Analysis of Treatment Plans Suggests Guidelines Impractical for Planning with IG-VMAT for Oropharynx Cancer

Study offers new planning objectives oropharynx cancer radiotherapy, shows inadequacy of consensus objectives

Radiotherapy objectives for sparing organs at risk with oropharynx cancer treatment should include more personalization than currently accounted for in published guidelines, according to a new study.

“Clinical presentation of oropharynx cancer is incredibly diverse, and treatment planning should develop accordingly,” says Shlomo Koyfman, MD, the study’s senior author and a radiation oncologist at Cleveland Clinic. “We found significant departure from published guidelines when we looked at what the textbooks tell us we can achieve versus what is realistic in delivering curative doses around organs at risk.”

The study, “One-size does not fit all: Planning objectives with IG-VMAT for oropharynx cancer and guidelines by clinical context,” is being presented this week at the ASTRO conference in San Diego.

Assessing the big picture

Dr. Koyfman and his team compared actual treatment plans for 79 oropharynx cancer patients with the published dose objectives for their disease.

All were nonoperative patients with narrow-margin disease whose radiotherapy planning was completed using image-guided volumetric modulated arc therapy (IG-VMAT). For the purpose of the study, narrow-margin was defined as a routine two to three millimeter expansion from gross tumor volume (GTV) to clinical tumor volume (CTV) and an additional two to three millimeter expansion from CTV to planning target volume (PTV).

The goal was to evaluate the practicality and achievability of current treatment planning objectives when seeking to optimize tissue sparing of organs at risk.

“Treatment planning in the VMAT era is complex, but it also offers profound nuance and opportunity,” says Dr. Koyfman. “Our results are simple: achievement of published dosing guidelines is often both impractical and inadequate.”

Offering the finer details

Armed with the knowledge that current objectives fall short, Dr. Koyfman and the team set out to propose more refined parameters that could help physicians maximize dosage while sparing organs at risk.

They split the 79-patient cohort into three groups, which correlated with dosimetric achievements: unilateral neck with cT1-2NO-2b, bilateral neck with cT1-2NO-2b and bilateral neck with cT3-4 or N2c-3.

Respective mean doses achievable in at least 75 percent of cases for the above-referenced treatment groups are:

• Posterior pharyngeal wall: 39, 50 and 53 Gy
• Supraglottis: 27, 47 and 54 Gy
• Oral cavity: 32, 37 and 67 Gy
• Glottis: 21, 30, and 32 Gy
• Contralateral submandibular: 15, 41 and 67 Gy

Moving into practice

While data gleaned from retrospective cohort studies can be valuable in setting a course for future clinical practice, these findings must be validated.

“We have what we believe is a solid starting point for developing more nuanced and clinically relevant treatment objectives,” says Dr. Koyfman. “It is incumbent upon us to translate this work into prospective studies that test our hypotheses in the clinic for current and future patients.”