Radiation Physics

PV QA 3 - Poster Viewing Q&A 3

TU_6_3171 - Hybrid Arc: Combining forward IMRT and double arc VMAT in locally advanced rectum cancer

Tuesday, October 23
1:00 PM - 2:30 PM
Location: Innovation Hub, Exhibit Hall 3

Hybrid Arc: Combining forward IMRT and double arc VMAT in locally advanced rectum cancer
Y. Saglam1, Y. Bolukbasi2,3, Z. V. Alpan Sr4, D. Sezen2, A. Bingolbali5, and U. Selek2,3; 1American Hospital, Department of Radiation Oncology, Istanbul, Turkey, 2Koc University, School of Medicine, Department of Radiation Oncology, Istanbul, Turkey, 3MD Anderson Radiation Oncology Outreach Center at American Hospital, Istanbul, Turkey, 4Amerikan Hospital, Department of Radiation Oncology, Istanbul, Turkey, 5Yildiz Technical University, Department of Bioengineering, Istanbul, Turkey

Purpose/Objective(s): To investigate the potential of increasing target dose conformity and organ at risk (OAR) sparing of HybridArc approach for patients with locally advanced rectum cancer (LARC) in comparison to VMAT and IMRT.

Materials/Methods: This planning study included thirteen patients who had LARC treated with VMAT in 25 Gy in 5 fractions. New plans for each patient were generated on treatment planning software by HybridArc technique combining forward IMRT (3 fields: 275°, 80°, 180°) with 20% weight and VMAT (double full arcs: 182°-178°) with 80% weight. Treatment plans; HybridArc, VMAT and IMRT, were assessed using dose-volume histogram (DVH) parameters of OARs doses for bladder (V25Gy %, V20Gy %, V15Gy %, V10Gy % and Dmean), small bowel (V25Gy cc, V15Gy cc, V10Gy cc, Dmax and Dmean), femur heads (V25Gy %, V15Gy %, Dmax and Dmean) and penile bulb (Dmax and Dmean) in male patients' cases. Additionally, monitor units (MU), conformity index (CI) and homogeneity index (HI) for clinical target volumes (CTV) were compared for all three techniques.

Results: Most DVH parameters pertaining to OARs significantly favored HybridArc technique compared to VMAT and IMRT. HybridArc provided significantly improved Bladder DVH parameters (V25Gy cc, V15Gy cc, V10Gy cc, Dmax and Dmean) in comparison to IMRT & VMAT. The Hybrid technique provided significantly lower small bowel doses in comparison to IMRT and VMAT for the all DVH parameters listed above including mean dose. The Hybrid technique yielded lower femoral head doses on V20Gy%, V15Gy% in comparison to VMAT. Mean and maximum doses of the penile bulb were found to be similar for all three techniques. Mean MU of IMRT was the highest one (MUIMRT = 1803, p = 0.001 vs VMAT; p = 0.023 vs HybridArc). The target dose conformity and homogeneity of VMAT were better than the other two techniques (CIVMAT = 1.16 vs CIHybrid = 1.19, p = 0.003; vs CIIMRT = 1.22, p = 0.001 and HIVMAT = 0.33 vs HIHybrid = 0.36, p = 0.01; vs HIIMRT = 0.37, p = 0.012).

Conclusion: Hybrid technique appears to combine the advantages of forward IMRT and VMAT to seek for better OAR sparing in comparison to VMAT and IMRT.

Author Disclosure: Y. Saglam: None. Y. Bolukbasi: None. Z.V. Alpan: None. D. Sezen: None. A. Bingolbali: None. U. Selek: Member of Board of Directors; Turkish Society for Radiation Oncology, Turkish Society of Lung Cancer.

yucel saglam, MS

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