Study of (a,ax) Reactions Induced by 200 MeV a-Particles

This work was supported by the National Science Foundation Grant NSF PHY 81-14339 and by Indiana Universit

Elastic Scattering of 100 MeV Polarized Protons from 4-He

This research was sponsored by the National Science Foundation Grant NSF PHy 87-1440

A Pragmatic Approach to the Continuum Spectrum in Quasifree Scattering

This work was supported by the National Science Foundation Grant NSF PHY 81-14339 and by Indiana Universit

Analyzing Power of the Proton Continuum for 150 and 200 MeV Polarized Protons on 12-C and 58,62-Ni

This work was supported by the National Science Foundation Grants NSF PHY 78-22774 A03, NSF PHY 81-14339, and by Indiana Universit

Theoretical methods for the calculation of Bragg curves and 3D distributions of proton beams

The well-known Bragg-Kleeman rule RCSDA = A dot E0p has become a pioneer work in radiation physics of charged particles and is still a useful tool to estimate the range RCSDA of approximately monoenergetic protons with initial energy E0 in a homogeneous medium. The rule is based on the continuous-slowing-down-approximation (CSDA). It results from a generalized (nonrelativistic) Langevin equation and a modification of the phenomenological friction term. The complete integration of this equation provides information about the residual energy E(z) and dE(z)/dz at each position z (0 <= z <= RCSDA). A relativistic extension of the generalized Langevin equation yields the formula RCSDA = A dot (E0 +E02/2M dot c2)p. The initial energy of therapeutic protons satisfies E0 << 2M dot c2 (M dot c2 = 938.276 MeV), which enables us to consider the relativistic contributions as correction terms. Besides this phenomenological starting-point, a complete integration of the Bethe-Bloch equation (BBE) is developed, which also provides the determination of RCSDA, E(z) and dE(z)/dz and uses only those parameters given by the BBE itself (i.e., without further empirical parameters like modification of friction). The results obtained in the context of the aforementioned methods are compared with Monte-Carlo calculations (GEANT4); this Monte-Carlo code is also used with regard to further topics such as lateral scatter, nuclear interactions, and buildup effects. In the framework of the CSDA, the energy transfer from protons to environmental atomic electrons does not account for local fluctuations.Comment: 97 pages review pape

SU‐E‐T‐646: Feasibility Study of Radiobiological Effectiveness‐Based Treatment Plan Optimization for Spot‐Scanned Proton Therapy Beams

Purpose: To develop novel methodologies for determination of the relative biological effectiveness (RBE) in treatment plans created with a feasibility search optimization scheme for the spot scanned proton pencil beams at the Proton Therapy Center in Houston. Methods: We explored methods with clinical practicality to calculate related physical and RBE‐weighted doses for spot scanned proton beams. We studied a test case in which an organ‐at‐risk (OAR) was surrounded by the PTV. Results were demonstrated with simulated proton therapy data. We optimized the dose distribution for a planning treatment volume (PTV) within a water phantom with a feasibility search method, used previously to design conventional photon and electron beam radiation therapy plans and applied here for the first time to proton therapy planning. Prospective and retrospective intercomparison scenarios were run with computed RBEs using linear quadratic model parameter values taken from the in vitro measured survival data of Chinese hamster V79 cells. Results: We designed methods to carry out intercomparisons between treatment plans with different modalities. We found a higher RBE‐ weighted dose in the OAR than that expected with a constant RBE value of 1.1, which is currently used in clinical practice for range modulated proton beams. The TCP (tumor control probability)/NTCP (normal tissue complication probability) dose‐response analysis showed that our test planned irradiation would not have been acceptable if the OAR structure connection were highly serial, such as in the spinal cord. Conclusion: This exploratory study has provided a framework which should be helpful in the ongoing search to include detailed RBE effects in intensity modulated proton therapy treatment planning

TU‐C‐AUD B‐04: Dose Perturbations Caused by Implanted Helical Gold Markers Used in Patients Receiving Proton Radiation Therapy for Prostate Cancer

Purpose: Implanted gold fiducial markers are widely used in radiation therapy to improve targeting accuracy; however recent investigations have revealed that metallic fiducial markers can cause extreme perturbations in dose distributions for proton therapy, suggesting that smaller markers should be considered. This study\u27s objective was to test the dosimetric impact of various small helical, gold markers for tumor localization in patients receiving proton therapy. Method and Materials: Small, medium, and large helical wire markers with lengths of 10 mm and respective diameters of 0.04 mm, 0.25 mm and 0.5 mm were implanted in an anthropomorphic phantom. Radiographic visibility was assessed for a kV x‐ray imaging system, and dosimetric impact was characterized by Monte Carlo simulations and measurements of proton dose. Acceptable dosimetric perturbation was estimated from previous studies to be 10%. Results: Radiographic visibility was confirmed for all markers considered. Monte Carlo simulations indicated that the size of the marker dose perturbation depended on marker size, orientation, and distance from the beam\u27s distal fall off. Simulations also revealed that dose perturbation in the lateral, opposed field treatment‐technique was 31% for large markers and 23% for medium markers in a typical orientation. Perturbation was not observed for the small marker, but it was deemed too fragile for transrectal implantation. Radiochromic film measurements confirmed the accuracy of the Monte Carlo model. Conclusion: Proton dose perturbations from medium and large sized markers exceeded 10%. This suggests that great care should be exercised if these markers are implanted in patients receiving proton therapy for prostate cancer. Conflict of Interest: A similar presentation of this work will be made at the ICRS, International Conference on Radiation Shielding; the ICRS presentation will be more preliminary and delivered to a different audience. © 2008, American Association of Physicists in Medicine. All rights reserved

WE‐D‐BRB‐01: Experimental Characterization of the Low‐Dose Envelope of Spot Scanning Proton Beams

Purpose: To measure the low‐dose envelope of spot scanning proton pencil beams. Method and Materials: Measurements were performed in the spot scanning proton pencil beam nozzle at M. D. Anderson Cancer Center. We directly measured the low‐dose envelope by measuring single pencil beams' lateral profiles at central axis to relative dose levels that were a factor of 10−4 lower than the central axis dose. We also indirectly measure the low‐dose envelope by measuring the effect of the filed size on central axis point doses using a plane parallel ionization chamber. Results: For lowest (72.5 MeV) and highest (221.8 MeV) energy beams in‐air at isocenter plane, the full width (FW) at half maximum ranged from 1.26 ± 0.02 cm to 3.43 ± 0.02 cm; the FW at 1% maximum ranged from 3.99 ± 0.25 cm to 11.41± 0.25 cm; and the FW at 0.1% maximum ranged from 6.6 ± 0.5 cm to 17.9 ± 0.5 cm, respectively. The effect of the field size on central axis point doses showed strong dependence with energy and depth. Conclusion: We showed that it is possible to accurately measure the low‐dose envelope down to a dose level of 10−4 of the central axis dose using standard dosimetric equipment. Because of the large lateral extent of the beams, care should be taken when measuring integral depth doses, which are input parameters for analytical dose calculation algorithms. Additionally, we observed that the in‐air fluence of the pencil beams has various components due to scattering in the beam line and cannot be accurately described by a single Gaussian function. Finally, we showed that because of the low‐dose envelope, the dose output's dependence on field size can vary for fields as large as 20 cm × 20 cm

Pion Production in A(p,pPi) Reactions

This work was supported by the National Science Foundation Grant NSF PHY 81-14339 and by Indiana Universit