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Dosimetric Evaluation of Conventional Proton Plans Against IMRT and VMAT Photon Plans for Pancreatic Cancer

K Harpool

K Harpool*, H Jin , E Schnell , T Herman , S Ahmad , T De La Fuente Herman , Oklahoma Univ. Health Sciences Ctr., Oklahoma City, OK


SU-I-GPD-T-136 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To evaluate and compare dose parameters of conventional proton plans of two and three fields with photon plans of IMRT and VMAT for radiation therapy of pancreatic cancer.

Methods: Photons and proton treatment plans were calculated for twenty pancreatic patients using Eclipse treatment planning system. Photon plans were IMRT (6-9 fields) or VMAT (2-arc fields) calculated with AAA dose calculation algorithm using 6 MV energy. Plans were also calculated with two and three fields using proton beams from the double scattered Mevion S-250 system. Prescription dose was 4950 cGy in 18 fractions. Plans were compared quantitatively based on Conformity Index (CI), dosimetric parameters of normal tissues (kidneys, liver, spinal cord, and bowel), and the results were statistically compared with two-tail’s student t-test where p-value <0.05 is considered significant.

Results: On average, for Proton2-field versus IMRT, Proton3-field versus IMRT, Proton2-field versus VMAT, and Proton3-field versus VMAT, proton plans had 51.20, 41.21, 56.35, and 47.41% less mean doses to the total kidneys (p< 0.01 for all), respectively, and 21.27 (p< 0.03), 37.81, 34.93, and 48.60% (p< 0.01, for all three) less mean dose to the liver, respectively. Additionally both Proton2-field and Proton3-field plans had (67.26%, 69.81%) and (73.29%, 75.37%) less dose to V1/3 of the liver (p<0.01 for all) compared to IMRT and VMAT plans, respectively. Doses to the spinal cord are much lower for Proton2-field plans compared to other plans. The Proton2-field plans provided on average, 14.83% (p< 0.01) less maximum dose to spinal cord than IMRT plans. The average CI for VMAT plans was 8.47% lower than both proton plans (p< 0.01). Detail dose volume metrics are presented.

Conclusion: Proton plans provide significantly less dose to the critical structures around the target volume while still maintaining adequate lesion coverage.

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