ESTRO 2022 - Abstract Book

S616

Abstract book

ESTRO 2022

the vast majority of trials for neuroblastomas, lymphomas and others, in addition to CNS tumors and sarcomas, embed PBT into the multimodality concept as a standard radiation modality in order to better protect immature tissues in children. Conclusion: PBT offers not only dosimetric but also clinical benefits for children with cancer. PBT has been established in the majority of clinical trials in pediatric oncology already. As PBT becomes more available, the role and benefit of PBT will be confirmed.

SP-0691 Against the motion (rebuttal)

H. Mandeville

United Kingdom Abstract not available

Symposium: New era of personalised radiotherapy in soft tissue sarcomas

SP-0693 Hypofractionated radiotherapy in soft tissue sarcomas: A new standard of care?

M. Spa ł ek 1

1 Maria Sklodowska-Curie National Research Institute of Oncology, Department of Soft Tissue/Bone Sarcoma and Melanoma, Warsaw, Poland Abstract Text There is growing evidence that hypofractionated radiotherapy (HFRT) could be a possible preoperative therapeutic approach in patients with localized soft tissue sarcomas (STS). Despite the encouraging data from several prospective phase 2 single-arm clinical trials with moderate and extreme hypofractionation, HFRT is still considered experimental in STS. HFRT was introduced in several cancers like rectal, prostate, and breast cancer. Moreover, it has a strong radiobiological rationale, mostly due to the predicted low α / β ratio for STS. Highly conformal radiotherapy techniques enabled significant sparing of healthy tissues that are at risk of late complications theoretically associated with HFRT. Furthermore, fears that HFRT could result in an unacceptably high rate of late radiation-induced toxicity was not confirmed in hypofractionated treatment for breast and prostate cancer patients where cosmetic and functional outcome played a very important role in conducted clinical trials. Are we ready for HFRT in SRS?

SP-0694 Hyperthermia and other radiosensitisers in sarcoma treatment

S. Semrau 1

1 Friedrich-Alexander-Universität Erlangen-Nürnberg, Strahlenklinik Erlangen , Erlangen, Germany

Abstract Text The completeness of the surgical removal has impact on local tumor control and patient survival, especially in high-grade soft tissue sarcomas. However, even with complete resection, 20-40% of patients develop local recurrences. Radiotherapy halves this rate, particularly through preoperative use; nevertheless, even in studies, the rate of local recurrence is rarely below 15%, which needs improvement. This is where locally synergistic therapies gained importance. There are many years of experience with anthracyclines, ifosfamide or trabectedin. Their additive effect results from cellular damage patterns that are comparable to those of radiation therapy. Recent findings from an unplanned analysis of the GEIS study showed a very low long-term local recurrence rate of 5% for a concurrent administration of doublet chemotherapy together with a conventional fractionated radiotherapy compared to a sequential administration. The fact that cytostatics can be administered without dose compromises makes the concept interesting not only for borderline resectable tumors, but also for high-grade sarcomas in general, which are most likely to benefit from early and uncompromising chemotherapy. Simultaneous therapy concepts without dose compromises also seem to be possible with trabectedin. High rates of pCR (>10%) can also be achieved with pazopanib or the intralesional use of NBTXR3 and this without significant additive local toxicity. However, the clinical horizon of experience is small. In addition, regional hyperthermia is considered to act as radio- and chemosensitizer. For the latter, data on improved local control and survival compared to perioperative chemotherapy alone are available from an EORTC-Trial. Synergistic effects result, for example, from thermally induced increased alkylation. The effects of radiotherapy are also increased by hyperthermia, particularly in hypoxic areas and based on impaired DNA-repair mechanisms and the emission of immunogenic damage signals. Cohort studies show a comparable effect of chemoradiotherapy and radiothermotherapy in sarcomas. Ultimately, the option of their combined use in high-grade sarcomas results from the favorable toxicity profile of hyperthermia and chemoradiotherapy, which is now considered feasible. Although the data on this is still sparse, neoadjuvant triplet therapy shows a further increase in pathological remission. This makes the application of the concept interesting for studies on multimodal therapy of soft tissue sarcomas.