Radiation Physicists Research Articles

Education and Training: Medical Physicists and Engineers

The primary purpose of this paper is to discuss the education and training needs and practice for physicists working in medical X ray imaging. There is also brief reference to similarities and differences in the training of engineers. First the role and responsibilities of clinical scientists in health care is reviewed in very general terms and then the best way to train for this role in medical physics, specifically as applied to diagnostic radiology, is considered. This part of the presentation draws heavily on the work of the European Federation of Organisations of Medical Physics (EFOMP). The second part of the paper reviews the new requirements and opportunities presented to radiation physicists by the recent Medical Exposures Directive (97/43). Ways in which physicists should be responding to these challenges, especially by harmonisation of standards through national registration schemes and continuing professional development are considered.

Development of Radiation Therapy Optimization

The principal radiobiological problems in the treatment of advanced tumors and the solution of many of them by radiobiologically optimized intensity-modulated radiation therapy are presented. Considerable improvements of the treatment outcome using radiobiologically optimized intensity-modulated treatments are achieved by: (a) increasing the tumor dose and dose per fraction; (b) keeping constant or even reducing slightly the dose and dose per fraction to organs at risk; (c) reducing the overall treatment time and the number of treatment fractions. The merits of the new radiation modalities and advanced intensity-modulated treatment techniques are compared in terms of equipment costs per patient cured. It is predicted that the new development of radiobiologically optimized intensity-modulated radiation therapy will rapidly become an important clinical tool, increasing the efficiency of the collaboration between radiation physicists, radiation biologists and radiation oncologists. Not only does it allow the optimal treatment of every patient, but it also promotes an efficient feedback of treatment outcome and complication data to improve the accuracy of known dose response relations to further augment future treatment results. Equipment costs may go up during a transition period until efficient interfaces between new diagnostic equipment, treatment-planning systems and intensity-modulated treatment units are fully developed. From then onwards the cost of high quality biologically optimized intensity-modulated treatments will decrease and so will the treatment time and personnel requirements, at the same time as the treatment quality is greatly improved particularly for more advanced tumors.

Practical Radiotherapy: Physics and Equipment

Contributors. Preface. Acknowledgements. Chapter 1 Basic skills for radiotherapy physics ( Elaine Ryan). Chapter 2 X-ray production ( Elaine Ryan). Chapter 3 Radiation dosimetry ( Janette Chianese and Fiona Chamberlain). Chapter 4 X-ray interactions with matter ( Kathryn Cooke). Chapter 5 Pre-treatment imaging ( Caroline Wright, Jonathan McConnell and Katheryn Churcher) Chapter 6 Simulation equipment ( Alan Needham). Chapter 7 Immobilisation equipment ( Helen and Nick White). Chapter 8 Megavoltage equipment ( David Flinton and Elizabeth Miles). Chapter 9 Kilovoltage equipment ( David Flinton). Chapter 10 Treatment planning and computer systems ( John Conway and Christopher M Bragg). Chapter 11 Methods of beam direction ( Anne Jessop). Chapter 12 Advanced treatment delivery ( Pete Bridge). Chapter 13 Treatment verification ( Cath Holborn). Chapter 14 Introduction to radiation protection ( Pete Bridge). Chapter 15 Use of radionuclides in imaging and therapy ( David Duncan). Chapter 16 Sealed sources in radiotherapy ( Tony Flynn and Bruce Thomadsen). Appendix Self-test answers. Index.

Intracoronary artery radiation.

