Image‐guided method for TLD‐based in vivo rectal dose verification with endorectal balloon in proton therapy for prostate cancer. Issue 5 (26th April 2013)

• Record Type: Journal Article
• Authors: Hsi, Wen C.; Fagundes, Marcio; Zeidan, Omar; Hug, Eugen; Schreuder, Niek
• Is Part Of: Medical physics. Volume 40:Issue 5(2013)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2013-04-26
• Subjects: Therapeutic applications, including brachytherapy -- Dose‐volume analysis -- X‐ray imaging; biological organs -- biomedical imaging -- dosimetry -- radiation therapy -- thermoluminescent dosimeters -- X‐ray imaging; Rectal balloon daily positioning -- metallic marker -- TLD in vivo dosimetry -- proton therapy -- prostate cancer; Radiation therapy -- Dosimeters; Thermoluminescent dosimeters -- Medical imaging -- Dosimetry -- Medical X‐ray imaging -- Protons -- X‐ray imaging -- Radiography -- Computed tomography -- Proton therapy -- Cancer; Medical physics -- Periodicals; Medical physics; Geneeskunde; Natuurkunde; Toepassingen; Biophysics; Periodicals; Periodicals; Electronic journals; 610.153
• DOI: 10.1118/1.4801901
• Languages: English
• ISSNs: 0094-2405

Abstract

Abstract : Purpose: : To present a practical image‐guided method to position an endorectal balloon that improves in vivo thermoluminiscent dosimeter (TLD) measurements of rectal doses in proton therapy for prostate cancer. Methods: : TLDs were combined with endorectal balloons to measure dose at the anterior rectal wall during daily proton treatment delivery. Radiopaque metallic markers were employed as surrogates for balloon position reproducibility in rotation and translation. The markers were utilized to guide the balloon orientation during daily treatment employing orthogonal x‐ray image‐guided patient positioning. TLDs were placed at the 12 o'clock position on the anterior balloon surface at the midprostatic plane. Markers were placed at the 3 and 9 o'clock positions on the balloon to align it with respect to the planned orientation. The balloon rotation along its stem axis, referred to as roll, causes TLD displacement along the anterior‐posterior direction. The magnitude of TLD displacement is revealed by the separation distance between markers at opposite sides of the balloon on sagittal x‐ray images. Results: : A total of 81 in vivo TLD measurements were performed on six patients. Eighty‐three percent of all measurements (65 TLD readings) were within +5% and −10% of the planning dose with a mean of −2.1% and a standard deviation of 3.5%. Examination of marker positions with in‐room x‐ray images of measured doses between −10% and −20% of the planned dose revealed a strong correlation between balloon roll and TLD displacement posteriorly from the planned position. The magnitude of the roll was confirmed by separations of 10–20 mm between the markers which could be corrected by manually adjusting the balloon position and verified by a repeat x‐ray image prior to proton delivery. This approach could properly correct the balloon roll, resulting in TLD positioning within 2 mm along the anterior‐posterior direction. Conclusions: : Our results show that image‐guided TLD‐based in vivo dosimetry for rectal dose verification can be perfomed reliably and reproducibly for proton therapy in prostate cancer.