Clinical Results of Spot-Scanning based Proton Radiotherapy: Experience at the Paul Scherrer Institute since 1996

Reviewer: Curtiland Deville, MD
The Abramson Cancer Center of the University of Pennsylvania
Last Modified: May 28, 2010

Presenter: E.B. Hug
Presenter Affiliation: Paul Scherrer Institute, Center for Proton Therapy, Villagen, Swiss Confederation


  • Spot scanning based proton therapy was pioneered at the Paul Scherrer Institute (PSI) and has been in routine clinical use there since 1996.
  • PSI remains the only facility with long-term experience in spot scanning.
  • While over 6000 patients have been treated predominantly in the eye program, over 500 patients have been treated in the non-eye program.
  • This analysis reviews the clinical experience, safety, and efficacy of the non-eye program.


  • 537 patients, ages 1-88, were treated from April 1996 – December 2009.
  • The volume of patients treated has significantly increased since the transition to year-round treatment facility in 2007.
  • 116 of these patients were treated in 2009.
  • The most frequent tumors treated were:
    • Chordomas and Chondrosarcomas (51%)
    • Soft tissue and osteogenic sarcomas (15%)
    • Meningiomas and primary CNS tumors (18%)
  • The most common anatomic sites: were: base of skull, CNS, paraspinal, and pelvis.
  • Between 1996-2005, patients were treated in 2.0 Gy(RBE) fractions four times a week.
  • Since 2007, patients have been treated with 1.8-2.0 Gy(RBE) fractions five times a week.


  • Several analyses have been published across tumor sites and select data are presented:
  • 5yr actuarial local contral data are available on 118 patients for:
  • base of skull chordomas (42 patients) with mean target dose of 74 Gy(RBE) was 81%
  • base of skull chondrosarcomas (22 patients) with mean target dose of 68 Gy(RBE) was 94%.
  • spinal chordomas (40 patients) was 66%, and 100% in 19 patients without major surgical stabilization; local control was significantly increased in the non-surgically stabilized vs. surgically stabilized patients (p = 0.003)
  • 3-yr local control for meningioma was 92%
  • 4-yr local control for soft tissue sarcoma was 74%
  • 280 patients have greater than 2 years of follow-up
  • high grade toxicity was 6% in the skull base and 5% in the paraspinal location.
  • 51 pediatric patients were treated between 2004-2007, including primarily CNS and STS.
  • Local control is 86% with a median follow-up of 29 months.
  • All pediatric patients are enrolled in late effects/QOL of study.

Author's Conclusions

  • The safety and efficacy of spot scanning proton therapy at PSI has been demonstrated across various anatomic sites and tumor types.
  • The future challenge of spot scanning proton therapy will be the expansion to other tumor types including left-sided breast cancer, and tumors with motion such as lung cancer.

Scientific Implications

  • The single institution experience of spot scanning proton therapy at PSI across various, but limited, tumor sites is encouraging.
  • The reduction in local control observed among surgically stabilized spinal chordomas requires further investigation and may be due to such factors as inherent tumor biology, nonrandomized patient selection, and/or range uncertainty and unfavorable dose distributions due to hardware artifacts.
  • Increased incorporation of spot scanning and continued long-term data on local control and treatment morbidity are needed.

From the National Cancer Institute