Therapeutic Beams Research Articles

Nanodosimetric quantities and RBE of a clinically relevant carbon-ion beam.

Although carbon-ion therapy is becoming increasingly attractive to the treatment of tumors, details about the ionization pattern formed by therapeutic carbon-ion beam in tissue have not been fully investigated. In this work, systematic calculations for the nanodosimetric quantities and relative biological effectiveness (RBE) of a clinically relevant carbon-ion beam were studied for the first time. The method combining both track structure and condensed history Monte Carlo (MC) simulations was adopted to calculate the nanodosimetric quantities. Fragments and energy spectra at different positions of the radiation field of a clinically relevant carbon-ion pencil beam were generated by means of MC simulations in water. Nanodosimetric quantities such as mean ionization cluster size ( ), the first moment of conditional cluster size ( ), cumulative probability ( ), and conditional cumulative probability ( ) at these positions were then acquired based on the spectra and the pre-calculated nanodosimetric database created by track structure MC simulations. What's more, a novel approach to calculate RBE based on the said nanodosimetric quantities was introduced. The RBE calculations were then conducted for the carbon-ion beam at different water-equivalent depths. Lateral distributions at various water-equivalent depths of both the nanodosimetric quantities and RBE values were obtained. The values of , , , and were 1.49, 2.67, 0.30, and 0.38 at the plateau at the beam central axis and maximized at 2.79, 5.69, 0.47, and 0.68 at the depths around the Bragg peak, respectively. At a given depth, and decreased laterally with increasing the distance to the beam central axis while and remained nearly unchanged at first and then decreased except for at the rising edge of the Bragg peak. The calculated RBE values were 1.07 at the plateau and 3.13 around the Bragg peak. Good agreement between the calculated RBE values and experimental data was obtained. Different nanodosimetric quantities feature the track structure of therapeutic carbon-ion beam in different manners. Detailed ionization patterns generated by carbon-ion beam could be characterized by nanodosimetric quantities. Moreover the combined method adopted in this work to calculate nanodosimetric quantities is not only valid but also convenient. Nanodosimetric quantities are significantly helpful for the RBE calculations in carbon-ion therapy.

Effects of indirect actions and oxygen on relative biological effectiveness: estimate of DSB inductions and conversions induced by therapeutic proton beams

Purpose: This study evaluated the DNA double strand breaks (DSBs) induced by indirect actions and its misrepairs to estimate the relative biological effectiveness (RBE) of proton beams.Materials and methods: From experimental data, DSB induction was evaluated in cells irradiated by 62 MeV proton beams in the presence of dimethylsulphoxide (DMSO) and under hypoxic conditions. The DNA damage yields for calculating the RBE were estimated using Monte Carlo Damage Simulation (MCDS) software. The repair outcomes (correct repairs, mutations and DSB conversions) were estimated using Monte Carlo Excision Repair (MCER) simulations.Results: The values for RBE of 62 MeV protons (LET = 1.051 keV/μm) for DSB induction and enzymatic DSB under aerobic condition (21% O2) was 1.02 and 0.94, respectively, as comparing to 60Co γ-rays (LET = 2.4 keV/μm). DMSO mitigated the inference of indirect action and reduced DSB induction to a greater extent when damaged by protons rather than γ-rays, resulting in a decreased RBE of 0.86. DMSO also efficiently prevented enzymatic DSB yields triggered by proton irradiation and reduced the RBE to 0.83. However, hypoxia (2% O2) produced a similar level of DSB induction with respect to the protons and γ-rays, with a comparable RBE of 1.02.Conclusions: The RBE values of proton beams estimated from DSB induction and enzymatic DSB decreased by 16% and 12%, respectively, in the presence of DMSO. Our findings indicate that the overall effects of DSB induction and enzymatic DSB could intensify the tumor killing, while alleviate normal tissue damage when indirect actions are effectively interrupted.

First application of a high-resolution silicon detector for proton beam Bragg peak detection in a 0.95 T magnetic field.

