A dose comparison of proton radiotherapy and photon radiotherapy for pediatric brain tumor

The purpose of this study was to investigate the effectiveness of photon radiotherapy and to compare the dose of treatment planning between proton radiotherapy and 3D conformal radiation therapy (3D-CRT) for pediatric brain tumor patients. This study was conducted in five pediatric brain tumor patients who underwent craniospinal irradiation treatment from October 2013 to April 2014 in the hospital. The study compared organs at risk (OARs) by assessing the dose distribution of normal tissue from the proton plan and 3D-CRT. Furthermore, this study assessed the treatment plans by looking at the homogeneity index (HI) and conformity index (CI). As a result, the study revealed OARs due to the small volume proton radiotherapy dose distribution in the normal tissue. Also, by comparing HI and CI between the 3D-CRT and proton radiotherapy plan, the study found that the dose of proton radiotherapy plan was homogenized. When conducting 3D-CRT and proton radiotherapy in a dose–volume histogram comparison, the dose of distribution turned out to be low. Consequently, proton radiotherapy is used for protecting the normal tissue, and is used in tumor tissue as a homogenized dose for effective treatment.     

Clinical simulations of prostate radiotherapy using BOMAB-like phantoms: Results for neutrons

This paper presents in-phantom photoneutron equivalent doses induced by external radiotherapy, these are necessary to assess organ-averaged equivalent doses to derive the risk of secondary cancer development, associated with non-target organ exposures. The measurements were performed by Working Group 9 “Radiation Protection Dosimetry in Medicine” of the European Radiation Dosimetry Group (EURADOS) for simulations of clinical radiotherapy treatments of prostate cancer. The photoneutron dose measurements were carried out in a BOMAB-like water-filled phantom, by means of superheated emulsions (superheated drop detectors SDD and bubble damage BTI^® detectors) and Poly-Allyl-Diglicol-Carbonate (PADC) solid state nuclear track detectors. Dose data were acquired in a three-dimensional matrix of reproducible measurement points, which are spaced according to detectors size. Four clinical protocols for the treatment of the prostate tumor were considered and compared, by measuring the doses delivered to the planning target volume (PTV) and to peripheral radiosensitive regions (i.e. colon-rectum and bladder). The clinical irradiations were performed in two clinical radiotherapy facilities based on Varian Clinac 2300 CD accelerator: Santa Chiara University Hospital (Pisa, Italy) and Centre of Oncology M. Skłodowska-Curie Memorial Institute (Krakow, Poland). An additional tomotherapy prostate cancer treatment was also simulated in Campo di Marte Hospital (Lucca, Italy). Radiation qualities of 6, 12, 15, 18 and 20 MV were used; all of these are capable of producing photoneutrons. Data from this work span most of the X-ray beam energies and prostate treatment modalities used in the current clinical practice. These data permit the assessment of doses absorbed by a radiotherapy patient either at the treatment volume or at out-of-field organs. Comparison of different dosimeters, under the same irradiation conditions, showed that dosimeters generally agreed within their 20% 1 SD uncertainty. Comparison of different treatment modalities in the two contributing clinical centers (Pisa and Krakow) were also possible, as well as a comparison of dose profiles resulting from the different treatment techniques, delivered at the same primary photon energy. It was in particular found that photon acceleration energies as low as 6 MV are able to produce a non-negligible photoneutron component, which causes an undue dose to the patient of the order of tens microsievert per unit photon dose delivered at the target volume.     

