The Dosimetric Outcome of a Rotational Planning Target Volume in Patients With Oropharyngeal Cancers.
Mona Arbab, Gregory Bartlett, Benjamin Dawson and 2 others
PMID 34283289WHAT IT FOUND
Shaping radiation targets to follow neck rotation lowered planned dose to swallowing muscles in 10 patients.
The study predicted, but did not observe, less swallowing trouble, so it is not proof of clinical benefit.
Key findings
01Using a rotational planning target volume reduced overlap between the high-dose target and the pharyngeal constrictor muscles, with reported reductions of 47% for the superior muscle and 60% for the middle muscle.
02The rotational plan lowered mean dose to the superior pharyngeal constrictor muscle by 355 cGy and to the middle pharyngeal constrictor muscle by 506 cGy. It also moved 40% of patients with superior-muscle dose above 5000 cGy below that threshold, and 20% for the middle muscle.
03The study predicted, rather than measured, a possible reduction in 6-month physician-rated dysphagia of more than 20% in 6 patients, with predicted reductions from 5.5% to 33.2%.
STILL TO COME
How it was doneWhat they foundWhat it means for SLPs
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What it does not show
Only 10 treatment plans were compared. The study compared planned dose, not actual swallowing outcomes in patients. Predicted dysphagia reductions came from statistical models, not from follow-up assessments. The dosimetrists knew which target volume was being planned, so the plan comparison was not blinded. The rotational target volume was manually constructed and limited to rotation in one plane. Translation errors were set to zero, so the plan did not fully model real setup movement. The method was not tested in HPV-positive patients receiving reduced-dose radiation.
The easy way to misread this
Do not read the predicted 20% dysphagia reduction as proof that patients will swallow better. The study only compared radiation plans in 10 patients, and the swallowing benefit was estimated by a model, not measured in people.