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Dosimetric Verification For Volumetric Modulated Arc Therapy Cranio-Spinal Irradiation Technique

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E Goksel

E Goksel1*, H Bilge2 , Y Yildiz Yarar3 , (1) Acibadem Kozyatagi Hospital, Istanbul, (2) Istanbul University Oncology Institute, Istanbul (3) Yildiz Technical University, Istanbul


SU-E-T-138 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: Dosimetric feasibility of cranio-spinal irradiation with volumetric modulated arc therapy (VMAT-CSI) technique in terms of dose distribution accuracy was investigated using a humanlike phantom.

Methods: The OARs and PTV volumes for the Rando phantom were generated on supine CT images. Eclipse (version 8.6) TPS with AAA algorithm was used to create the treatment plan with VMAT-CSI technique. RapidArc plan consisted of cranial, upper spinal (US) and lower spinal (LS) regions that were optimized in the same plan. US field was overlapped by 3cm with cranial and LS fields. Three partial arcs for cranium and 1 full arc for each US and LS region were used. The VMAT-CSI dose distribution inside the Rando phantom was measured with thermoluminescent detectors (TLD) and film dosimetry, and was compared to the calculated doses of field junctions, target and OARs. TLDs were placed at 24 positions throughout the phantom. The measured TLD doses were compared to the calculated point doses. Planar doses for field junctions were verified with Gafchromic films. Films were analyzed in PTW Verisoft application software using gamma analysis method with the 4 mm distance to agreement (DTA) and 4% dose agreement criteria.

Results: TLD readings demonstrated accurate dose delivery, with a median dose difference of -0.3% (range: -8% and 12%) when compared with calculated doses for the areas inside the treatment portal. The maximum dose difference was 12% higher in testicals that are outside the treatment region and 8% lower in lungs where the heterogeinity was higher. All planar dose verifications for field junctions passed the gamma analysis and measured planar dose distributions demonstrated average 97% agreement with calculated doses.

Conclusion: The dosimetric data verified with TLD and film dosimetry shows that VMAT-CSI technique provides accurate dose distribution and can be delivered safely.

Funding Support, Disclosures, and Conflict of Interest: This study was supported by Yildiz Technical University Scientific Research project coordinatorship.

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