Dosimetric Effect of Online Image-Guided Anatomical Interventions for Postprostatectomy Cancer Patients

• Published in: International journal of radiation oncology, biology, physics Vol. 79; no. 2; pp. 623 - 632
• Main Authors: Diot, Quentin, Olsen, Christine, Kavanagh, Brian, Raben, David, Miften, Moyed
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 01.02.2011; Elsevier
• Subjects: Aged; Applied radiobiology (equipment, dosimetry...); Biological and medical sciences; Biological effects of radiation; BLADDER; BODY; Cone-Beam Computed Tomography; DEFORMATION; DIGESTIVE SYSTEM; DISEASES; Dose Fractionation; DOSES; Dosimetry; Fundamental and applied biological sciences. Psychology; GASTROINTESTINAL TRACT; GLANDS; Hematology, Oncology and Palliative Medicine; Humans; Intervention; INTESTINES; LARGE INTESTINE; Male; MALE GENITALS; MEDICINE; Middle Aged; MOTION; Movement; NEOPLASMS; NUCLEAR MEDICINE; Organ motion; Organ Size; ORGANS; Organs at Risk - radiation effects; Postprostatectomy; PROSTATE; Prostatectomy; Prostatic Neoplasms - diagnostic imaging; Prostatic Neoplasms - pathology; Prostatic Neoplasms - radiotherapy; Prostatic Neoplasms - surgery; RADIATION DOSES; Radiation Injuries - prevention & control; RADIOLOGY; RADIOLOGY AND NUCLEAR MEDICINE; RADIOTHERAPY; Radiotherapy Planning, Computer-Assisted; Radiotherapy, Intensity-Modulated - methods; RECTUM; Rectum - anatomy & histology; Rectum - diagnostic imaging; Retrospective Studies; SHAPE; SURGERY; THERAPY; Tissues, organs and organisms biophysics; Tumor Burden; Urinary Bladder - anatomy & histology; Urinary Bladder - diagnostic imaging; URINARY TRACT; VOLUME; Intervention; Postprostatectomy; Organ motion; Dosimetry; Guidance; Human; Motion; Malignant tumor; Anatomy; Cancer
• ISSN: 0360-3016; 1879-355X; 1879-355X
• DOI: 10.1016/j.ijrobp.2010.04.020

To assess daily variations in delivered doses in postprostatectomy patients, using kilovoltage cone-beam CT (CBCT) datasets acquired before and after interventions to correct for observed distortions in volume/shape of rectum and bladder. Seventeen consecutive patients treated with intensity-modulated radiotherapy to the prostate bed were studied. For patients with large anatomical variations, quantified by either a rectal wall displacement of >5 mm or bladder volume change of >50% on the CBCT compared with the planning CT, an intervention was performed to adjust the rectum and/or bladder filling. Cumulative doses over the pre- and post-intervention fractions were calculated by tracking the position of the planning CT voxels on different CBCTs using a deformable surface-mapping algorithm. Dose and displacements vectors were projected on two-dimensional maps, the minimal dose received by the highest 95% of the planing target volume (PTV D95) and the highest 10% of the rectum volume (D10) as well as the bladder volume receiving >2 Gy (V2) were evaluated. Of 544 fractions, 96 required intervention. Median (range) number of interventions per patient was 5 (2–12). Compared with the planning values, the mean (SD) pre- vs. postintervention value for PTV D95 was −2% (2%) vs. −1% (2%) ( p < 0.12), for rectum D10 was −1% (4%) vs. +1% (4%) ( p < 0.24), and for bladder V2 was +6% vs. +20% ( p < 0.84). Interventions to reduce treatment volume deformations due to bladder and rectum fillings are not necessary when patients receive daily accurate CBCT localization, and the frequency of those potential interventions is low. However, for hypofractionated treatments, the relative frequency can significantly increase, and interventions can become more dosimetrically beneficial.