Range modulators for protons and heavy ions

Koehler, Andreas; Schneider, Robert J.; Sisterson, J. M.

doi:10.1016/0029-554x(75)90430-9

Cited by 217 publications

(113 citation statements)

References 9 publications

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“…The treatment beam had an energy of 250 MeV (range = 37.9 cm in water) as it entered the nozzle. The beam passed through a range modulator wheel (Koehler et al 1975) that yielded an SOBP of 11 cm width, a foil that laterally flattened and spread the beam to generate a 25.5 cm diameter uncollimated proton field, and an adjustable range shifter to produce a water-equivalent range at the surface of the patient of 27.5 cm. As part of the planning process, a field-specific custom block made of brass was designed to collimate the treatment beam to cover the target volume.…”

Section: Treatment Planmentioning

confidence: 99%

Reducing stray radiation dose to patients receiving passively scattered proton radiotherapy for prostate cancer

et al. 2008

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Proton beam radiotherapy exposes healthy tissue to stray radiation emanating from the treatment unit and secondary radiation produced within the patient. These exposures provide no known benefit and may increase a patient's risk of developing a radiogenic second cancer. The aim of this study was to explore strategies to reduce stray radiation dose to a patient receiving a 76 Gy proton beam treatment for cancer of the prostate. The whole-body effective dose from stray radiation, E, was estimated using detailed Monte Carlo simulations of a passively scattered proton treatment unit and an anthropomorphic phantom. The predicted value of E was 567 mSv, of which 320 mSv was attributed to leakage from the treatment unit; the remainder arose from scattered radiation that originated within the patient. Modest modifications of the treatment unit reduced E by 212 mSv. Surprisingly, E from a modified passive-scattering device was only slightly higher (109 mSv) than from a nozzle with no leakage, e.g., that which may be approached with a spot-scanning technique. These results add to the body of evidence supporting the suitability of passively scattered proton beams for the treatment of prostate cancer, confirm that the effective dose from stray radiation was not excessive, and, importantly, show that it can be substantially reduced by modest enhancements to the treatment unit.

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Section: Treatment Planmentioning

confidence: 99%

Reducing stray radiation dose to patients receiving passively scattered proton radiotherapy for prostate cancer

et al. 2008

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“…1,2 Passively scattered proton fields use scattering devices placed in the path of the beam to produce a laterally uniform field 3,4 and a range modulation system to create a spread-out Bragg peak. A brass aperture close to the patient protects healthy tissue lateral to the field edge and a range compensator conforms the distal edge of the spread-out Bragg peak to the target volume.…”

mentioning

confidence: 99%

Assessment of out‐of‐field absorbed dose and equivalent dose in proton fields

et al. 2009

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Purpose:In proton therapy, as in other forms of radiation therapy, scattered and secondary particles produce undesired dose outside the target volume that may increase the risk of radiation-induced secondary cancer and interact with electronic devices in the treatment room. The authors implement a Monte Carlo model of this dose deposited outside passively scattered fields and compare it to measurements, determine the out-of-field equivalent dose, and estimate the change in the dose if the same target volumes were treated with an active beam scanning technique. Methods: Measurements are done with a thimble ionization chamber and the Wellhofer MatriXX detector inside a Lucite phantom with field configurations based on the treatment of prostate cancer and medulloblastoma. The authors use a GEANT4 Monte Carlo simulation, demonstrated to agree well with measurements inside the primary field, to simulate fields delivered in the measurements. The partial contributions to the dose are separated in the simulation by particle type and origin. Results: The agreement between experiment and simulation in the out-of-field absorbed dose is within 30% at 10-20 cm from the field edge and 90% of the data agrees within 2 standard deviations. In passive scattering, the neutron contribution to the total dose dominates in the region downstream of the Bragg peak ͑65%-80% due to internally produced neutrons͒ and inside the phantom at distances more than 10-15 cm from the field edge. The equivalent doses using 10 for the neutron weighting factor at the entrance to the phantom and at 20 cm from the field edge are 2.2 and 2.6 mSv/Gy for the prostate cancer and cranial medulloblastoma fields, respectively. The equivalent dose at 15-20 cm from the field edge decreases with depth in passive scattering and increases with depth in active scanning. Therefore, active scanning has smaller out-of-field equivalent dose by factors of 30-45 in the entrance region and this factor decreases with depth. Conclusions: The dose deposited immediately downstream of the primary field, in these cases, is dominated by internally produced neutrons; therefore, scattered and scanned fields may have similar risk of second cancer in this region. The authors confirm that there is a reduction in the out-of-field dose in active scanning but the effect decreases with depth. GEANT4 is suitable for simulating the dose deposited outside the primary field. The agreement with measurements is comparable to or better than the agreement reported for other implementations of Monte Carlo models. Depending on the position, the absorbed dose outside the primary field is dominated by contributions from primary protons that may or may not have scattered in the brass collimating devices. This is noteworthy as the quality factor of the low LET protons is well known and the relative dose risk in this region can thus be assessed accurately.

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“…[10][11][12][13] For beam ranges between 6 and 27 cm, a single physical modulator device is used for a defined modulation width. In this system, the lateral dose uniformity in the plane of the isocenter is optimized for different beam ranges by displacing the first scatterer towards or away from the isocenter.…”

Section: Introductionmentioning

confidence: 99%

Range and modulation dependencies for proton beam dose per monitor unit calculations

Hsi¹,

Schreuder

Moyers³

et al. 2009

Medical Physics

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Calculations of dose per monitor unit ͑D/MU͒ are required in addition to measurements to increase patient safety in the clinical practice of proton radiotherapy. As in conventional photon and electron therapy, the D/MU depends on several factors. This study focused on obtaining range and modulation dependence factors used in D/MU calculations for the double scattered proton beam line at the Midwest Proton Radiotherapy Institute. Three dependencies on range and one dependency on modulation were found. A carefully selected set of measurements was performed to discern these individual dependencies. Dependencies on range were due to: ͑1͒ the stopping power of the protons passing through the monitor chamber; ͑2͒ the reduction of proton fluence due to nuclear interactions within the patient; and ͑3͒ the variation of proton fluence passing through the monitor chamber due to different source-to-axis distances ͑SADs͒ for different beam ranges. Different SADs are produced by reconfigurations of beamline elements to provide different field sizes and ranges. The SAD effect on the D/MU varies smoothly as the beam range is varied, except at the beam range for which the first scatterers are exchanged and relocated to accommodate low and high beam ranges. A geometry factor was devised to model the SAD variation effect on the D/MU. The measured D/MU variation as a function of range can be predicted within 1% using the three modeled dependencies on range. Investigation of modulated beams showed that an analytical formula can predict the D/MU dependency as a function of modulation to within 1.5%. Special attention must be applied when measuring the D/MU dependence on modulation to avoid interplay between range and SAD effects.

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Range modulators for protons and heavy ions

Cited by 217 publications

References 9 publications

Reducing stray radiation dose to patients receiving passively scattered proton radiotherapy for prostate cancer

Reducing stray radiation dose to patients receiving passively scattered proton radiotherapy for prostate cancer

Assessment of out‐of‐field absorbed dose and equivalent dose in proton fields

Range and modulation dependencies for proton beam dose per monitor unit calculations

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