Out-of-Field Dose Equivalents Delivered by Passively Scattered Therapeutic Proton Beams for Clinically Relevant Field Configurations

Wroe, Andrew; Clasie, B; Kooy, Hanne M.; Flanz, Jay; Schulte, R.; Rosenfeld, Anatoly B.

doi:10.1016/j.ijrobp.2008.09.030

Cited by 45 publications

(32 citation statements)

References 26 publications

(45 reference statements)

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“…These values are comparable to previously determined values of approximately 0.03 mSv/Gy at 25.00 cm and 0.02 mSv/Gy at 50.00 cm displacement from the isocenter by Massachusetts General Hospital (MGH) [3]. Recently silicon microdosimetry was used to at MGH determine that the external field neutron dose equivalent value ranges from 0.60 mSv/Gy at 2.50 cm to 0.07 mSv/Gy at 10.00 cm displacement from the field edge for a range of 2.70 cm and an SOBP beam of 2.50 cm with a 2.80 cm pre-collimation field diameter [12]. In spite of differences in the eye snout design and the collimator field size, their results are relatively consistent with our findings when comparing the large field observed in the proton double-scattering mode or by a spot beam [3,4].…”

Section: Discussionmentioning

confidence: 99%

Secondary neutron dose measurement for proton eye treatment using an eye snout with a borated neutron absorber

et al. 2013

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BackgroundWe measured and assessed ways to reduce the secondary neutron dose from a system for proton eye treatment.MethodsProton beams of 60.30 MeV were delivered through an eye-treatment snout in passive scattering mode. Allyl diglycol carbonate (CR-39) etch detectors were used to measure the neutron dose in the external field at 0.00, 1.64, and 6.00 cm depths in a water phantom. Secondary neutron doses were measured and compared between those with and without a high-hydrogen–boron-containing block. In addition, the neutron energy and vertices distribution were obtained by using a Geant4 Monte Carlo simulation.ResultsThe ratio of the maximum neutron dose equivalent to the proton absorbed dose (H(10)/D) at 2.00 cm from the beam field edge was 8.79 ± 1.28 mSv/Gy. The ratio of the neutron dose equivalent to the proton absorbed dose with and without a high hydrogen-boron containing block was 0.63 ± 0.06 to 1.15 ± 0.13 mSv/Gy at 2.00 cm from the edge of the field at depths of 0.00, 1.64, and 6.00 cm.ConclusionsWe found that the out-of-field secondary neutron dose in proton eye treatment with an eye snout is relatively small, and it can be further reduced by installing a borated neutron absorbing material.

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Section: Discussionmentioning

confidence: 99%

Secondary neutron dose measurement for proton eye treatment using an eye snout with a borated neutron absorber

et al. 2013

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“…4͑a͒, where the absorbed dose due to neutrons dominates at 10-15 cm from the field edge at 22.3 cm water-equivalent depth. The average weighting factor from this work ͑using n =10͒ is compared to the average quality factor of Wroe et al 33 in Fig. 9.…”

Section: Ivb Neutron Contribution To the Total Dosementioning

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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“…Light grey area: Range of measured (Yan et al 2002; Mesoloras et al 2006; Wroe et al 2007, 2009; Moyers et al 2008; Yonai et al 2008; Clasie et al 2010) and simulated (Polf and Newhauser 2005; Zheng et al 2007; Moyers et al 2008; Zacharatou Jarlskog et al 2008; Clasie et al 2010) data for a variety of proton beam configurations using passive scattered beam delivery. Dark grey area: Results for scanned proton beams (Schneider et al 2002; Clasie et al 2010).…”

Section: Figmentioning

confidence: 99%

Assessment of the Risk for Developing a Second Malignancy From Scattered and Secondary Radiation In Radiation Therapy

Paganetti¹

2012

Health Physics

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With the average age of radiation therapy patients decreasing and the advent of more complex treatment options comes the concern that the incidences of radiation-induced cancer might increase in the future. The carcinogenic effects of radiation are not well understood for the entire dose range experienced in radiation therapy. Longer epidemiological studies are needed to improve current risk models and reduce uncertainties of current risk model parameters. On the other hand, risk estimations are needed today to judge the risks vs. benefits of modern radiation therapy techniques. This paper describes the current state-of-the-art in risk modeling for radiation-induced malignancies in radiation therapy, distinguishing between two volumes. First, the organs within the main radiation field receiving low or intermediate doses (typically between 0.1 and 50 Gy). Second, the organs far away from the treatment volume receiving low doses mainly due to scattered and secondary radiation (typically below 0.1 Gy). The dosimetry as well as the risk model formalisms are outlined. Furthermore, example calculations and results are presented for intensity-modulated photon therapy vs. proton therapy.

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Out-of-Field Dose Equivalents Delivered by Passively Scattered Therapeutic Proton Beams for Clinically Relevant Field Configurations

Cited by 45 publications

References 26 publications

Secondary neutron dose measurement for proton eye treatment using an eye snout with a borated neutron absorber

Secondary neutron dose measurement for proton eye treatment using an eye snout with a borated neutron absorber

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

Assessment of the Risk for Developing a Second Malignancy From Scattered and Secondary Radiation In Radiation Therapy

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