ESTRO 37 Abstract book

S1224

ESTRO 37

skin (1cm 2 ) isodose≥85% were calculated as measures for skin toxicity risk. Results 22 specimen were included for spacer injection; 11 HA, 11 PEG. Success of the intervention was 100% for HA and 90.9% for PEG (p=0.999). Mean injected volumes were 8.4ml for HA and 7.3ml for PEG (p=0.141). Hydrodissection was possible in 81.8% with HA and 63.6% with PEG (p=0.635). Mean SUS score was 96 for HA and 81 for PEG (p<0.001). Mean V 100 was 95.9% without spacer and 94.3% with spacer (p=0.001). Mean V 200 was 22.5% without spacer and 28.1% with spacer (p<0.001). Mean D 0.2cc was 80.8Gy with and 53.5Gy without spacer (p<0.001). Mean D 0.05cc was 78.1Gy with and 52.4Gy without spacer (p<0.001). Skin isodose≥85% was present in 13/22 (59.1%) specimen without spacer and 1/22 (4.5%) specimen with spacer (p<0.001). Conclusion This pilot study shows a very high success rate of a subcutaneous spacer injection for skin protection during breast brachytherapy. A spacer thickness of ≥5mm can reduce the skin dose dramatically. For this purpose, HA is superior to PEG. Clinical evaluation of the effect on skin toxicity is needed. This intervention could potentially protect the skin during several forms of brachytherapy in the future. EP-2214 New angular indicator of Ring Applicator in brachytherapy reconstruction/commissioning procedure V. Stserbakov 1 , K. Aru 1 1 North-Estonian Regional Hospital Cancer Center, Department of Radiotherapy and Oncology, Tallinn, Estonia Purpose or Objective Introduce into clinical practice angular indicator (AI) of Varian titanium Ring Applicator for more precise identification radiation source first position in magnet resonance image. Estimate the visibility of new landmark. To compare/discuss used "zig-zag” method of applicator reconstruction/ commissioning with another approaches for this procedure in an attempt to more accurate take into account 'snaking effect” of the source cable. Material and Methods For making distinct MR mark on ring applicator the diameter 5 mm groove in acetal build-up cap was chosen for reason of a good visibility on MR pictures since, as have been seen on MR images, the 1.5 mm diameter needle hole in the cap is quite identifiable on picture if the hole is filled with water. For ring applicator reconstruction/commissioning we use 'zig-zag” method, in which it is realized procedure for achieving the coincidence between commissioned data for source positions and edited library applicator source locations in three points: in positions no. 1, 4 and 9 (step size=1 cm). The first position of the source (no.1) located in its accurate point using known angular shift from AI (in this case it is a zero of angular coordinate), for example, 21.0° from AI (0°). The source dwell-positions no. 4 and 9 are adjusted by inserting 'zig-zag” between 1 and 2 source positions achieving compromised coincidence between measured and library angular coordinate for these points. Essential adventure of 'zig-zag” reconstruction method that it is needed only ones Gafromic film-test measurement for source dwell-times position has to be done (step size = 1 cm and offset = 0.0 cm) and subsequently library applicator data then will be adjusted to measured angular values. Adjustment by 'zig- Electronic Poster: Brachytherapy: Gynaecolgy

zag” method is smooth and quit sensitive while other known methods of correction are 1 mm stepwise and need more than one Gafromic film-test measurements. The shortcoming of 'Varian method”, for example, that position no.1 is excluded from using.

Results 5 mm diameter plastic tube filled with water inserted into groove of acetal build-up cap demonstrates good visibility in MR images even in cases when patient was slightly moving. The outlining the build-up cap on the Gafromic film-test in commissioning procedure provides precise direction of AI. For discussed applicator reconstruction method (as desired) the measured and planned source positions coincide for position no.1. For dwell positions no. 4 and 9 differences between measured and planned source positions do not exceed ±0.6° order of magnitude or ±0.2 mm length on ring source path.

Conclusion As an angular reference point new angular indicator of ring applicator proved high visibility and distinctness in MR images. Applicator reconstruction using 'three points” technique with 'zig-zag” method provides adequate taking into account the cable 'snaking effect” and a good coincidence between commissioning film-test data for source positions and edited library applicator source locations. EP-2215 Anatomic variations impact on organs at risk doses during 3D adjuvant cervical cancer brachytherapy A. Tomasevic 1 , V. Plesinac Karapandzic 1 , S. Stojanovic Rundic 1 , M. Tomasevic 2 , S. Vuckovic 1 , B. Rakovic 1 , M. Mikovic 1 , D. Marjanovic 1 1 Institute for Oncology & Radiology of Serbia, Department of Radiotherapy, Belgrade, Serbia 2 Institute for Students’ Healthcare, Department of General practice, Belgrade, Serbia Purpose or Objective To investigate the influence of the anatomic variations on the registered doses on organs at risk (OARs) during computed tomography (3D) based brachytherapy