Medical physics aspects of cancer care in the Asia Pacific region: 2014 survey results.

It was the aim of this work to assess and track the workload, working conditions and professional recognition of radiation oncology medical physicists (ROMPs) in the Asia Pacific region over time. In this third survey since 2008, a structured questionnaire was mailed in 2014 to 22 senior medical physicists representing 23 countries. As in previous surveys the questionnaire covered seven themes: 1 education, training and professional certification, 2 staffing, 3 typical tasks, 4 professional organisations, 5 resources, 6 research and teaching, and 7 job satisfaction. The response rate of 100% is a result of performing a survey through a network, which allows easy follow-up. The replies cover 4841 ROMPs in 23 countries. Compared to 2008, the number of medical physicists in many countries has doubled. However, the number of experienced ROMPs compared to the overall workforce is still small, especially in low and middle income countries. The increase in staff is matched by a similar increase in the number of treatment units over the years. Furthermore, the number of countries using complex techniques (IMRT, IGRT) or installing high end equipment (tomotherapy, robotic linear accelerators) is increasing. Overall, ROMPs still feel generally overworked and the professional recognition, while varying widely, appears to be improving only slightly. Radiation oncology medical physics practice has not changed significantly over the last 6 years in the Asia Pacific Region even if the number of physicists and the number and complexity of treatment techniques and technologies have increased dramatically.

A dual two dimensional electronic portal imaging device transit dosimetry model based on an empirical quadratic formalism.

OBJECTIVE: This study describes a two dimensional electronic portal imaging device (EPID) transit dosimetry model that can predict either: (1) in-phantom exit dose, or (2) EPID transit dose, for treatment verification. METHODS: The model was based on a quadratic equation that relates the reduction in intensity to the equivalent path length (EPL) of the attenuator. In this study, two sets of quadratic equation coefficients were derived from calibration dose planes measured with EPID and ionization chamber in water under reference conditions. With two sets of coefficients, EPL can be calculated from either EPID or treatment planning system (TPS) dose planes. Consequently, either the in-phantom exit dose or the EPID transit dose can be predicted from the EPL. The model was tested with two open, five wedge and seven sliding window prostate and head and neck intensity-modulated radiation therapy (IMRT) fields on phantoms. Results were analysed using absolute gamma analysis (3%/3 mm). RESULTS: The open fields gamma pass rates were >96.8% for all comparisons. For wedge and IMRT fields, comparisons between predicted and TPS-computed in-phantom exit dose resulted in mean gamma pass rate of 97.4% (range, 92.3-100%). As for the comparisons between predicted and measured EPID transit dose, the mean gamma pass rate was 97.5% (range, 92.6-100%). CONCLUSION: An EPID transit dosimetry model that can predict in-phantom exit dose and EPID transit dose was described and proven to be valid. ADVANCES IN KNOWLEDGE: The described model is practical, generic and flexible to encourage widespread implementation of EPID dosimetry for the improvement of patients' safety in radiotherapy.

Cancer care in Singapore.

Singapore is a small country, but it is ideally and centrally located to conveniently serve not only its population but also patients from the surrounding regions. It's economy is sufficiently strong to maintain highly sophisticated and expensive equipment to manage a high level of healthcare, including oncology services.Cancer incidences in Singapore are on an upward trend based on the report of the Singapore Cancer Registry for the period of 2001-2005. Cancer is the number one cause of death in Singapore. The three most common cancers for males in Singapore, in decreasing occurrences, are colorectal, lung, and prostate. For females, the three most common cancers are breast, colorectal, lung cancers. Technological advances and advances in anti-cancer drugs have transformed cancer management leading to improved outcomes worldwide and in Singapore as well. The epidemiology and management of these common cancers in Singapore are presented. While Singapore presently has five radiotherapy centres (3 public, 2 private) to service its population of 4.5 million and regional needs, the government has plans to expand its radiotherapy services to accommodate the aging population and the rising expectations of increasingly affluent cancer patients seeking advanced cancer care. The current and future initiatives spearheaded by Singapore to achieve excellence in this aspect are discussed.

Covering the CSF space: does teaching make a difference?

Following a paediatric teaching course for radiation oncology registrars which specifically addressed the method for planning cranial irradiation, a lateral skull simulation film was sent to all attendees to assess the effect of the teaching. To assess current clinical practice in New Zealand, a copy of the same radiograph was sent to radiation oncologists who had not attended the course. Recommendations from the course were that 10-mm margins should be placed in the regions of the cribiform plate and the floor of the middle cranial fossa. However, only 6.9% of the attendees marked the film with the recommended 10-mm margins. Dose profiles are also presented to support the use of 10-mm margins.

Field size dependence of effective source distance and field factors of a 9 MeV electron beam.

Effective source distances and field factors were measured for a number of square and rectangular fields using a 9 MeV electron beam from a Varian 2100-C linear accelerator. Mathematical relationships between effective source distance and field size, and field factor and field size were derived. For 9 MeV electrons, effective source distance is dependent on the field area and applicator cone, while field factors are dependent on the elongation of the field, the field area and applicator cone. Measured field factor data for rectangular fields were compared to field factors obtained using the "square root" method and found to agree to within 0.5%. In some instances, field factors can vary up to 10% for the same field size in different electron applicator cones.

Total-body irradiation on an isocentric linear accelerator: a radiation output compensation technique.

A treatment technique for total-body irradiation (TBI) is proposed that combines arc therapy with dynamic output control to achieve high-grade dose uniformity. The patient lies on a low couch and receives exposure in the prone and supine positions from a modulated arcing beam. The technique has been validated using a personal computer to control the linear accelerator and we demonstrate that only minor alterations to current dynamic therapy systems would be required. We have examined the practical application of this treatment with emphasis on methods of conformal therapy where an optimized dose distribution is prepared from a matrix of caliper measurements taken from the patient. This technique provides a means for regular TBI treatment on a computer-controlled linear accelerator that is easy to set up, requires short exposure times and is comfortable for the patient.