ESTRO 2020 Abstract Book

S651 ESTRO 2020

rectosigmoid ulceration. No patients had >Grade 3 toxicity.

Poster: Clinical track: Paediatric tumours

PO-1237 Assessing the role of IMRT relative to VMAT in children with medulloblastoma treated with CSI W. Rongthong 1 , S. Pleanarom 1 , N. Suntornpong 1 , T. Treechairusame 1 , K. Thephamongkhol 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 and normal tissue sparing between IMRT and VMAT. Material and Methods Patients 3-18 years old with standard risk medulloblastoma treated with computer-based planning CSI in supine position between 2006 and 2016 were selected for treatment planning simulation. Both IMRT and VMAT were done and compared for each patient. The prescription was CSI 23.4Gy 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 by the second author and evaluated by the first author. Results Nine patients’ CT data set were available for dose calculation and evaluation. Better target coverage was observed in IMRT: IMRT 1967.96 cc vs. VMAT 1939.31 cc (p=0.006). More conformal dose distribution and homogeneous dose distribution were noted in VMAT: IMRT 0.83 vs. VMAT 0.87 (p=0.011) and IMRT 1.12 vs. VMAT 1.09 (p=0.02), respectively. VMAT significantly reduced dose to eyes and thyroid gland. IMRT significantly reduced dose to lungs, liver, and kidneys (Table). Doses to lens, optic nerves, optic chiasm, cochleae, heart, and non-target tissue were no difference between 2 techniques. Table. Dosimetric comparison between IMRT and VMAT Parameter s IMRT (mean±SD ) VMAT (mean±SD ) P Go al Endpoint s PTV95% (cc) 1967.96± 195.09 1939.31± 197.43 0. 006 NA PTV107% (cc) 48.23±11 1.44 18.00±20 .61 0.3 9 NA CI 0.83±0.0 2 0.87±0.0 3 0. 011 1 HI 1.12±0.0 3 1.09±0.0 1 0. 02 ≤2

Fig 1: Kaplan-Meier estimates of LRFS and OS.

Cataract, blindness, double vision, dry eyes Cataract, blindness, double vision, dry eyes Hypothyr

0.

Right eye (mean±SD)

19.52±1.

17.91±2.

<1

017

69

74

0

0.

Left eye (mean±SD)

19.70±2.

18.01±2.

<1

029

12

86

0

Fig 2: Cumulative incidence of local failure. Conclusion

0.

Thyroid (mean±SD) Left lung (mean ±SD) Right lung (mean ±SD)

15.40±2.

12.96±1.

<1

003

30

63

0

oidism

Re-RT with spine SBRT with or without combination surgery offers the chance of radiographic control and effective symptom relief with acceptable toxicity for recurrent chordomas. Given the unfavorable tumor biology, even after optimal LC is obtained, the propensity for metastases must also be addressed to substantially change OS.

Abnormal

0.

5.64±1.0

6.54±0.7

<7

lung function

022

0

7

Abnormal

0.

5.24±1.0

6.23±0.6

lung function

023

2

8

<7