International Journal of Radiation Oncology*Biology*Physics
Clinical InvestigationSpot-Scanning Proton Radiation Therapy for Pediatric Chordoma and Chondrosarcoma: Clinical Outcome of 26 Patients Treated at Paul Scherrer Institute
Introduction
Chordomas (CH) are rare tumors with an annual incidence rate of 0.1 case per 1,000,000 inhabitants (1). Only 5% occur in the pediatric population 2, 3. They arise from remnants of the embryonic notochord, metastasize infrequently; most frequently they are located in the spheno-occipital region and less commonly in the sacrococcygeal region and mobile spine.
Pediatric chondrosarcomas (CS) are also extremely rare and challenging to treat. They primarily affect long bones and pelvis, with less than 10% occurring in the head and neck region (4). Because of the localization of these tumors with proximity to critical structures, such as cranial nerves, brainstem, spinal cord, optic pathway, major blood vessels, brain parenchyma, kidneys, nerve roots, and rectum, complete resection often remains elusive for many patients despite all advancements in microscopic, image-guided, and endoscopic surgical procedures. Maximum safe tumor resection is considered the treatment of choice, followed by high-dose radiation therapy; improvements in outcome after radiation therapy have been reported, with tumor doses exceeding 70 Gy. Proton therapy (PT) has repeatedly demonstrated the ability to achieve higher local control (LC) and survival rates than previously reported series with photons 5, 6. In addition, in pediatric patients, the physical dose characteristics of protons are used furthermore for clinical advantages of reducing incidence and severity of late side effects as well as incidence of second malignancies.
Several studies in pediatric patients in general have demonstrated the dosimetric superiority of protons in comparison to external beam photon techniques including intensity modulated RT (IMRT), because of the fact that with protons, there is no exit dose to normal tissues, thus decreasing the amount of normal tissues irradiated (7).
This publication reports, for the first time, long-term results of the use of spot-scanning PT for the treatment of such pediatric patients.
Section snippets
Patients characteristics
Between June 2000 and June 2010, 26 patients with histologically proven diagnosis of CH (19 patients [73%]) or CS (7 patients [27%]) originating in the skull base or axial skeleton were treated postoperatively with PT at Paul Scherrer Institute (PSI) with curative intent. The median age of patients was 13.2 years (range, 3.7-20.8 years old). In the group of CH patients, the tumor originated from the skull base in 12 patients and from the axial skeleton in 7.
For the CS patients, the tumor
Local control
Twenty-three patients (88%) remained locally controlled; specifically, 17 of 19 patients (89%) with CHs and 6 of 7 patients (86%) with CS tumors. This resulted in 5-year actuarial LC rates of 81% for CH and 80% for CS (Fig. 2).
In the CH subgroup, 2 patients (11%) experienced therapy failure. One patient was a 3.7-year-old male with primary craniocervical junction undifferentiated chordoma who presented with lung metastasis at time of diagnosis; the patient received 6 consecutive cycles of
Discussion
Although photon radiation therapy is routinely applied in adult CH and CS patients, there are no specific publications reporting outcomes of photon radiation therapy in the pediatric CH/CS cohort.
Numerous dosimetric studies of a variety of pediatric tumors have demonstrated superiority of proton radiation therapy compared to external beam photon techniques, including IMRT, in the reduction of dose delivered to normal tissues (7). In the case of pediatric CH and CS patients, several clinical
Conclusions
Our study contributes to the small but growing body of literature demonstrating effectiveness and safety of PT for treating pediatric chordomas and chondrosarcomas. Spot-scanning technology was applied routinely and without technical difficulties or complications in this young patient population. High radiation doses were used at levels similar to those used in adult patients. Proton therapy in combination with optimum surgery offers realistic chances of cure with acceptable risks of side
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Data collection was supported by Oncosuisse grant 01694-04-2005.
Conflict of interest: none.