Temperature-Controlled Immobilization for Testicular Irradiation: A Technical Report of a Single Case

Background: Testicular irradiation presents technical challenges due to the temperature-dependent cremasteric reflex causing positional variability, yet detailed immobilization protocols addressing this issue and cone-beam computed tomography (CBCT)-based setup data remain lacking. This formative and preliminary single-patient descriptive technical report describes a temperature-controlled immobilization technique and reports preliminary setup observations from its clinical application. Methods: A 74-year-old male with primary testicular diffuse large B-cell lymphoma (DLBCL) received prophylactic contralateral testicular irradiation. The immobilization protocol combined a custom thermoplastic device with infrared warming to maintain the scrotal surface temperature at 36-36.5 °C, intended to facilitate a relaxed scrotal position prior to and during each fraction under temperature-controlled conditions. Treatment was delivered using a three-field three-dimensional conformal radiotherapy (3D-CRT) technique (30.6 Gy in 17 fractions), and seven CBCT scans were used to document interfraction setup measurements. Results: The treatment was completed as planned with adequate target coverage (clinical target volume [CTV] D97% = 100%) and minimal organ-at-risk (OAR) doses. Setup measurements showed a CTV root-mean-square displacement (RMS) of 3.8 mm and a mean Dice similarity coefficient (DSC) of 0.85, while the testis alone showed an RMS of 5.2 mm and a mean DSC of 0.73. Conclusions: The temperature-controlled immobilization technique was feasibly implemented, and the setup measurements observed during its application showed a CTV RMS of 3.8 mm and a mean DSC of 0.85. These findings may provide a practical reference for institutions encountering this rare clinical scenario.