This very successful meeting, commissioned by the Radiation Protection Committee of The British Institute of Radiology, was the ®rst UK symposium on this new clinical topic. Over 100 delegates from departments of cardiology, clinical oncology, radiation physics and industry attended this fascinating meeting, which provided not only important information about standard practices in each discipline but advanced insights into the physical (mechanical and radiation), biological and medical factors that interact in the use of radiotherapy to prevent intracoronary artery restenosis after angioplasty. A lucid description of the present management of atheromatous coronary narrowing by percutaneous angioplasty and stent insertion was given by Dr AH Gershlick (Leicester). The angioplasty balloon transmits 8±10 atmospheres of hydraulic pressure to split the atheromatous plaque and simultaneously dilate the arterial wall. This results in oedema and an in ammatory response controlled by speci®c growth factors that induce (via fos and c-myc receptors) a proliferation of smooth muscle cells derived from the adventitia. In approximately 40±50% of patients this process invades the media and breaches the disrupted internal elastic lamina, resulting in narrowing of the arterial lumen owing to a thickened neo-intima (initimal hyperplasia), a process called negative remodelling [1]. The alternative therapeutic approach is to perform a stent insertion, which in favourable situations termed benestent (short, proximal lesions) reduces restenosis to 10±15%. A larger restenosis rate (up to 40%) occurs in complex, distal lesions and in diabetic patients. It is apparent that the stent itself does not inhibit intimal hyperplasia but maintains vessel patency by its physical presence. Restenosis, particularly if diffuse, is dif®cult to treat. Reballooning restenosis rates are around 60%. Debulking by mechanical devices (rotablator or directional atherectomy) may help, but the most promising technique is brachytherapy (short range radiation therapy using sealed radioactive isotopes). Otherwise, coronary artery bypass grafts may be necessary. As yet, no bene®t has been detected in 38 clinical trials of drug therapy designed to reduce this process. The physics of radiotherapy in this situation were considered by Mr S Bachelor (Guy's Hospital, London). Brachytherapy by temporary intracoronary insertion of a radioactive source must be completed in less than 15 min because of the risks of protracted vascular occlusion: such treatments need high activity source(s) and must be delivered at a high dose rate. In contrast, radioactive-coated stents may deliver low dose rate treatment (with a reduction in biological effect so that higher doses may need to be given). Beta emitters (P and Y) and gamma emitters (Ir and I) can be used, although the prescribed dose will depend on the class of radiation owing to fall off characteristics. Gamma emitters are indicated for larger vessels. Several commercially produced narrow gauge afterloading catheters and intralumenal centralization devices are now available for intracoronary and peripheral artery brachytherapy. Dr WG Bass (Washington, USA) provided further physics information. Beta radiation duration is usually shorter, but there may be dose inhomogeneities due to remaining calcium plaques in the vessel wall. In order to treat the entire vessel media, the radiation dose should be adequate as far as the adventitia, which is approximately 3 mm from the central lumen in most affected coronary arteries. The dose is most frequently prescribed at 2 mm, but the target may be non-uniform. Table 1 shows the dose±distance relationships for Y and Ir. The use of b or c radiation emitters for brachytherapy requires additional radiation protection in cardiac catheter theatres/laboratories. Additional shielding around the patient requires a different geometry to that used for uoroscopy. Personnel shielding devices can be used but are of limited bene®t with penetrating gamma radiations such as Ir. Additional personnel, such as a radiation physicist and radiation oncologist, are required to be present at the procedure in the USA. Personnel are not allowed in the treatment room during therapy with Ir and additional wall shielding is required for safety in adjacent Received 14 May 1999 and accepted 8 July 1999.

Spreadsheet calculations of absorbed dose to water for photons and electrons according to established dosimetry protocols

The calculation of absorbed dose to water according to a Code of Practice demands a strict adherence to the rules and data of the protocol. To ease the calculations and to avoid computational and methodological errors, we have developed a number of spreadsheets to perform the calculations in accordance with an established dosimetry protocol—in our case those of the International Atomic Energy Agency (IAEA) and the Institution of Physics and Engineering in Medicine and Biology (IPEMB). The spreadsheets are implemented as Microsoft Excel V5.0 worksheets. Only a limited selection of dosimetry equipment is used for calibration, which is performed according to only one of the methods allowed by the protocol. This voluntary limitation of equipment and methods is reflected in a spreadsheet that is beam-specific, compact, focused, and very practical. There are four main spreadsheets: high-energy photons (IAEA), high-energy electrons (IAEA), medium energy X rays (IPEMB), and low-energy X rays (IPEMB). The sheets allow the input of setup and measured data, but tabulated data and formulas are protected. Parameter values are copied from the protocols, and the relevant value is found by linear interpolation. Once the spreadsheets are drawn up correctly and thoroughly checked, protocol calculations are performed easily and accurately. The spreadsheets presented are tailored to suit our specific needs but can easily be modified to conform to the practices of any other institution. They are not intended as “cookbooks” but need to be filled in by a radiation physicist with the input data checked by a second professional. The same method is also used for calculating the Reference Air Kerma Rate of brachytherapy sources.

