Treatment of Skull Base Tumors With Proton Therapy
Presenter: Norbert J. Liebsch
Affiliation: Massachusetts General Hospital
The treatment of base of skull tumors is extremely complex. Surgical resection is difficult due to toxicity associated with large resections. External beam radiation with photons can reduce the recurrence rates, however the results are still not optimal. Proton therapy has become the standard of care for treatment of these tumors due to the ability to give much higher doses of radiation without increasing the toxicity compared to photons. This presentation reports on an extensive experience at a single institution for the treatment of base of skull tumors with proton therapy.
Materials and Methods
This was a retrospective review of 340 patients with low grade chondrosarcoma (CS) of the base of skull and 550 patients with chordoma (CH) of the clivus treated with protons since 1975 at the Harvard Cyclotron and MGH. The CS patients age ranged from 10-79 years with 6% < 18 years. The male to female ratio was 1:1.3. Base of skull involvement included the tempero-occipital (66%), spheno-occipital (28%) and spheno-ethmoid (6%) areas. Most patients presented with cranial nerve deficits (81%) and many patients suffered from headaches (40%). Surgical resections included a gross total resection (5%), subtotal resection (74%), or partial resection/biopsy (22%). The CH patients ranged from 1-82 years with 15% < 18 years. Local control in this series was defined as the absence of tumor progression. CS were treated with 70 CGE in 35 fractions. CH were treated with 70-83 CGE in 37-44 fractions in adults and 79 CGE in 42 fractions in children. Doses were limited to < 62-66 CGE for the optic pathway, < 67-70 CGE to the surface of the brainstem and < 55-58 CGE to the center of the brainstem.
Local control was 98% and 95% at 5 and 10 years respectively for CS. For CH the local control in adults was 75% at 5 years and 55% at 10 years. The local control in males was 80% and 65% at 5 and 10 years respectively. The corresponding local control rate in females was 65% and 45%. Children experienced a local control rate of 80% at both 5 and 10 years for a diagnosis of CH without gender differences. The metastatic rate for both CS and CH was < 1%.
CS and CH of the base of skull are locally invasive with low metastatic potential. Both are successfully treated with combined surgery and proton therapy. For maximal tumor control the following approach is recommended:
CS- Biopsy to establish diagnosis, limited tumor resection to improve functional deficits followed by proton beam radiation.
CH- Gross total resection if acceptable morbidity based on tumor size and location or maximal debulking of tumor recommended, followed by proton beam therapy.
Clinical and Scientific Implications
This is one of the largest series in the world of base of skull tumors treated with proton therapy. Protons are considered the standard of care for CS and CH of the base of skull based on reports from this series of patients. It has been clearly shown the past that proton therapy is superior to photon irradiation of these tumors for local control and survival. It is also clear that there is a difference in behavior of CS versus CH. It is very important to establish the proper diagnosis to guide the extent of surgical resection prior to proton beam therapy. Proton therapy should remain as part of the standard management of these patients with base of skull tumors.