To report on experimental results of a high spatial resolution silicon-based detector exposed to therapeutic quality proton beams in a 0.95T transverse magnetic field. These experimental results are important for the development of accurate and novel dosimetry methods in future potential real-time MRI-guided proton therapy systems. A permanent magnet device was utilized to generate a 0.95T magnetic field over a 4×20×15cm3 volume. Within this volume, a high-resolution silicon diode array detector was positioned inside a PMMA phantom of 4×15×12cm3 . This detector contains two orthogonal strips containing 505 sensitive volumes spaced at 0.2mm apart. Proton beams collimated to a circle of 10mm diameter with nominal energies of 90MeV, 110MeV, and 125MeV were incident on the detector from an edge-on orientation. This allows for a measurement of the Bragg peak at 0.2mm spatial resolution in both the depth and lateral profile directions. The impact of the magnetic field on the proton beams, that is, a small deflection was also investigated. A Geant4 Monte Carlo simulation was performed of the experimental setup to aid in interpretation of the results. The nominal Bragg peak for each proton energy was successfully observed with a 0.2mm spatial resolution in the 0.95T transverse magnetic field in both a depth and lateral profiles. The proton beam deflection (at 0.95T) was a consistent 2 ±0.5mm at the center of the magnetic volume for each beam energy. However, a pristine Bragg peak was not observed for each energy. This was caused by the detector packaging having small air gaps between layers of the phantom material surrounding the diode array. These air gaps act to degrade the shape of the Bragg peak, and further to this, the nonwater equivalent silicon chip acts to separate the Bragg peak into multiple peaks depending on the proton path taken. Overall, a promising performance of the silicon detector array was observed, however, with a qualitative assessment rather than a robust quantitative dosimetric evaluation at this stage of development. For the first time, a high-resolution silicon-based radiation detector has been used to measure proton beam Bragg peak deflections in a phantom due to a strong magnetic field. Future efforts are required to optimize the detector packaging to strengthen the robustness of the dosimetric quantities obtained from the detector. Such high-resolution silicon diode arrays may be useful in future efforts in MRI-guided proton therapy research.

Offline imaging of positron emitters induced by therapeutic helium, carbon and oxygen ion beams with a full-ring PET/CT scanner: experiments in reference targets

In vivo verification of light ion therapy based on positron-emission tomography (PET) imaging of irradiation induced patient activation relies on activity predictions from Monte-Carlo (MC) or analytical computational engines for comparison to the measurements. In order to achieve the necessary accuracy, experimental data are indispensable for the validation of the calculation models. For this we irradiated thick reference targets with mono-energetic helium, carbon and oxygen ion beams and measured the resulting material activation offline with a commercial full-ring PET/CT scanner located nearby the treatment room.Acquired PET data were analysed over time to separate the activity contribution of different radionuclides. Determined production yields were compared to published findings obtained from in-beam activation measurements with a limited-angle double-head PET camera. In addition, we investigated the time-dependence of the measured radionuclide-specific contributions and of the distal activity range, as well as the lateral spread of the activity signal as a function of beam penetration depth.We present radionuclide-specific depth-resolved activity distributions and production yields for the radionuclides , and , dominating irradiation-induced patient activation. We observe systematically lower production yields with a ratio between the dual-head and our full-ring PET measurements of, on average, 1.7 and 1.3 for the oxygen and carbon beam irradiations, and 1.7 (2.1) for the high (low) energy helium beam irradiations. Findings on the temporal development of the activity range confirm the expectation, with the oxygen beam induced signal being the most sensitive scenario.The experimental data reported in this work, acquired with a state-of-the-art full ring PET scanner, provide a comprehensive and consistent basis for the benchmarking of PET signal calculation engines. In particular, they can support a fine-tuning of the underlying physics models used by the respective implementation and therefore improve the accuracy of PET-based therapy verifications at current and future treatment facilities.

Calculating dose from a 2.5MV imaging beam using a commercial treatment planning system.

