An Analysis of PET Maximum SUV Among Head and Neck Cancer Patients Receiving Photon and Proton Radiation.

INTRO: One main advantage of proton therapy versus photon therapy is its precise radiation delivery to targets without exit dose, resulting in lower dose to surrounding healthy tissues. This is critical given the proximity of head and neck tumors to normal structures. However, proton planning requires careful consideration of factors including air-tissue interface, anatomical uncertainties, surgical artifacts, weight fluctuations, rapid tumor response, and daily variations in setup and anatomy, as these heterogeneities can lead to inaccuracies in targeting and creating unwarranted hotspots to a greater extent than photon radiation. Additionally, the elevated relative biological effectiveness (RBE) at the Bragg peak's distal end can also increase hot spots within and outside the target area.

PURPOSE/METHODS: The purpose of this study was to evaluate for a difference in PET SUV uptake following definitive treatment, between IMPT or IMRT. Additionally, we compared the biologic dose between PET areas of high and low uptake within the CTV-primary of patients treated with IMPT. This work is assuming that the higher SUV uptake may potentially result in higher toxicities. For the purposes of this short communication, we are strictly focusing on the SUV uptake, and do not have correlation with toxicity outcomes. To accomplish this, we compared the 3- and 6-month post-treatment FDG PET scans for 100 matched oropharyngeal cancer patients treated definitively without surgery using either IMPT (n=50) or IMRT (n=50).

RESULTS: Our study found a significant difference in biologic dose between the high and low-uptake regions on 3-month post-treatment scans of IMPT. However, this difference did not translate to a significant difference in PET uptake in the CTV-primary at 3 and 6-months follow-up between IMPT and IMRT patients.

CONCLUSION: Studies propose proton's higher RBE at the Bragg peak could lead to tissue inflammation. Our study did not corroborate these findings. This study's conclusion underscores the need for further investigations with ultimate correlation with clinical toxicity outcomes.