Radiation Physicists Research Articles

TH‐D‐224C‐02: The State of Radiotherapy Physics Through The Eyes of a Quality Auditor

Purpose: To assess the radiotherapy programs of institutions participating in NCI sponsored clinical trials and assist them to implement remedial actions. Materials and Methods: The Radiological Physics Center (RPC) has developed an extensive Quality Assurance (QA) program over the past 38 years. This program includes on‐site dosimetry reviews where measurements on therapy machines are made, records are reviewed and personnel are interviewed. The program's remote audit tools include mailed dosimeters (TLD) to verify output calibration, comparison of dosimetry data with RPC “standard” data, evaluation of benchmarkd and patient calculations to verify the treatment planning algorithms, review of institution's QA procedures and records, and use of anthropomorphic phantoms to verify tumor dose delivery. The RPC assists institutions in finding the origins of discrepancies, and in resolving them. Results: The percent of institutions receiving dosimetry recommendations has been level at 70% for the past 5 years. The most frequent recommendations were for maintenance of an appropriate QA program, beam calibration, depth dose and wedge factors. Since TG‐51 was published, the number of reference calibrations meeting the RPC's ±3% criterion has decreased. The TLD program shows that only ∼3% of the beams are outside our ±5%/±5mm criteria, but these discrepancies are distributed over nearly 15% of the institutions. There continues to be a 33% percent first time failure rate for the IMRT H&N anthropomorphic phantom. The other anthropomorphic phantoms, i.e. pelvic IMRT, lung stereotactic and liver stereotactic, have higher pass rates. Conclusion: Numerous dosimetry errors continue to exist and the RPC's QA program plays an important role in identifying and helping institutions resolve these errors to improve not only the quality of clinical trial patients' treatments, but also all patients treated at the participating institution.This work was supported by PHS grants CA10953 and CA081647 awarded by NCI.

Patterns of care for brachytherapy in Europe results in Spain

In 2003 ESTRO began a project whose primary objective, was to make a map in the European area of infrastructures in technology and personnel for brachytherapy. A survey and a web site were elaborated. The survey was sent to the 76 Spanish Radiation Oncology departments in May 2003. By the end of 2003, 66 (86.8%) services had responded, 40 (71.4%) of which had brachytherapy. The services with brachytherapy treated 73.5% of the total patients, an average of 1,199 patients. The mean number of patients treated with brachytherapy by department was 135.5 and the number of applications was 265 annually. The average number of specialists was 7, 4 of them trained in brachytherapy. The average weekly work load of the radiation oncologists, physicists, and technicians was 22.6 h, 13.8 h and 21.0 h, respectively. The mean time dedicated to each patient by radiation oncologists, physicists and technicians was 9.2 h; 6.19 h; 7.2 h, respectively. The total number of afterloaders was 43 (22 HDR, 18 LDR, 3 PDR). The tumours most frequently treated with brachytherapy were gynaecological (56.24%), breast (14.2%) and prostate (11.7%). High dose rate was used in 47.46% of the patients and low dose rate in 47.24%. Between 1997 and 2002 there was an increase of 50.53% in patients treated with brachytherapy. The survey shows the brachytherapy resources and activity in Spain up to 2003. Increased use of brachytherapy in prostate tumours, prevalence of gynaecology brachytherapy and similar number of treatments with HDR and LDR are demonstrated in the Patterns of Care of Brachytherapy in Europe (PCBE) study in Spain.

