The FLAME trial (NCT01168479) showed that isotoxic focal boosting to the intraprostatic lesion(s) in patients with intermediate- and high-risk prostate cancer improves 5-year disease-free survival (DFS). Although the near-minimum dose to the gross tumor volume (D98%) was associated with improved outcomes, a closer look suggested that this might not be the same for all patients. Therefore, we investigated whether risk factors that are associated with a benefit of focal boosting can be identified.
We described the distribution of clinical characteristics and the number of high-risk factors with respect to the D98% in 526 FLAME trial patients. We used penalized Cox regression to develop a prediction model. To investigate a potential benefit in patient subgroups, we compared the model-based predictions of 5-year DFS assuming standard whole-gland radiation therapy of 77 Gy to the predictions assuming an additional focal boost with D98% of 95 Gy.
Patients with high-risk factors were well represented in the group of 120 patients that received D98% > 85 Gy and showed fewer recurrences compared with the group that received 77 Gy. Applying the model simulating a standard dose of 77 Gy, we predicted a high DFS for grade group (GG) 1 patients, whereas patients with high-risk characteristics appeared to show a low DFS. All risk groups showed a high level of DFS when simulating D98% of 95 Gy.
Our results suggest that GG 1 patients already show a low level of failure at a standard dose of 77 Gy, limiting the additional benefit of focal boosting. In contrast, patients with high-risk characteristics, especially GG 4 or 5, show a low 5-year DFS, while focal boosting might improve this substantially. This suggests that reaching a high focal boost dose may be particularly beneficial for these patients.
International journal of radiation oncology, biology, physics. 2023 Sep 18 [Epub ahead of print]
Karolína Menne Guricová, Veerle Groen, Floris Pos, Evelyn Monninkhof, Sjoerd G Elias, Karin Haustermans, Robert J Smeenk, Jochem van der Voort van Zyp, Cédric Draulans, Sofie Isebaert, Petra J van Houdt, Linda G W Kerkmeijer, Uulke A van der Heide
Department of Radiation Oncology, The Netherlands Cancer Institute (NKI-AVL), Amsterdam, The Netherlands., Department of Radiation Oncology, University Medical Center Utrecht, Utrecht, The Netherlands., Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, Utrecht University, Utrecht, The Netherlands., Department of Radiation Oncology, University Hospitals Leuven, Leuven, Belgium., Department of Radiation Oncology, Radboud University Medical Center, Nijmegen, The Netherlands., Department of Radiation Oncology, University Medical Center Utrecht, Utrecht, The Netherlands; Department of Radiation Oncology, Radboud University Medical Center, Nijmegen, The Netherlands., Department of Radiation Oncology, The Netherlands Cancer Institute (NKI-AVL), Amsterdam, The Netherlands. Electronic address: .