A prospective trial was conducted to see if modulated electro-hyperthermia (mEHT) might be used as a boost to preoperative chemoradiation in patients with locally advanced rectal cancer. With the addition of mEHT, a relatively low dose of 40 Gy radiation produced equivalent pathologic therapeutic outcomes and manageable toxicity profiles, suggesting that part of the radiation dose could be replaced in neoadjuvant treatment for rectal cancer.
60 patients with histologically proven rectal adenocarcinoma requiring preoperative treatment were age of 19 to 85 years, primary tumor located within 15 cm from anal verge, clinical T3–4 or N+ staged by magnetic resonance (MR) and computed tomography (CT) imaging, Eastern Cooperative Oncology Group performance status ECOG ≤2, no prior pelvic irradiation, and proper function of the bone marrow, kidney, and liver. The initial lymph node status was positive for all cases. The median clinical tumor volume was 52.7 cm3 (range 22.4–233.1 cm3).
Preoperative radiation was delivered by the technique of external beam X-ray from a linear accelerator. The beam energy was 6–15 MV. Three-dimensional planning was performed following a planning CT scan. Three- or four-field technique in the supine position was used depending on the location and the extent of the disease. The clinical target volume included the tumor, the mesorectum, the internal iliac nodes, and presacral nodes up to the sacral promontory level. During treatment, all patients underwent weekly medical examinations with a complete blood count check.
mEHT was performed on a twice-weekly schedule during the radiotherapy period using 13.56 MHz capacitive coupled device (EHY2000). All patients were treated in the supine position. A 30 cm diameter sized electrode was applied as an upper pole, whose center was located on the middle of the clinical target volume to cover the tumor and elective pelvic lymph node area. The duration of mEHT treatment was 60 minutes and the radiotherapy of that day followed immediately within one hour. At the beginning of treatment, the power was started at 100 W during the first 20 min, maintained at least at 120 W for the next 20 min, and fixed at 140 W for the last 20 min. From the subsequent treatment session, the power was constantly fixed at 140 W if there were no toxicity problems.
Treatment-related toxicities were easily tolerated. Hematologic toxicity of Grade 2 or higher was mainly found as leukopenia in 16 patients (26.7%) and neutropenia in 6 patients (10.0%). In the cases of anemia, Grade 2 or higher was observed in 7 patients (11.7%). Genitourinary toxicity was generally low (only one Grade 2 or higher patient), which presented as non-infective cystitis related symptoms. Nineteen patients (31.7%) experienced Grade 2 or higher gastrointestinal toxicities presenting as pelvic pain, nausea, ordiarrhea. There was no Grade 3 or higher non-hematologic toxicity. For heat-related toxicity, the highest was Grade 2 in only one case.
Downstaging and tumor regression
After surgery, T-downstaging was observed in 40 patients (66.7%). Regarding the lymph nodes, N- downstaging occurred in 53 patients (88.3%). The proportion of pathologic complete response for T-stage (ypT0) and N-stage (ypN0) was 15.0% (9 patients) and 76.7% (46 patients), respectively. The patient number of minimal, moderate, near total, and total regression grade for primary tumors was 9 (15.0%), 31 (51.7%), 11 (18.3%), and 9 (15.0%), respectively.
Non-inferior primary tumor regression and excellent lymph node response are sufficient to indicate the mEHT boosts as a useful option for rectal cancer treatment. Radiation was shown to be sufficiently supplemented by mEHT, with acceptable toxicity levels and feasibility in multimodality management. Therefore, mEHT can be combined as a boosting method with radiation. More active mEHT application needs to be attempted with various approaches to improve clinical outcomes from the perspective of non- thermal effects.