A CLINICAL EVALUATION OF THE OPTICAL CHARACTERISTICS OF THE PROSTATE IN MEN WITH PROSTATE CANCER

Introduction & Objectives The use of lasers is becoming increasingly common in urology, particularly in the prostate. Low power laser is used in photodynamic therapy in order to activate a photosensitising drug. The extent of the photodynamic effect is dependent upon the optical characteristics of the prostate. These characteristics, which encompass both scattering and absorption, can be expressed as the depth of penetration of the laser energy. We report a study using 763nm light to assess variability in laser penetration depth throughout the prostate. Material & Methods The study was carried out in patients having high dose rate brachytherapy (HDRB). These patients have up to 22 hollow clear plastic needles in the prostate for 36 hours. The needles are inserted under general anaesthetic, using transrectal ultrasound and a perineal template. A CT scan is taken once the patient is awake, and the radiotherapy dose is planned by the radiotherapy medical and physics team. The radiotherapy dose is given by sliding an iridium wire along each needle, which rests at different positions along the needle for different times. The doses are given 6, 24 and 30 hours after needle placement. Prior to the first radiotherapy dose, we used the needles to position optical delivery and detection fibres in multiple positions throughout the prostate. A 763 nm laser was used to deliver light via a 2cm diffusing fibre. An isotropic optical detector was slid along nearby needles, and optical readings taken every 6mm. The exact separation distance of the delivery and detector fibre at each of the optical measurement positions was then measured on different slices of the CT scan. The Boltzmann approximation to the transport equation was used to calculate the penetration depth (PD), which is defined as the depth at which 63% of light intensity is lost. Results Over 1000 data points in 8 patients were assessed. The mean PD was 3.7 mm with a range of 1.35 - 33 mm. The PD varied within patients by up to a factor of up to 12 times, with the mean variation within an individual patient of 4 times. Between patient variability of the PD was not as significant as intra patient variability. From examination of the CT scans of the patients it was not possible to identify any factors which would predict PD. Conclusions This study shows that there is marked variability of laser penetration both within and between patients with prostate cancer. It will be important to see if this translates to a difference in therapeutic effect in treatments which use lasers, in this patient group.

Lauriston Sale Taylor

Lauriston Sale Taylor

A research program in medical physics for remote students

The University of Adelaide in co-operation with the Royal Adelaide Hospital offers a degree of Master of Science (Medical Physics) which is available both to students resident in Adelaide and to remote students employed in hospitals in Australia or New Zealand. The program comprises research carried out in the work place, and courses delivered from Adelaide. The courses Radiation Biology, Protection and Epidemiology and Radiotherapy Physics are currently delivered on-line. A project has commenced to modify the presentation of all courses so that remote students can interact with their fellow students in weekly tutorials and engage in informal discussions through a discussion forum.

Over the next decade the success of radiation treatment planning will be judged by the immediate biological response of tumor cells rather than by surrogate measures such as dose maximization and uniformity.

Over the next decade the success of radiation treatment planning will be judged by the immediate biological response of tumor cells rather than by surrogate measures such as dose maximization and uniformity.

WE‐D‐T‐6C‐03: Development of Image Software Tools for Radiation Therapy Assessment

There has been extensive recent interest in the potential power of emerging imaging tools for early prediction of therapy effectiveness, both related to tumor control and normal tissue damage. These prognostic indicators are the results of combining improved imaging hardware, specialized scanning protocols, and advanced image processing and analysis paradigms. In order to study and eventually use these tools routinely in the radiotherapy process, serious consideration needs to be given to the software environment necessary for proper data collection and analysis ties to individual patients' treatments. Imaging for therapy assessment (IAT) presents a multidimensional information environment, requiring data from different imaging modalities and acquisition methods, as well as handling temporal data series, combined over short (breathing, dynamic contrast) and long (temporal changes over weeks of treatment) time periods. The information needed for relating these data sets for analysis (non‐rigid transformations, proper labeling of studies to measurement states) exceeds the capacities of existing DICOM standards. The extraction of analyzed information and relation to regional (radiation) dose should be multidimensional, and not restricted to voxel‐specific regions. Examples of imaging studies underway for therapy assessment will be presented. Software requirements will be demonstrated through an example system currently in use to support clinical trials at the University of Michigan. This system was designed around the unique needs of IAT, and is able to combine information from multiple sources (e.g., MRI, MRS, CT, PET, radiation dose) and time periods in an intuitive interface. This system has been used for studies of blood flow and volume, regional venous perfusion, vascular permeability, water diffusion, metabolite, and local contrast enhancement for high dose radiotherapy trials in the brain, lung, and liver to date.Educational Objectives:1. Understanding the unique needs related to imaging for assessment of radiation therapy.2. Understanding the required tools beyond those found in a typical treatment planning system3. Understanding a common ground needed for combining efforts of imaging physicists, radiation physicists, physicians and statisticians.4. Understanding opportunities for novel paradigm and algorithm development

SU‐FF‐E‐03: RadSim, a Program to Simulate Individual Radiation Interactions for Teaching Purposes

