Proton penetration and control in nonhomogeneous phantoms

Wingate, Catharine L.; Archambeau, John O.; Koehler, Andreas; Bennett, G.W.

doi:10.1118/1.594365

Cited by 9 publications

(6 citation statements)

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“…In particular, the finite range of a proton beam may be adjusted such that the therapeutic dose vanishes beyond the tumor. The proton range, which is commonly expressed in terms of its equivalent range in liquid water, may be precisely controlled by the accelerator (Coutrakon et al 1997), energy degrader system (Jongen et al 1996), a range shifter in the treatment head (Newhauser et al 2007b) and a range compensator (Wingate et al 1977, Fontenot et al 2007). …”

Section: Introductionmentioning

confidence: 99%

Calculation of water equivalent thickness of materials of arbitrary density, elemental composition and thickness in proton beam irradiation

Zhang

Newhauser

2009

Phys. Med. Biol.

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In proton therapy, the radiological thickness of a material is commonly expressed in terms of water equivalent thickness (WET) or water equivalent ratio (WER). However, the WET calculations required either iterative numerical methods or approximate methods of unknown accuracy. The objective of this study was to develop a simple deterministic formula to calculate WET values with an accuracy of 1 mm for materials commonly used in proton radiation therapy. Several alternative formulas were derived in which the energy loss was calculated based on the Bragg–Kleeman rule (BK), the Bethe–Bloch equation (BB) or an empirical version of the Bethe–Bloch equation (EBB). Alternative approaches were developed for targets that were ‘radiologically thin’ or ‘thick’. The accuracy of these methods was assessed by comparison to values from an iterative numerical method that utilized evaluated stopping power tables. In addition, we also tested the approximate formula given in the International Atomic Energy Agency's dosimetry code of practice (Technical Report Series No 398, 2000, IAEA, Vienna) and stopping power ratio approximation. The results of these comparisons revealed that most methods were accurate for cases involving thin or low-Z targets. However, only the thick-target formulas provided accurate WET values for targets that were radiologically thick and contained high-Z material.

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Section: Introductionmentioning

confidence: 99%

Calculation of water equivalent thickness of materials of arbitrary density, elemental composition and thickness in proton beam irradiation

Zhang

Newhauser

2009

Phys. Med. Biol.

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“…Range compensators are designed to spare normal tissue just distal to the target from unwanted dose by adjusting the penetration of the proton beam to account for the shape of the target, patient surface, and heterogeneities within the patient. [8][9][10][11] Standardized methods for measuring the absorbed dose in clinical proton beams-critical for ensuring accuracy and consistency in dose reporting-have not yet been fully established. Traditionally, clinical D / MU values have been determined by measuring dose in a water or plastic phantom, [12][13][14] a relatively simple but labor-intensive approach.…”

Section: Introductionmentioning

confidence: 99%

Determination of output factors for small proton therapy fields

Fontenot¹,

Newhauser²,

Bloch³

et al. 2007

Medical Physics

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Current protocols for the measurement of proton dose focus on measurements under reference conditions; methods for measuring dose under patient-specific conditions have not been standardized. In particular, it is unclear whether dose in patient-specific fields can be determined more reliably with or without the presence of the patient-specific range compensator. The aim of this study was to quantitatively assess the reliability of two methods for measuring dose per monitor unit (DIMU) values for small-field treatment portals: one with the range compensator and one without the range compensator. A Monte Carlo model of the Proton Therapy Center-Houston double-scattering nozzle was created, and estimates of D/MU values were obtained from 14 simulated treatments of a simple geometric patient model. Field-specific D/MU calibration measurements were simulated with a dosimeter in a water phantom with and without the range compensator. D/MU values from the simulated calibration measurements were compared with D/MU values from the corresponding treatment simulation in the patient model. To evaluate the reliability of the calibration measurements, six metrics and four figures of merit were defined to characterize accuracy, uncertainty, the standard deviations of accuracy and uncertainty, worst agreement, and maximum uncertainty. Measuring D/MU without the range compensator provided superior results for five of the six metrics and for all four figures of merit. The two techniques yielded different results primarily because of high-dose gradient regions introduced into the water phantom when the range compensator was present. Estimated uncertainties (approximately 1 mm) in the position of the dosimeter in these regions resulted in large uncertainties and high variability in D/MU values. When the range compensator was absent, these gradients were minimized and D/MU values were less sensitive to dosimeter positioning errors. We conclude that measuring D/MU without the range compensator present provides more reliable results than measuring it with the range compensator in place.

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“…Using this technique, a narrow, nearly monoenergetic, proton beam is transformed to a clinically useful size by using scattering foils to laterally spread and flatten the beam and a range modulator wheel to increase the width of the Bragg peak [7–9]. The final components that the beam pass through are patient-specific devices, consisting of an aperture to collimate the field, and a range compensator to distally shape the beam [10–13]. A challenge that arises from use of the passive scattering proton beam delivery technique is the determination of beam output that is needed to deliver a prescribed dose, namely, calibrating the dose per monitor unit (DMU).…”

Section: Introductionmentioning

confidence: 99%

Investigation on Patient/Compensator Scatter Factor for Monitor Unit Calculation in Proton Therapy

Prusator

Ahmad

Chen

2018

International Journal of Particle Therapy

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Purpose:It is the goal of this study to use both Monte Carlo (MC) simulation and the pencil beam dose algorithm (PBA) in the treatment planning system to investigate Patient scatter factor (PSF) and Compensator scatter factor (CSF) for calibrating the dose per monitor unit (DMU) for a passive scattering proton therapy system.Materials and Methods: PSFs and CSFs for brain, lung, pancreas, and prostate treatment sites were calculated by using MC simulation and PBA from the treatment planning software to evaluate the agreement between the two.Results:This study shows that the CSF values are always greater than 1, with some reaching nearly 4% above unity, and depending strongly on the shape of the compensator. Monte Carlo and PBA-calculated CSF factors agree very well, with average differences below 1%. PSF values calculated in this study ranged from 0.919 to 1.023 and are largely dependent on the type of tissue heterogeneities in the treatment field. Monte Carlo and PBA-calculated PSF factors show differences, with the largest discrepancies seen in lung cases, with an average difference of 1.9%. It is also shown that dense bone will drive a PSF to values greater than unity, while large quantities of air decrease the PSF to below unity.Conclusion:We have showed that the compensator and patient anatomy can have a significant impact on clinical proton dose distribution. It is recommended that both Monte Carlo and treatment planning system should be used to take these factors into account in the final DMU calculation.

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Proton penetration and control in nonhomogeneous phantoms

Cited by 9 publications

References 0 publications

Calculation of water equivalent thickness of materials of arbitrary density, elemental composition and thickness in proton beam irradiation

Calculation of water equivalent thickness of materials of arbitrary density, elemental composition and thickness in proton beam irradiation

Determination of output factors for small proton therapy fields

Investigation on Patient/Compensator Scatter Factor for Monitor Unit Calculation in Proton Therapy

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