ESTRO 37 Abstract book

S1201

ESTRO 37

Purpose or Objective CBCT is a standard and effective method in IGRT, however, it is time-consuming and causes an additional dose, meanwhile, it cannot be monitored the errors. Catalyst™ system is a novel optical surface imaging system for patient positioning and surveillance during radiotherapy. It has some attractive features in radiotherapy for patient positioning such as set-up, monitoring and gating, however, the application of it is also limited by relative movement of the skin and the deep tumor. In our study, we compare set-up displacements derived from Catalyst™ system to displacements derived from CBCT in order to explore the possibility of using of Catalyst™ system to replace CBCT- based IGRT. Material and Methods Set-up displacements from Catalyst TM (C-RAD, Uppsala, Sweden) and CBCT were compared for a total of 928 set- ups in 52 patients. Amongst them, 15 patients treated in the head and neck (A), 18 patients in the thorax (B) and 10 patients in abdomen (C), all patients in these three groups were fixed with the thermoplastic film. In addition, there are 9 patients treated in abdomen-thorax were fixed with vacuum pad, 5 of them with free breath (D), the other 4 patients used active breathing control (ABC) (E). Patients were using CBCT at first positioned and then scanned with the Catalyst TM , surface data captured by Catalyst TM at the first treatment fraction (CSref) was used as a reference for the Catalyst TM , while bony structures from the planning CT were used as a reference for the CBCT method. As comparison, the patient outline extracted from the planning CT was used as Catalyst TM system reference (CTref). The displacements detected by the CBCT was also used for comparison. Results The mean differences and standard deviation of 52 patients between the Catalyst TM and CBCT displacements in 6 dimensions direction (lateral/longitudinal/vertical/rotation/roll/pitch) were - 0.24±3.64mm, 1.63±5.88mm, 0.58±3.41mm, -0.11±1.55°, 0.05±1.40° and 0.10±1.14°. Which in group A were - 0.16±2.67mm, -0.81±2.31mm , 0.56±2.53mm, 0.40±1.36°, -0.16±1.33° and 0.36±1.17°; in group B were 0.00±4.08mm, 0.22±5.57mm, 0.46±3.04mm, -0.36±1.43°, 0.23±1.26° and -0.10±1.02°; in group C were 0.03±4.01mm, 4.90±8.07mm , 0.50±3.46mm, - 0.10±1.10°, 0.29±1.66° and 0.19±1.14°; in group D were - 2.36±5.14mm, 4.57±7.81mm , 1.91±4.45mm, - 1.45±1.96°, 0.50±1.26° and -0.44±1.09°; in group E were -0.23±2.34mm, 0.74±3.56mm, -0.01±2.76mm, 0.46±2.52°, 0.92±1.30° and -0.17±1.21°, respectively. Compared with CBCT, the Catalyst TM for radiotherapy guided placement in the head and neck region and abdmen–thorax (application with ABC) are more accurate (0.70

volume delineated in the planning CT, thus boost delivery data was not in the data bank. For the continuous data, the fraction of outliers and extreme outliers between manually reported and data bank values were calculated. These were defined as data differences outside box-plot- whiskers of 1.5 or 3 times the interquartile range, respectively. Except for date of RT and volume of CTV which had ~5% and ~2% of outliers and extreme outliers, the typical fractions were ~20% and ~10%, respectively. A major part of the differences could be related to either mistyping of numbers (e.g. interchange of digits), while others were related to a misunderstanding of which value to report (e.g. V95 or 1-V95). However, some of the deviation was also related to uncertainty of reported max dose values, which are sensitive to the specific algorithm used to calculate these values. Checks on all dose parameters showed consistency between treatment plans used for manual reporting and those in the data bank.

Conclusion The data quality of the data bank is superior to the quality of the manually reported values - in particular for the continuous data. In the current study, 10% of the continuous data were classified as extreme outliers and could influence results from clinical trials. However, some of the wrong manual data would have been detected, since the values were off by orders of magnitude, but the majority would be hard to detect without input from the data bank. The superior data quality of the data bank, and the detailed information available, support the use of data banks for future research. EP-2170 A feasibility study of optical surface imaging technology in radiotherapy L. Yang 1 , G. Han 1 , Q. Song 1 , C. Ruan 1 , L. Li 2 , R. Zhong 2 , S. Bai 2 1 Renmin Hospital of Wuhan University, Department of Oncology, Wuhan, China 2 West China Hospital of Sichuan University, Radiation physics technology center, Chengdu, China