title: Dose-volume factors to select patient-specific image-guidance action thresholds in prostate cancer.
abstract: For radiation delivery tracking systems that monitor intrafraction prostate motion, generalized departmental threshold protocols may be used. The purpose of this study is to determine whether predefined action thresholds can be generally applied or if patient-specific action thresholds may be required. Software algorithms were developed in the MatLab (The Mathworks Inc., Natick, MA) software environment to simulate shifts of the patient structure set consisting of prostate, bladder, and rectum. These structures were shifted by 1/2 10 mm in each direction in 1 mm increments to simulate displacements during treatment, without taking into consideration organ deformity. Dose-volume data at each shift were plotted and analyzed. A linear relationship was observed between planning dose-volume parameters and shifted dose-volume parameters. For a 5 mm anterior shift, it was observed that individual rectal V70 values increased by absolute magnitudes of 6-15%, dependent on the planning rectal V70 of each patient. Likewise, for a 5 mm inferior shift, individual bladder V70 values increased by 1-14%, dependent on planning bladder V70. This linear relationship was observed for all levels of shifts up to 10 mm. Since rectum and bladder dose-volume changes due to patient shifts are dependent on dose-volume parameters, this study suggests that patient-specific action thresholds may be necessary.
authors.affiliation: Stritch School of Medicine and Department of Radiation Oncology, Loyola University Medical Center, 2160 S. First Ave. Maguire Center - Rm. 2946, Maywood, IL 60153, USA.
authors.forename: A M
authors.initials: AM
authors.lastname: Block
authors.forename: J
authors.initials: J
authors.lastname: Lin
authors.forename: M A
authors.initials: MA
authors.lastname: Hoggarth
authors.forename: M
authors.initials: M
authors.lastname: Quinn
authors.forename: R
authors.initials: R
authors.lastname: Garza
authors.forename: C A
authors.initials: CA
authors.lastname: Mantz
authors.forename: J C
authors.initials: JC
authors.lastname: Roeske
mesh_terms: D000230:Adenocarcinoma / Q000000981:diagnostic imaging*; D000368:Aged; D006801:Humans; D008297:Male; D008875:Middle Aged; D011187:Posture; D057285:Precision Medicine; D011467:Prostate / Q000000981:diagnostic imaging; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D012007:Rectum / Q000000981:diagnostic imaging; D012189:Retrospective Studies; D012984:Software; D014057:Tomography, X-Ray Computed; D001743:Urinary Bladder / Q000000981:diagnostic imaging