ESTRO 2024 - Abstract Book

S6035

RTT - Treatment planning, OAR and target definitions

ESTRO 2024

A total of 36 treatment plans were evaluated. The mean prescription dose was 54.4 Gy ranging between 45 and 60 Gy. All treatment plans, with both techniques, achieved appropriate target volume coverage and were considered clinically acceptable. VMAT plans yielded lower doses to the heart with mean MHD of 10.64 Gy vs 15.33 Gy and V30 Gy of 12.7% vs 22.57% (p<0.01), respectively in VMAT and 3D conformal plans. Doses delivered to coronary arteries including LM, LAD and LCx were statistically lower in VMAT plans when compared to 3D conformal plans (table 1). The RCA was either proximal or included in the planning target volume in 72% of cases. VMAT plans did not show any benefit in terms of RCA sparing beyond 3D conformal plans.

Table 1 : Compared coronary arteries doses in VMAT versus 3D conformal RT for thymic epithelial tumors

Coronary Arteries

VMAT plans

3D Conformal plans

p value

LM Dmax

15.46

40.23

<0.001

LM Dmean

10.31

35.51

<0.001

RCA Dmax

42.38

32.01

0.01

RCA Dmean

15.97

12.71

0.02

LCx Dmax

15.76

38.64

<0.001

LCx Dmean

4.86

14.63

<0.001

LAD Dmax

33.06

38.53

0.03

LAD Dmean

10.82

21.42

0.01

Conclusion:

This study showed that VMAT radiotherapy resulted in a better sparing of the heart and main coronary arteries when compared to 3D conformal radiotherapy. As thymic epithelial tumor patients are usually long survivors, radiation oncologists should use the best available techniques to minimize heart subvolumes exposure and reduce the risk of radiation induced cardiac morbidity.

Keywords: Thymic tumors, VMAT, 3D conformal

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Proffered Paper

Quantifying safe distances to OAR when treating with high-dose on a MRL for patients with liver mets

Andrea Shessel, Michael Velec, Teodor Stanescu, Ali Hosni