ESTRO 38 Abstract book

S1165 ESTRO 38

individual IMRTQA measurement. (n) is total number of measurements. Results The average pass rate of volumetric 3D gamma index for global normalization with criteria 3%,3mm, the specific tolerance limit and action limits for each anatomical site were shown in table 1. Gamma values resulted outside LCL only for about 6%, 2.5%, 4% of cases for Head and Neck, Prostate, post Prostatectomy and Pelvic case respectively. The chart control limit was constructed for each site based on the SCP. An example for Head and Neck patient is presented in

Conclusion In terms of robustness, the 6F approach could be considered similar to the 8F one. Nevertheless, 6F delivery time is reduced by 20% compared to the 8F technique. Indeed, for a comparable amount of spots, the couch movements between fields are reduced from 7(8F) to 5(6F), thus reducing intrafraction motion. 6F approach should therefore be preferred over the 8F one, even if other cases should be investigated to strenghten our conclusion. EP-2106 Statistical process control analysis of pre- treatment VMAT QA for different anatomical sites H. Omar Ghafour 1 , S. Russo 2 , M. Esposito 2 , S. Pini 2 , A. Ghirelli 2 , G. Zatelli 2 1 Ministry of Health KRG / Sulaymani directorate of health of Health/ Zhianawa Cancer Center, Zhianawa Cancer Center, Sulaymaniyha, Iraq ; 2 Azienda USL Toscana Centro, Medical Physics Unit- Azienda USL Toscana Centro- Sede di Firenze-, Firenze-, Italy Purpose or Objective Pre-treatment patients specific QA are used to validate the dosimetry of VMAT plans and to evaluate dosimetric performance over time of VMAT QA process. Discrepancy tolerance limits between calculated and delivered radiation doses are neither well defined nor consistently applied. The aim of this work is to determine the Tolerance limit and the Action Limit for the dose delivery process for different anatomical sites. Material and Methods QA measurements were performed by PTW Octavius 4D 729 in the PTW Octavius 4D phantom for 464 VMAT plan for six anatomical sites: Head and Neck, Lung, Breast, Prostate, post prostatectomy , Abdominal and Pelvic case. Measurements were compared with TPS Elekta Monaco 5.1 computed doses via 3D global gamma analysis 3%G/3mm (global normalization point value >90% of maximum dose) by using PTW VeriSoft software 6.1. The Action limit and tolerance limit were established, by using the concept of Statistical control process (SPC), as suggested by AAPM Task Group 218: ΔA=βχ SQRT( σ² +(x̅-T) Eq(1) Action limit=(100- ΔA/2) Eq(2) Tolerance limit (LCL) = x̅ - 2.66 x (mean moving range ) Eq(3) Mean moving range (MR)=1/(n-1) χ ∑ |Xi-Xi- 1| Eq(4) where ΔA is the difference between the upper and lower action limits (typically written as ± ΔA /2); T is the process target value (100% for QA VMAT); σ² and x̅ are the process variance and process mean, respectively and β is a parameter whose suggested value is equal to 6. The moving range is absolute difference between two successive point data in the time ordered data and can be calculated according equation (4), where (X) is an

Conclusion The action limits and tolerance limits for the specific couple of linac and measuring system used in this work were determined and stratified for different anatomical site. The Control chart limit approach indicates that the process is under control. EP-2107 DQA gamma Analysis evaluation criteria for prostate SBRT using MLC InCise 2 of a Cyberknife-M6 A. Ruiz 1 , K. Torzsok 1 , M. Ribeiro 1 , H. Broqué 1 , J. Aponte 1 , F. Marangoni 1 1 Fundación Arturo López Pérez, Radiotherapy, Santiago de Chile, Chile Purpose or Objective A multileaf collimator (MLC) for radiosurgery on a robotic arm is new worldwide. The Cyberknife M6 ® shapes the beam in 3 ways, one through the MLC InCise2 ® consisting of 26 leaf pairs, each with a width of ≈ 2 mm. The maximum field size is 115 mm × 100.1 mm. Patient specific quality assurance evaluation criteria recommended internationally are scarce. The objective of this work is to determine tolerance criteria and gamma approval rates achievable for evaluation and validation of the gamma index and CC01 IBA ® ionization chamber point dose measurements in prostate SBRT performed with the MLC InCise2 ® on a sample of 22 treated patients. Material and Methods A film dosimetry method was developed. A 24 hours calibration curve was made with EBT3 films and Omnipro software for evaluation of SBRT prostate plans, 2 dose planes and film background correction were used for each patient. Absolute and relative calculations were made, with different criteria to test approval rates ranges, as well as, the average gamma to obtain with this MLC with statistical parameters. Physics time investment per patient was ≈3.5 hours. The algorithm used by treatment planning system (TPS) is equivalent path length type A. MLC less collimation limits given by the manufacturer were evaluated, considering tests analogous to those proposed by James L Bedford et al. Results Different criteria of approval rate value, as well as modulation factor (MF) has not shown a defined trend