Multifield optimization intensity modulated proton therapy for head and neck tumors: a translation to practice

Abstract

Background: We report the first clinical experience and toxicity of multifield optimization (MFO) intensity modulated proton therapy (IMPT) for patients with head and neck tumors.

Methods and materials: Fifteen consecutive patients with head and neck cancer underwent MFO-IMPT with active scanning beam proton therapy. Patients with squamous cell carcinoma (SCC) had comprehensive treatment extending from the base of the skull to the clavicle. The doses for chemoradiation therapy and radiation therapy alone were 70 Gy and 66 Gy, respectively. The robustness of each treatment plan was also analyzed to evaluate sensitivity to uncertainties associated with variations in patient setup and the effect of uncertainties with proton beam range in patients. Proton beam energies during treatment ranged from 72.5 to 221.8 MeV. Spot sizes varied depending on the beam energy and depth of the target, and the scanning nozzle delivered the spot scanning treatment "spot by spot" and "layer by layer."

Results: Ten patients presented with SCC and 5 with adenoid cystic carcinoma. All 15 patients were able to complete treatment with MFO-IMPT, with no need for treatment breaks and no hospitalizations. There were no treatment-related deaths, and with a median follow-up time of 28 months (range, 20-35 months), the overall clinical complete response rate was 93.3% (95% confidence interval, 68.1%-99.8%). Xerostomia occurred in all 15 patients as follows: grade 1 in 10 patients, grade 2 in 4 patients, and grade 3 in 1 patient. Mucositis within the planning target volumes was seen during the treatment of all patients: grade 1 in 1 patient, grade 2 in 8 patients, and grade 3 in 6 patients. No patient experienced grade 2 or higher anterior oral mucositis.

Conclusions: To our knowledge, this is the first clinical report of MFO-IMPT for head and neck tumors. Early clinical outcomes are encouraging and warrant further investigation of proton therapy in prospective clinical trials.

Figure 1

Average DVHs of all three patients with bilateral oropharyngeal tumors treated with IMPT alone to 66 Gy (RBE) in 30 fractions. (Ipsi = ipsilateral, Contra = contralateral, SMG = submandibular gland, CTV = clinical target volume)

Figure 2

Unresectable T4N0M0 adenoid cystic carcinoma of the nasopharynx in a 33-year-old woman. Panels a and d, CT scans showing tumor invasion the carotid space, extending circumferentially around the lateral aspect of C1 with epidural extension and perineural spread into the left hypoglossal canal, left vidian canal, left foramen rotundrum, and left foramen ovale. The tumor also extended into the left middle cranial fossa and encased the left internal carotid artery up to the petrous carotid canal. Panels b and e, isodose lines of the MFO IMPT treatment plan in the axial (b) and coronal (e) planes (gross disease is contoured in maroon). Panels c and f, CT scans obtained at 6 weeks after concurrent chemoradiation therapy to 70 Gy(RBE) in 33 fractions with cisplatin illustrate a clinical and radiographic complete response. The patient remains without evidence of disease three years from treatment.

Figure 3

T2N2b human papillomavirus–positive squamous cell carcinoma of the right tongue base in a 67-year-old man. Panels a and e, PET/CT scans show avid primary tumor and cervical node metastases. Panels b and f, isodose lines of the MFO IMPT treatment plan in the axial (b) and coronal (f) planes. Panels c and g, confluent mucositis at the tongue base with no mucositis at the anterior local tongue (c) and grade 2 radiation dermatitis on the neck (g) after receipt of 66 Gy(RBE) with concurrent cetuximab illustrate treatment reactions consistent with the treatment plan. Panels d and h, PET/CT scans obtained at 10 weeks after treatment illustrate complete clinical, metabolic, and radiographic. The patient remains without evidence of disease two and a half years from treatment.