around the scar wire. If a bolus is used, it needs to encompass the exposed field.
Place the reference point in the near vicinity of the scar wire and calculate.
The reference point is to be placed in the location of dmax. Begin by moving the viewing planes to isocenter. By using the dose profile tool, drag the cursor along the central axis of the field, starting from a few CM outside the body and ending it a few CM past the scar wire. A dose profile will appear on the screen, and by moving the cursor to the peak of the curve, a blue line seen on the axial view will indicate the location where the reference point will be moved.
If the secondary check (e.g. RadCalc) does not pass, move the reference point to the dmax of a different slice. You may also move the reference point transversely to the central axis at dmax.
Visually, the 90% isodose line should cover the area under the wire.
The constraints for a scar boost follow the guideline of ALARA (as low as reasonably achievable). It is recommended to use the lowest electron energy possible that provides adequate coverage to the target so that the ipsilateral lung does not receive significant dose.