Patient dose from 2.5 MV images on the TrueBeam linear accelerator is not easily quantified, primarily because this beam energy is not normally modeled by commercial treatment planning systems. In this work we present the feasibility of using the Eclipse® treatment planning system to model this beam. The Acuros XB and the AAA dose calculation algorithms were tested. Profiles, PDDs, and output factors were measured for the 2.5 MV unflattened imaging beam and used for beam modeling. The algorithms were subsequently verified using MPPG 5.a guidelines. Calculated doses with both algorithms agreed with the measurement data to within the following criteria recommended for conventional therapeutic MV beams: 2% local dose‐difference in the high‐dose region, 3% global difference in the low‐dose region, 3 mm distance to agreement in the penumbra, and a gamma pass rate of >95% for 3%/3 mm criteria. Acuros was able to accurately calculate dose through cork and bone‐equivalent heterogeneities. AAA was able to accurately calculate dose through the bone‐equivalent heterogeneity but did not pass within the recommended criteria for the cork heterogeneity. For the 2.5 MV imaging beam, both the AAA and Acuros algorithms provide calculated doses that agree with measured results well within the 20% criteria for imaging beams recommended by AAPM TG‐180.

Novel On-line PET Imaging for Intra-Beam Range Verification and Delivery Optimization: A Simulation Feasibility Study.

On-line PET image-based method uses an initial particle beam to measure the particle beam range (BR) within the same fraction so that any measured range-shift with respect to the predicted BR can be compensated before the rest therapeutic beam deliveries. However, the method requires to use a low-dose initial beam to minimize the risk of beam overshooting, which leads to low image count and inaccurate BR measurement. In this in-silico study, we evaluated the feasibility of a new on-line PET imaging method that measures BR at the mid-plane of a target volume with part of the high-dose therapy beams to verify BR and guide adaptive treatment re-planning. Simulations included various processes of proton beam radiations to a tumor inside a human brain phantom, positron and PET image generation at the mid-plane with initial beams, activity range measurement, and range-shift compensated beam delivery. The results demonstrated that the new method, under the simulated conditions, can achieve ~1.1 mm mid-plane BR measurement accuracy and closely match the delivered range-shift compensated dose distribution with the planned one. Overall, it is promising that this new method may significantly improve particle therapy accuracy.

Measurement of PET isotope production cross sections for protons and carbon ions on carbon and oxygen targets for applications in particle therapy range verification

Measured cross sections for the production of the PET isotopes , and from carbon and oxygen targets induced by protons (40–220 ) and carbon ions (65–430 ) are presented. These data were obtained via activation measurements of irradiated graphite and beryllium oxide targets using a set of three scintillators coupled by a coincidence logic. The measured cross sections are relevant for the PET particle range verification method where accurate predictions of the emitter distribution produced by therapeutic beams in the patient tissue are required. The presented dataset is useful for validation and optimization of the nuclear reaction models within Monte Carlo transport codes. For protons the agreement of a radiation transport calculation using the measured cross sections with a thick target PET measurement is demonstrated.

Imaging Cherenkov photon emissions in radiotherapy with a Geiger-mode gated quanta image sensor.

The emission of Cherenkov photons from human and animal tissue can be observed during clinical x-ray or particle beam irradiation. However, imaging this weak emission with the necessary single-photon sensitivity in the clinical room is challenging because of milliwatt-level ambient room lighting and the presence of stray high-energy radiation. In this Letter, we demonstrate, to the best of our knowledge, the first Cherenkov imaging with a time-gated quanta image sensor employing a large single-photon avalanche diode (SPAD) array. Detecting single Cherenkov photons was possible with high photon avalanche gain, fast temporal gating, and moderately high ∼7% photon detection probability. Single-bit digitization and active SPAD quenching enabled stray x-ray noise suppression and photon-noise-limited imaging in a clinical environment. This type of imaging allows the knowledge of location, shape, and surface dose of the therapeutic beam radiotherapy with the stability of solid state-based detection.

