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Re-Irradiation Of The Prostate Utilizing 120 Leaf MLC On A TrueBeam Linac

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S Klash

S Klash1*, T Smith2 , C Matthews3 , (1) Wesley Medical Center, Wichita, KS, (2) SightLine Health, Bellaire, Texas, (3) Lonestar Radiation Oncology, Trophy Club, TX


SU-I-GPD-T-559 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To determine the quality of plan that can be achieved for re-irradiation of the prostate by delivering an SBRT treatment using a static IMRT fields with a 120 leaf MLC on a Varian TrueBeam™

Methods: Prescription was 3000 cGy delivered in 5 fractions (600 cGy/fxn) using 9 static IMRT fields. Planning constraints used for plan optimization were: 1) Prostate covered by ≥95% of Rx dose; 2) Rectum ≤100% of Rx Dose; 3) Bladder ≤100% of Rx Dose; 4) Urethra ≤120% of Rx Dose; 5) a 2 mm margin around the prostate was utilized as an ITV since OBI imaging was to be performed prior to the patient being treated each day. Patient had inflated rectal balloon inserted each day of treatment.

Results: DVH results from plan optimization were: 1) Prostate covered by ≥97.3% of Rx Dose; 2) Rectum ≤104.1% of Rx Dose; Max. corr. EDQ2 ≤ 89 Gy; 3) Bladder ≤104.5% of Rx Dose, Max Corr. EDQ2 ≤89 Gy; 4) Urethra ≤105% of Rx Dose; 5) RTOG Conformity Index - 1.526; 6) Quality of Coverage = 97.3%. DVH results of the plan met the criteria of the references referred to in the planning process with the exception of the rectum and bladder optimization limits stated by D.B. Fuller et al. The issue with the Fuller paper is that the paper does not clearly state the planning dose objectives used were actually met.

Conclusion: Based on the results, a suitable plan to re-irradiate a prostate can be achieved that will deliver the prescribed radiation dose to the prostate while limiting the dose to critical structures to acceptable levels. The resulting DVH is comparable to DVHs created by the CyberKnife planning system in other published works. Patient follow-up visit after 8 months showed normal PSA levels, no sign of disease.

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