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Comparison of Prone Versus Supine Position and Different Planning Technique of Anal Cancer Treated with Pencil-Beam Scanning Proton Beam: Cross Institutional Dosimetric and IGRT Studies

S Ito1*, A Anand2, J Lentz2, C Beltran3, (1) Mayo Clinic, Rochester, MN, (2) Mayo Clinic Arizona, Phoenix, AZ, (3) Mayo Clinic, Jacksonville, FL


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

Room: AAPM ePoster Library

Purpose: retrospective study comparing impact of prone versus supine ano-rectal cancer patient setup on scanning proton beam therapy is presented.

Methods: supine Mayo Clinic Rochester (MCR) patients planned with Multi field Optimization (MFO) technique; were compared against 4 prone Mayo Clinic Arizona (MCA) patients planned with Individual Field Simultaneous Optimization (IFSO). Verification plans were generated from weekly verification CTs. All plans were normalized to 95% Isodose lines for comparisons. Plan robustness was evaluated with 3% range and 5mm of setup errors. Verification plans were also generated to further assess the robustness of these plans. Daily positional shifts and image guided setup times were obtained from Record and Verify systems and analyzed.

Results: of target coverage and OAR sparing for 4 prone and 4 supine patients planned with both MFO/MCR and IFSO/MCA techniques are summarized in table 1. Target coverage (D95) was above 96.6% in all verification plans. The average positional 6D shifts (vertical, longitudinal, lateral in mm, rotation, pitch, and roll in deg) in bone matching were (0.5, 2.3, 0.9, 0.07, 0.01, 0.42) for supine patients and (1.4, 1.9, 1.4, 0.04, 0.35, 0.17) for prone patients. The average setup times (in mins) were 4:35 (max: 37:15, min: 0:59) for supine patients and 4:40 (max: 13:57, min: 1:07) for prone patients.

Conclusion: result shows plan robustness to be generally independent of both setup and treatment planning techniques. The average positional shifts were similar between supine and prone setups and the average setup time was also very similar between two different setups.


Dosimetry, Protons


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

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