Feasibility of clinical electron beam formation using polymer materials produced by fused deposition modeling

The main challenge in electron external beam radiation therapy with clinical accelerators is the absence of integrated systems to form irregular fields. The current approach to provide conformal irradiation is to use additional metallic shaping blocks, with inefficient and expensive workflows. This work presents a simple method to form therapeutic electron fields using 3D printed samples. These samples are manufactured by fused deposition modeling, which can affect crucial properties, such as material homogeneity, due to the presence of residual air-filled cavities. The applicability of this method was therefore investigated with a set of experiments and Monte Carlo simulations aimed at determining the electron depth dose distribution in polymer materials. The results show that therapeutic electron beams with energies 6–20 MeV can be effectively absorbed using these polymeric samples. The model developed in this study provides a way to assess the dose distribution in such materials and to calculate the appropriate thickness of polymer samples for therapeutic electron beam formation. It is shown that for total absorption of 6 MeV electron beams the material thickness should be at least 4 cm, while this value should be at least 8 cm for 12 MeV and 11 cm for 20 MeV, respectively. The results can be used to further develop 3D printing procedures for medical electron beam profile formation, allowing the creation of a collimator or absorber with patient-specific configuration using rapid prototyping systems, thus contributing to improve the accuracy of dose delivery in electron radiotherapy within a short manufacturing time.

Clinical application of ionization density dependence of the glow curve for measuring linear energy transfer in therapeutic proton beams

Linear energy transfer (LET) is related to the relative biological effect caused by particle therapy. LET is a candidate parameter for optimizing proton therapy treatment plans by considering the biological effects. Therefore, being able to measure LET in clinical sites has become crucial. The purpose of this study was to develop a feasible LET measurement system for clinical therapeutic proton therapy by using the ionization density dependence of the heating-induced fluorescence (LiF):Mg,Ti glow curve in the high-temperature region. The integrated thermoluminescent (TL) intensity over the specified high-temperature region after exposure to a proton beam was divided by that after exposure to a photon beam to obtain the high-temperature ratio (HTR). The relationship between the HTR and LET was determined. TL dosimeters (TLDs) were irradiated with the same dose at several depths of a water phantom using three types of radiation: a60Co gamma source at the National Measurement Laboratory of the Institute of Nuclear Energy Research, a 6-MV photon beam, and a 190-MeV proton beam at Chang Gung Memorial Hospital. The LET dependence on depth was simulated using a Monte Carlo code called TOPAS (version 3.0.1). The LET values ranged from 1 to 10 keV/μm in estimations using LiF:Mg,Ti for a proton beam. The LET measurement system was developed by comparing TL signals caused by proton beams with those caused by 60Co gamma rays or 6-MV X-rays. A system incorporating Linac X-rays would be most convenient for the majority of hospitals. Therefore, TLDs can not only be dosimeters but also LET detectors in proton therapeutic sites.

Microdosimetry at the CATANA 62 MeV proton beam with a sealed miniaturized TEPC

A new mini-TEPC with cylindrical sensitive volume of 0.9 mm in diameter and height, and with external diameter of 2.7 mm, has been developed to work without gas flow. With such a mini counter we have measured the physical quality of the 62 MeV therapeutic proton beam of CATANA (Catania, Italy). Measurements were performed at six precise positions along the Spread-Out Bragg Peak (SOBP): 1.4, 19.4, 24.6, 29.0, 29.7 and 30.8 mm, corresponding to positions of clinical relevance (entrance, proximal, central, and distal-edge of the SOBP) or of high lineal energy transfer (LET) increment (distal-dose drop off). Without refilling the microdosimeter with new gas, the measurements were repeated at the same positions 4 months later, in order to study the stability of the response in sealed-mode operation.From the microdosimetric spectra the frequency-mean lineal energy y-F and the dose-mean lineal energy y-D were derived and compared with average LET values calculated by means of Geant4 simulations. The comparison points out, in particular, a good agreement between microdosimetric y-D and the total dose-average LET¯d, which is the average LET of the mixed radiation field, including the contribution by nuclear reactions.

