Dosimetric Method Research Articles

Evaluation of Sonochemiluminescence in a Phantom in the Presence of Protoporphyrin IX Conjugated to Nanoparticles

Introduction When a liquid is irradiated with high-intensity and low-frequency ultrasound, acoustic cavitation occurs and there are some methods to determine and quantify this phenomenon. The existing methods for performing these experiments include sonochemiluminescence (SCL) and chemical dosimetric methods. The particles in a liquid decrease the ultrasonic intensity threshold needed for cavitation onset. In this study, a new nanoconjugate made up of Protoporphyrin IX (PpIX) and gold nanoparticles (GNP), i.e., Au-PpIX was used to provide nucleation sites for cavitation. The nonradiative relaxation time of PpIX in the presence of GNPs is longer than the similar time for PpIX without GNPs. This effect can be used in medical diagnostic and therapeutic applications. Materials and Methods The acoustic cavitation activity was investigated studying integrated SCL signal in the wavelength range of 400-500 nm in polyacrylamide gel phantom containing luminol using a cooled CCD spectrometer at different intensities of 1 MHz ultrasound. In order to confirm these results, a chemical dosimetric method was utilized, too. Results SCL signal level in gel phantom containing Au-PpIX was higher than the other phantoms. These results have been confirmed by the chemical dosimetric data. Conclusion This finding can be related to the existence of PpIX as a sensitizer and GNPs as cavitation nuclei. In other words, nanoparticles have acted as the sites for cavitation and have increased the cavitation rate. Another theory is that activation of PpIX has produced more free radicals and has enhanced the SCL signal level.

Silicon strip detector for a novel 2D dosimetric method for radiotherapy treatment verification

The aim of this work is to characterize a silicon strip detector and its associated data acquisition system, based on discrete electronics, to obtain in a near future absorbed dose maps in axial planes for complex radiotherapy treatments, using a novel technique. The experimental setup is based on two phantom prototypes: the first one is a polyethylene slab phantom used to characterize the detector in terms of linearity, percent depth dose, reproducibility, uniformity and penumbra. The second one is a cylindrical phantom, specifically designed and built to recreate conditions close to those normally found in clinical environments, for treatment planning assessment. This system has been used to study the dosimetric response of the detector, in the axial plane of the phantom, as a function of its angle with respect to the irradiation beam. A software has been developed to operate the rotation of this phantom and to acquire signals from the silicon strip detector. As an innovation, the detector was positioned inside the cylindrical phantom parallel to the beam axis. Irradiation experiments were carried out with a Siemens PRIMUS linac operating in the 6MV photon mode at the Virgen Macarena Hospital. Monte Carlo simulations were performed using Geant4 toolkit and results were compared to Treatment Planning System (TPS) calculations for the absorbed dose-to-water case. Geant4 simulations were used to estimate the sensitivity of the detector in different experimental configurations, in relation to the absorbed dose in each strip. A final calibration of the detector in this clinical setup was obtained by comparing experimental data with TPS calculations.

EURAMET.RI(I)-S7 comparison of alanine dosimetry systems for absorbed dose to water measurements in gamma- and x-radiation at radiotherapy levels

The National Physical Laboratory (NPL), the Physikalisch-Technische Bundesanstalt (PTB) and the Laboratoire National Henri Becquerel (LNE-LNHB) are involved in the European project 'External Beam Cancer Therapy', a project of the European Metrology Research Programme. Within this project, the electron paramagnetic resonance (EPR)/alanine dosimetric method has been chosen for performing measurements in small fields such as those used in IMRT (intensity modulated radiation therapy). In this context, these three National Metrology Institutes (NMI) wished to compare the result of their alanine dosimetric systems (detector, modus operandi etc) at radiotherapy dose levels to check their consistency. This EURAMET.RI(I)-S7 comparison has been performed with the support of the Bureau International des Poids et Mesures (BIPM) which collected and distributed the results as a neutral organization, to ensure the comparison was 'blind'.Irradiations have been made under reference conditions by each laboratory in a 60Co beam and in an accelerator beam (10 MV or 12 MV) in a water phantom of 30 cm × 30 cm × 30 cm in a square field of 10 cm × 10 cm at the reference depth. Irradiations have been performed at known values of absorbed dose to water (Dw) within 10% of nominal doses of 5 Gy and 10 Gy, i.e. between 4.5 Gy and 5.5 Gy and between 9 Gy and 11 Gy, respectively. Each participant read out their dosimeters and assessed the doses using their own protocol (calibration curve, positioning device etc) as this comparison aims at comparing the complete dosimetric process.The results demonstrate the effectiveness of the EPR/alanine dosimetry systems operated by National Metrology Institutes as a method of assuring therapy level doses with the accuracy required. The maximum deviation in the ratio of measured to applied dose is less than 1%.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by EURAMET, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Patterns of care for brachytherapy in Europe: updated results for Spain

