Assessment of daily dose accumulation for robustly optimized intensity modulated proton therapy treatment of prostate cancer

Yihang Xu, Tejan Diwanji, Nellie Brovold, Michael Butkus, Kyle Padgett, Ryder M. Schmidt, Adam King, Alan Dal Pra, Matthew C Abramowitz, Alan Pollack, Nesrin Dogan

Research output: Contribution to journalArticlepeer-review

Abstract

Purpose: To implement a daily CBCT based dose accumulation technique in order to assess ideal robust optimization (RO) parameters for IMPT treatment of prostate cancer. Methods: Ten prostate cancer patients previously treated with VMAT and having daily CBCT were included. First, RO-IMPT plans were created with ± 3 mm and ± 5 mm patient setup and ± 3% proton range uncertainties, respectively. Second, the planning CT (pCT) was deformably registered to the CBCT to create a synthetic CT (sCT). Both daily and weekly sampling strategies were employed to determine optimal dose accumulation frequency. Doses were recalculated on sCTs for both ± 3 mm/±3% and ± 5 mm/±3% uncertainties and were accumulated back to the pCT. Accumulated doses generated from ± 3 mm/±3% and ± 5 mm/±3% RO-IMPT plans were evaluated using the clinical dose volume constraints for CTV, bladder, and rectum. Results: Daily accumulated dose based on both ± 3mm/±3% and ±5 mm/±3% uncertainties for RO-IMPT plans resulted in satisfactory CTV coverage (RO-IMPT3mm/3% CTVV95 = 99.01 ± 0.87% vs. RO-IMPT5mm/3% CTVV95 = 99.81 ± 0.2%, P = 0.002). However, the accumulated dose based on ± 3 mm/3% RO-IMPT plans consistently provided greater OAR sparing than ±5 mm/±3% RO-IMPT plans (RO-IMPT3mm/3% rectumV65Gy = 2.93 ± 2.39% vs. RO-IMPT5mm/3% rectumV65Gy = 4.38 ± 3%, P < 0.01; RO-IMPT3mm/3% bladderV65Gy = 5.2 ± 7.12% vs. RO-IMPT5mm/3% bladderV65Gy = 7.12 ± 9.59%, P < 0.01). The gamma analysis showed high dosimetric agreement between weekly and daily accumulated dose distributions. Conclusions: This study demonstrated that for RO-IMPT optimization, ±3mm/±3% uncertainty is sufficient to create plans that meet desired CTV coverage while achieving superior sparing to OARs when compared with ± 5 mm/±3% uncertainty. Furthermore, weekly dose accumulation can accurately estimate the overall dose delivered to prostate cancer patients.

Original languageEnglish (US)
Pages (from-to)77-85
Number of pages9
JournalPhysica Medica
Volume81
DOIs
StatePublished - Jan 2021

Keywords

  • Dose accumulation
  • IMPT
  • Prostate cancer

ASJC Scopus subject areas

  • Biophysics
  • Radiology Nuclear Medicine and imaging
  • Physics and Astronomy(all)

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