FOOT: a new experiment to measure nuclear fragmentation at intermediate energies

Abstract Particle therapy uses proton or 12 C beams to treat deep-seated solid tumors. Due to the advantageous characteristics of charged particles energy deposition in matter, the maximum of the dose is released to the tumor at the end of the beam range, in the Bragg peak region. However, the beam nuclear interactions with the patient tissues induces fragmentation both of projectile and target nuclei and needs to be carefully taken into account. In proton treatments, the target fragmentation produces low energy, short range fragments along all the beam range, that may deposit a non negligible dose in the entry channel. In 12 C treatments the main concern is represented by long range fragments due to projectile fragmentation that release their dose in the healthy tissues surrounding the tumor. The FOOT experiment (FragmentatiOn Of Target) of INFN is designed to study these processes, in order to improve the nuclear interactions description in next generation Treatment Planning Systems software, and hence the treatment plans quality. Target ( 16 O and 12 C nuclei) fragmentation induced by 150-250 MeV proton beams will be studied via an inverse kinematic approach, where 16 O and 12 C therapeutic beams collide on graphite and hydrocarbon targets to provide the nuclear fragmentation cross section on hydrogen. The projectile fragmentation of these beams will be explored as well. The FOOT detector includes a magnetic spectrometer for the fragments momentum measurement, a thin plastic scintillator for ΔE and time of flight measurements and a scintillating crystal calorimeter to measure the fragments kinetic energy. These measurements will be combined in order to make an accurate fragment charge and isotopic identification.

Microdosimetric Spectra Measurements on a Clinical Carbon Beam at Nominal Therapeutic Fluence Rate With Silicon Cylindrical Microdosimeters

The use of protons and heavy ions for the treatment of tumors is increasing since it provides a better relative biological effectiveness (RBE) than traditional radiotherapy. Accurate knowledge of the energy deposition at submicrometric scales is paramount for RBE characterization. This paper shows the latest version of the silicon cylindrical microdosimeter array developed by the Instituto de Microelectronica de Barcelona, Centro Nacional de Microelectronica (IMB-CNM, Spain). The detector consists of a matrix of $11 \times 11$ cylindrical sensitive unit cells with individual readout etched within the silicon substrate available in different diameters and pitches between detectors. The detector employed in this paper had a diameter of $15~\mu \text{m}$ , a pitch of $200~\mu \text{m}$ , and a thickness of $5.5~\mu \text{m}$ . The detectors were tested in the clinical facilities of Fondazione Centro Nazionale di Adronterapia Oncologica (CNAO) (Pavia, Italy) employing a 12C pencil beam at a therapeutic beam fluence rate. Microdosimetric spectra of lineal energy were measured in different depths of polymethyl methacrylate (PMMA) up to the Bragg peak. Results were then compared with Monte Carlo simulations using the FLUKA particle transport code, showing an excellent agreement between experimental and simulated microdosimetric distributions even at the high fluence rates associated with clinical beams.

Technical Note: Monte Carlo study on the reduction in x-ray contamination of therapeutic electron beams for Intraoperative Radiation Therapy by means of improvements in the design of scattering foils.

This work is aimed at studying the feasibility of reducing stray x-ray contamination of therapeutic electron beams used in Intraoperative Radiation Therapy (IOERT) through improvements in the design of the dual foil beam forming system. We assess the validity of a known method for designing the primary scattering foil. To this end, we perform, for the first time, a systematic computational study of the performance of beam forming systems equipped with primary scattering foils of different thicknesses, including a foil designed according to the currently used method. In this study, we further develop and apply a recently proposed method for optimization of dual foil systems. For each of the considered primary foils, a secondary foil that minimizes the stray x-ray contamination was designed under additional conditions on the clinically acceptable therapeutic range and flatness of off-axis dose profile. For comparison, we also designed secondary foils that enable the production of the best flattened beams irrespective of x-ray contamination and therapeutic range. By means of a comparative analysis, we demonstrated that currently employed design methods do not lead to an optimal solution in terms of stray x-ray contamination and therapeutic range. It is further demonstrated that, in comparison to older designs, reduction in x-ray contamination exceeding 30% may be expected in a system designed using the novel method developed here. Such a reduction is beneficial for IOERT delivered in a regular, unshielded operating room.