A survey of in vivo diode dosimetry in the UK

A clear rationale exists for routine in vivo dosimetry as part of an overall quality assurance (QA) programme within a radiotherapy department. A survey was undertaken in order to identify the extent of diode dosimetry practice within the UK.Questionnaires were distributed to 57 radiotherapy physics departments in the UK in order to determine the extent of central axis diode dosimetry and the protocols implemented, the range of other in vivo measurements performed using diodes and the type of equipment used. Fifty-four responses were received. Eighteen departments undertook some form of central axis entrance dosimetry. Fifteen departments could be considered to be doing this routinely. Seven departments indicated planned future use. Six centres routinely undertook exit dosimetry with a further 3 indicating planned future use. Varied protocols for use were reported by those centres undertaking central axis dosimetry. Thirty-two respondents used a diode system for other forms of in vivo measurements with critical organ and TBI dosimetry being the most common. The vast majority used Scanditronix equipment.Despite the distinct benefits of central axis diode dosimetry, this continues to be infrequently adopted as part of a departmental QA programme. However, an indication of a number of departments planning to implement such an approach is reassuring.

The american brachytherapy society perspective on intravascular brachytherapy

Background. Recent clinical studies indicate that intravascular brachytherapy (IVB) can reduce the rate of restenosis substantially after angioplasty procedures. However, no clinical guidelines exist for optimal therapy. Methods. The members of the IVB Subcommittee of the American Brachytherapy Society (ABS) identified the areas of consensus and controversies in IVB to issue the ABS perspective on IVB, based on analysis of published reports and the clinical experience of the members in brachytherapy. Results. IVB is still experimental. The long-term efficacy, toxicity, the target tissue, and dose required for IVB are not established. The ABS recommends that IVB procedures must be performed, with careful attention to radiation-related issues, in the context of controlled multidisciplinary clinical trials with the approval of the institutional review board, the Nuclear Regulatory Commission, the Food and Drug Administration, and under an Investigational Device Exemption. The therapeutic radiologist, with a qualified radiation physicist, is responsible for dose prescription and delivery and needs to be present during the IVB procedure as part of this multidisciplinary team. The long-term outcome from these studies should be reviewed critically and published in peer-reviewed journals. The ABS endorsed the dosimetric guidelines of the American Association of Physicists in Medicine Task Group 60 (AAPM TG-60) report. The ABS recommends that dose specification be defined clearly; to allow comparisons between studies, the dose should be prescribed at 2 mm from the source for intracoronary brachytherapy and at an average luminal radius of +2 mm for peripheral vascular brachytherapy. The prescription doses at the above point is generally in the 12–18 Gy range. Comprehensive procedures for quality assurance, radiation protection, and emergencies should be in place before initiating an IVB program. Higher energy beta sources, lower energy gamma sources, dose-volume histograms, and correlation of three-dimensional reconstructions of delivered dose with patterns of failure are areas for further research. Conclusion. The ABS perspective on IVB is presented to assist the interventional team in developing protocols for the use of IVB in the prevention of restenosis. Long-term outcome data with a standardized reporting system are needed to establish the role of brachytherapy in preventing vascular restenosis. Endovascular brachytherapy is a new and evolving modality, and these recommendations are subject to modifications as new data become available.

Book Reviews

Endovascular Treatment of Intracranial AneurysmsMRI Atlas of the Chest: Normal Anatomy and PathologyThe Use of Plane Parallel Ionization Chambers in High Energy Electron and Photon BeamsThe Physics of Radiotherapy X‐Rays from Linear Accelerators

The Physics of Conformal Radiotherapy: Advances in Technology, edited by Steve Webb

<i>The Physics of Conformal Radiotherapy: Advances in Technology</i>, edited by Steve Webb

Building software agents for training systems: A case study on radiotherapy treatment planning

The main aim of this paper is to discuss the design issues and implications that relate to the use of software agents in Training Systems. We have designed and implemented a Radiotherapy Treatment Planning Learning Environment (called RATAPLAN), which incorporates an interface intelligent agent to support training of Simulation Technologists and Radiation Physicists in this knowledge domain. The learning environment consists of an interactive simulation. The interface agent (called Consulta) acts both as demonstrator and assistant to the users. The paper describes in depth the agent's architecture and illustrates the agent–user interaction and communication. With Consulta we promote the collaboration between novice and expert practitioners in Radiotherapy Treatment Planning.

An independent check of treatment plan, prescription and dose calculation as a QA procedure

In many radiotherapy centres where planning for external beam treatments is performed by radiation therapists, the treatment sheet and its calculations are independently checked by staff from a different educational background, typically a radiotherapy physicist. The benefits of this practice were evaluated in a radiotherapy department with two linear accelerators, one combined superficial-orthovoltage unit and one telecaesium unit. Within the 19 months of the investigation period, 2328 checks were performed on the treatment sheets of 1579 patients. In six cases, errors in excess of 5% were detected, which if uncorrected, could potentially have affected local tumour control or caused normal tissue complications. It was found that an independent check of treatment sheets assists in keeping these errors as low as can be achievable in clinical practice, and suggests that treatment sheet checking and in vivo dosimetry play a complementary role in this aim. Independent treatment sheet checking is an important quality assurance (QA) activity, with additional advantages such as improved communication in the department, education of staff and in vivo dosimetry targeting. Therefore the advantages of the procedure seem to outweigh the additional workload of approximately 0.3 full-time staff per 1000 patients per year.