The aim of this follow-up pattern of care study was to evaluate current clinical practices, staffing and equipment, and to compare these results to a study performed 5 years previously. This descriptive, pattern of care study was carried out via an online questionnaire. The survey was sent to a total of 95 cancer care centres in Spain. Seventy-three centres (76.8%) responded to the survey. More than half (57.5%) of responding centres offered brachytherapy (BT). A mean of 120 patients/centre were treated by BT in 2007. The most common localisations were the endometrium (29.6% of cases), prostate (29.6%), cervix uteri (14.6%), breast (12.6%), head and neck (3.6%) and vagina (2.5%). Other sites accounted for less than 2% of cases each. Most centres that offered BT (33/40 = 82.5%) were equipped with a dedicated BT operating room. The most commonly reported dosimetric method was CT dosimetry (31 of 40 centres = 77.5%), followed by plain film (30/40 = 75%), ultrasound (26/40 = 65%), MRI (8/40 = 20%), in vivo (7/40 = 17.5%) and PET-CT (5/40 = 12.5%) dosimetry. The three most common treatment sites (gynaecological, breast and prostate) remain unchanged from 2002, with prostate treatments showing large increase. Advanced dosimetric techniques (MRI, PET-CT and CT-dosimetry) continue to gain adherents. Some centres treat small numbers of patients, a finding that deserves more attention in terms of cost and quality of care. Although BT remains strong in Spain, it could be further strengthened by making modern dosimetric techniques and treatments more widely available.

Fricke gel dosimetric catheters in high dose rate brachytherapy. In phantom dose distribution measurements of a 5 catheter implant

Due to the complexity and the many steps involved in a high dose rate brachytherapy process, radiation dose delivered to the patient during the treatment is susceptible to many inaccuracies and may not accurately match the planned dose. In vivo dosimetry is a reliable solution to compare planned and delivered dose distributions, representing therefore a valid tool to systematically perform a quality control of the radiotherapic process and eventually increment treatment accuracy. In this study, Fricke gel dosimetric catheters (FGDC) were investigated to perform dose distribution measurements of a brachytherapy implant. The brachytherapy implant was established in a water phantom with five flexible plastic needles and irradiation was performed with a high dose rate remote afterloading device provided with an Ir-192 radioactive source. Comparison between dose distributions measured with ten FGDC located in the proximity of the implant needles and calculated by the treatment planning system shows very good agreement for seven out of ten dosimeters, whereas the remaining three show a local underestimation of the dose. In phantom results indicate that Fricke gel dosimetric catheters might be valid candidates for performing in vivo dosimetry in high dose rate brachytherapy. However, further measurements are still required to validate this dosimetric method.

SU‐E‐T‐313: Ionization Chamber Measurements in a Small, Non‐Uniform Beam ‐ Applications for Synchrotron Beam Dosimetry

Purpose: The aim of this ongoing work is to develop a dosimetric method suitable for the biomedical beamlines at the Canadian Light Source (CLS), which offer novel imaging and therapy modalities. As a step in this process, we analyzed the response of a clinical, cylindrical ionization chamber to small, non‐uniform synchrotron beams to determine absolute dose rates in air based on clinical calibration factors obtained under broad‐beam conditions.Methods: Three detectors (Gafchromic EBT2 film, Capintec PR06C ion chamber, and PTW diamond detector) were used to determine the vertical profile of the filtered beam produced by the CLSˈs bending magnet beamline. The radial response function of the ion chamber was determined using a 100 micrometer slit beam. Matlab code incorporated this information to predict the relative ion chamber output as a function of nominal vertical beam collimation (0.1 – 8.7 mm) for both stationary and scanning ion chamber geometries. The beam‐size dependent output was also measured directly with the ion chamber.Results: The beam profile was Gaussian in shape, and measurements with all three detectors were in substantive agreement. The ion chamber response function showed the walls and inner electrode of the chamber. Predicted and measured values for the ion chamber response with varying field size were in excellent agreement for both the scanning and stationary measurements, validating the MATLAB algorithm. Based on the algorithm and using an interpolated clinical calibration factor, the dose rates for the filtered bending magnet beam ranged from 1.7 – 1.9 Gy/s at the maximum CLS storage ring current Conclusions: The excellent agreement between the predicted and measured results provides confidence that the developed model of ion chamber response to the small, non‐uniform beam is valid and suggests that absolute dose rates can be measured accurately using clinical ion chambers.

