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SU‐GG‐T‐102: Implementation of a Comprehensive Quality Assurance Regime for the Deliverance of Electron Conformai Radiotherapy Using Custom Bolus Compensators
Author(s) -
Denton T,
Coffey C,
MoralesPaliza M
Publication year - 2010
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3468491
Subject(s) - fiducial marker , dosimetry , quality assurance , radiation therapy , radiation treatment planning , image guided radiation therapy , bolus (digestion) , nuclear medicine , dosimeter , medical imaging , fluence , medicine , radiosurgery , medical physics , radiology , irradiation , physics , surgery , external quality assessment , pathology , nuclear physics
Purpose : Quality Assurance (QA) practices for bolus conformai electron radiotherapy have not been well‐established. This study proposes a three‐step QA program for patient‐specific electron bolus radiotherapy encompassing planning, imaging, compensator design, dosimetry verification, and patient alignment. Method and Materials : First, to evaluate patient‐specific compensator design, a re‐CT of the patient was taken with the manufactured bolus to compare dose calculation results with the initial planned virtual bolus. However, the standard visual dose inspection was extended to include a gamma analysis of the exported fluence plane of the virtual and real compensator. Next, to evaluate absolute skin dosimetry at treatment delivery, optically‐stimulated luminescent (OSL) dosimeters were placed on the patient surface below the compensator, and dose measurements were compared to the treatment planning system calculation. Finally, accurate treatment delivery is most dependent on the ability to position the compensator with each fraction. To aid this, imaged‐guided cone‐beam CT radiotherapy was incorporated with fiducial markers adhered onto the compensator and skin for patient alignment. Relative three‐dimensional adjustment was carried out and evaluated prior to treatment using image‐to‐image fiducial alignment. Results : Dose fluence planes were compared using a three‐millimeter distance‐to‐agreement and three‐percent gamma calculation representing the percentage of pixels with gamma factors greater than unity. Retrospective patient fluence comparisons showed high correlation between ineligible compensator placements and reportable gamma results. OSL dosimeters were found to be a reliable and convenient means of first‐fraction dose verification. Additionally, surface fiducial markers may indicate better positioning via image alignment. Conclusions : Additional QA steps beyond current practice are needed for the clinical implementation of bolus electron radiotherapy. These steps represent an end‐to‐end test which may be used to design patient eligibility criteria while maintaining quality of care for these patients. Conflict of Interest : This study was sponsored by .decimal, Inc., Sanford, Florida.