基于TPS和蒙特卡罗计算的12C肿瘤放射治疗In-beam PET剂量监测研究

In-beam PET成像是碳离子放射治疗剂量监测的有效手段,可以对碳离子放疗过程的物理剂量分布和生物剂量分布进行实时监测。结合放射治疗计划系统(TPS)和蒙特卡罗(MC)模拟分别对静态均匀水模体和腹部肿瘤CT图像进行治疗计划设计、MC计算和PET成像,比较TPS肿瘤靶区剂量分布、MC模拟剂量分布和PET成像三者之间的一致性。TPS和MC模拟中相对生物学效应(RBE)的计算均采用线性二次模型(LQ)。研究结果显示,TPS和MC计算的静态均匀水模体、单野治疗腹部肿瘤的物理剂量、RBE加权剂量在SOBP区域的平均误差均在0.5%和2%以内。碳离子束流能量为120~400 MeV/u时,束流方向剂量深度分布与PET成像在SOBP区域的位置差异均在8 mm以内。In-beam PET可作为碳离子放射治疗中位置验证和剂量验证的有效手段。     

Assessment of undesirable dose to eye-melanoma patients after proton radiotherapy

Radiotherapy with a proton beam of initial energy 55–80 MeV is presently the clinically recommended therapy for some cases of intraocular melanoma such as large melanomas or tumours adjacent to critical organs. Evaluation and optimization of radiation doses outside the treatment volume may contribute to reducing undesirable side-effects and decreasing the risk of occurrence of secondary cancers, particularly for paediatric patients. In this work the undesired doses to organs were assessed basing on Monte Carlo calculation of secondary radiation transport and on results of measurements of neutron and γ-ray doses at the proton therapy facility of the Institute of Nuclear Physics at Kraków. Dosimetry was performed using a He-3-based FHT 762 neutron monitor (Wendi II), a FH40G proportional counter (for γ-rays), and MTS-7 (LiF:Mg,Ti) thermoluminescence detectors (TLDs). Organ doses were calculated in the ADAM anthropomorphic phantom using the MCNPX Monte Carlo transport code and partly verified, for γ-ray doses, with TLD measurements in the RANDO Anderson anthropomorphic phantom. The effective dose due to undesired radiation, including exposure from scattered radiation during the entire process of proton radiotherapy and patient positioning using X-rays, does not exceed 1 mSv.     

Franco-Russian comparison of mixed neutron and gamma radiation field dosimeters at the Silène reactor

This paper gives the results of dosimetry measurements carried out in the Silène reactor at Valduc (France) with neutron and photon dosimeters in mixed neutron and gamma radiation fields, in the frame of a Franco-Russian comparison of dosimeters. Neutron dosimetry was supplied by passive semiconductors, activation detectors and nuclear track detectors. For photon dosimetry, thermoluminescent and passive semiconductor detectors were used. The experiments were located at 3 m from the reactor core, in free air and also at the front and back of a tissue-equivalent phantom. The pulse operating mode of the reactor was used to simulate a criticality accident with solid fissile material, while the free evolution mode simulated a criticality accident in a fissile solution. The photon absorbed dose showed a slight increase on entering the phantom compared to measurements in free air, probably due to backscattering by the phantom. At the rear of the phantom, the neutron kerma was four times lower than on the front, whereas the photon dose was only two times lower. The heterogeneity of dose inside the phantom was far greater for neutrons than for photons.     

The use of recombination chambers at radiation therapy facilities

The paper presents an overview of the applications of recombination chambers for dosimetric measurements at radiotherapy facilities. The chambers were used at electron, proton and heavy ion accelerators, in the beam and in the vicinity of the accelerators at very different dose rates. The examples of measurements discussed in the paper include: the determination of the absorbed dose and radiation quality parameters of a 170 MeV proton beam and BNCT (boron neutron capture therapy) beam, neutron dose measurements at a phantom surface outside the beam of a 15 MV electron medical accelerator, determination of ambient dose equivalent, H1 (10) outside the irradiated phantom in the proton therapy treatment room at JINR (Dubna, Russia), and at working places outside the shielding of the heavy ion therapy facility at GSI (Darmstadt, Germany).     

