Novel Technique for Intensity Modulated Proton Therapy With Custom Oral Device is Associated With Reduced Oral Cavity Doses and Favorable Outcomes

Abstract

Particle therapies are well-suited for the adjuvant treatment of lip and buccal mucosa malignancies. Intensity modulated radiation therapy (IMRT) is often utilized but can result in increased moderate doses to sensitive organs including the oral cavity. Herein, we describe a novel treatment utilizing Intensity Modulated Proton Therapy (IMPT) with custom oral dental putty devices employed to protect non-target oral cavity by limiting the range of IMPT beams. We hypothesized that this technique would allow for optimal treatment of the post-operative bed and regional lymphatics/cranial nerves with very low non-target oral cavity doses. We also proposed that this oral cavity sparing would be more pronounced with IMPT than IMRT. On an IRB-approved retrospective review, we identified patients treated at our institution with this novel IMPT and oral device technique for the treatment of lower lip and buccal mucosa malignancies. Patient and tumor characteristics along with dosimetric and outcomes data were collected. Each patient had a comparative volumetric modulated arc therapy (VMAT) plan generated for comparison of non-target oral cavity sparing with the same planning scans including dental putty. Five patients were treated with IMPT and a custom oral device with a median follow up of 5.2 months (range, 1.1–21.5). Three patients were treated for squamous cell carcinoma (SCC) of the lip and two for adenoid cystic carcinoma (ACC) of the lip or buccal mucosa. Three patients had regional lymph nodes included in the target (SCC), and two had V3 electively covered (ACC). To date, there were no grade ³3 acute or subacute toxicities, there have been no failures and all patients remain alive. There was no appreciable difference in CTV coverage between the VMAT and IMPT plans. Table 1 includes V10Gy, V20Gy, V30Gy, and mean oral cavity dose, all of which were statistically significantly lower with IMPT than VMAT (p<0.01). Compared to VMAT, oral cavity mean dose decreased with IMPT from a median of 29.8Gy (range, 23.2 – 32.6) to 14.3Gy (range 6.21 – 19.7) (p<0.01). Use of IMPT with custom dental putty oral devices for dose attenuation is a novel, effective, and simple technique to reduce toxicity for patients with lower lip and buccal head and neck malignancies requiring radiation coverage of regional lymphatics and/or cranial nerves. While follow up is limited, outcomes and acute/subacute toxicity rates to date are excellent with a decrease of ∼50% mean dose to the oral cavity when compared with VMAT.Tabled 1Abstract 2813; TableOral Cavity Dosimetric ValueIMRT: Median (range)IMPT: Median (range)V10Gy (%)97.0 (87.7 – 100.0)42.9 (17.2 – 58.8)V20Gy (%)62.0 (46.5 – 86.0)30.3 (11.0 – 39.2)V30Gy (%)35.7 (20.5 – 53.2)18.3 (7.4 – 27.4)Mean Dose (Gy)29.8 (23.2 – 32.6)14.3 (6.21 – 19.7) Open table in a new tab