A survey of current in vivo radiotherapy dosimetry practice.

A questionnaire was sent out to 57 radiotherapy physics departments in the United Kingdom to determine the type of dosemeters used for in vivo measurements inside and outside X-ray treatment fields, and whether any correction is made for energy dependence when the dose to critical organs outside the main beam is estimated. 44 responses were received. 11 centres used a semi-conductor for central axis dosimetry compared with only two centres which used thermoluminescent dosimetry (TLD). 37 centres carried out dosimetry measurements outside the main beam; 25 centres used TLD and 12 centres used a semi-conductor detector. Of the 16 centres measuring the dose at both sites. 11 used a semi-conductor for the central axis measurement, but only four of those 11 changed to TLD for critical organ dosimetry despite the latter's lower variation in energy response. None of the centres stated that they made a correction for the variation in detector energy response when making measurements outside the main beam, indicating a need for a more detailed evaluation of the energy response of these detectors and the energy spectra outside the main beam.

Treatment planning for primary breast cancer: A patterns of care study

Purpose : The 1989 Patterns of Care Study included treatment planning or early breast cancer. A Consensus Committee of radiation physicists and oncologists determined current guidelines and developed questionnaires to determined treatment planning and delivery processes used by the participating institutions (e.g., use of portal films). This article present adn analyzes the results of that survey. Methods and Materials : The survey included 449 respondents, distributed as follows: 136 (30%) from Strata I (academic facilities); 169 (38%) from Strata II (hospital based facilities); and 144 (32%) from Strata III (freestanding facilities). The treatment planning procedures surveyed included: whether individualized tissue compensators are used, whether inhomogeneity corrections are used in dose calculations, the use of computerized tomography, whether isodose distributions for external beam tangents and interstitial implants are generated, the use of lymphoscintigraphy, immobilization devices, simulations, portal films, etc. Results : The survey results demonstrated that out of 305 patients from Strata I and II institutions, 237 (78%) had simulated tangential fields. Consistent with this finding is that 76% of patients from Strata I and II institutions were immobilized, while only 51% of Strata III patients were. Moreover, only 18 out of the 449 (4%) of cases did not have any type of external beam dose distribution calculated—presumably, in these cases missing tissue compensation would be unlikely. On the other hand, 41% of the Strata II, 27% of Strata III, but only 19% of Strata I ( p < 0.0002) cases received CT. Surprisingly, 19% of the Strata I, 35% of the Strata II, and 25% of the Strata III ( p = 0.0011) patients received lymphoscintigraphy, perhaps reflecting the use of wide tangents to encompass the internal mammary nodes in these patients. In terms of optmizing treatment, 74% of Strata I, 70% of Strata II, and 78% of Strata III patients had wedges used on both tangential fields, although in 5, 12, and 14%, respectively, no beam modification of any sort was used. Furthermore, it should be noted that in 7% of the Strata I, 23% of Strata II, and 37% of Strata III cases there was no attempt to reduced the divergence of the tangential fields into the lung. On the other hand, if one considers the 135 (of 449) patients where matching of the tangential and supraclavicular fields was applicable, 41% of Strata I, 22% of Strata II and 46% of Strata III patients had those fields matched in a vertical plane, which would involve sophisticated alignment procedures. Quality control of treatment delivery was high: 97% of all surveyed received portal films at least once. The use of thermoluminescent dosimetry (TLD) to measure the dose to the contralateral breast was of little interest: only 4 of the 305 Strata I and II patients received invivo measurements. Conclusions : This national survey has established the patterns of treatment planning for early breast cancer. It shows a generally consistent approach—although a number of statistically significant variations have been identified.

