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A quality assurance study: Comparison of 2 immobilization devices for 4D CT lung scans

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A Quality Assurance Study: Comparison of 2 Immobilization Devices For Radical Lung Radiation Treatments


Ann Foo MRT(T) BSc , Lisa Peden MRT(T) BSc, Raja Ravi MRT(T) BSc





An increase in the number of Radical lung patients has led to Vaclok shortages and storage problems at the Peel Regional Cancer Centre (PRCC), causing radiation therapists to look for an alternative and more efficient mode of immobilization for this group of patients. A study performed by Li et al. (2010) at the Princess Margaret Hospital illustrated that the MedTec board used for breast radiation treatments is comparable in setup reproducibility for thoracic and other upper gastro-intestinal sites as  the Vaclok. A small scale quality assurance study was initiated at PRCC on 10 radical lung patients. The goal was to comparedthe differences, if any, existed between the stability of using vaclok vs MedTec board. Findings from this study allowed a departmental policy changes in the use of immobilization devices for all radical lung setups.


 10 radical lung patients were used for this study. The first 5 patients were placed in Arm A where they were scanned and treated using the small blue pelvis Vaclok following the current departmental protocol at time of study.  The following 5 patients were placed in Arm B where they were scanned and treated using the MedTec board. Pre-treatment cone-beam computed tomography ,CBCT, was performed daily. Lateral, longitudinal and vertical shifts with references to original CT dataset were corrected prior to the initiation of treatments. Weekly post-treatment CBCTs were also acquired. Data was analyzed to evaluate the magnitude of corrections needed before each treatment as well as if any variance occurred during treatment.  The values measured for each immobilization device, in the vertical (vrt), lateral (lat), and longitudinal (lng) were compared. A T-test was used to analyze the data


 The T-test illustrated there was no statistical significant difference between the MedTech and the Vaclok in the vrt, lat, and lng direction.  The magnitudes of the shifts were averaged between each group respectively. It was found that these averages varied approximately by 0.2cm for both Arm A and Arm B.


 The pilot QA project lasted several weeks and was done on a total of 10 patients (5 Vaclok, 5 MedTec board). Some of the primary concerns prior to the implementation of the project were patient comfort, ease of setup and gantry clearance of the two arm supports during treatment and cone-beam CT acquisition. Immediately following the conclusion of the study, we asked for staff feedback at the next staff meeting and reported positive findings as a result of the change. First off, staff found no significant change in patient comfort or ease of setup. The MedTec board allowed for sufficient immobilization while providing enough adjustable components (wrist support, arm rotation/incline) to ensure patient comfort through their course of treatment. In addition, a lateral offset of the MedTec board (if any lateral shifts) or centering the board allowed for sufficient gantry and CBCT clearance. As such, given our results and positive staff feedback the Peel Regional Cancer Center has begun using the MedTec board for immobilizing all  Radical lung patients.

Next Steps

 Since the implementation of the MedTec board for all non-apical lung 4DCT plans, there has been discussion regarding the use of the board for other sites. Potential sites of interest are patients receiving radiation to the distal esophagus and select upper GI patients. Given the fact that patients are simulated in a similar position (arms up, chin extended), there is potential to investigate whether a MedTec board can be used in place of a vaclok.



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