Dosimetric accuracy of proton therapy for chordoma patients with titanium implants.

PURPOSE To investigate dosimetric errors in proton therapy treatment planning due to titanium implants, and to determine how these affect postoperative passively scattered proton therapy for chordoma patients with orthopedic hardware. METHODS The presence of titanium hardware near the tumor may affect the dosimetric accuracy of proton therapy. Artifacts in the computed tomography (CT) scan can cause errors in the proton stopping powers used for dose calculation, which are derived from CT numbers. Also, clinical dose calculation algorithms may not accurately simulate proton beam transport through the implants, which have very different properties as compared to human tissue. The authors first evaluated the impact of these two main issues. Dose errors introduced by metal artifacts were studied using phantoms with and without titanium inserts, and patient scans on which a metal artifact reduction method was applied. Pencil-beam dose calculations were compared to models of nuclear interactions in titanium and Monte Carlo simulations. Then, to assess the overall impact on treatment plans for chordoma, the authors compared the original clinical treatment plans to recalculated dose distributions employing both metal artifact reduction and Monte Carlo methods. RESULTS Dose recalculations of clinical proton fields showed that metal artifacts cause range errors up to 6 mm distal to regions affected by CT artifacts. Monte Carlo simulations revealed dose differences >10% in the high-dose area, and range differences up to 10 mm. Since these errors are mostly local in nature, the large number of fields limits the impact on target coverage in the chordoma treatment plans to a small decrease of dose homogeneity. CONCLUSIONS In the presence of titanium implants, CT metal artifacts and the approximations of pencil-beam dose calculations cause considerable errors in proton dose calculation. The spatial distribution of the errors however limits the overall impact on passively scattered proton therapy for chordoma.

[1]  Matthias Fippel,et al.  A pencil beam algorithm for intensity modulated proton therapy derived from Monte Carlo simulations , 2005, Physics in medicine and biology.

[2]  The water equivalence of solid materials used for dosimetry with small proton beams. , 2002, Medical physics.

[3]  J. Verburg,et al.  CT metal artifact reduction method correcting for beam hardening and missing projections , 2012, Physics in medicine and biology.

[4]  Axén,et al.  Total reaction cross section calculations in proton-nucleus scattering. , 1996, Physical review. C, Nuclear physics.

[5]  S. Incerti,et al.  Geant4 developments and applications , 2006, IEEE Transactions on Nuclear Science.

[6]  Harald Paganetti,et al.  Dose to water versus dose to medium in proton beam therapy , 2009, Physics in medicine and biology.

[7]  M Goitein,et al.  A pencil beam algorithm for proton dose calculations. , 1996, Physics in medicine and biology.

[8]  T. N. Nasr,et al.  Measurements of the total reaction cross section for protons on Ti and B between 20 and 50 MeV , 1978 .

[9]  T. Bortfeld,et al.  Correlation between CT numbers and tissue parameters needed for Monte Carlo simulations of clinical dose distributions. , 2000, Physics in medicine and biology.

[10]  Robert J. Schneider,et al.  Multiple Coulomb scattering of 160 MeV protons , 1993 .

[11]  A. O. Hanson,et al.  MEASUREMENT OF MULTIPLE SCATTERING OF 15.7-MEV ELECTRONS , 1951 .

[12]  B. Yeap,et al.  Phase II study of high-dose photon/proton radiotherapy in the management of spine sarcomas. , 2009, International journal of radiation oncology, biology, physics.

[13]  U. Oelfke,et al.  Two-dimensional pencil beam scaling: an improved proton dose algorithm for heterogeneous media. , 2002, Physics in medicine and biology.

[14]  Gert Moliere,et al.  Theorie der Streuung schneller geladener Teilchen II Mehrfach-und Vielfachstreuung , 1948 .

[15]  W. Bauhoff,et al.  Tables of reaction and total cross sections for proton-nucleus scattering below 1 GeV , 1986 .

[16]  Radhe Mohan,et al.  Comprehensive analysis of proton range uncertainties related to patient stopping-power-ratio estimation using the stoichiometric calibration , 2012, Physics in medicine and biology.

[17]  G. Igo,et al.  10-Mev PROTON REACTION CROSS SECTIONS FOR SEVERAL ELEMENTS , 1963 .

[18]  H Paganetti,et al.  TOPAS: an innovative proton Monte Carlo platform for research and clinical applications. , 2012, Medical physics.

[19]  N. Hintz,et al.  Charged Particle and Total Reaction Cross Sections for Protons at 9.85 Mev , 1960 .

[20]  V. Highland,et al.  Some Practical Remarks on Multiple Scattering , 1975 .

[21]  J. Griffith,et al.  Proton total reaction cross sections at 9.1 MeV , 1968 .

[22]  Francesca Albertini,et al.  Spot-scanning-based proton therapy for extracranial chordoma. , 2011, International journal of radiation oncology, biology, physics.

[23]  Arjan J. Koning,et al.  Local and global nucleon optical models from 1 keV to 200 MeV , 2003 .

[24]  Radhe Mohan,et al.  Can megavoltage computed tomography reduce proton range uncertainties in treatment plans for patients with large metal implants? , 2008, Physics in medicine and biology.

[25]  Katia Parodi,et al.  PET/CT imaging for treatment verification after proton therapy: a study with plastic phantoms and metallic implants. , 2007, Medical physics.

[26]  M Goitein,et al.  Compensating for heterogeneities in proton radiation therapy. , 1984, Physics in medicine and biology.

[27]  Oliver Jäkel,et al.  The influence of metal artefacts on the range of ion beams , 2007, Physics in medicine and biology.

[28]  M. Bussière,et al.  Treatment Planning for Conformal Proton Radiation Therapy , 2003, Technology in cancer research & treatment.

[29]  G. Moliere,et al.  Theory of the scattering of fast charged particles. 2. Repeated and multiple scattering , 1948 .

[30]  Thomas Bortfeld,et al.  Reducing the sensitivity of IMPT treatment plans to setup errors and range uncertainties via probabilistic treatment planning. , 2008, Medical physics.

[31]  Radhe Mohan,et al.  Density heterogeneities and the influence of multiple Coulomb and nuclear scatterings on the Bragg peak distal edge of proton therapy beams , 2008, Physics in medicine and biology.