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

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.

Keywords

Not Applicable / None Entered.

Taxonomy

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

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