TY - JOUR
T1 - Commissioning of Varian ring & tandem HDR applicators
T2 - Reproducibility and interobserver variability of dwell position offsets
AU - McMahon, Ryan
AU - Zhuang, Tingliang
AU - Steffey, Beverly A.
AU - Song, Haijun
AU - Craciunescu, Oana I.
PY - 2011
Y1 - 2011
N2 - Studies have shown that source dwells within Varian's HDR CT/MR compatible ring applicators can deviate from intended positions by several millimeters. Quantifying this offset is an important part of commissioning. The aims of this study were to: 1) determine the reproducibility of the offset, 2) study the interobserver variation in the offset's measurement, and 3) quantify the dosimetric impact of the offset. Offsets were measured for four ring applicators: two 30°, one 45°, and one 60°. Dwell positions were measured five times for each ring to determine the reproducibility of source positioning. Experiments were done to compare two separate source wires, as well as different time points within a single source wire's lifecycle. Data were analyzed by three independent observers. To quantify the dosimetric impact of the offset, a treatment plan was generated using BrachyVision. The dose to point A, and the D2cc metric for rectum and bladder were calculated with and without the offset. For the 45° and 60° rings, measured offsets were 3.0mm and 3.6 mm, respectively. The 30° ring showed substantial variation in distal dwell positions (maximum difference between the five experiments of 2.9 mm). Subsequent testing of a replacement ring showed an offset of 2.4 mm that was more reproducible. Offsets varied less than 1 mm between different source wires, and changed less than 1 mm over the course of a source wire's lifecycle. When comparing observers, the average range in a measurement of a dwell position was 0. 5mm (σ = 0.2 mm, max 1.3 mm). The offset resulted in dose variations to point A, bladder, and rectum of less than 1%, 2%, and 5%, respectively. Results indicate that Varian rings can show systematic and random offsets of more than 3 mm. Some can be considered defective and should be replaced. Each applicator should be individually commissioned and reproducibility should be confirmed with multiple tests.
AB - Studies have shown that source dwells within Varian's HDR CT/MR compatible ring applicators can deviate from intended positions by several millimeters. Quantifying this offset is an important part of commissioning. The aims of this study were to: 1) determine the reproducibility of the offset, 2) study the interobserver variation in the offset's measurement, and 3) quantify the dosimetric impact of the offset. Offsets were measured for four ring applicators: two 30°, one 45°, and one 60°. Dwell positions were measured five times for each ring to determine the reproducibility of source positioning. Experiments were done to compare two separate source wires, as well as different time points within a single source wire's lifecycle. Data were analyzed by three independent observers. To quantify the dosimetric impact of the offset, a treatment plan was generated using BrachyVision. The dose to point A, and the D2cc metric for rectum and bladder were calculated with and without the offset. For the 45° and 60° rings, measured offsets were 3.0mm and 3.6 mm, respectively. The 30° ring showed substantial variation in distal dwell positions (maximum difference between the five experiments of 2.9 mm). Subsequent testing of a replacement ring showed an offset of 2.4 mm that was more reproducible. Offsets varied less than 1 mm between different source wires, and changed less than 1 mm over the course of a source wire's lifecycle. When comparing observers, the average range in a measurement of a dwell position was 0. 5mm (σ = 0.2 mm, max 1.3 mm). The offset resulted in dose variations to point A, bladder, and rectum of less than 1%, 2%, and 5%, respectively. Results indicate that Varian rings can show systematic and random offsets of more than 3 mm. Some can be considered defective and should be replaced. Each applicator should be individually commissioned and reproducibility should be confirmed with multiple tests.
KW - Brachytheraphy
KW - Commissioning
KW - High-dose rate
KW - Offset
KW - Tandem and ring
UR - http://www.scopus.com/inward/record.url?scp=81855211969&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=81855211969&partnerID=8YFLogxK
U2 - 10.1120/jacmp.v12i4.3447
DO - 10.1120/jacmp.v12i4.3447
M3 - Article
C2 - 22089000
AN - SCOPUS:81855211969
SN - 1526-9914
VL - 12
SP - 50
EP - 62
JO - Journal of applied clinical medical physics
JF - Journal of applied clinical medical physics
IS - 4
ER -