Purpose: To develop a computer program to simulate individual particle interactions in a visual way, as a teaching aid in radiotherapy physics. Method and Materials: A program, RadSim, was developed using the RealBasic software development environment. A Graphical User Interface allows users to select individual interactions to be simulated for photons, electrons and positrons in the energy range encompassing radiation oncology (1 keV — several hundred MeV). The program is designed to operate in two modes. In the Manual mode a single interaction is performed. In the Simulated mode the user can run a short Monte Carlo simulation for a small number of particles. In the latter mode statistics on the interaction variables are displayed graphically. The program is made available in versions for the Windows, Linux and Mac operating systems, via free download from a website. Results: The user can simulate the following types of interactions: for photons: Compton scatter, photoelectric effect with characteristic x‐rays, Rayleigh scattering and pair‐production, for electrons: inelastic nuclear scattering with Bremsstrahlung production, electron‐electron scattering, for positrons: Bhabha scattering and annihilation. The Manual mode allows visual evaluation of kinematic equations. The user can initialize any combination of a minimally required set of interaction variables and the program evaluates the remaining variables, and displays the interaction visually showing incoming and outgoing particles. In the Simulated mode, the user can only change the kinetic variables of the initial particle. The final state of all particles involved is generated from a Monte Carlo simulation. The user defines the number of particles used in the simulation and frequency distributions are displayed during the simulation so that the user can watch the distributions grow. Conclusion: The program RadSim enables virtual radiation experiments in the classroom and for self‐learning and is found to be a useful addition to textbook teaching.

Accuracy of the photon and electron physics in GEANT4 for radiotherapy applications

This work involves a validation of the photon and electron transport of the GEANT4 particle simulation toolkit for radiotherapy physics applications. We examine the cross sections and sampling algorithms of the three electromagnetic physics models in version 4.6.1 of the toolkit: Standard, Low-energy, and Penelope. The depth dose distributions in water for incident monoenergetic and clinical beams are compared to the EGSNRC results. In photon beam simulations, all three models agree with EGSNRC to within 2%, except for the buildup region. Larger deviations are found for incident electron beams, and the differences are affected by user-imposed electron step limitations. Particle distributions through thin layers of clinical target materials, and perturbation effects near high-Z and low-Z interfaces are also investigated. The electron step size artifacts observed in our studies indicate potential problems with the condensed history algorithm. A careful selection of physics processes and transport parameters is needed for optimum efficiency and accuracy.

My Life in Science, Not the Restaurant Business

My Life in Science, Not the Restaurant Business

Peter Wootton

Peter Wootton

Clinical Radiotherapy Physics. 2nd edition

Clinical Radiotherapy Physics. 2nd edition

Management issues in radiotherapy physics: a census of heads of radiotherapy physics in the nhs

an investigation of human resource issues in radiotherapy physics services in the nhs, including an evaluation of the extent to which the management of human resources was strategic, was undertaken as part of mba level research by a radiotherapy clinical scientist. the research incorporated a telephone census of heads, or acting heads, of radiotherapy physics services. this census looked at the establishment and scale of radiotherapy physics services, issues around recruitment and flexibility, business management, strategy and strategy formation and human resource management practices.a 96% response rate was obtained with 55 out of a potential population of 57 subjects participating in the survey. it was found that at the time of the survey, 11.0% of all radiotherapy physicist posts were vacant. this was due predominantly to recruitment difficulties. furthermore, 42% of radiotherapy physicists in post were relatively inexperienced, having spent less than 6 years in the discipline. eighty-seven per cent of services had re-graded radiotherapy physicist posts in order to recruit. additionally, 53% of services had changed their skill mix by increasing the ratio of technologists to physicists. fifty-nine per cent of those services did so because of difficulties in recruiting radiotherapy physicists.whereas 38 respondents (69% of total) said they had a human resource strategy linked to the service's business strategy, only 12 respondents (22% of total) claimed to undertake appraisal and training needs analyses coupled with personal development plans and continuing professional development. relatively little succession planning was undertaken, and only 14 services (26% of total) had well-developed succession plans.recommendations are made as to how human resource management in nhs radiotherapy physics services could be more strategic.

The shortage of radiotherapy physicists

The difficulties many radiotherapy facilities have in hiring new medical physicists indicate a shortage in the production and supply of these specialists. It appears that about 130 out of 350 new positions go unfilled each year. This projection matches well with the estimate that around 217 new medical physicists graduate per year. The problem is likely to become worse as a large cohort of practitioners reach retirement age in a couple of years. The radiotherapy physicists in the field tend to be working longer and harder, potentially leading to burnout or increases in errors. Addressing the difficulty in finding trained medical physicists, some facilities may start hiring untrained physicists or assigning technological personnel to perform the functions of a medical physicist, both of which could pose dangerous situations. While more physics undergraduates are showing interest in medical physics as a career, and medical physics graduate programs have increased enrollment by more than 30% over the last two years, further significant increases seem unlikely soon because of limited resources. Increasing resources (mostly faculty at the teaching universities) will require more research funding from governmental agencies—a situation unlikely in the near future. New mechanisms of funding medical post-graduate education are needed.