Electromagnetic and Thermal Dosimetric Techniques in Humans and its Application

There has been increasing public concern about the adverse health effects of human exposure to radio frequency fields. Radio frequency fields are also used for medical application. This paper reviews electromagnetic and thermal computational dosimetric techniques, which has been developed by the authors. The feature of the thermal dosimetric method is that body core temperature can be computed reasonably unlike conventional method. This scheme is particularly useful for intense localized or whole-body electromagnetic wave exposure. Computational examples are shown to verify the effectiveness of the proposal.

ガラスバッジを用いた単純Ｘ線撮影における患者被ばく線量の測定

Radiography is used in medical practices based on the principles of justification and optimization. Patients' exposure doses should be kept as low as still allows for image quality that does not disturb the diagnostic processes. To optimize diagnostic radiological procedures, the international commission on radiological protection (ICRP) advocated the establishment of diagnosis reference levels (DRLs) in the new basic recommendation (Publication 103) in 2007 by stating that "The DRL should be expressed as a readily measurable patient-dose-related quantity for the specified procedure." In this context, a simple and standardized dosimetric method is needed to verify the adaptability of a radiation dose to the DRLs. As a measuring instrument that has good availability, high accuracy, and easy operability, we adopted the glass badge system, which has been used for individual exposure dose management. We evaluated the accuracy of the system as a tool of simplified dosimetry of diagnostic X-rays by comparing it to the standard dosimetry of an ionization chamber. In an energy range of 50 to 140 kV for X-ray exposure, the glass badge showed values within 7% of or closer to those measured by the standard ionization chamber. Moreover, the glass badge measurement was independent of the rectification modes of the X-ray tubes. In conclusion, glass badge measurement is feasible for verifying diagnostic X-ray doses in relation to DRLs and can be widely used in hospitals and clinics.

EPR dosimetry with tooth enamel: A review

When tooth enamel is exposed to ionizing radiation, radicals are formed, which can be detected using electron paramagnetic resonance (EPR) techniques. EPR dosimetry using tooth enamel is based on the (presumed) correlation between the intensity or amplitude of some of the radiation-induced signals with the dose absorbed in the enamel. In the present paper a critical review is given of this widely applied dosimetric method. The first part of the paper is fairly fundamental and deals with the main properties of tooth enamel and some of its model systems (e.g., synthetic apatites). Considerable attention is also paid to the numerous radiation-induced and native EPR signals and the radicals responsible for them. The relevant methods for EPR detection, identification and spectrum analyzing are reviewed from a general point of view. Finally, the needs for solid-state modelling and studies of the linearity of the dose response are investigated. The second part is devoted to the practical implementation of EPR dosimetry using enamel. It concerns specific problems of preparation of samples, their irradiation and spectrum acquisition. It also describes how the dosimetric signal intensity and dose can be retrieved from the EPR spectra. Special attention is paid to the energy dependence of the EPR response and to sources of uncertainties. Results of and problems encountered in international intercomparisons and epidemiological studies are also dealt with. In the final section the future of EPR dosimetry with tooth enamel is analyzed.

