Authors: Sandra M. Meyers, PhD, MCCPM ^∗, Jeff D. Winter, PhD, MCCPM ^†,‡, Yazan Obeidi, MD^§, Peter Chung, MD, FRCPC ^†,‡, Cynthia Menard, MD, FRCPC ^?, Padraig Warde, MD, FRCPC ^†,‡,Heng Fong, MD^¶, Andrew McPartlin, MD, MRCP(UK)^†,‡, Saibishkumar Parameswaran, MD, FRCPC ^#, Alejandro Berlin, MD, MSc ^†,‡, Andrew Bayley, MD, FRCPC ^‡,∗∗, Charles Catton, MD, FRCPC ^†,‡,Tim Craig, PhD, MCCPM ^†,‡,1

^∗ Department of Radiation Medicine and Applied Sciences, Moores Cancer Center, University of California, San Diego, La Jolla, CA, USA
^† Radiation Medicine Program, Princess Margaret Cancer Centre, Toronto, Ontario, Canada
^‡ Department of Radiation Oncology, University of Toronto, Toronto, Ontario, Canada
^§ IBM, Toronto, Ontario, Canada
^? Centre Hospitalier de l’Université de Montréal, Montréal, Québec, Canada
^¶ The Ministry of Health Malaysia, Daerah Timur Laut, Penang, Malaysia
^# BC Cancer Agency, Victoria, British Columbia, Canada
^∗∗ Department of Radiation Oncology, Sunnybrook Odette Cancer Center, University of Toronto, Toronto, Ontario, Canada

Postoperative prostate radiotherapy requires large planning target volume (PTV) margins to account for motion and deformation of the prostate bed. Adaptive radiation therapy (ART) can incorporate image- guidance data to personalize PTVs that maintain coverage while reducing toxicity. We present feasibility and dosimetry results of a prospective study of postprostatectomy ART. Twenty-one patients were treated with single-adaptation ART. Conventional treatments were delivered for fractions 1 to 6 and adapted plans for the remaining 27 fractions. Clinical target volumes (CTVs) and small bowel delineated on fraction 1 to 4 CBCT were used to generate adapted PTVs and planning organ-at-risk (OAR) volumes for adapted plans. PTV volume and OAR dose were compared between ART and conventional using Wilcoxon signed-rank tests. Weekly CBCT were used to assess the fraction of CTV covered by PTV, CTV D99, and small bowel D_1cc. Clinical metrics were compared using a Student’s t-test (p < 0.05 signi?cant). O?ine adaptive planning required 1.9 ± 0.4 days (mean ± SD). ART decreased mean adapted PTV volume 61 ± 37 cc and bladder wall D50 compared with conventional treatment (p < 0.01). The CTV was fully covered for 96% (97%) of fractions with ART (conventional). Reconstructing dose on weekly CBCT, a nonsigni?cant reduction in CTV D99 was observed with ART (94%) compared to conventional (96%). Reduced CTV D99 with ART was signi?cantly correlated with large anterior-posterior rectal diameter on simulation CT. ART reduced the number of fractions exceeding our institution’s small bowel D1c limit from 14% to 7%. This study has demonstrated the feasibility of o?ine ART for post-prostatectomy cancer. ART facilitates PTV volume reduction while maintaining reasonable CTV coverage and can reduce the dose to adjacent normal tissues.

As of January 1, 2022, ARRT requires CE Credits for Directed Journal Readings to be based on the word count for each article. So, the number of CE Credits for each DJR article will vary for ARRT. For this article, the ARRT CE Credit will be 0.75 Credit. The MDCB CE Credits will remain at 2.5 Credits.

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