Characterization of the radiation shielding properties of US and Russian EVA suits using passive detectors

Radiation measurements using passive detectors were carried out to assess the shielding properties of the US Extravehicular Mobility Unit (EMU) space suit and the Russian Orlan-M suit during irradiations of the suits and a tissue-equivalent phantom by monoenergetic proton and electron beams at the Loma Linda University Medical Center (LLUMC). During irradiations of 6 MeV electrons and 60 MeV protons, absorbed dose as a function of depth was measured using thermoluminescent detector (TLD) exposed behind swatches of the two suit materials and inside the two extravehicular activity (EVA) helmets. Considerable reduction in electron dose was measured behind all suit materials on exposure to 6 MeV electrons. Slowing of the proton beam in the suit materials led to an increase in dose measured on exposure to 60 MeV protons. During 232 MeV proton irradiations, measurements were made with TLD and CR-39 plastic nuclear track detector (PNTD) at five organ locations inside a tissue-equivalent phantom, exposed both with and without the two EVA suits. The EVA helmets produced a 13% to 27% reduction in total absorbed dose and a 0% to 25% reduction in dose equivalent when compared to measurements made in the phantom head alone. Differences in absorbed dose and dose equivalent between the suit and non-suit irradiations for the lower portions of the two EVA suits tended to be smaller. Proton-induced target fragmentation was found to be a significant source of increased dose equivalent, especially within the two EVA helmets, and average quality factor inside the EMU and Orlan-M helmets was 2% to 14% greater than that measured in the bare phantom head.     

Radiation tests of the extravehicular mobility unit space suit for the international space station using energetic protons

Measurements to characterize the shielding properties of the EMU space suit and a human phantom were performed using 155 and 250 MeV proton beams at the Loma Linda University Medical Center (LLUMC). The beams simulate radiation encountered in low-Earth orbit (LEO), where trapped protons having kinetic energies on the order of 100 MeV are abundant. Protons at these energies can penetrate many g/cm² of matter and deliver a dose to the skin and internal organs. The dose can be enhanced or reduced by shielding, either from the space suit or the self-shielding of the body, but minimization of the risk depends on knowledge of the detailed energy spectrum and on the dose responses of the critical organs. Nuclear interactions of energetic protons in materials produce highly ionizing secondary radiation that increases dose and dose-equivalent beyond what would be expected simply from increasing ionization energy loss along the Bragg curve. Here, we present results obtained using silicon detectors in the LLUMC proton beams. Bare-beam data were taken to characterize the beams and calibrate the detectors. Data were also taken with the detectors placed inside a human phantom within the EMU suit. Because many secondaries have very high LET and short range, they are best measured in passive track detectors such as CR-39 or in much thinner silicon detectors than those used here. Our data complement the CR-39 data in the LET range below , where CR-39 is insensitive. Our results suggest that optimizing the radiation shielding properties of space suits is a formidable task—simply adding mass may not reduce the net risk, because adding material to reduce the dose delivered at or near the skin by low-energy particles can increase the dose delivered by more energetic particles to sites deeper in the body. The depth-dose relation therefore depends critically on the energy distribution of the incident protons.     

Angular distribution of neutron spectral fluence around phantom irradiated with high energy protons

Extended Bonner Spheres spectrometer was used to measure the angular distribution of neutron spectral fluence around NYLON6 phantom irradiated with pencil beam of 100, 150 and 200 MeV protons at the Proton Therapy Center Praha. Measurements were supplemented by a calculation of neutron spectral fluences at different depths of the phantom. The calculation of neutron spectral fluence at different depth of the phantom demonstrated that the majority of high energy neutrons was generated at the beginning of the proton trajectory in the phantom and the neutron yield decreased with increasing depth, with a minimum at the depth corresponding to the Bragg peak. Therefore, attention should be paid not only to the tissue behind the irradiated volume, but also to the preceding tissue. However, the neutron spectral fluence in the vicinity of the treated tissue can only be determined by calculation, mainly due to the dimensions of the neutron spectroscopic instrumentation. This paper presents a suitable technique and experimental conditions to acquire reliable data necessary for the proper determination of neutron spectral fluence. From the measured spectral fluences, the neutron fluence in whole-range and partial energy intervals were determined together with the corresponding ambient dose equivalents at measurement positions. The obtained results indicate that high energy neutrons predominate at the direction of the proton beam and more neutrons are generated by higher energy protons.     

