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ISAC trial

Hypofractionated Ion Irradiation of Sacrococcygeal Chordoma


Dr. Matthias Uhl, E-Mail Opens window for sending emailMatthias.Uhl@med.uni-heidelberg.de
Karen Lossner, E-Mail Opens window for sending emailKaren.Lossner@med.uni-heidelberg.de


Chordomas are rare malignant tumors (1-4% of all malignant bone tumors). These slow-growing tumors arise from remnants of the notochord, an embryonic structure. About one third of chordomas arise in the sacral region. Surgical resection is still considered standard in the treatment of sacral chordoma. However, a complete removal with a sufficient safety margin is often difficult to perform due to the size, proximity to nerve / blood vessels and the complex anatomy of the pelvis. A radical surgery with safety margins often leads to bladder and bowel paralysis and other motoric and sensoric deficits. A postoperative radiotherapy is necessary due to the high risk of tumor regrowth. High irradiation doses next to the normal tissue are required for a sufficient tumor control. Therefore, particle therapy (proton / heavy ion) is the current gold standard. Due to radiobiological considerations a more effective dose can be administered to the chordoma cells by increasing the single dose per fraction, without increasing the risk of side effects. A Japanese trial with carbon ion irradiation confirmed this radiobiological model in patients with unresectable sacral chordomas. The data show excellent tumor control rates after irradiation with carbon ions in patients with inoperable sacral chordoma. The local control rate at 5 years was 88%.

This study is a single-center, prospective, randomized clinical phase II trial at the Heidelberg Ion-beam therapy center (HIT). Patients with sacrococcygeal chordoma are randomized either to proton therapy or carbon ion therapy. The total biologically effective dose in both treatment arms is 64 GyE. This dose is given in 16 radiation sessions. Hence, the biological dose to the tumor is 96 Gy.The primary endpoint of this study is the feasibility and toxicity. Other endpoints are local control of the tumor and survival.

Main inclusion criteria
  • Karnofsky index ≥ 70%
  • Age between 18 and 80 years
  • Histologically confirmed sacrococcygeal chordoma
  • Macroscopic (residual) tumor detection in MRI

Main exclusion criteria
  • Stage IV (distant metastases)
  • craniocaudal tumor extension, which technically can not be treated at HIT in scan mode (currently> 16 cm)
  • Metal implants at the level of chordoma affecting the treatment planning
  • Previous pelvic radiotherapy
  • Pregnancy
  • simultaneous chemotherapy or immunotherapy
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