Determining the energy spectrum of clinical linear accelerator using an optimized photon beam transmission protocol.

The complex beam delivery techniques for patient treatment using a clinical linear accelerator (linac) may result in variations in the photon spectra, which can lead to dosimetric differences in patients that cannot be accounted for by current treatment planning systems (TPSs). Therefore, precise knowledge of the fluence and energy spectrum (ES) of the therapeutic beam is very important. However, owing to the high energy and flux of the beam, the ES cannot be measured directly, and validation of the spectrum modeled in the TPS is difficult. The aim of this study is to develop an efficient beam transmission measurement procedure for accurately reconstructing the ES of a therapeutic x-ray beam generated by a clinical linac. The attenuation of a 6MV photon beam from an Elekta Synergy Platform clinical linac through different thicknesses of graphite and lead was measured using an ion chamber. The response of the ion chamber as a function of photon energy was obtained using the Monte Carlo (MC) method in the Geant4 simulation code. Using the curves obtained in the photon beam transmission measurements and the ion chamber energy response, the ES was reconstructed using an iterative algorithm based on a mathematical model of the spectrum. To evaluate the accuracy of the spectrum reconstruction method, the reconstructed ES (ESrecon ) was compared to that determined by the MC simulation (ESMC ). The ion chamber model in the Geant4 simulation was well validated by comparing the ion chamber perturbation factors determined by the TRS-398 calibration protocol and EGSnrc; the differences were within 0.57%. The number of transmission measurements was optimized to 10 for efficient spectrum reconstruction according to the rate of increase in the spectrum reconstruction accuracy. The distribution of ESrecon obtained using the measured transmission curves was clearly similar to the reference, ESMC , and the dose distributions in water calculated using ESrecon and ESMC were similar within a 2% local difference. However, in a heterogeneous medium, the dose discrepancy between them was >5% when a complex beam delivery technique composed of 171 control points was used. The proposed measurement procedure required a total time of approximately 1h to obtain and analyze 20 transmission measurements. In addition, it was confirmed that the transmission curve of high-Z materials influences the accuracy of spectrum reconstruction more than that of low-Z materials. A well-designed transmission measurement protocol suitable for clinical environments could be an essential tool for better dosimetric accuracy in patient treatment and for periodic verification of the beam quality.

Miniature spherical silicon diode as a dosimeter during carbon-ion beam therapy

Abstract As the best use of the Bragg curve nature, hypofractionated ion-beam therapy is being actively explored for therapeutic applications in various cancer treatments. In the case of prostate cancer treatment, radical hypofractionation has been performed by selectively reducing the urethral dose located at the center of the prostate tumor. Establishing an in-vivo dosimeter to confirm if the dose to the urethra is surely reduced during therapeutic irradiation is strongly needed. This study investigated the application of miniature spherical silicon diode as an in-vivo dosimeter candidate for therapeutic carbon-ion beam. The spherical geometry of silicon caused a slight broadening of pristine Bragg peak of the carbon-ion beam; however, for practical therapeutic carbon-ion beam applications, it showed a superior dosimetric response, free from LET (linear energy transfer) dependency, and almost comparable to those measured using an ionization chamber . The spherical diode caused minor field perturbations, and displayed a gradual decrease in sensitivity as a function of integral dose from radiation damage. However, output linearity on dose, subtle incident angular dependence, compactness, and safeness of the silicon diode make the diode a good candidate for an in-vivo dosimeter during ion-beam therapy.

Study of the charge sensing node in the MAPS for therapeutic carbon ion beams

Beam monitoring system in heavy ion therapy facilities ensures the beam energy deposition can accurately cover the dedicated tumour region. For the purpose of building a high-precision beam monitoring system, a Monolithic Active Pixel Sensor (MAPS) is under development. The charge sensing node in the MAPS is formed by an n-well −p− epitaxial layer junction and it collects charge by drift and diffusion. In order to optimize the performance of the charge sensing node, the depletion region, the diode capacitance, the charge collection efficiency and the charge collection time have been studied with TCAD simulations. This paper discusses the simulation results with different bias voltage, node structures and heavy ion hitting locations.