Guidelines for education and training of medical physicists in radiotherapy: Recommendations from an ESTRO/EFOMP working group

PurposeTo provide a guideline curriculum covering theoretical and practical aspects of education and training for medical physicists in radiotherapy within Europe. Material and methodsGuidelines have been developed for the specialist theoretical knowledge and practical experience required to practice as a medical physicist in radiotherapy. It is assumed that the typical entrant into training will have a good initial degree in the physical sciences, therefore these guidelines also require that and are additional to it. National training programmes of medical physics, radiation physics and radiotherapy physics from a range of European countries and from North America were reviewed by an expert panel set up by the European Society of Therapeutic Radiology and Oncology (ESTRO) and the European Federation of Organisations for Medical Physics (EFOMP). A draft document prepared by this group was circulated, via the EFOMP infrastructure, among national professional medical physics societies in Europe for review and comment and was also discussed in an education session in the May 2003 EFOMP scientific meeting in Eindhoven. ResultsThe resulting guideline curriculum for education and training of medical physicists in radiotherapy within Europe discusses the EFOMP terms, qualified medical physicist (QMP) and specialist medical physicist (SMP), and the group's view of the links to the EU (Directive 97/43) term, medical physics expert (MPE). The minimum level expected in each topic in the theoretical knowledge and practical experience sections is intended to bring trainees up to the requirements of a QMP. The responses from the circulation of the document to national societies and its discussion were either to agree its content, with no changes required, or to suggest changes, which were taken into account after consideration by the expert group. Following this the guidelines have been endorsed by the parent organisations. ConclusionsThis new joint ESTRO/EFOMP European guideline curriculum is a first step to harmonise specialist training of medical physicists in radiotherapy within Europe. It provides a common framework for national medical physics societies to develop or benchmark their own curricula, but is also flexible enough to suit different situations of initial physics qualifications, medical physics training programmes, accreditation structures, etc. The responsibility for the implementation of these standards and guidelines will lie with the national training bodies and authorities.

Current status and potential perspectives in classical radiotherapy technology

After purchase of radiotherapy equipment in 2003, classic radiation therapy in Serbia will reach the highest world level. In order to define the highest standards in radiation technology, we analyzed the current status and potential perspectives of radiation therapy. An analysis of present situation in the USA, assumed as the most developed in the world, was done. Available data, collected in the last 3 years (equipment assortment, therapy modalities, workload and manpower) for 284 radiotherapy centers, out of potential 2050, were analyzed. Results were presented as crude percentage and matched to point current status. The analysis showed that CLINAC accelerators are the most popular (82.7%), as well as, ADAC (43.7%) and Focus (CMS) (27.4%) systems for therapy planning. Movement towards virtual simulation is evident (59.3%), although classic "simulation" is not fully eliminated from the radiotherapy chain. The most popular brachytherapy afterloader is Microselectron HDR (71%). About 64.4% centers use IMPAC communication/verification/record system that seems more open than Varis. All centers practice modern radiotherapy modalities and techniques (CPRT, IMRT, SRS/SRT, TBI, IORT, IVBHRT, HDR BHRT, etc.). CT and MRI availability is out of question, but PET is available in 3% of centers, however this percentage is rapidly growing. Up to 350 new patients per year are treated by one accelerator (about 35 pts. a day). Centers are relatively small and utilize 2-3 accelerators on average. Average FTE staffing norm is 4 radiation oncologists, 2-3 medical radiotherapy physicists, about 3 certified medical dosimetrists and about 6 radiotherapy technologists. In the past 5 years relative stagnation in classic radiotherapy has been observed. In spite of substantial investments in technology and consequent improvements, as well as wide introduction of computers in radiotherapy, radiotherapy results have not changed significantly. Vendor developement strategies do not point that this trend will change in the next 5 years. On the other hand, wide introduction of the PET in each radiotherapy chain ring (diagnostics, planning, follow-up), could improve results (local and regional control, as well as quality of patients' life).

