Out‐of‐field dose equivalents delivered by proton therapy of prostate cancer

Wroe, Andrew; Rosenfeld, Anatoly B.; Schulte, R.

doi:10.1118/1.2759839

Cited by 102 publications

(94 citation statements)

References 23 publications

(33 reference statements)

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“…6͑b͒. Wroe et al 36,33 measured the dose equivalent for prostate cancer and cranial medulloblastoma fields and their results are smaller by factors of 1-3 compared to Fig. 6.…”

Section: Ivb Neutron Contribution To the Total Dosementioning

confidence: 99%

“…Figure 6 shows the dose equivalent using average neutron weighting factor of 10, which is similar to the average used in measurements with passive scattering in many previous publications. 14,29,[33][34][35][36] We compare the simulated dose to other publications for further validation of the Monte Carlo model. Tayama et al 32 used a MLC, 16 cm range in water, and three MLC settings.…”

Section: Ivb Neutron Contribution To the Total Dosementioning

confidence: 99%

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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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“…6͑b͒. Wroe et al 36,33 measured the dose equivalent for prostate cancer and cranial medulloblastoma fields and their results are smaller by factors of 1-3 compared to Fig. 6.…”

Section: Ivb Neutron Contribution To the Total Dosementioning

confidence: 99%

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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“…Active delivery techniques produce less neutrons out-of-field in comparison with passive delivery as has been demonstrated by Monte Carlo studies [82,83]. Dose equivalents out-of-field using SOI microdosimeters were measured within a polystyrene phantom for different clinical scenarios at the Loma Linda University Medical Centre (LLUMC) and Massachusetts General Hospital (MGH) proton therapy facilities [84,85]. Fig.…”

Section: Semiconductor Dosimetry For Dose Equivalent In Charged Partimentioning

confidence: 94%

“…This is in good agreement with the quality factor along the central axis for the beam block and downstream of the SOBP where only neutrons are presented. More detailed information on the dose equivalent and Q-factors measured by SOI microdosimeters in out-of-field proton therapy can be found in [84,85]. An advantage of SOI microdosimetry is the small physical size of the detector SV in comparison with most TEPC and Bonner spheres.…”

Section: Semiconductor Dosimetry For Dose Equivalent In Charged Partimentioning

confidence: 99%

Advanced Semiconductor Dosimetry in Radiation Therapy

Rosenfeld

2011

AIP Conference Proceedings

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Modern radiation therapy is very conformal, resulting in a complexity of delivery that leads to many small radiation fields with steep dose gradients, increasing error probability. Quality assurance in delivery of such radiation fields is paramount and requires real time and high spatial resolution dosimetry. Semiconductor radiation detectors due to their small size, ability to operate in passive and active modes and easy real time multichannel readout satisfy many aspects of in vivo and in a phantom quality assurance in modern radiation therapy. Update on the recent developments and improvements in semiconductor radiation detectors and their application for quality assurance in radiation therapy, based mostly on the developments at the Centre for Medical Radiation Physics (CMRP), University of Wollongong, is presented. Abstract. Modern radiation therapy is very conformal, resulting in a complexity of delivery that leads to many small radiation fields with steep dose gradients, increasing error probability. Quality assurance in delivery of such radiation fields is paramount and requires real time and high spatial resolution dosimetry. Semiconductor radiation detectors due to their small size, ability to operate in passive and active modes and easy real time multichannel readout satisfy many aspects of in vivo and in a phantom quality assurance in modern radiation therapy. Update on the recent developments and improvements in semiconductor radiation detectors and their application for quality assurance in radiation therapy, based mostly on the developments at the Centre for Medical Radiation Physics (CMRP), University of Wollongong, is presented.

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“…The value decreased significantly with lower beam energy and increasing distance of fetus from the field edge. There are other studies of out‐of‐field secondary neutron both with Monte Carlo (MC) calculations or experimental measurements that could be used to estimate the neutron H to the fetus for passive scattering and uniform scanning beams 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 . However, most of these studies were made for a specific proton beam configuration, and the reported values of neutron H vary markedly because of different machine designs, experimental setups, and measurement instruments.…”

Section: Introductionmentioning

confidence: 99%

Spot scanning proton therapy minimizes neutron dose in the setting of radiation therapy administered during pregnancy

Wang

Poenisch

Zhu

et al. 2016

J Applied Clin Med Phys

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This is a real case study to minimize the neutron dose equivalent (H) to a fetus using spot scanning proton beams with favorable beam energies and angles. Minimum neutron dose exposure to the fetus was achieved with iterative planning under the guidance of neutron H measurement. Two highly conformal treatment plans, each with three spot scanning beams, were planned to treat a 25‐year‐old pregnant female with aggressive recurrent chordoma of the base of skull who elected not to proceed with termination. Each plan was scheduled for delivery every other day for robust target coverage. Neutron H to the fetus was measured using a REM500 neutron survey meter placed at the fetus position of a patient simulating phantom. 4.1 and 44.1 44.1 μSv/fraction were measured for the two initial plans. A vertex beam with higher energy and the fetal position closer to its central axis was the cause for the plan that produced an order higher neutron H. Replacing the vertex beam with a lateral beam reduced neutron H to be comparable with the other plan. For a prescription of 70 Gy in 35 fractions, the total neutron H to the fetus was estimated to be 0.35 mSv based on final measurement in single fraction. In comparison, the passive scattering proton plan and photon plan had an estimation of 26 and 70 mSv, respectively, for this case. While radiation therapy in pregnant patients should be avoided if at all possible, our work demonstrated spot scanning beam limited the total neutron H to the fetus an order lower than the suggested 5 mSv regulation threshold. It is far superior than passive scattering beam and careful beam selection with lower energy and keeping fetus further away from beam axis are essential in minimizing the fetus neutron exposure.PACS number(s): 87.53.Bn, 87.55.D‐, 87.55.N‐

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Out‐of‐field dose equivalents delivered by proton therapy of prostate cancer

Cited by 102 publications

References 23 publications

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

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

Advanced Semiconductor Dosimetry in Radiation Therapy

Spot scanning proton therapy minimizes neutron dose in the setting of radiation therapy administered during pregnancy

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