Clinical tests of large area thermoluminescent detectors under radiotherapy beams

Two-dimensional (2D) thermoluminescence (TL) dosimetry systems based on LiF:Mg,Cu,P, together with the newly developed, based on CaSO4:Dy, were tested under radiotherapy beams. The detectors were irradiated in a water phantom with 6 MV X-ray beams from linac and read with a dedicated TLD reader. Dose distributions of differently shaped fields and of a full stereotactic plan were measured and compared with planned distributions.Maximum distance-to-agreement (DTA) in the penumbra region was 1 mm for both LiF:Mg,Cu,P and CaSO4:Dy TL sheets, for all the measured fields. Maximum percentage dose difference (DA%) between planned and measured dose value in low dose gradient regions was up to 11% for LiF:Mg,Cu,P TL sheets and 18% for CaSO4:Dy TL sheets. Concerning the full stereotactic plan, the percentage of points with γ-index below 1 is 54.9% for the LiF:Mg,Cu,P-based foil and 96.9% for the CaSO4:Dy TL sheets. Both 2D TL detector types can be considered to be a promising tool for bi-dimensional dose measurements in radiotherapy. Non-homogeneity, presumably due to the TL sheets manufacture, still affects dosimetric distribution and the agreement between planned and measured distributions may depend on the chosen sample.     

Off-axis dose distribution for rectangle proton beam

This papcr modifies an analytical algorithm originally developed for electron dose calculations to evaluate the off-axis dose distribution of rectangle proton bcam. This spatial distribution could be described by Fermi-Eyges theory since a proton undergoes small-angle scattering when it passes through medium. Predictions of the algorithm for relative off-axis dose distribution by a 6 cm ＊ 6 cm initial monoenergetic proton beam are compared with the results from the published Monte Carlo simulations. The excellent level of agreement between the results of these two methods of dose calculation （〈 2%） demonstrates that the off-axis dose distribution from rectangle proton beam may be computed with high accuracy using this algorithm. The results also prompts the necessity to consider the off-axis distribution when the proton is applied to clinical radiotherapy since the penumbra is significant at the distal of its range （about 0.6 cm at the Bragg-peak depth）.     

Microdosimetric characterisation of a therapeutic proton beam used for conjunctival melanoma treatments

In this study we have investigated the radiation quality of proton beams used to treat conjunctival melanomas at the Biomedical Cyclotron in Nice. To quantify radiation quality we have used a mini tissue-equivalent proportional counter (TEPC). Microdosimetric spectra have been measured at different depths and lateral positions in a Plexiglas eye phantom. A weighting function, which was derived from evaluations of the early effects on the mouse intestine, was applied to the spectra to obtain the microdosimetric assessment of relative biological effectiveness (RBEμ).Data show that RBEμ varies significantly in the eye phantom, from 1.1 to 1.7. However, within the conjunctiva the RBE-weighted dose varies in a similar fashion to the absorbed, although it is up to 20% higher than the corresponding absorbed dose.     

Measurement of target fragments produced by 160 MeV proton beam in aluminum and polyethylene with CR-39 plastic nuclear track detectors

Production of target fragments from reactions of 160 MeV proton beams in aluminum and polyethylene was measured with CR-39 plastic nuclear track detectors (PNTD). Due to the detection limit of PNTD, primary protons cannot be detected; only low-energy short-range target fragments are registered. As a feasibility study, a so called “two step etching method” was employed to get the linear energy transfer (LET) spectra, absorbed dose, and dose equivalent. This method is discussed in this paper, together with the measured results.     

