Set-up verification on a belly-board device using electronic portal imaging

Efficacy and workload analysis of a fixed vertical couch position technique and a fixed-action-level protocol in whole-breast radiotherapy

Quantification of the setup errors is vital to define appropriate setup margins preventing geographical misses. The no-action-level (NAL) correction protocol reduces the systematic setup errors and, hence, the setup margins. The manual entry of the setup corrections in the record-and-verify software, however, increases the susceptibility of the NAL protocol to human errors. Moreover, the impact of the skin mobility on the anteroposterior patient setup reproducibility in whole-breast radiotherapy (WBRT) is unknown. In this study, we therefore investigated the potential of fixed vertical couch position-based patient setup in WBRT. The possibility to introduce a threshold for correction of the systematic setup errors was also explored. We measured the anteroposterior, mediolateral, and superior-inferior setup errors during fractions 1-12 and weekly thereafter with tangential angled single modality paired imaging. These setup data were used to simulate the residual setup errors of the NAL protocol, the fixed vertical couch position protocol, and the fixed-action-level protocol with different correction thresholds. Population statistics of the setup errors of 20 breast cancer patients and 20 breast cancer patients with additional regional lymph node (LN) irradiation were calculated to determine the setup margins of each off-line correction protocol. Our data showed the potential of the fixed vertical couch position protocol to restrict the systematic and random anteroposterior residual setup errors to 1.8 mm and 2.2 mm, respectively. Compared to the NAL protocol, a correction threshold of 2.5mm reduced the frequency of mediolateral and superior-inferior setup corrections with 40% and 63%, respectively. The implementation of the correction threshold did not deteriorate the accuracy of the off-line setup correction compared to the NAL protocol. The combination of the fixed vertical couch position protocol, for correction of the anteroposterior setup error, and the fixed-action-level protocol with 2.5 mm correction threshold, for correction of the mediolateral and the superior-inferior setup errors, was proved to provide adequate and comparable patient setup accuracy in WBRT and WBRT with additional LN irradiation.

Prone belly board device training improves geometric setup accuracy in lower GI radiotherapy

Background

Patients having a course of radiotherapy (RT) must be appropriately immobilised for stability and accuracy. Having opened a new cancer service in June 2009 and commenced treating lower gastrointestinal cancers in 2010, a prone belly board device (BBD) was introduced as the standard radiotherapy immobilisation. A training package was created to aid clinical skills retention of therapeutic radiographers and manage setup quality. Setup reproducibility using the BBD was retrospectively assessed with electronic portal image (EPI) verified geometric displacements as the main outcome measure both before and after the introduction of training.

Method

Twenty retrospective Pinnacle computed tomography-planned patients and their geometric displacements on treatment were evaluated between 2010 and 2011—ten prior to (Patient Group A) and ten following training (Patient Group B). The only inclusion criterion was that patients were immobilised for RT on the Medtec ContouraTM carbon fibre BBD. Patients were prone and were treated to 45–50·4 Gy in 25–28 fractions on a 6–10 MV LinAc equipped with EPI. Reproducibility was assessed by comparing geometric measurement of the bony pelvis on the Pinnacle digitally reconstructed radiograph (DRR) with an EPI captured at day 0, 1, 2 and weekly during treatment for each patient. Systematic and random errors were analysed with respect to the average geometric displacement with standard deviation per patient between the Pinnacle DRR and the EPI.

Results

The age range was 41–77 years and there were 15 male and five female patients with diagnosed rectal cancers (T3–T4, N0–N2, M0). Three hundred and seventy one images were analysed. An improvement in population systematic and random error was most notable in the superior–inferior direction (Patient Group A Σpop = 3·1 mm, σpop = 3·6 mm to Patient Group B Σpop = 2·0 mm, σpop = 2·3 mm, respectively).

Discussion/Conclusion

There is evidence that the use of the BBD is more reproducible when accompanied by a task-specific training package. Based on the results of this study, further work will be carried out on training standardisation for patient positioning with a BBD for reducing systematic and random geometric displacements.