Radiation Physics

PV QA 3 - Poster Viewing Q&A 3

TU_19_3307 - Retrospective assessment of the plan of the day approach in the management of prostate cancer

Tuesday, October 23
1:00 PM - 2:30 PM
Location: Innovation Hub, Exhibit Hall 3

Retrospective assessment of the plan of the day approach in the management of prostate cancer
E. Galvan, H. Parenica, D. Saenz, Z. Shi Jr, C. S. Ha, K. Rasmussen, N. Kirby, N. Papanikolaou, and S. Stathakis; University of Texas Health San Antonio Cancer Center, San Antonio, TX

Purpose/Objective(s): To evaluate the cone-beam CT (CBCT) soft tissue localization differences in the treatment of intact prostate and post-prostatectomy cases and the impact of plan-of-the-day treatment approach.

Materials/Methods: Six patients with 231 daily CBCTs were used for this study. Using the clinically “worst” CBCT of the first week—the CBCT with the least bladder filling and the most rectal filling—a new set of organs at risk (OARs) and CTV were segmented. The selected CBCT and original planning CT were fused using rigid registration, and these data were exported to the treatment planning system to optimize an entirely new plan and exported to the record-and-verify system, which was available to be used when necessary. Daily CBCTs were exported to an imaging informatics system and OARs were delineated on each CBCT. The daily CBCTs were then rigidly registered to the planning CT, and the doses were then overlaid to produce the daily DVHs for evaluation. Radiation therapy technologists evaluated the patient anatomy daily using CBCT and chose either the initial plan or the modified plan for the treatment.

Results: Bladder and rectum volumes and doses were evaluated for this study. The frequency of the When compared to original planning volumes, the daily bladder volumes ranged between 43.4% to 186.2%, and the rectum daily volumes ranged from 56.2% to 108.9%. The DVH mean and max dose for the bladder using the adapted plan had a difference of 5.2 ± 12.1% and 1.1 ± 3.4%. The DVH mean and max dose differences for the rectum were 10.6 ± 9.2% and 0.1 ± 3.5%. The dose to other critical structures has not been evaluated yet, but we have seen that, qualitatively, large bladder changes affect daily positioning of the sigmoid and small bowel. It was determined, based on bladder and rectum filling, that nearly one third (77 out of the 231 CBCTs) the time the adapted plan should be used to maximize normal tissue sparing.

Conclusion: Advanced imaging modalities such as CBCT allow for adaptive radiotherapy for prostate cancer. The superior target volume coverage and increased healthy tissue sparing theoretically allow better tumor control through dose escalation while reducing long‐term radiation‐induced toxicity. We are expanding our study to include more OARs such as sigmoid and small bowel to evaluate the overall benefit of implementing this approach in our clinic.

Author Disclosure: E. Galvan: None. H. Parenica: None. D. Saenz: None. Z. Shi: None. C.S. Ha: Board Member; KASTRO. K. Rasmussen: None. N. Papanikolaou: Research Grant; BrainLab. site visitor for ACR Radiation Oncology Practice Accreditation; ACR. Speaker's Bureau; BrainLab. treasurer/secretary; Texas Radiological Society. medical physics advisory committee member; Texas Medical Board.

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