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A Comprehensive Dosimetric Study of Pancreatic Cancer Treatment Using Three Dimensional (3D) Conformal Radiation Therapy, Intensity-Modulated Radiation Therapy (IMRT), Volumetric Modulated Radiation Therapy (VMAT), Passive Scattering and Modulated Scanning Proton Therapy (PT)

X Ding

X Ding*, S Avery, A Kassaee, J Metz, V Prionas, L Huang, S McQuiggan, I Butterwick, A Martinsen, UNIVERSITY OF PENNSYLVANIA, Philadelphia, PA

SU-E-T-684 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

This study is to evaluate different radiation therapy modalities in pancreas cancer treatment and to explore the potential role of organs-at-risk (OARs) sparing using proton therapy (PT).

Seven consecutive pancreatic cancer patients who had been previously treated with passive-scattering PT were identified. The clinical target volume (CTV) include the pancreatic tumor bed as well as the adjacent high risk nodal areas. Treatment plans were generated using three-field and four-field 3DCRT, five-field IMRT, two-arc VMAT, two-field passive-scattering and modulated-scanning PT. All plans delivered 50.4Gy to the initial planning target volume (PTV). 98% of PTV is covered by 95% of the prescription dose and 98% of CTV received 98% prescription dose. Posterior and right posterior oblique proton beams were used to minimize the range uncertainty and improve PT robustness. Pencil beam scanning (PBS) fields with single field uniform dose technique was used for modulated-scanning PT.

All proton plans significantly reduced patient's body integrated dose. Both modulated-scanning and passive-scattering PT offer lower doses to the left kidney (mean and V18Gy) and bowel (mean and V20Gy). Modulated-scanning PT reduced average stomach's mean dose to 168.2 cGy compare to 3-field 3DCRT (1618.9 cGy P=0.0059), 4-field 3DCRT (1565.3 cGy P=0.0062) IMRT (1003.47 cGy P=0.0162) and VMAT (1213.4 cGy P=0.0163), and average right kidney's mean dose to 765.7 cGy compared to 3-field 3DCRT (2205.6 cGy P=0.0013), 4-field 3DCRT(1825.9 cGy P=0.0009), IMRT(1515.5 cGy P=0.0028) and VMAT (1470.6 cGy P=0.0013). Moreover, modulated-scanning PT offer lower bowel V20Gy(15.07%) compared to the passive-scattering PT(28.18% P=0.006). However, IMRT and VMAT offer better target conformity compared to passive-scattering PT (Passive-scattering Conformity Index 80% =2.10±0.4, vs IMRT CI80=1.59 ±0.10 P=0.007, vs VMAT CI80=1.44 ±0.15 P=0.0015)

The dosimetric advantage of modulated-scanning PT points to the possibility of treating tumor bed and comprehensive nodal areas while providing a more tolerable treatment course.

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