Time-domain characterization of a microstrip patch antenna with circular corner truncation to achieve polarization reconfigurability is presented. By applying zero bias, forward bias, and reverse bias to the four PIN diodes, the antenna can radiate with linear polarization (LP), right hand circular polarization (RHCP), and left hand circular polarization (LHCP). The circular cuts reduce centre-frequency shift from linear to circularly polarized states, compared with conventional straight cuts. Time-domain simulation and measurement are carried out to show the switching characteristics of the proposed antenna, and it is established that satisfactory switching speed can be obtained using a simple low-cost driver circuit.

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.

Purpose: Having previously reviewed the implementation of systematic in vivo dosimetry at the Norfolk and Norwich Hospital this paper examines the results of entrance dose measurements for specific sites/techniques and determines whether different action/alert protocols are required for these different categories.

Methods and materials: Entrance dose measurements using p-type diodes were analysed for the following treatment categories: Breast, head and neck in beam direction shell, abdomino-pelvic and intrathoracic. A 4% tolerance was applied.

Results: Mean deviations from expected dose and proportion of measurements exceeding tolerance were: Breast: +1.15%±3.04% (1SD), 238/1073≥4%; Head and neck: +0.35%±2.20% (1SD), 21/326≥4%; Abdomino-pelvic: +0.52%±2.75% (1SD), 93/712≥4%; Intrathoracic: −0.01%±2.75% (1SD), 22/119≥4%. Significant improvements in results for breast patients were noted following the introduction of a commercial breast board. The results for abdomino-pelvic patients confirmed a substantial variation in diode response under short FSD, wedged fields at 16MV (that had not been corrected for). The statistical uncertainty in dose measurement for each treatment category was calculated in order to assist determination of appropriate tolerance levels.

Conclusions: A blanket tolerance of 4% was generally too low given the extent of measurement uncertainty. The relatively high number of readings outside tolerance where identification of errors was difficult/impossible resulted in inconsistent application of the action protocol. Some widening of tolerances is likely to improve quality of procedure and treatment. Appropriate action levels are recommended for each treatment category.

Purpose: This paper describes our experiences of implementing systematic in vivo dosimetry at the Norfolk and Norwich Hospital and reviews the results of 2,254 entrance dose measurements made over a 17-month period.

Methods and materials: Entrance dose measurements using p-type diodes were performed on all new planned patients. The calibration procedure and correction factors applied are described. A 4% tolerance was applied.

Results: The results of all measurements indicated a small mean deviation from expected entrance dose of 10.77% and a standard deviation of 2.85%. 16.7% of all measurements exceeded the 4% tolerance with 9.2% exceeding a 5% level. The estimated overall errors for 578 treatments were calculated using the weighted averages of all beams. A narrower SD of 1.96% combined with only 4.8% of all treatments exceeding a 4% tolerance show that large deviations from a single field do not always translate into significant overall errors.

Conclusions: Global dosimetric accuracy was within clinically acceptable limits and variations between measured and expected doses were mainly attributable to factors affecting diode reading. A number of errors in calculating deviations and the inconsistent application of the protocol suggest the need for interfacing the diode system with software control.