Studying the potential of point detectors in time-resolved dose verification of dynamic radiotherapy

Modern megavoltage x-ray radiotherapy with high spatial and temporal dose gradients puts high demands on the entire delivery system, including not just the linear accelerator and the multi-leaf collimator, but also algorithms used for optimization and dose calculations, and detectors used for quality assurance and dose verification. In this context, traceable in-phantom dosimetry using a well-characterized point detector is often an important supplement to 2D-based quality assurance methods based on radiochromic film or detector arrays. In this study, an in-house developed dosimetry system based on fiber-coupled plastic scintillator detectors was evaluated and compared with a Farmer-type ionization chamber and a small-volume ionization chamber. An important feature of scintillator detectors is that the sensitive volume of the detector can easily be scaled, and five scintillator detectors of different scintillator length were thus employed to quantify volume averaging effects by direct measurement. The dosimetric evaluation comprised several complex-shape static fields as well as simplified dynamic deliveries using RapidArc, a volumetric-modulated arc therapy modality often used at the participating clinic. The static field experiments showed that the smallest scintillator detectors were in the best agreement with dose calculations, while needing the smallest volume averaging corrections. Concerning total dose measured during RapidArc, all detectors agreed with dose calculations within 1.1 ± 0.7% when positioned in regions of high homogenous dose. Larger differences were observed for high dose gradient and organ at risk locations, were differences between measured and calculated dose were as large as 8.0 ± 5.5%. The smallest differences were generally seen for the small-volume ionization chamber and the smallest scintillators. The time-resolved RapidArc dose profiles revealed volume-dependent discrepancies between scintillator and ionization chamber response, which confirmed that correction factors for ionization chambers in high temporal and spatial dose gradients are dominated by the volume averaging effect. The unique scaling of the scintillator volumes indicated how such time-dependent volume averaging corrections could be quantified. The time-resolved measurements further supported the claim that small-volume water equivalent detectors are most likely to accurately detect changes in dose delivery, although exact positioning of detectors remains critical.     

Fast-neutron dose evaluation in BNCT with Fricke gel layer detectors

Boron neutron capture therapy (BNCT) is a cancer radiotherapy that uses epithermal and thermal neutron beams. The determination of the absorbed dose in healthy tissue, separating the various dose contributions having different radiobiological effectiveness (RBE) is of great importance for therapy planning. However, a standard code of practice has not yet been established because suitable methods for dosimetry in BNCT are still in progress.A study about the characterization of the epithermal column of the LVR-15 research reactor in ?e? (CZ) has been performed, in particular concerning the fast-neutron dose. This dose is not negligible and its determination is important owing to its high RBE. Fast-neutron and photon dose distributions in a water phantom have been measured by means of Fricke gel layer dosimeters. Even if gel layer dosimetry is not yet standardized, it is presently the only method for obtaining images of each dose contribution in BNCT neutron fields.The results were compared with values measured with thermoluminescence detectors, twin ionization chambers data taken from literature and Monte Carlo simulations.     

Comparative Study of Depth Dose Distribution of Fast Neutrons Using Solid State Nuclear Track Detectors

A comparative study was made for measuring neutron depth dose distribution in a water phantom by means of different solid state nuclear track detectors. The used detectors were Makrofol, CR-39 and LR-115 with threshold energies of 1 and 0.1 MeV, respectively. Two exposure positions were used, the source in contact with the surface and at 30 cm from the phantom surface. The fluence distribution of ²⁵²Cf as a function of distance in air and in the water phantom were investigated. It was found that the neutron build up factor depends on the irradiation geometry, its values were 1.7 and 1.4 for both exposure positions. These results are in good agreement with the calculated results given in literature. The neutron attenuation and relaxation length had been also determined.     

