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Treatment Planning Comparison of SFUD Proton and 4π Radiotherapy for Prostate Cases

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A Tran

A Tran1*, J Zhang2 , K Woods1 , V Yu1 , D Nguyen1 , K Sheng1 , (1) UCLA ,Los Angeles, CA, (2) Willis-Knighton Cancer Center, Shreveport, LA


SU-E-T-765 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Single-Field Uniform Dose (SFUD) proton scanning beams and non-coplanar 4π intensity-modulated radiation therapy (IMRT) represent the most advanced treatment methods based on heavy ion and X-rays, respectively. Here we compare their performance for prostate treatment.

Methods: Five prostate patients were planned using 4π radiotherapy and SFUD to an initial dose of 54Gy to a planning target volume (PTV) that encompassed the prostate and seminal vesicles, then a boost prescription dose of 25.2Gy to the prostate for a total dose of 79.2 Gy. 4π plans were created by inversely selecting and optimizing 30 beams from 1162 candidate non-coplanar beams using a greedy column generation algorithm. The SFUD plans utilized two coplanar, parallel-opposing lateral scanning beams. The SFUD plan PTV was modified to account for range uncertainties while keeping an evaluation PTV identical to that of the X-ray plans for comparison. PTV doses, bladder and rectum dose volumes (V40, V45, V60, V70, V75.6, and V80), R50, and PTV homogeneity index (D95/D5) were evaluated.

Results: Compared to SFUD, 4π resulted in 6.8% lower high dose spillage as indicated by R50. Bladder and rectum mean doses were 38.3% and 28.2% lower for SFUD, respectively. However, bladder and rectum volumes receiving >70Gy were 13.1% and 12% greater using proton SFUD. Due to the parallel-opposing beam arrangement, SFUD resulted in greater femoral head (87.8%) and penile bulb doses (43.7%). 4π PTV doses were slightly more homogeneous (HI 0.99 vs. 0.98) than the SFUD dose.

Conclusion: Proton is physically advantageous to reduce the irradiated normal volume and mean doses to the rectum and bladder but it is also limited in the beam orientations and entrance dose, which resulted in greater doses to the femoral heads and penile bulb, and larger volumes of rectum and bladder exposed to high dose due to the required robust PTV definition.

Funding Support, Disclosures, and Conflict of Interest: This project is supported by Varian Medical Systems.

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