Optimizing the response, precision, and cost of a DNA double-strand break dosimeter

We developed a dosimeter that measures biological damage following delivery of therapeutic beams in the form of double-strand breaks (DSBs) to DNA. The dosimeter contains DNA strands that are labeled on one end with biotin and on the other with fluorescein and attached to magnetic microbeads. Following irradiation, a magnet is used to separate broken from unbroken DNA strands. Then, fluorescence is utilized to measure the relative amount of broken DNA and determine the probability for DSB. The long-term goal for this research is to evaluate whether this type of biologically based dosimeter holds any advantages over the conventional techniques. The purpose of this work was to optimize the dosimeter fabrication and usage to enable higher precision for the long-term research goal. More specifically, the goal was to optimize the DNA dosimeter using three metrics: the response, precision, and cost per dosimeter. Six aspects of the dosimeter fabrication and usage were varied and evaluated for their effect on the metrics: (1) the type of magnetic microbeads, (2) the microbead to DNA mass ratio at attachment, (3) the type of suspension buffer used during irradiation, (4) the concentration of the DNA dosimeter during irradiation, (5) the time waited between fabrication and irradiation of the dosimeter, and (6) the time waited between irradiation and read out of the response. In brief, the best results were achieved with the dosimeter when attaching 4.2 µg of DNA with 1 mg of MyOne T1 microbeads and by suspending the microbead-connected DNA strands with 200 µl of phosphate-buffered saline for irradiation. Also, better results were achieved when waiting a day after fabrication before irradiating the dosimeter and also waiting an hour after irradiation to measure the response. This manuscript is meant to serve as guide for others who would like to replicate this DNA dose measurement technique.

Radiotherapy after tumour prostheses-status, indication, coordination

Patients with complex tumour prostheses often require radiotherapy or radiochemotherapy. Possible tumour diagnoses, indications, planning and therapy procedures, and prognosis of radiotherapy in the context of an interdisciplinary treatment for bone sarcomas are reviewed, including interactions of metal prostheses with radiation and possible subsequent complications. Literature search, summary of personal experience. Complex prosthetic procedures are usually applied to patients suffering from Ewing sarcoma or osteosarcoma. In patients with Ewing sarcoma, radiotherapy is an integral part of multimodal treatment, while in patients with osteosarcoma radiotherapy is indicated in special situations. Planning and implementation of radiotherapy treatment can be impaired by metal implants within the target volume (artefacts in the planning computerized tomography, interaction of metal with the therapeutic beam). However, it is-to our knowledge-apoint of debate whether radiotherapy after implantation of aprosthesis could impair healing or prosthesis fixation to bone. The data available in the literature suggest that prostheses implanted after radiotherapy entail ahigher rate of complications. Multidisciplinary treatment improves the prognosis for these patients markedly. Patients with sarcomas of the bone undergoing interdisciplinary treatment consisting of surgery, radiotherapy and chemotherapy have afavourable prognosis and an acceptable functionality of the limb can be expected.

Multi-slit prompt-gamma camera for locating of distal dose falloff in proton therapy

Abstract In this research, a multi-slit prompt-gamma camera was developed to locate the distal dose falloff of the proton beam spots in spot scanning proton therapy. To see the performance of the developed camera, therapeutic proton beams were delivered to a solid plate phantom and then the prompt gammas from the phantom were measured using the camera. Our results show that the camera locates the 90% distal dose falloff (= d90%), within about 2–3 mm of error for the spots which are composed 3.8 × 108 protons or more. The measured location of d90% is not very sensitive to the irradiation depth of the proton beam (i.e., the depth of proton beam from the phantom surface toward which the camera is located). Considering the number of protons per spot for the most distal spots in typical treatment cases (i.e., 2 Gy dose divided in 2 fields), the camera can locate d90% only for a fraction of the spots depending on the treatment cases. However, the information of those spots is still valuable in that, in the multi-slit prompt-gamma camera, the distal dose falloff of the spots is located solely based on prompt gamma measurement, i.e., not referring to Monte Carlo simulation.