SU-GG-T-441: Monte Carlo Dosi metric Verification Based on Double Source Model

Purpose: In dose calculation and dosimetric verification for radiotherapy, the Monte Carlo method is a “gold rule”in accuracy given the same condition. Yet the results of the traditional Monte Carlo's method may disagree with the practical situation due to lack of practical information of a given medical accelerator such as energy spectra. For another, the previous dosimetric verification method mainly focused on 1D or 2D verification by use of film, thermoluminescence detector, ionization chamber, etc, and they usually fail to apply in vivo but vitro of a patient. Considering whatever producing high energy photon or electron beam, the medical accelerator also produced contamination radiation beam, such as photonbeam to electron contamination. With these, the purpose of this study was to improve the accuracy of the dosimetric verification in Monte Carlo method.Method and Materials: A double sourcemodel combined the Monte Carlo method for the photon and electron radiation was constructed. Namely, the photon and electron energy spectra, photon or electron contamination etc were input into the Monte Carlo engine as EGSnrc to realize the double sourcedose calculation, and the superimposed results between electron dose map and photondose map were as the final one. Results: The testing samples from AAPM report No.55 (energy as 4MeV and 18MeV) indicated that the root‐mean‐square error was less than 0.21% in the 4MeV' sample and 0.18% in the 18MeV's sample respectively, comparing with the measurement data of corresboding centeral axis percentage depth dose in this report. Conclusion: This method may not only overcome the traditional dosimetric verification confine in 1D/2D dose map, but also get the 3D dose map of the whole space and increase the accuracy of the dosimetric verification. So it can be applied to the clinic dosimetric verification and quality assurance in radiotherapy.

Characterisation of protracted low-level exposure to uranium in the workplace: A comparison of two approaches

Retrospective estimates of internal doses received by workers in the nuclear industry following intake of radionuclides, based on bioassay data, are a benchmark method in epidemiological studies. Nonetheless, full information relative to thousands of people included in an epidemiological cohort is rarely available, thus implying difficulties to estimate exposure precisely. To evaluate the cumulative exposure to uranium in a cohort of the AREVA NC Pierrelatte plant workers, we compared the epidemiological Job Exposure Matrix (JEM) method with the dosimetric method based on biological monitoring of exposure for 30 workers randomly selected within the cohort. A moderate to strong correlation was observed between the estimators resulting from the two approaches, thereby validating the JEM as a tool that can be used to characterise cumulative exposure to uranium in the cohort. In addition, this study showed that the JEM is a valuable complement to the interpretation of bioassy, (1) in providing information on exposure periods as well as on physical and chemical form of the radionuclides and (2) in compensating for the lack of exposure data regarding the very earliest periods. Combining the two methods may improve the precision in reconstructing cumulative exposure for epidemiological studies.

Methods of determining the effective dose in dental radiology

A wide variety of X-ray equipment is used today in dental radiology, including intra-oral, orthopantomographic, cephalometric, cone-beam computed tomography (CBCT) and computed tomography (CT). This raises the question of how the radiation risks resulting from different kinds of examinations should be compared. The risk to the patient is usually expressed in terms of effective dose. However, it is difficult to determine its reliability, and it is difficult to make comparisons, especially when different modalities are used. The classification of the new CBCT units is also problematic as they are sometimes classified as CT units. This will lead to problems in choosing the best dosimetric method, especially when the examination geometry resembles more on an ordinary orthopantomographic examination, as the axis of rotation is not at the centre of the patient, and small radiation field sizes are used. The purpose of this study was to present different methods for the estimation of the effective dose from the equipment currently used in dental radiology, and to discuss their limitations. The methods are compared based on commonly used measurable and computable dose quantities, and their reliability in the estimation of the effective dose.

Evaluation of Extremely Low Frequency (ELF) Electromagnetic Fields and Their Probable Relationship with Hematological Changes among Operators in Heavy Metal Industry

Introduction: It is important that biological and health effects from the induction of currents and fields in the body by extremely low frequency (ELF) fields are fully explored to determine the effects produced at the molecular, cellular and organ levels. The objective of this study was to evaluate the intensity of ELF electromagnetic fields and its probable relationship with hematological changes among operators in a heavy metal industry site. This is a case study. In the present study, 205 workers exposed to electromagnetic fields (EMF) were working in four categories: (1) induction furnace workers, (2) induction hardening workers, (3) welders, (4) computer operators. Material and Methods: A variety of methods for exposure assessment have been devised and applied to epidemiological studies of the effects of EMF in occupational settings. The methods range from rather crude job-classification methods, to sophisticated job-exposure matrix (JEM) modeling based on personal exposure measurements and reconstruction of past exposure. Monitoring procedures were carried out to measure the levels of exposure to ELF electric and magnetic fields. The strength of the electric and magnetic fields were measured by a dosimetric method (NIOSH 203).Workers’ blood samples were collected and analyzed for identifying different blood parameters. The results of hematological changes of workers in their medical files were also used for evaluation. Results: Measurements showed a high strength of ELF field at the induction furnace workplace. Total electric field ranged from 2.3 to 2452.3 V/M and magnetic field from 1 to 325.1 μT. In other workshops including induction hardening, total electric field ranged from 2.45 to 68.5 V/M, magnetic field from 1.3 to 20.4 μT, total electric field from 1.02 to 11.23 V/M, magnetic field from 0.12 to 3.25 μT in the welding department and finally for computer operators this range was 20.1 to 186.2 V/M for electric field and 0.07 to 0.25 μT for magnetic field. Conclusion: Mean value of WBC and MCV increased significantly among exposed induction furnace workers group (P < 0.05), but RBC decreased. Mean value of WBC, MCHC and MCV increased significantly among the exposed induction hardening workers group (P < 0.05), but RBC and Hgb decreased. Mean value of WBC, MCV and Hgb increased significantly among the exposed welders group (P < 0.05), but Hgb in relation with age decreased. Mean value of RBC and MCH decreased significantly among exposed computer operators group (P < 0.05).

