ESTRO 2024 - Abstract Book

S1465

Clinical - Lower GI

ESTRO 2024

Figure 2: cCR as a function of EQD2 fitted with bounded logistic regression. Data point size is scaled towards size of patient cohort in study arm. RT-radiotherapy, CT-chemotherapy, CRT-chemoradiotherapy, TNT-total neoadjuvant therapy, BT-brachytherapy.

Conclusion:

This exploratory analysis of sterilizations rates following completion of different treatment modalities for rectal cancers further suggests the existence of a radiation dose-response relationships for pCR and cCR as described by Appelt et al. [1]. The work is limited by using a single-dependent model among a group of patients with significant heterogeneity in both the clinical stages and risk factors that likely biases the sterilization rates for earlier stages (cT1-T2) compared to more advanced disease (cT3, N+). Rates of cCR appear to plateau around doses of 100 Gy EQD2. There was no significant correlation between treatment time and sterilization rates. Rates of toxicities varied significantly depending on the treatment modality but were highest in treatment regimens using adjuvant chemotherapy or chemotherapy alone, however, multivariate analyses still needs to be explored to verify these differences are significant. The radiation dose-response relationship should be investigated in prospective future trials, and more rigorously correlated with other known risk factors for local and distant recurrence, and long-term outcomes. Given the different toxicity profiles and treatment time for different therapies, shared decision making with patients remains an integral part of selecting the optimal therapeutic modality.

Keywords: Dose-response, treatment time, toxicity

References:

[1] Appelt, A., et al. "PH-0162: Is there a radiation dose-response relationship for non-operative management of rectal cancer?." Radiotherapy and Oncology 152 (2020): S76-S77.