ESTRO 2023 - Abstract Book

S1770

Digital Posters

ESTRO 2023

PO-1996 Dosimetric assessment of 3D Radiotherapy and IMRT in Wilms’ tumor : benefit-risk balance

N. Bouzid 1 , R. Zanzouri 1 , B. Amri 1 , M. Souissi 1 , S. Tbessi 1 , S. Belaajouza 1 , S. Tebra 1

1 Farhat Hached Hospital, Radiation Oncology Department, Sousse, Tunisia

Purpose or Objective This study was performed to compare dose distributions between 3D conformal radiotherapy (3D-RT) and intensity modulated radiotherapy (IMRT) in children with wilms tumor (WT) that received flank irradiation. Materials and Methods A descriptive, analytical, study carried out with 13 patients who received flank irradiation for WT using 3D-RT, between 2014 and 2020, and who were replanned afterword using IMRT with simultaneous integrated boost (SIB), at the radiation oncology department of the Farhat Hached Hospital, Sousse, Tunisia. Techniques were compared according to dose volume histograms (DVHs) analysis. For the volume of interest, the planning target volume doses, conformity index (CI) and homogeneity index (HI) were calculated. Dose constraints of all the organs at risk (OAR) and dose received by normal tissues : Low doses (V10%, V30%) and normal tissue integral dose (NTID) were compared. Results The median age was 5 years [2-13] with a slight female predominance [sex ratio = 0.85]. Fifty three percent of patients had right-sided tumours. Prescribed dose was 14.4 Gy for 7 patients and 25.2 Gy for 6 patients. IMRT was associated with better PTV coverage as compared with 3D-RT, with superior results for all the evaluated parameters (V95%, V98%, V100% et D95 ; p<0.05). The HI was statistically better for IMRT than for 3D-RT (0.07 IMRT versus 0,32 3D ; p=0.001) but there was little difference in the CI (0,94 IMRT versus 0,68 3D ; p=0.054). For comparative plans, maximum, minimum, median doses and V10% were lower for the remaining kidney with IMRT than with 3D-CRT (p<0.05). There was no significant difference in Dmax and Dmoy in the pancreas, but there was a significant decrease in Dmin in favor of IMRT (p=0.03). There was a significant improvement in small bowel dose (Dmin and Dmoy) with IMRT (p<0.05). The mean dose delivered to the spleen and liver in the IMRT and 3D-RT showed no statistical difference. For the vertebrae, no significant difference in Dmax was found, however, the HI was improved by IMRT (0.04 IMRT versus 0.5 3D ; p=0.003). Dosimetric values were compared using the Wilcoxon signed-rank test

IMRT increased the volume of normal tissue receiving at least 10% and 30% of the prescribed dose : V10% (2536.5 IMRT versus 1599 3D ; p=0.001) and V30% (1752 IMRT versus 1171 3D ; p=0.001).

NTID was significantly higher in IMRT: the median NTID was 20196.7 and 18133.3 the IMRT and 3D, respectively (p=0.01).

Conclusion The use of IMRT is an efficient radiotherapy technique. It is associated with better coverage to the PTV and lower radiation doses to the remaining kidney and other OAR and when compared with 3D-RT for flank irradiation in WT. This last objective is mainly relevant in children. However, IMRT increases dose received by normal tissues, factor of risk for Radiation-induced second malignancies.

PO-1997 Dosimetric comparison of multileaf and fixed cone collimator plans with cyberknife

C. Demiroz Abakay 1 , Z. Kıray 1 , S. Çetinta ş 1 , M. Kurt 1

1 Uludag University Faculty of Medicine, Radiation Oncology, Bursa, Turkey

Purpose or Objective Stereotactic radiosurgery (SRS) is an increasingly utilized and well tolerated treatment for benign skull base tumors such as glomus jugulare and acoustic schwannoma. Treatment planning of those tumors is particularly complex because of the close proximity of the critical structures.CyberKnife (CK) is a SRS technique that ensures highly conformal dose distrubutions using a linac based robotic arm and image guidance with real-time tumor tracking. We retrospectively aimed to evaluate the clinical feasibility and dosimetric outcomes of the target and the normal tissues with MLC and fixed cone- based plans in benign skull base tumors. Materials and Methods Eleven acoustic schwannoma and 7 glomus jugulare patients were treated with CK-M6 and the plans with different collimators were retrospectively evaluated. Parameters such as treatment time, homogenity index (HI), conformity index (CI) and gradient index (GI), monitor units (MUs) and volumetric doses of brain, brainstem, cochlea, were analyzed. The obtained dosimetric outcomes were compared to each other to define the best treatment technique. Results In our analysis, cochlea dose was significantly lower in MLC plans compared to fixed ones (p:0,023). Brainstem maximum point dose and also V10 Gy and V15 Gy of brain were significantly lower in MLC plans (p:0,021, p:0,014, p:0,000, retrospectively). Due to MLC plans consist of less nodes and segments in comparison to fixed plans, use less MU and are deliverable in a shorter treatment time (p: 0,00). The average delivered MUs in MLC plans are lower by 45 % (p:0,000).