Small SRS photon field profile dosimetry performed using a PinPoint air ion chamber, a diamond detector, a novel silicon‐diode array (DOSI), and polymer gel dosimetry. Analysis and intercomparison

Small photon fields are increasingly used in modern radiotherapy and especially in IMRT and SRS/SRT treatments. The uncertainties related to small field profile measurements can introduce significant systematic errors to the overall treatment process. These measurements are challenging mainly due to the absence of charged particle equilibrium conditions, detector size and composition effects, and positioning problems. In this work four different dosimetric methods have been used to measure the profiles of three small 6 MV circular fields having diameters of 7.5, 15.0, and 30.0 mm: a small sensitive volume air ion chamber, a diamond detector, a novel silicon-diode array (DOSI), and vinyl-pyrrolidone based polymer gel dosimeter. The results of this work support the validity of previous findings, suggesting that (a) air ion chambers are not suitable for small field dosimetry since they result in penumbra broadening and require significant corrections due to severe charged particle transport alterations; (b) diamond detectors provide high resolution and rather accurate small field profile measurements, as long as positioning problems can be addressed and the necessary dose rate corrections are correctly applied; and (c) the novel silicon-diode array (DOSI) used in this study seems to be adequate for small field profile measurements overcoming positioning problems. Polymer gel data were assumed as reference data to which the other measurement data were compared both qualitatively and quantitatively using the gamma-index concept. Polymer gels are both phantom and dosimeter, hence there are no beam perturbation effects. In addition, polymer gels are tissue equivalent and can provide high-spatial density and high-spatial resolution measurements without positioning problems, which makes them useful for small field dosimetry measurements. This work emphasizes the need to perform beam profile measurements of small fields (for acceptance, commissioning, treatment planning systems data feed, and periodic quality assurance purposes) using more than one dosimetric method. The authors believe this to be a safe way towards the reduction of the overall uncertainty related to SRS/SRT treatments.

DOsimetry of BIological EXperiments in SPace (DOBIES) with luminescence (OSL and TL) and track etch detectors

The objective of the “DOsimetry of BIological EXperiments in SPace” (DOBIES) project is to develop a standard dosimetric method as a combination of different techniques to estimate absorbed dose, dose equivalent, and linear energy transfer (LET) spectrum in biological samples in space experiments. The detectors investigated in the project include various types of thermoluminescence detectors (TLDs), such as LiF:Mg,Ti, LiF:Mg,Cu,P, CaSO 4 :Dy, as well as Al 2 O 3 :C used as TLD and optically stimulated luminescence detectors (OSLDs), and track-etch detectors (TED). This paper describes the DOBIES project and reports preliminary results obtained during the BASE-A experiment carried out at the International Space Station (ISS) in September, 2006. The results are compared to data from previous space exposures carried out by the members of the DOBIES project.

Comparison between ENEA and RADCARD TL photon cards based on LiF:Mg,Cu,P

Two photon TL dosemeters based on LiF:Mg,Cu,P fixed onto cards are tested in order to compare their dosimetric performance. ENEA cards have been used as a routine since 1995 and they contain chips of GR200A (Solid Dosimetric Detector and Method Laboratory—SSDML, China), whilst cards by RADCARD have been commercially available only recently and they contain chips of MCP-N (made in Poland). The cards, which have the same dimensions, were both read out with a Harshaw 6600 Automated TLD reader, according to the reading cycle recommended by the manufacturer. A sample of 10 cards of the two types were compared on their performance relating to gamma-sensitivity, detection threshold, linearity, dose range, coefficient of variation, repeatability, and residual signal. Moreover, tests have been performed to evaluate their plastic resistance when heated at a temperature higher than 240 ∘ C . Results are reported and discussed.

