C.W. Kong

EP-1637: Dosimetric impact on different target separations in craniocaudal direction using dynamic jaws in Tomotherapy

was 74.2Gy and it ranged from 75.3Gy-77.2Gy in the deformed plans. V65 and V70 of bladder ranged from 7%28.3% and 5.7%-24.3% versus 13.7% and 11.5% in the pCT respectively. Prostate D98 and D2 ranged from 75Gy-75.8Gy and 77.2Gy-77.9Gy versus 74.2Gy and 76.2Gy in the pCT. Mean deformed volume of the prostate ranged is 40.6cm (35.5-44.4cm) versus 40.4cm in the pCT. Mean centre of mass (COM) shifts of the prostate in the x-y and z directions were -0.02cm, -0.16cm and -0.02cm respectively. Mean bladder volume is 171.4cm (83.3-268.9cm) versus 195.9cm in the pCT. Mean Dice Similarity Coefficient (DSC) of the prostate was 0.894. Conclusions: SmartAdapt is a useful tool in generating various statistical parameters such as COM shifts, DSC and volume of contoured structures. The DIR algorithm had performed well in achieving DSC >0.8 for the prostate structure set. Daily dose statistics can also be analysed for evaluation of the delivered doses with consideration of anatomical changes.

EP-1407: Quality Assurance on Helical Tomotherapy Treatments with small target and high modulation factor using ArcCHECK

planning systems: Varians Eclipse for extracranial treatments and with Brainlabs iplan for intracranial treatments. Results: Output factors of 1000 SRS agreed with semiflex measurements for field size between 3x3cm2 and 10x10 cm2. The larger deviations were observed for the 1x1 cm2 field size: compared to microDiamond, deviations of 1.6%, 2.5%, 1.7% and 3.3% were observed for 6, 10 MV FF and 6, 10 MV FFF respectively. For the 2x2 cm2 field size, deviations were less than 1.5% for 6 MV FF and 6 MV FFF and 2.5% for 10 MV FF and 10 MV FFF. The 1000 SRS showed large dependent dose rate response. This effect was about 1% for 6, 10 MV FF and increased to 2.5% for 6 MV FFF and 4% for 10 MV FFF. Stereotactic treatment plans gave excellent agreement with more than 95% of pixels passing 2%/2mm gamma criteria.

EP-1421: Reduction of delivery time in tomotherapy stereotactic radiosurgery using dynamic jaw technique

An IMRT (Sliding Window) plan was designed with the Eclipse for each patient and each density approach. Photon beams of 6 MV from a Varian Clinac 2100 CD equipped with the Varian Millennium 120 MLC were used. Patients dose distributions were calculated with AAA algorithm. The plans were optimized to meet the dosimetric requirements given by the ROSEL protocol (www.clinicalTrials.gov; ID = NCT00687986). All Eclipse plans (a total of 20) were sent to the Mobius3D software (M3D, Mobius Medical Systems, LP, Houston, TX) to be recomputed using CCCS algorithm, by keeping the same monitor units. The CCCS algorithm was factory-configured with independent basic input data for our linac model. Only the linac output and the MLC dynamic leaf gap were adjusted in the M3D system in order to match our linac. The plans computed by the Eclipse and the M3D software were compared using the 3D gamma tool. The global gamma criteria of 5%/3 mm was used. Passing gamma rate was the metric used for the PTV and OARs for comparison aim. The 95% PTV coverage (minimum dose received by the 95% of the PTV) was also compared for both systems (Eclipse and M3D). Results: 1) 3D Gamma of the PTV: when the density was not overwritten, a gamma passing rate of 74.4% was detected in a case (range: 74.4% to 100.0%). When the density correction was performed, gamma passing rates were always ≥ 90.0% (range: 91.6% to 100%). 2) 3D Gamma of the OARs: gamma passing rates ≥ 99.0% were observed for all OARs, irrespectively of the density approach adopted. 3) 95% PTV coverage: when density was not overridden, differences ≥ ±5% were observed (range: -11.3% to 2.0%). When the density correction was performed, differences ≤ ±5% were found (range: -1.8% to 4.8%) Conclusions: Better dosimetric agreement between the Eclipse/AAA and the M3D system was found when the density overwriting approach was performed. Our results suggest to perform the density overwriting approach when lung SABR is planned using the Eclipse/AAA.

ELECTRONIC POSTER: PHYSICS TRACK: DOSE MEASUREMENTSEP-1153: Application of ArcCHECK in TomoTherapy quality assurance

Previous images show the 2D dose maps obtained with the GEM detector in 64 seconds. On the right there is the map for a 2,4 x 2,4 cm X-rays irradiation field, on the left the one for a 4,0 x 4,0 cm Xrays irradiation field. Conclusions: Our detector could represent significant improvement compared to measurement systems used until today. The results confirm its potentialities especially in terms of spatial resolution, acquisition time and linearity.