Proton Beam Therapy for Clival Chordomas

Reviewer: William Levin
Abramson Cancer Center of the University of Pennsylvania
Last Modified: May 29, 2007

Presenter: K. Tsuboi
Presenter's Affiliation: University of Tsukuba, Tokyo University Hospital
Type of Session: Scientific

Background

Clival Chordomas are rare tumors that arise from the embryonic notochord.
These particular chordomas are located at the base of skull.
These tumors are characterized by slow growth, with local destruction of bone and extension into the adjacent soft tissue.
Very rarely, distant metastases are encountered.
Surgery is the mainstay of treatment.
Because adequate surgical margins are not frequently obtained, local recurrences following surgery are common.
Accordingly, clinicians have employed the use of radiation therapy to help in the treatment of these tumors.
Historically, administration of adequate radiation doses has not been achieved due to potential side effects to surrounding normal tissue (central nervous system).
More recently, investigators have employed the use of proton radiation in an effort to escalate dose and minimize toxicity to normal tissue.

Materials and Methods

20 patients with clival chordoma treated with protons +/- photon radiation were retrospectively reviewed.
Patients were split into two series.
Thirteen patients were in series #1, treated between 1989 and 2000.
Seven patients were treated in series #2, between 2000 and 2006.
Median tumor doses of 72.0Gy (63.0-95.0Gy) and 70.2Gy (59.4-70.4Gy) were delivered in series #1 and series #2, respectively.
The median follow-up was 69.3 months (14.6-123.4 months) and 33.8 months (4.5-55.2 months) in series #1 and series #2, respectively.

Results

In series #1 cause specific survival, overall survival, and disease-free survival rates at five years were 72.2%, 66.7%, and 42.2%, respectively.
The local control rate was higher for those with pre-operative tumors less than 30ml.
Three cases of radiation necrosis were observed and two cases showed sarcomatous transformation.
In contrast, in series #2, all tumors have been controlled so far, and neither radiation necrosis or sarcomatous transformation has been observed.

Author's Conclusions

Proton beam therapy is effective for the control of Clival Chordomas, especially for those patients with small tumors.
Despite successful control of these tumors side effects such as sarcomatous transformation and radiation necrosis are still a concern.

Clinical/Scientific Implications

As indicated above, with the use of proton radiation clinicians are now able to achieve adequate doses (70Gy or higher) while being able to minimize dose to healthy surrounding tissue including the brain and optic pathway.
Despite improvements in local control and overall survival, problematic side effects such as radiation necrosis and sarcomatous transformation have been observed.
It is believed that radiation necrosis may be minimized by using different beam arrangements in an effort to reduce dose to the temporal lobes, which seem to be exquisitely sensitive to the effects of radiation.
The etiology of sarcomatous transformation is less clear.
This phenomenon may occur spontaneously or the transformation may be induced by the use of ionizing radiation.