Profile of radiotherapy departments contributing to the Cooperative Group of Radiotherapy of the European Organization for Research and Treatment of Cancer

Since 1982, the Radiotherapy Group of the European Organization for Research and Treatment of Cancer (EORTC) is carrying out a Quality Assurance program that includes the evaluation of the structure and human resources of 50 centers actively participating in protocols of clinical research in radiotherapy. One or two site visits were made by a team of radiation physicists and physicians. A detailed questionnaire was circulated to these radiotherapy centers to collect and update standardized figures on the status and activities of each center, to clarify some obscurities encountered during on-site visits, and to extend investigations to issues that were not addressed during local audits. This article reports on departmental infrastructure, staff and equipment workload, and quality control procedures carried out by single institutions. Large variations in equipment and staff are observed among participating centers. Comparisons between data collected in the early 1980s and during a recent update show no difference in workload per megavoltage equipment and per simulator. The number of cancer patients treated per year per radiotherapist seems to slightly diminish, especially in centers that experienced a considerable staff shortage a few years ago. The most significant improvement is observed for the number of cases treated per year per member of the radiation physics team. The radiographer's workload shows an opposite trend. Our database provides participating centers with strong comparative arguments to correct staff and equipment unbalances and to convince administrative authorities of priorities in decision making. The current analysis shows that the situation for equipment is unchanged in comparison with that observed 6 years ago. Efforts have to be put forth in some institutions to reduce the workload at simulators. A tentative profile and guidelines for minimum recommendations for European radiotherapy departments involved in clinical research are presented.

Meetings and Courses

A Practical and Theoretical Course in Radiotherapy Physics (Part II) 26 February – 1 March, 1996 Sutton, UK Further details: Dr Alan Nahum, Joint Department of Physics, Royal Marsden NHS Trust, Downs Road, Sutton, Surrey SM2 5PT. Tel. 0181 642 6011

Treatment planning for carcinoma of the cervix: A patterns of care study report

Purpose : The Patterns of Care Study (PCS) of patients treated in 1988–1989 included “patterns of treatment planning” for radiotherapy of carcinoma of the uterine cervix. A Consensus Committee of radiation physicists and oncologists established current guidelines and developed questionnaires to assess the treatment planning process (i.e., the general structure, methodology, and tools) of institutions involved in the Patterns of Care Study. This paper reports the findings of the assessment. Methods and Materials : The PCS surveyed 73 radiotherapy facilities, of which 21 ae academic institutions (AC), 26 hospital-based facilities (HB), and 26 free-standing centers (FS). In total, 242 cases were assessed with 39% from academic centers, 33% from hospital-based centers, and 28% from free-standing centers. The survey collected treatment planning information such as the use of computed tomography (CT), simulation procedures, contouring of patient outlines, tumor or target delineation, identification of critical structures, method of dose prescription (point or isodose), etc. Data also obtained concerning implant boost, e.g. radioisotope used, use of midline block for external beam treatment, availability of remote afterloader, practice of interstitial implants, combination with hyperthermia, etc. Results : There is a high degree of compliance relative to the basic treatment planning standards. For example, 171 cases (out of 173) from AC and HB institutions included simulation and 169 used port film; for cases from FS centers, 61 out of 69 involved simulation and 66 out of 69 included port film. Most institutions used linacs (231 out of 242); in five cases, Co-60 units and in six cases betatron was used. In terms of treatment planning, 53% used skin contours, but only 14% had target volume delineation, with AC and HB being slightly more conscientious in these efforts. Critical organs did not appear to be explicitly considered in external beam treatment planning, with only 3% outlining the bladder, 5% the rectum, and less than 1% the small bowel. Only 11% of the centers used CT in treatment planning, and none reported the used of magnetic resonance imaging (MRI). For patients receiving implants, about 40% had midline blocking during external beam treatment, of which one out of three were shielded by standard blocks and two out of three with customized ones. About 11% of the patients receiving implants were treated with remote afterloading devices, 5% received interstitial implants, and none were treated in combination with hyperthermia. Conclusion : The treatment planning aspects of radiotherapy of carcinoma of the cervix have been established by this Patterns of Care Study Survey. There is a high level of uniformity in the approach. Some variations exist among centers in the different strata.

158 - Invited lecture: Towards the eradication of severe complications in radiotherapy of cervical cancer: A 25-year cooperation between radiation physicists and radiation therapists

158 - Invited lecture: Towards the eradication of severe complications in radiotherapy of cervical cancer: A 25-year cooperation between radiation physicists and radiation therapists

176 - Structure and staffing of radiotherapy physics in the UK

176 - Structure and staffing of radiotherapy physics in the UK

183 - A quality management system for radiotherapy physics

183 - A quality management system for radiotherapy physics

Meetings and Courses

A Practical and Theoretical Course in Radiotherapy Physics (Part II) 13–17 March, 1995 Sutton, UK Further details: Dr A Nahum, Joint Department of Physics, Royal Marsden NHS Trust, Downs Road, Sutton, Surrey SM2 5PT. Tel. 0181 642 6011, ext. 3513