Neoadjuvant Radiochemotherapy Combined with Locoregional Hyperthermia in Locally Advanced Rectal Cancer: Feasibility and Tolerance of Short-Course Versus Long-Course Radiotherapy Schedules

Background: Integrating deep regional hyperthermia (HT) with neoadjuvant chemoradiotherapy (CRT) may enhance treatment efficacy in locally advanced rectal cancer (LARC), yet feasibility and tolerance data remain scarce for both short-course (SCRT) and long-course (LCRT) radiotherapy (RT) regimens. Methods: In this single-center prospective observational study, 67 LARC patients received neoadjuvant RT and chemotherapy (CT) combined with deep radiative HT using a phased-array system (ALBA 4D). Patients treated with SCRT (5 × 5 Gy) were prescribed two HT sessions; those treated with LCRT (25 × 2 Gy) were prescribed ten. HT planning was guided by dedicated software, and real-time thermometry ensured precise thermal delivery. Feasibility was defined as completion of ≥50% of prescribed sessions. Tolerance and toxicity were assessed with standardized clinical scales (QMHT, UMC, CTCAE v4.03). Results: HT was feasible in both groups: 100% of SCRT and 63.6% of LCRT patients completed ≥50% of prescribed sessions. In total, 243 sessions were delivered. Most symptoms were mild and transient, predominantly localized pain. No grade ≥3 HT-related toxicities occurred. All scheduled RT and surgery proceeded without delay. Median T50 was 40.3 °C (SCRT) and 40.4 °C (LCRT); the median RT-to-HT interval was 42 min in both groups. Conclusion: This first Spanish experience shows that deep radiative HT can be seamlessly integrated into both SCRT and LCRT neoadjuvant protocols for rectal cancer. High adherence, favorable tolerance, and reliable thermal control support clinical implementation. Any between-schedule observations are descriptive only; no formal comparative testing was performed. The study was not designed or powered to establish comparative effectiveness between SCRT and LCRT, and the sample size was insufficient to detect rare HT-specific adverse events.