Merkel cell of the face:
Patient was diagnosed with malignant neoplasm of skin of other and
unspecified parts of face; Merkel cell carcinoma, cT1N1.
The patient was planned for a definitive course of radiotherapy to his cutaneous nasal bridge primary and bilateral facial & parotid lymphatic's & bilateral neck levels IB-V. All plans were sequential with all targets dosed at 200cGy per fraction. The sequence was:
1) First 25 fractions (to 50Gy): IMRT photon plan to 40Gy to PTV50 (bolus was used until clinical desquamation began at which point a non-bolus plan to 50Gy was implemented).
2) Subsequent 5 fractions (to 60Gy): IMRT photon plan without bolus to remaining PTV60 target.
3) Subsequent 3 fractions (to 66 Gy): Rapid-Arc photon plan without bolus to remaining PTV66 target.
Patient was planned on Eclipse vs10 software to a target area that involved the nasal bridge and bilateral facial region, of which a 1.0cm custom bolus was attached. The bilateral unbolused neck area was also included in the target volume.
In addition to containing the dose to the critical structures I also had to plan around a pacemaker.
The width and length of the target area as well as the pacemaker decreased the flexibility of the treatment planning strategy. As a result, the best plan was an 11 beam coplanar IMRT plan with Varian IEC angles of 179, 147, 114, 81, 40, 15, 342, 309, 276, 243, and 210. Six of the 11 beams utilized a fixed collimator setting to avoid the pacemaker.
BEV's displayed below.
The patient was planned for a definitive course of radiotherapy to his cutaneous nasal bridge primary and bilateral facial & parotid lymphatic's & bilateral neck levels IB-V. All plans were sequential with all targets dosed at 200cGy per fraction. The sequence was:
1) First 25 fractions (to 50Gy): IMRT photon plan to 40Gy to PTV50 (bolus was used until clinical desquamation began at which point a non-bolus plan to 50Gy was implemented).
2) Subsequent 5 fractions (to 60Gy): IMRT photon plan without bolus to remaining PTV60 target.
3) Subsequent 3 fractions (to 66 Gy): Rapid-Arc photon plan without bolus to remaining PTV66 target.
Patient was planned on Eclipse vs10 software to a target area that involved the nasal bridge and bilateral facial region, of which a 1.0cm custom bolus was attached. The bilateral unbolused neck area was also included in the target volume.
In addition to containing the dose to the critical structures I also had to plan around a pacemaker.
The width and length of the target area as well as the pacemaker decreased the flexibility of the treatment planning strategy. As a result, the best plan was an 11 beam coplanar IMRT plan with Varian IEC angles of 179, 147, 114, 81, 40, 15, 342, 309, 276, 243, and 210. Six of the 11 beams utilized a fixed collimator setting to avoid the pacemaker.
BEV's displayed below.
Why did I choose to fix the collimator on these 6 beams? This is simply experience and knowing what your optimizer will give you as you attempt to dose the target coming in through the shoulders and preserve pacemaker function.
Tips when planning a difficult case:
- Run the plan on the target volumes only and observe how the optimizer is considering the dose distribution.
- Be open to gantry and collimator changes.
- If an area is too hot or needs to be avoided, fix the most reasonable collimator jaws.
- Apply changes gradually to build your plan.
- Once your plan is the way you want it, try starting over using all your acquired knowledge. This typically will lower the MU and give a more homogeneous plan.
Desquamation effects caused the physician to change the original plan and give just 20 treatments with the bolus and 5 treatments without bolus for the first 50Gy.
The sum dose to 5000cGy is displayed above.
Sum isodose to 6600cGy
DVH Statistics:
Results yielded maximum dose of: brain_5190cGy, brainstem_4335cGy, chiasm_2322cGy, left optic nerve_3116cGy, and right optic nerve_3499cGy.
The right eye had a maximum dose of 4517cGy and a mean dose of 2750cGy while the left eye had a maximum dose of 4389cGy and a mean dose of 2526cGy.
The approach also yielded a maximum point dose to the pacemaker of 546cGy and a mean dose of 198cGy.
Results yielded maximum dose of: brain_5190cGy, brainstem_4335cGy, chiasm_2322cGy, left optic nerve_3116cGy, and right optic nerve_3499cGy.
The right eye had a maximum dose of 4517cGy and a mean dose of 2750cGy while the left eye had a maximum dose of 4389cGy and a mean dose of 2526cGy.
The approach also yielded a maximum point dose to the pacemaker of 546cGy and a mean dose of 198cGy.
