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Program Information

Pretreatment Test and Post-Treatment Evaluation for Iso-NTCP Dose Guided Adapive Radiotherapy (DGART), Experience with Prostate Cancer Patients Treated with Rectal Balloons


J Yu

J Yu1,5*, N Hardcastle1,2,3 , E Bender1 , K Jeong1,4 , Y Xiao5 , M Ritter1 , W Tome'1,3,4 , (1) The University of Wisconsin-Madison, Madison, WI,(2) Peter MacCallum Cancer Centre, Melbourne, Australia, (3) University of Wollongong, Wollongong, Australia, (4) Montefiore Medical Center/Albert Einstein College of Medicine, Bronx, New York, (5) Thomas Jefferson Univ Hospital, Philadelphia, PA,

Presentations

SU-E-J-97 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:To explore the feasibility of pretreatment test for iso-NTCP DGART and to compare the pretreatment test results with post-treatment evaluations.

Methods:NTCP here refers to late rectal wall toxicity only and is calculated with the ring rectal wall DVH. Simulation for one time iso-NTCP DGART starts after half of the total dose was done for 10 patients to investigate if TCP gains could be achieved. Six patients were treated using a 12-fraction 4.3Gy technique and four using 16-fraction 3.63Gy technique.

For each of the 12-fraction cases a VMAT plan was generated in Pinnacle3â„¢ using the daily CT obtained prior to the 6th fraction. A pretreatment simulation was performed using only the first 6 daily CTs. The idea is to add the 6 original plan delivered doses with 6 DGART plan delivered doses by deformable dose accumulation (DDA) on each of the first 6 CTs, resulting in 6 rectal wall doses (RWDs) and NTCPs. The 95% confidence interval (95%CI) for the 6 NTCPs were computed.

The post-treatment evaluation was done by: a) copy the DGART plan to 6 CTs for fraction 7-12 and calculate the 6 actual DGART delivered fractional doses; b) sum the 6 actual DGART doses with the 6 original plan delivered doses by DDA on each of the 12 CTs resulting in 12 post-treatment RWDs and NTCPs; c) boxplot the 12 post-treatment NTCPs.

Results:Target dose gain is 0.76-1.93 Gy. The 95%CI widths of the pretreatment tests NTCPs were 1.1-2.7%. For 5 patients, the planned NTCP fell within the 95%CI. For 4 patients, the planned NTCP was lower than the 95%CI lines. Post-treatment results show that for 7 patients, the upper quartile was within the 95%CI; for 2 patients, the upper quartile were higher than the 95%CI.

Conclusion:The pretreatment test yields conservative prediction of the actual delivered NTCP.


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