Treatment planning and verification of proton therapy using spot scanning: Initial experiences
- 29 October 2004
- journal article
- clinical trial
- Published by Wiley in Medical Physics
- Vol. 31 (11), 3150-3157
- https://doi.org/10.1118/1.1779371
Abstract
Since the end of 1996, we have treated more than 160 patients at PSI using spot-scanned protons. The range of indications treated has been quite wide and includes, in the head region, base-of-skull sarcomas, low-grade gliomas, meningiomas, and para-nasal sinus tumors. In addition, we have treated bone sarcomas in the neck and trunk—mainly in the sacral area—as well as prostate cases and some soft tissuesarcomas. PTV volumes for our treated cases are in the range 20–4500 ml, indicating the flexibility of the spot scanning system for treating lesions of all types and sizes. The number of fields per applied plan ranges from between 1 and 4, with a mean of just under 3 beams per plan, and the number of fluence modulated Bragg peaks delivered per field has ranged from 200 to 45 000. With the current delivery rate of roughly 3000 Bragg peaks per minute, this translates into delivery times per field of between a few seconds to 20–25 min. Bragg peak weight analysis of these spots has shown that over all fields, only about 10% of delivered spots have a weight of more than 10% of the maximum in any given field, indicating that there is some scope for optimizing the number of spots delivered per field. Field specific dosimetry shows that these treatments can be delivered accurately and precisely to within ±1 mm (1 SD) orthogonal to the field direction and to within 1.5 mm in range. With our current delivery system the mean widths of delivered pencil beams at the Bragg peak is about 8 mm (σ) for all energies, indicating that this is an area where some improvements can be made. In addition, an analysis of the spot weights and energies of individual Bragg peaks shows a relatively broad spread of low and high weighted Bragg peaks over all energy steps, indicating that there is at best only a limited relationship between pencil beam weighting and depth of penetration. This latter observation may have some consequences when considering strategies for fast re-scanning on second generation scanning gantries.Keywords
This publication has 13 references indexed in Scilit:
- The PSI Gantry 2: a second generation proton scanning gantryZeitschrift für Medizinische Physik, 2004
- Treating Cancer with ProtonsPhysics Today, 2002
- Performance of a fluorescent screen and CCD camera as a two-dimensional dosimetry system for dynamic treatment techniquesMedical Physics, 2000
- Intensity modulated radiotherapy with charged particle beams: Studies of inverse treatment planning for rotation therapyMedical Physics, 2000
- Intensity modulation methods for proton radiotherapyPhysics in Medicine & Biology, 1999
- Beam optics design of compact gantry for proton therapyMedical & Biological Engineering & Computing, 1995
- The 200‐MeV proton therapy project at the Paul Scherrer Institute: Conceptual design and practical realizationMedical Physics, 1995
- Spot scanning system for proton radiotherapyMedical Physics, 1980
- Range modulators for protons and heavy ionsNuclear Instruments and Methods, 1975
- Radiological Use of Fast ProtonsRadiology, 1946