碳离子在不同材料叶片的多叶光栅上产生的次级粒子研究

在碳离子放射治疗中，碳离子束与治疗头设备和患者身体相互作用产生的次级粒子可以到达患者体内的许多区域，在产生的次级粒子中以中子和$\gamma $射线的产额为最大。在不影响束流配送功能的情况下，减少碳离子放疗中产生的次级中子和$\gamma $射线对于降低放疗后出现的正常组织并发症及二次肿瘤风险有着非常重要的意义。本文利用蒙特卡罗(Monte Carlo)方法模拟计算了被动式束流配送系统下，400 MeV/u碳离子束照射到由不同材料叶片构成的多叶光栅(MLC)形成典型的10 cm×10 cm方形射野时，在水模体中产生的次级中子和$\gamma $射线所沉积的剂量及空间分布等。模拟结果显示:碳离子束通过MLC形成射野后在水模体中产生的次级中子主要分布在水模体的入射端，次级$\gamma $射线较为均匀的分布在整个水模体内，且较多分布在具有展宽Bragg峰(SOBP)射野在水模体中贯穿时的坪区。对于MLC叶片材料的选择，则需根据实际情况对叶片厚度以及次级粒子当量剂量的要求来确定。本文通过模拟研究不同MLC叶片材料产生次级粒子的情况，为被动式束流配送系统中MLC叶片及其他元件的材料选择提供了科学依据。     

Scatter radiation dose at the height of the operator's eye in interventional cardiology

This paper presents the first experimental result for scatter dose at the height of the operator's eye measured for a Polymethyl methacrylate (PMMA) phantom simulating an adult patient in an interventional laboratory at Belo Horizonte, Brazil. Values for scattered radiation doses at the height of the operator's eye are reported for procedures performed with and without a ceiling-suspended screen. Correlations between scatter radiation doses and different angiographic projections, phantom entrance dose and kerma area product, were obtained.Experimental measurements were made in an angiography X-ray system equipped with flat-panel detector. A cine and three fluoroscopy modes: low, medium and high dose were available. Scattered radiation doses were measured at three angiographic projections: anterior-posterior (AP), left anterior oblique 90° and left anterior oblique 45° with cranial 30° (spider) angulations. The detector measuring scatter radiation was positioned at the usual distance of the cardiologist's eye and the detector measuring phantom entrance dose was positioned at the bottom of the PMMA phantom.The phantom entrance dose for fluoroscopy low, medium, high and cine were 15, 29, 36 ± 4 and 184 ± 18 mGy/min, respectively to AP projection. A good linear correlation exists between phantom entrance doses rate and scatter dose rate to AP projection. There is a good linear correlation between the kerma-area product and scatter dose at the height of the operator's eye, coefficient of determination R² were 0.9728 and 0.9913 with and without ceiling-suspended screen. An experimental correlation factor of 0.1 and 3.5 μSv/Gy*cm2 has been found for the AP projection with and without ceiling-suspended screen, respectively. Scatter dose at the eyes cardiologist position depends on the C-arm angulation an increase of the scatter radiation dose by a factor of 5 was found.The highest dose rate in the lens was 19.74 ± 1.97 mSv/h without ceiling-suspended screen in cine mode for “spider” projection. For lateral projection in cine mode, the ceiling-suspended screen reduced dose by a factor 0.01. Interventional operator may therefore easily exceed the lens dose limit if ceiling-suspended screen is not used.     

Gamma Knife® 3-D Dose Distribution Mapping by Magnetic Resonance Imaging

In medical processes where ionizing radiation is used, dose planning and dose delivery are the key elements to patient safety and treatment success, particularly, when the delivered dose in a single session of treatment can be an order of magnitude higher than the regular doses of radiotherapy. Therefore, the radiation dose should be well defined and precisely delivered to the target while minimizing radiation exposure to surrounding normal tissues [1]. Several methods have been proposed to obtain three-dimensional (3-D) dose distribution [2, 3]. In this paper, we propose an alternative method, which can be easily implemented in any stereotactic radiosurgery center with a magnetic resonance imaging (MRI) facility. A phantom with or without scattering centers filled with Fricke gel solution is irradiated with Gamma Knife^® system at a chosen spot. The phantom can be a replica of a human organ such as head, breast or any other organ. It can even be constructed from a real 3-D MR image of an organ of a patient using a computer-aided construction and irradiated at a specific region corresponding to the tumor position determined by MRI. The spin–lattice relaxation time T ₁ of different parts of the irradiated phantom is determined by localized spectroscopy. The T ₁-weighted phantom images are used to correlate the image pixels intensity to the absorbed dose and consequently a 3-D dose distribution with a high resolution is obtained.