ESTRO 2020 Abstract Book

S652 ESTRO 2020

Veno-

ipsilateral kidney V18Gy

46.61±25.7 3

51.17±23.7 9

0.

Liver (mea n±SD)

4.67±0.7

5.40±0.6

<1

<75%

0.84

occlusive disease Chronic renal dysfunctio n renal dysfunctio n Chronic

012

3

0

0

V14Gy

<100% 73.88±15.9 7

85.41±3.80 0.83

Right kidney (me an±SD) Left kidney (me an±SD)

0.

5.28±1.2

7.68±0.7

<1

contralateral kidney 18Gy liver V15Gy

<25% 11.28±8.91 12.20±9.53 1.00

001

5

3

7.8

<25% 16.20±7.66 13.49±5.80 0.14 <50% 45.93±6.57 44.82±5.28 1.00 <15Gy 9.14±1.08 8.81±0.79 0.62

V8Gy

0.

5.21±1.0

7.13±1.1

<1

Dmean

002

3

2

7.8

irradiated vertebrae D80%

>16.8G y

19.72±1.02 19.48±1.33 0.98

Abbreviations: CI, conformity index; Dmean, mean dose; HI, homogeneity index; PTV, planning target volume; PTVx%, volume of PTV receiving ≥ x% of prescribed dose. Conclusion We observed the better target coverage in IMRT. With the more conform and homogeneous dose, VMAT achieved better normal tissue sparing in head and neck region while IMRT provided better dose reduction to organs at risk in chest and abdominal regions. PO-1238 Dosimetric study comparing IMRT to VMAT in completed resection pediatric abdominal neuroblastoma T. Treechairusame 1 , N. Suntornpong 1 , K. Thephamongkhol 1 , P. Ieumpongpaibool 1 , W. Rongthong 1 1 Faculty of Medicine Siriraj Hospital, Radiation Oncology, Bangkok, Thailand Purpose or Objective This study evaluates and compares the dose distribution of target coverage, integral dose and normal tissue sparing between IMRT and VMAT in completed resection pediatric abdominal neuroblastoma Material and Methods Patients 1 month to 15 years old with completed resection abdominal neuroblastoma treated with induction chemotherapy followed by completed resection and radiotherapy between 2011 and 2018 were selected for treatment planning simulation. The contours of patients were reviewed by two radiation oncologists. Then, both IMRT and VMAT techniques were done and compared for each patient. The dose prescription was 21.6 Gy in 1.8 Gy- fraction. Planning target volume (PTV) was the first priority; at least 95% of PTV was covered by 95% of prescribed dose for both plans. All patients were re- planned and re-evaluated. Results Patients were divided into two groups; 4 patients without radical nephrectomy group and 4 patients with radical nephrectomy. Target coverage was achieved in all cases with 2 techniques without statistically significant (98.29% vs 96.60%, p=0.083 in IMRT and VMAT respectively). The conformal dose distribution and homogeneous dose distribution of IMRT was also similar to VMAT: IMRT 1.28 vs VMAT 1.21 (p=0.64) and IMRT 0.08 vs VMAT 0.11 (p=0.55), respectively. The integral dose was lower in VMAT than IMRT without statistically significant (0.96 vs 0.89, p=0.18). Reduced dose to ipsilateral kidney in IMRT was observed without statistically significant . Doses to contralateral kidney, liver, vertebrae were no difference between 2 techniques(Table). Overall passing criteria of VMAT was higher than IMRT (62.5% vs 87.5%). Parameter(mean±S D) Goal IMRT VMAT P- valu e PTV V95% 95% 98.29±1.40 96.60±1.07 0.08 CI 1 1.28±0.17 1.21±0.2 0.64 PCI 1 0.77±0.09 0.78±.0.10 3 1.00 HI 0 0.08±0.02 0.11±.02 0.06 Integral dose 0.96±0.62 0.89±0.56 0.18

Dmax

22.89±0.34 22.93±0.13 1.00

Abbreviations: CI, RTOG conformity index; PCI, Paddick's conformity index; Dmean, mean dose; Dmax, max dose; HI, homogeneity index; PTV, planning target volume; VxGy, volume of organ receiving ≥ x Gy, Dx%; dose at x% of volume of organ receiving Conclusion We observed no difference in target coverage, conformity index and homogeneous index and integral dose. VMAT achieved better normal tissue sparing in better overall passing rate than IMRT without statistically significant in reducing dose to organ at risk. PO-1239 Post-TBI amylase value as a prognostic marker for transplant outcomes in the pediatric population F. Baldo 1 , R. Vidimari 2 , F. Ciriello 3 , R. Simeone 4 , F. Cupardo 2 , N. Maximova 5 1 University of Trieste, Department of Medical Sciences, Trieste, Italy ; 2 ASUITS, Medical Physics, Trieste, Italy ; 3 ASUITS, Radiotherapy, Trieste, Italy ; 4 IRCCS Burlo Garofolo, Department of Transfusion Medicine, Trieste, Italy ; 5 IRCCS Burlo Garofolo, Bone Marrow Transplant Unit, Trieste, Italy Purpose or Objective We observed a variable increase in serum total amylase during TBI-based conditioning regimen for allogeneic hematopoietic stem cell transplantation (HSCT). This study aimed to determine a cut-off value of the TBI- related total amylase increase that might be a specific prognostic marker for transplant outcomes in the pediatric population. Material and Methods The study included 78 pediatric patients with acute lymphoblastic leukemia (ALL) who received TBI-based standard myeloablative conditioning in preparation for an allogeneic HSCT between 2000 and 2018. We defined two TBI protocol groups: the first received a standard dose of 12 Gy, delivered in 6 fractions; the second one received 7.5 Gy in a single dose. A linear, accelerator-based, latero- lateral irradiation was used in all TBI treatments. Plexiglass slabs to compensate the missing tissue in the head and neck and lead tablet in the lower leg regions were routinely used, as well as lung shielding with upper limbs in lateral position. In vivo dosimetry was performed using TLD only until 2003. Thereafter, double-check of the dose delivered and dose homogeneity were performed with gafchromic EBT3 film and MOSFET. Serum total and pancreatic amylase were evaluated daily, before and after the TBI, until their normalization. We evaluated the validity of total amylase (TA) in predicting transplant outcomes by assessing their respective AUC and ROC curves. Youden index was used to establish the ideal cut- off for sensitivity and specificity of TA. Kaplan-Meier curves were generated for a graphical explanation of the various clinical outcomes. Results TBI total dose was 12 Gy for 57 (73.1%) patients, and 7.5 Gy for 21 (26.9%) patients. Mean dose-rate ± SD was 14.0 ± 2.0 cGy/min and 18.7 ± 1.7 cGy/min, respectively. The mean percent variation ± SD in dosimetry was -0.9 ± 1.9%