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Dosimetric Advantage of Individual Field Simultaneously Optimized Scanning Proton Beam Therapy Over VMAT for Gynecological Cancer

R Ger*, J Lentz, S Vora, M Bues, D Hernandez Morales, C Schulz, P Lara, A Ridgway, J Gagneur, A Anand, Mayo Clinic Arizona, Phoenix, AZ

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: To compare the dosimetric impact on organs at risk in gynecological cancer treated with individual field simultaneous optimized (IFSO) proton therapy compared to volumetric arc (VMAT) photon therapy.


Methods: Fourteen patients treated with IFSO proton beam therapy were selected and a VMAT photon plan was created for dosimetric comparison. All patients were treated to a total dose of 45Gy in 25 fractions. The IFSO plan utilized three beams: one posterior beam and combinations of lateral or lateral-anterior beams. These plans are optimized such that there is simultaneous optimization of partial target volumes while maintaining nearly uniformly optimized dose for non-overlapping targets. The VMAT plans were designed with four full arcs. To allow for objective comparison between the proton and photon plans, all plans were normalized for 100% of the prescription dose to cover 99% of the CTV. DVH metrics were extracted for the bladder, bone marrow, femoral heads, rectum, and small bowel. Paired t-tests were used to analyze the DVH metrics.


Results: The bladder was the only organ that had none of the DVH metrics improved by the proton plan. For bone marrow, V10Gy (Proton???=58%, Photon???=86%) and V20Gy (Proton???=47%, Photon???=58%) were significantly improved by the proton plan (p=4.5x10?¹° and p=8.3x10?6, respectively). Both femoral head mean doses (Proton???=11Gy, Photon???=13Gy) were significantly improved by the proton plan (left p=0.03, right p=0.02). The small bowel V20Gy (Proton???=21%, Photon???=56%) and V35Gy (Proton???=15%, Photon???=17%) were all significantly improved in the proton plan (p=3.7x10?8 and p=0.04, respectively). Lastly, the rectum mean dose (Proton???=20Gy, Photon???=23Gy) was improved by the proton plan (p=0.007).


Conclusion: IFSO offers a unique signature of dose distribution of multi-field optimization utilizing scanning proton beams. IFSO proton radiotherapy significantly improves bone marrow, femoral head, small bowel, and rectum doses compared to photon radiotherapy.

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Keywords

Not Applicable / None Entered.

Taxonomy

TH- External Beam- Particle/high LET therapy: Proton therapy – treatment planning/virtual clinical studies

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