Prospective randomized-controlled trial: efficacy of 37 °C-preheated thermoplastic elastomer (TPE) bolus in postoperative radiotherapy for breast cancer patients.

Objective: This randomized-controlled trial aimed to investigate whether preheating thermoplastic elastomer (TPE) bolus to 37 °C reduces setup errors and improves patient comfort during post-mastectomy radiotherapy (PMRT).

Methods: From July 2023 to June 2024, breast cancer patients requiring PMRT were randomized (1:1) to receive either preheated (37 °C, 30 min) or room-temperature TPE bolus. Bolus was applied during the first half of treatment (15/25 or 8/15 fractions). Weekly cone-beam computed tomography (CBCT) assessed setup errors (lateral [Lat], longitudinal [Lng], vertical [Vrt], and rotational [Rtn]). Secondary endpoints included thorax anteroposterior diameter changes (ΔZ), skin toxicity (CTCAE v3.0), and comfort (modified Likert scale).

Results: Among 154 analyzed patients, preheating significantly reduced Vrt (0.24 ± 2.43 mm vs. - 0.64 ± 2.46 mm, p < 0.01) and Lat errors (- 0.12 ± 2.49 mm vs. 0.63 ± 2.49 mm, p < 0.01). The preheating group reported higher temperature comfort scores (4.32 ± 0.55 vs. 3.59 ± 0.72, p < 0.01). No significant differences were observed in Grade 2 (46.6% vs. 44.3%, p = 0.661) or Grade 3 (2.7% vs. 2.9%, p = 1.000) radiation dermatitis.

Conclusion: Preheated TPE bolus improves setup accuracy in the Vrt and Lat directions, enhances patient comfort, and maintains skin safety, supporting its clinical utility in PMRT.