Equivalent dose and effective dose from stray radiation during passively scattered proton radiotherapy for prostate cancer

Fontenot, Jonas D.; Taddei, Phillip J.; Zheng, Yuanshui; Mirković, Dragan; Jordan, Thomas; Newhauser, Wayne D.

doi:10.1088/0031-9155/53/6/012

Cited by 69 publications

(103 citation statements)

References 41 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It has been reported in the literature that, for passive scattering proton therapy, external neutrons are the dominant source of neutrons when treating small fields, as in prostate cancer. 53 In the spectrum reported here (Fig. 3), the fluence in the direct neutron peak (∼70 MeV) is lower than that in the evaporation peak (∼0.5 MeV).…”

Section: Discussionmentioning

confidence: 51%

“…They estimated that the contribution from internal neutrons generated in the phantom was relatively low (∼20%) because the incident field size was small (5 × 5 cm 2 ) and thus external neutrons were the dominant source of neutrons. 12,53 Given the various differences in the beamlines, detector types, and experimental set-ups between the two studies (most of which caused our dose to be higher), an agreement of 30% is very good.…”

Section: Discussionmentioning

confidence: 89%

See 1 more Smart Citation

Secondary neutron spectrum from 250‐MeV passively scattered proton therapy: Measurement with an extended‐range Bonner sphere system

Howell

Burgett

2014

Medical Physics

View full text Add to dashboard Cite

Purpose: Secondary neutrons are an unavoidable consequence of proton therapy. While the neutron dose is low compared to the primary proton dose, its presence and contribution to the patient dose is nonetheless important. The most detailed information on neutrons includes an evaluation of the neutron spectrum. However, the vast majority of the literature that has reported secondary neutron spectra in proton therapy is based on computational methods rather than measurements. This is largely due to the inherent limitations in the majority of neutron detectors, which are either not suitable for spectral measurements or have limited response at energies greater than 20 MeV. Therefore, the primary objective of the present study was to measure a secondary neutron spectrum from a proton therapy beam using a spectrometer that is sensitive to neutron energies over the entire neutron energy spectrum. Methods: The authors measured the secondary neutron spectrum from a 250-MeV passively scattered proton beam in air at a distance of 100 cm laterally from isocenter using an extended-range Bonner sphere (ERBS) measurement system. Ambient dose equivalent H*(10) was calculated using measured fluence and fluence-to-ambient dose equivalent conversion coefficients. Results: The neutron fluence spectrum had a high-energy direct neutron peak, an evaporation peak, a thermal peak, and an intermediate energy continuum between the thermal and evaporation peaks. The H*(10) was dominated by the neutrons in the evaporation peak because of both their high abundance and the large quality conversion coefficients in that energy interval. The H*(10) 100 cm laterally from isocenter was 1.6 mSv per proton Gy (to isocenter). Approximately 35% of the dose equivalent was from neutrons with energies ≥20 MeV. Conclusions: The authors measured a neutron spectrum for external neutrons generated by a 250-MeV proton beam using an ERBS measurement system that was sensitive to neutrons over the entire energy range being measured, i.e., thermal to 250 MeV. The authors used the neutron fluence spectrum to demonstrate experimentally the contribution of neutrons with different energies to the total dose equivalent and in particular the contribution of high-energy neutrons (≥20 MeV). These are valuable reference data that can be directly compared with Monte Carlo and experimental data in the literature. © 2014 Author(s)

show abstract

Section: Discussionmentioning

confidence: 51%

Section: Discussionmentioning

confidence: 89%

Secondary neutron spectrum from 250‐MeV passively scattered proton therapy: Measurement with an extended‐range Bonner sphere system

Howell

Burgett

2014

Medical Physics

View full text Add to dashboard Cite

show abstract

“…Stray doses from proton therapy treatments (e.g. neutrons) were determined fromMonte Carlo simulations (Newhauser et al 2009b, Fontenot et al 2008), while stray doses from IMRT (e.g. leakage) were determined from available data (Howell et al 2006, Kry et al 2005).…”

Section: Methodsmentioning

confidence: 99%

Estimate of the uncertainties in the relative risk of secondary malignant neoplasms following proton therapy and intensity-modulated photon therapy

Fontenot¹,

Bloch²,

Followill³

et al. 2010

Phys. Med. Biol.

View full text Add to dashboard Cite

Theoretical calculations have shown that proton therapy can reduce the incidence of radiation-induced secondary malignant neoplasms (SMN) compared with photon therapy for patients with prostate cancer. However, the uncertainties associated with calculations of SMN risk had not been assessed. The objective of this study was to quantify the uncertainties in projected risks of secondary cancer following contemporary proton and photon radiotherapies for prostate cancer. We performed a rigorous propagation of errors and several sensitivity tests to estimate the uncertainty in the ratio of relative risk (RRR) due to the largest contributors to the uncertainty: the radiation weighting factor for neutrons, the dose-response model for radiation carcinogenesis and interpatient variations in absorbed dose. The interval of values for the radiation weighting factor for neutrons and the dose-response model were derived from the literature, while interpatient variations in absorbed dose were taken from actual patient data. The influence of each parameter on a baseline RRR value was quantified. Our analysis revealed that the calculated RRR was insensitive to the largest contributors to the uncertainty. Uncertainties in the radiation weighting factor for neutrons, the shape of the dose-risk model and interpatient variations in therapeutic and stray doses introduced a total uncertainty of 33% to the baseline RRR calculation.

show abstract

“…Zacharatou Jarlskog et al 2 determined that the internal doses to the eyes are 15% and 40% of the total dose for field diameters of 6 and 9 cm, respectively, for the treatment of tumors in the intracranial region. Fontenot et al 23 determined that 12% of the dose is due to internally produced neutrons in the colon positioned at 22 cm from the isocenter. The combined results suggest that the out-of-field dose is 3-100 times smaller for a scanned beam in the region 10-20 cm from the field edge.…”

Section: Ivd Passive Scattering Vs Active Scanningmentioning

confidence: 99%

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

et al. 2009

View full text Add to dashboard Cite

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.

show abstract

Equivalent dose and effective dose from stray radiation during passively scattered proton radiotherapy for prostate cancer

Cited by 69 publications

References 41 publications

Secondary neutron spectrum from 250‐MeV passively scattered proton therapy: Measurement with an extended‐range Bonner sphere system

Secondary neutron spectrum from 250‐MeV passively scattered proton therapy: Measurement with an extended‐range Bonner sphere system

Estimate of the uncertainties in the relative risk of secondary malignant neoplasms following proton therapy and intensity-modulated photon therapy

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

Contact Info

Product

Resources

About