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Application of Film Dosimetry and Comparison to Delta4 to Patient-Specific Preclinical Dosimetric Verification of RapidArc

R Srivastava

R Srivastava1*, C De Wagter2, (1) Ghent University Hospital, Gent, ,(2) Ghent University Hospital, Gent,

SU-E-T-75 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: Radiotherapy treatment modalities are becoming more complex in order to enable advanced patient treatments with a higher dose to irregularly shaped tumor volumes while sparing nearby organs at risk. VMAT as well as RapidArc incorporate capabilities such as variable dose-rate, variable gantry speed, and accurate and fast dynamic multileaf collimators (DMLC), to optimize dose conformity, delivery efficiency, accuracy and reliability. There is very little information on QA systems and techniques regarding the patient-specific QA. Therefore, we compared the results obtained with radiographic film to those from the Delta4 phantom.

Methods: RapidArc treatment plans were generated using the Varian Eclipse treatment planning software version 8.9 (Varian Medical Systems, Palo Alto, CA). A single but complete (358°) RapidArc was planned. RapidArc treatment plans were delivered to the Delta4 (Delta4) cylindrical (1069 p-Si Silicon diodes) phantom from Scandidos Uppsala, Sweden, as well as to an equivalent home-made polyethylene (HD 1000) cylindrical phantom (two longitudinal halves, density 0.94 g/cm³) for EDR2 film dosimetry.

Results: The correspondence between D4 and cylindrical phantom measured were analyzed in radial and longitudinal (GT) profiles. The film in the 40° plane displayed a ±3.1% agreement in radial and a 2.2% agreement in GT direction with Delta4 phantom. A small difference was found between the planes because the cylindrical phantom joining the two halves parts has some gaps which might generate the discrepancy between radial and GT direction. The film-measured dose in the isocenter of the 50° radial and GT plane showed an agreement within ±2.7% with the Delta4 phantom.

Conclusion: Film dosimetry validated the Delta4 measurements and it clearly provided more useful information than single point dose measurement.

Funding Support, Disclosures, and Conflict of Interest: GHENT UNIVERSITY BOF08/DOS/052

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