ESTRO 2023 - Abstract Book

S1788

Digital Posters

ESTRO 2023

algorithm employed by the TPSs during the transfer, to improve the understanding of the main possible cause of such variations.

PO-2014 Does Hippocampal Sparing in Stereotactic Radiosurgery Increase Whole Brain Volumetric Parameters?

T. Ulu 1,1 , C. Azak 1 , S. Sahin 2 , M.B. Altundag 3 , F. Goksel 1 , G.S. Kilicoglu 1 , E. Karakaya 1

1 Dr. Abdurrahman Yurtaslan Ankara Oncology Training and Research Hospital, Radiation Oncologist, Ankara, Turkey; 2 Dr. Abdurrahman Yurtaslan Ankara Oncology Training and Research Hospital , Physicist(PhD Student), Ankara, Turkey; 3 Dr. Abdurrahman Yurtaslan Ankara Oncology Training and Research Hospital , Radiation Oncologist, Ankara, Turkey Purpose or Objective The role of hippocampus (HC) in both memory and cognitive impairment has been well defined and cranial irradiation has a long term negative effects on these functions .So our aim in this study is to investigate whether hippocampal sparing during in SRS via CyberKnife®(CK) can effect whole brain (WB) doses , coverage of target volume or not. Materials and Methods Ten consecutive patients' 21 radiosurgery plans for 21 brain metastatic lesions who underwent SRS via CK without avoding hippocampus and WB were utilized retrosectively.The median SRS dose was 18 Gy (18-20Gy).21 metastatic lesions were re- planned again in CK taking ino account HC as an OAR.These 21 metastatic lesions' plans were compared separately as if single metastatic lesions with and without HC sparing. Results The comparison of 21 plans (with and without HC sparing) were summarised in table 1 in terms of hippocampus, WB doses and target volume coverage doses.Right and left HC were evaluated separately. For HC dose constraints ; Dmax(maximum dose), D100(dose as a cGy taken by %100 of the organ at risk volume),D40 (dose as a cGy taken by %40 of the organ at risk volume),Dmean(mean dose) were reported.For WB ; V(WB-GTV)4mm3, V(WB-GTV)8mm3 , V(WB-GTV)12mm3, V(WB- GTV)16mm3 (the volume of the WB-GTV as a mm3 receiving 4 ,8,12,16 Gy ,respectively)were investigated.In addition for tumor coverage , PTVD98cGy( dose as a cGy receiving by the %98 of the PTV volume), PTVDmaxcGy (maximum dose of the PTV), PTVDmincGy (minimum dose of the PTV) , Homogeneity index (maximum dose /prescribed dose of the target), Conformity index(prescribed isodose volume/target isodose volume) were reported.Out of all parameters investigated, only V(WB-GTV)8mm3,V(WB-GTV)12mm3 values were statistically significant and and R Hippocampus D40(p=0,094)has a trend for significancy,respectively(Wilcoxon test results).Also, when GTV was categorised as 2 separate volumes( ≤ 0,6cm3vs>0,6cm3), all WB volumetric parameters were higher wth bigger gtv. Median Median

p value constraints(<)

( sparing+)

( sparing-)

V(WB-GTV)4mm3 V(WB-GTV)8mm3 V(WB-GTV)12mm3 V(WB-GTV)16mm3

20652,4 6890,3 3468,5 1595,5 1821,6

20144,4 0,170

0,05

6659,5 3405,5

,0181 <7850

1599 1800 2278 1728 1,27

0,590 0,842 0,637 0,330 0,339 0,541 0,274 0,140 0,317 N/A 0,094 0,246 0,455

PTVD98cGy PTVDmaxcGy PTVDmincGy

2278 1739 1,27

HI

Conformity index R Hippocampus DmaxcGy L Hippocampus DmaxcGy R Hippocampus D100cGy L Hippocampus D100cGy R Hippocampus D40cGy L Hippocampus D40cGy R Hippocampus DmeancGy L Hippocampus Dmean PTV %coverage Number of beams

1,35 104,41 88,89

1,37 120,41 139,45

1600

0 0

1600 900 900 730 730

0 0

26,32 25,97 34,48

26,67 26,67 31,92

all nonsignificant all nonsignificant all nonsignificant

Conclusion SRS via CK®seems has an advantage in protecting hippocampus and WB even without hippocampal sparing.When hippocampal sparing plans were performed, V(WB-GTV)8mm3 and V(WB-GTV)12mm3 were higher,however target coverage was not effected.So when protecting hippocampus, attention should be given to WB doses.

PO-2015 The role of Acuros XB in the inverse optimization of lung VMAT plans evaluated by 4DCT reality