Craniospinal irradiation using pencil beam Scanning: The PSI experience

Area of Science:

• Medical Physics
• Radiation Oncology
• Pediatric Oncology

Background:

• Craniospinal irradiation (CSI) is a critical treatment for pediatric central nervous system tumors.
• Proton beam therapy (PBS-PT) offers dosimetric advantages for CSI.
• Evaluating treatment accuracy and outcomes is essential for optimizing pediatric cancer care.

Purpose of the Study:

• To assess the dosimetric accuracy of proton CSI at the Paul Scherrer Institute (PSI).
• To investigate the relationship between treatment accuracy, local recurrences, and late toxicities in pediatric patients.
• To compare treatment outcomes between prone and supine patient positioning.

Main Methods:

• Retrospective analysis of 71 pediatric patients receiving proton CSI between 2004 and 2021.
• Comparison of treatment accuracy between prone (Gantry1) and supine (Gantry2) patient setups.
• Dosimetric evaluation of CSI plans and detailed analysis of local failures and late toxicities in selected patients.

Main Results:

• Supine patient positioning demonstrated improved accuracy with lower systematic (0.25 mm) and random (1.4 mm) errors compared to prone positioning (0.4 mm and 1.8 mm, respectively).
• No correlation was found between local failures and dose inaccuracies or treatment plan robustness.
• No association was observed between patient toxicities and enhanced linear energy transfer (LET).

Conclusions:

• Proton CSI at PSI is dosimetrically accurate and robust, with supine positioning offering improved setup accuracy.
• Treatment accuracy does not appear to influence local recurrence rates in pediatric CSI.
• Observed late toxicities are not linked to enhanced LET, suggesting a favorable safety profile for proton CSI.