High-Dose Radioimmunotherapy with 90Y-Ibritumomab Tiuxetan: Comparative Dosimetric Study for Tailored Treatment

High-dose (90)Y-ibritumomab tiuxetan therapy and associated autologous stem cell transplantation (ASCT) were applied after dosimetry. This paper reports dosimetric findings for 3 different methods, including image corrections and actual organ mass corrections. Our first goal was to identify the most reliable and feasible dosimetric method to be adopted in high-dose therapy with (90)Y-ibritumomab tiuxetan. The second goal was to verify the safety of the prescribed activity and the best timing of stem cell reinfusion. Twenty-two patients with refractory non-Hodgkin's lymphoma were enrolled into 3 activity groups escalating to 55.5 MBq/kg. A somewhat arbitrary cutoff of 20 Gy to organs (except red marrow) was defined as a safe limit for patient recruitment. ASCT was considered of low risk when the dose to reinfused stem cells was less than 50 mGy. (111)In-Ibritumomab tiuxetan (185 MBq) was administered for dosimetry. Blood samples were collected up to 130 h after injection to derive individual blood clearance rates and red marrow doses. Five whole-body images were acquired up to 7 d after injection. A transmission scan and a low-dose CT scan were also acquired. The conjugate-view technique was used, and images were corrected for background, scatter, and attenuation. Absorbed doses were calculated using the OLINDA/EXM software, adjusting doses for individual organ masses. The biodistribution data were analyzed for dosimetry by the conjugate-view technique using 3 methods. Method A was a patient-specific method applying background, scatter, and attenuation correction, with absorbed doses calculated using the OLINDA/EXM software and doses adjusted for individual organ masses and individually estimated blood volumes. Method B was a reference method using the organ masses of the reference man and woman phantoms. Method C was a simplified method using standard blood and red marrow volumes and no corrections. The medians and ranges (in parentheses) for dose estimates (mGy/MBq) according to method A were 1.7 (0.3-3.5) for lungs, 2.8 (1.8-10.6) for liver, 1.7 (0.6-3.8) for kidneys, 1.9 (0.8-5.0) for spleen, 0.8 (0.4-1.0) for red marrow, and 2.8 (1.3-4.7) for testes. None of patients had to postpone ASCT. Absorbed doses from method B differed from method A by up to 100% for liver, 80% for kidneys, 335% for spleen, and 80% for blood because of differences between standard and actual masses. Compared with method A, method C led to dose overestimates of up to 4-fold for lungs, 2-fold for liver, 5-fold for kidneys, 7-fold for spleen, 2-fold for red marrow, and 2-fold for testes. Patient-specific dosimetry with image correction and mass adjustment is recommended in high-dose (90)Y-ibritumomab tiuxetan therapy, for which liver is the dose-limiting organ. Overly simplified dosimetry may provide inaccurate information on the dose to critical organs, the recommended values of administered activity, and the timing of ASCT.

A simple geometric algorithm to predict optimal starting gantry angles using equiangular‐spaced beams for intensity modulated radiation therapy of prostate cancer

A fast, geometric beam angle optimization (BAO) algorithm for clinical intensity-modulated radiation therapy (IMRT) was implemented on ten localized prostate cancer patients on the Radiation Therapy Oncology Group (RTOG) 0126 protocol. The BAO algorithm computed the beam intersection volume (BIV) within the rectum and bladder using five and seven equiangular-spaced beams as a function of starting gantry angle for comparison to the V 75 Gy and V 70 Gy. A mathematical theory was presented to explain the correlation of BIV with dose and dose-volume metrics. The class solution 'W' pattern in the rectal V 75 Gy and V 70 Gy as a function of starting gantry angle using five equiangular-spaced beams (with two separate minima centered near 20 degrees and 50 degrees) was reproduced by the 5 BIV within the rectum. A strong correlation was found between the rectal 5 BIV and the rectal V 75 Gy and V 70 Gy as a function of starting gantry angle. The BAO algorithm predicted the location of the two dosimetric minima in rectal V 75 Gy and V 70 Gy (optimal starting gantry angles) to within 5 degrees. It was demonstrated that the BIV geometric variations for seven equiangular-spaced beams were too small to translate into a strong dosimetric effect in the rectal V 75 Gy and V 70 Gy. The relatively flat distribution with starting gantry angle of the bladder V 75 Gy and V 70 Gy was reproduced by the bladder five and seven BIV for each patient. A geometric BAO method based on BIV has the advantage over dosimetric BAO methods of simplicity and rapid computation time. This algorithm can be used as a standalone optimization method or act as a rapid calculation filter to reduce the search space for a dosimetric BAO method. Given the clinically infeasible computation times of many dosimetric beam orientation optimization algorithms, this robust geometric BIV algorithm has the potential to facilitate beam angle selection for prostate IMRT in clinical practice.

