ESTRO 2024 - Abstract Book

S6028

RTT - Treatment planning, OAR and target definitions

ESTRO 2024

Seven patients were female and two were male. Mean age was 65.6±9.8 years. Primary tumor was non-small cell lung cancer in three cases, breast cancer in two cases, each one case hepatocellular cancer, malignant melanoma, rectal cancer and urothelial cancer each. The shortest distance from metastases to CST (lesion-to-CST-distance) was on average 0.20 cm (range, 0 – 1.1 cm). In 5 of 9 cases, the PTV overlapped with PRV-FTTMS, with 0.6% (range, 0,1 – 1.5 %) of PRV-FTTMS. Maximum and mean dose (Dmax, Dmean) were 32.9±14.9 Gy and 2.5±1.2 Gy for LGK and 31.5±12.1 Gy and 2.5±1.2 Gy for VMAT plans (p=0.5 and 0.2), respectively.For each plan spatial relation of PRV-FTTMS and the treatment volume was characterized by the proportional overlaps of PRV-FTTMS with specific isodose levels. This was expressed in V33.25Gy(95% of prescribed dose), V17.5Gy(50%), and V8.75Gy(25%) based on a dose-volume histogram (DVH) for GK and VMAT: 0.42±0.8% vs. 0.41±0.7%, 2.1±3.12% vs. 3.14±4.5% (p<0.05) and 7.3±7.1% vs. 8.8±6.4 % (p<0.05). Dose conformity was assessed based on the following parameter: Coverage= PTIV/PTV, where PTIV is the target volume encompassed by the prescription isodose volume (PIV)(=PIV Ç PTV). Coverage for LGK and VMAT plans was 0.99 and 1.0, respectively (p<0.05).

Conclusion:

In stereotactic N-RT of brain metastases dose exposition of the primary motor areas depends on spatial relation of PTV with FTmot.TMS. In light of recently published NTCP models proposing > 20 Gy EQD2 as critical doses for cortical atrophy and white matter injury (1), motor cortex and CST seem worth being respected in definitive and neoadjuvant RT.

Keywords: brain metastases, neoadjuvant SRS, tractography

References:

1) Connor M. et al, Int J Radiat Oncol Biol Phys. 2023 May 6:S0360-3016(23)00436-4.

3092

Poster Discussion

Heart subvolumes sparing in bilateral breast cancer RT: Is VMAT better than 3D conformal RT?

Zeineb Naimi, Awatef Hamdoun, Meriem Bohli, Raouia Ben Amor, Ghada Bouguerra, Rihab Haddad, Lotfi Kochbati

Abderrahmen Mami Hospital Ariana, Radiation Oncology Department, Ariana, Tunisia

Purpose/Objective:

This study aimed to compare heart substructures exposure between VMAT versus 3D conformal radiotherapy in bilateral breast cancer irradiation.