Protocolo de tratamiento en un servicio de Oncología Radioterápica para minimizar la dosis al embrión-feto en mujeres embarazadas

This report presents the radiotherapy protocol developed at the Hospital Universitario de la Princesa to minimize fetal dose in women requiring radiotherapy during pregnancy. Information necessary for determining the potential effects of radiotherapy affecting the developing fetus include the gestational age, absorbed fetal dose-equivalent and dose-rate. It is essential for a radiation physicist to perform a fetal dose estimation prior to initiation of radiation therapy. Radiation oncologist should inform pregnant patients about recommendations and the possible side effects in the developing fetus. This information may be included in the informed consent. Both, the radiation oncologist and the radiation physicist, should study the cost/benefit of the different techniques for decreasing fetal exposure.

VERIDOS: a new tool for quality assurance for intensity modulated radiotherapy.

The use of intensity modulated radiation fields needs an extended quality assurance concept. This consists of a linac related part and a case related part. Case related means the verification of an individual treatment plan, optimized on a CT data set of an individual patient and prepared for the treatment of this patient. This part of the quality assurance work is usually time consuming, delivers only partially quantitative results and is uncomfortable without additional help. It will be shown in this paper how the software VERIDOS will improve the optimization of the case related part of the quality assurance work. The main function of the software is the quantitative comparison of the calculated dose distribution from the treatment planning software with the measured dose distribution of an irradiated phantom. Several additional functions will be explained. Two self-developed phantoms made of RW3 (solid water) and GAFCHROMIC films or Kodak EDR2 films for the measurement of the dose distributions were used. VERIDOS was tested with the treatment planning systems Helay-TMS and Brainscan. VERIDOS is a suitable tool for the import of calculated dose matrices from the treatment planning systems Helax-TMS and Brainscan and of measured dose matrices exported from the dosimetry software Mephysto (PTW). The import from other treatment planning systems and scanning software applications for film dosimetry is generally possible. In such case the import function has to be adapted to the special header of the import matrix. All other functions of this software tool like normalization (automatically, manually), working with corrections (ground substraction, factors), overlay/comparison of dose distributions, difference matrix, cutting function (profiles) and export functions work reliable. VERIDOS improves the optimization of the case related part of the quality assurance work for intensity modulated radiation therapy (IMRT). The diverse functions of the software offer the radiation physicist a wide base to verify the IMRT plan independent from the mode of its delivery (compensator technology or MLC technology).

Polymer gels for magnetic resonance imaging of radiation dose distributions at normal room atmosphere

Polymer gels whose NMR and optical properties change when irradiated offer unique advantages for measuring radiation dose distributions. To date, all acrylic polymer gel dosimeters must be manufactured, stored and irradiated in hypoxic conditions which severely limits their use and stability. A new formulation of acrylic dosimeter gel has been developed that responds well in normal atmosphere and which we have named MAGIC (Methacrylic and Ascorbic acid in Gelatin Initiated by Copper). To produce dosimeter gels, an aqueous solution of gelatin, open to the atmosphere, is mixed with methacrylic acid, copper(II) ions, ascorbic acid and hydroquinone. It is believed that the copper(II) and ascorbic acid form a complex with oxygen which (with radiolysis of water) serves as a free radical source for the initiation of the polymerization of methacrylic acid. At room air the water proton spin relaxation rate R2 in MAGIC gels is proportional to absorbed dose though the precise relationship depends on the composition of the gel and the initiating complex. For example, in the range 0–30 Gy the slope of the response of R2 versus dose at 20 MHz was 0.300, 0.519 and 0.681 s−1 Gy−1, respectively, when the concentration of MAA was 3, 6 and 9%. The slopes increased to 0.310, 0.567 and 0.868 s−1 Gy−1 at 85 MHz. An important determinant of the sensitivity to detect small dose changes is shown to be the slope-to-intercept ratio of the dose–response curve. These varied from 0.08 to 0.17, comparable to hypoxic gels described earlier. MAGIC gels can be manufactured and used much more easily than the previous formulations and can be imaged by magnetic resonance imaging or optical scanning, and thus they will likely be of considerable interest to radiation physicists.

EGS-Ray, ein Programm zur Visualisierung von Monte-Carlo-Rechnungen in der Strahlenphysik

A Windows program is introduced which allows a relatively easy and interactive access to Monte Carlo techniques in clinical radiation physics. Furthermore, this serves as a visualization tool of the methodology and the results of Monte Carlo simulations. The program requires only little effort to formulate and calculate a Monte Carlo problem. The Monte Carlo module of the program is based on the well-known EGS4/PRESTA code. The didactic features of the program are presented using several examples common to the routine of the clinical radiation physicist.