A dosimetric calibration method for a double‐focused multileaf collimator

A method based on penumbra measurements and not on light field, is proposed for the calibration of the Siemens 82-leaf Optifocus multileaf collimator (MLC). The measurements were performed using MLCSoft version 1.2.0.4. (PTW-Freiburg, Germany), which is a software tool based on the LA48 measuring system (a linear array of 47 liquid-ionization chambers). The new leaf positions for each of the leaf banks are calculated from the MLCSoft results using an external spreadsheet. Using the proposed method the MLC calibration is directly performed in terms of dosimetry settings with improved precision. The nominal resulting accuracy of 0.5 mm is highly imposed by the limitations of the moving mechanism of the leaves and not by the method itself. To test the results of the MLC calibration, in-water measurements of off-axis dose profiles have been measured in order to verify different field sizes.

IMAT‐SIM: A new method for the clinical dosimetry of intensity‐modulated arc therapy (IMAT)

Dynamic-gantry multi-leaf collimator (MLC)-based, intensity-modulated radiotherapy (IMAT) has been proposed as an alternative to tomotherapy. In contrast to fixed-gantry, MLC-based intensity-modulated radiotherapy (IMRT), where commercial treatment planning systems (TPS) or dosimetric analysis software currently provide many automatic tools enabling two-dimensional (2D) detectors (matrix or electronic portal imaging devices) to be used as measurement systems, for the planning and delivery of IMAT these tools are generally not available. A new dosimetric method is proposed to overcome some of these limitations. By converting the MLC files of IMAT beams from arc to fixed gantry-angle modality, while keeping the leaf trajectories equal, IMAT plans can be both simulated in the TPS and executed as fixed-gantry, sliding-window DMLC treatments. In support of this idea, measurements of six IMAT plans, in their double form of original arcs and converted fixed-gantry DMLC beams (IMAT-SIM), have been compared among themselves and with their corresponding IMAT-SIM TPS calculations. Radiographic films and a 2D matrix ionization chamber detector rigidly attached to the accelerator gantry and set into a cubic plastic phantom have been used for these measurements. Finally, the TPS calculation-algorithm implementations of both conformal dynamic MLC arc (CD-ARC) modalities, used for clinical IMAT calculations, and DMLC modalities (IMAT-SIM), proposed as references for validating IMAT plan dose-distributions, have been compared. The comparisons between IMAT and IMAT-SIM delivered beams have shown very good agreement with similar shapes of the measured dose profiles which can achieve a mean deviation (+/-2sigma) of (0.35+/-0.16) mm and (0.37+/-0.14)%, with maximum deviations of 1.5 mm and 3%. Matching the IMAT measurements with their corresponding IMAT-SIM data calculated by the TPS, these deviations remain in the range of (1.01+/-0.28) mm and (-1.76+/-0.42)%, with maximums of 3 mm and 5%, limits generally accepted for IMRT plan dose validation. Differences in the algorithm implementations have been found, but by correcting CD-ARC calculations for the leaf-end transmission offset (LTO) effect the IMAT and IMAT-SIM simulations agree well in terms of final dose distributions. The differences found between IMAT and the IMAT-SIM beam measurements are due to the different controls of leaf motion (via electron gun delay in the latter) that cannot be used in the former to correct possible speed variations in the rotation of the gantry. As the IMAT delivered beams are identical to what the patient will receive during the treatment, and the IMAT-SIM beam calculations made by the TPS reproduce exactly the treatment plans of that patient, the accuracy of this new dosimetric method is comparable to that which is currently used for static IMRT. This new approach of 2D-detector dosimetry, together with the commissioning, quality-assurance, and preclinical dosimetric procedures currently used for IMRT techniques, can be applied and extended to any kind of dynamic-gantry MLC-based treatment modality either CD-ARC or IMAT.