Photobiomodulation Eased Trismus-Related Pain During Head and Neck Radiotherapy
Head and neck radiotherapy can leave patients struggling to open their mouths, eat, speak, and tolerate routine oral care. In this randomized, triple-blind, placebo-controlled trial, photobiomodulation therapy was tested as a preventive strategy against trismus in patients receiving intensity-modulated radiotherapy and volumetric modulated arc therapy for head and neck cancer.
The intervention did not change mouth opening at six months.
It did, however, blunt the pain burden that often accompanies jaw stiffness during treatment, suggesting a meaningful palliative effect even when the mechanical endpoint itself remained unchanged.
Trial Design and Laser Delivery Across the Masticatory Apparatus
Forty-six patients undergoing radiotherapy for head and neck cancer entered the study and were randomly assigned in equal numbers to active photobiomodulation or placebo. The trial was structured as triple-blind, an approach that strengthens internal validity in a symptom-driven intervention where both expectation and assessor bias can distort outcomes. Daily assessments tracked mouth opening, pain during mouth opening, and pain on palpation of the masticatory muscles using the Visual Analog Scale.
The laser protocol was highly specific. Investigators used an extraoral infrared laser at approximately 808 nm, with power of 0.1 W, energy of 3 J, and 30 seconds per point, corresponding to 107 J/cm². Treatment was delivered extraorally to the anterior temporalis, masseter, and temporomandibular joints, and intraorally to the medial pterygoid muscle. In practical terms, the protocol targeted the structures most likely to become fibrotic, inflamed, or painful during radiation exposure, especially when high-dose fields involve the jaw, pterygoid region, and adjacent soft tissues.
That anatomical logic matters. Trismus in head and neck cancer is rarely a single-muscle problem; it reflects a convergence of mucosal injury, fibrosis, edema, muscular spasm, and pain avoidance. By directing light energy to both superficial and deeper masticatory targets, the intervention aimed to interrupt the cascade before it hardened into fixed limitation.
Pain Improved Even When Mouth Opening Did Not
The central finding was mixed but clinically relevant. Mouth opening did not differ between groups at the six-month follow-up, so the intervention did not demonstrate durable superiority on the most structural outcome measured in this study. Yet photobiomodulation was effective in preventing trismus and masticatory muscle pain during radiotherapy itself, which is when many patients face the steepest functional burden.
For patients, the distinction is concrete. A mouth that opens no wider at six months can still hurt less during treatment, and less pain can determine whether a patient eats, speaks, brushes teeth, or tolerates oral examination without escalating distress. In head and neck oncology, symptom control is not cosmetic; it shapes adherence, nutrition, and the feasibility of supportive care.
The biologic rationale is plausible. Photobiomodulation is generally used to modulate local inflammation, improve microcirculatory function, and influence cellular repair pathways. In the setting of radiation injury, those effects could dampen the inflammatory amplification that makes jaw movement painful before fibrosis becomes fixed. The study’s pattern fits that model: symptomatic relief appeared during the active treatment period, while the later structural endpoint remained unchanged.
Quality of Life and Oral Function Were Measured Alongside Symptoms
Beyond pain and mouth opening, the trial included the Food Quality Inventory and oral health-related quality of life assessment using the OHIP-14. Those measures are important because trismus is not just a measurement on a goniometer. It changes how patients chew, swallow, speak, and interact with oral hygiene routines, all of which can deteriorate during radiotherapy and compound the burden of mucositis or xerostomia.
The abstract does not provide the detailed numerical shifts in these secondary measures, so no stronger claim should be made about their direction or magnitude. Still, their inclusion reflects a broader clinical aim: preventing trismus is valuable not only to preserve jaw excursion but also to preserve day-to-day function across treatment.
What the Result Means for Head and Neck Oncology Practice
The trial adds to the small body of supportive care strategies aimed at reducing late and acute toxicities in head and neck radiotherapy. Because the cohort was treated with IMRT and VMAT, the findings are most relevant to modern conformal radiation platforms where clinicians still cannot fully spare the masticatory musculature from injury. Even with more precise dose shaping, the jaw remains vulnerable when tumors are close to the oral cavity, oropharynx, pterygoid region, or temporomandibular apparatus.
A simple reading would be to dismiss the negative six-month mouth-opening result. That would be too narrow. In supportive oncology, a therapy that eases daily pain without adding known harm can still be worth clinical attention, especially when the alternative is passive observation until restriction becomes established. Pain relief during radiotherapy may also preserve movement itself by reducing avoidance behavior, although this study’s endpoint set does not allow a direct causal claim on that point.
The sample size was modest, and the study design does not support broad generalization across every head and neck radiotherapy scenario. Long-term functional effects remain uncertain from the abstract alone, and the lack of difference in mouth opening at six months raises the possibility that prevention of pain does not automatically translate into durable prevention of restriction. Still, the signal is clinically coherent: a targeted laser protocol may help patients get through treatment with less masticatory pain, even if the later mechanical endpoint is unchanged.
Registration and Study Context
The trial was registered as RBR-67qxnt9 on 16/04/2025. Publication in Lasers in Medical Science places the work within an expanding supportive care literature that continues to test nonpharmacologic adjuncts for treatment toxicity in oncology.
The most actionable takeaway is narrow but real: in head and neck cancer patients receiving radiotherapy, photobiomodulation therapy reduced pain during treatment, while six-month mouth opening remained unchanged. The remaining question is whether different dosing, timing, or longer follow-up would alter the structural endpoint, or whether the main value of this intervention will remain symptomatic rather than anatomical.