Toxicity Burden in Head and Neck Cancer: Past, Present, and Future Strategies

Radiation therapy has been a major modality employed in the treatment of head and neck (H&N) cancer for decades. In that time, radiation technology has evolved considerably. Thirty years ago radiation therapy for H&N cancer consisted of two-dimensional techniques using plain field radiographs, bony anatomy, and hand drawn blocks [1]. Beam set ups were generally quite simple and plans generally consisted of opposed lateral fields matched to an anteroposterior supraclavicular field. Nearly a decade later, several technologic developments combined to catapult radiation therapy into a new era. Three-dimensional imaging technologies such as computed tomography (CT) and magnetic resonance imaging (MRI) were integrated with radiation planning technologies creating three-dimensional conformal radiation therapy (3DCRT). The CT simulator rapidly came to replace the x-ray simulator. With CT simulation, the radiation oncologist could now take into account axial anatomy; thereby more accurately identify tumor volumes and institute more complex beam arrangements in treatment planning [2]. During the decade that followed, the cerrobend block was replaced by the multileaf collimator and advances in computer optimization algorithms gave birth to intensity modulated radiation therapy (IMRT). This technological improvement allowed us to modulate the number of radiation fields and the intensity of radiation within each field. Instead of the physician choosing the beam angle, block, and weighting, computer optimization techniques would create a distribution of beamlets based on dose parameters to contoured structures (a process referred as inverse planning) [3, 4]. IMRT changed the practice of radiation oncology by providing the user unprecedented ability to sculpt the radiation dose. Since the advent of IMRT there have been several "technological advances." Image guided radiation therapy (IGRT), adaptive radiation therapy (ART), and now proton therapy (PRT) represent new technologies that are either actively used or being incorporated into the treatment of H&N cancer. The H&N region is an ideal site to examine a new radiation treatment paradigm. The tissues in the H&N are exquisitely sensitive to the acute and late effects of radiation treatment. Even in the present day, toxicities such as mucositis, dermatitis, soft tissue fibrosis, and xerostomia commonly arise from irradiation of the H&N [5-7]. Head and neck cancer patients historically face long-term difficulties with eating, speaking, tasting, dry mouth, decreased range of motion, and wound healing [8, 9]. Radiation treatment of H&N cancer bears a high toxicity burden. Therefore, technological advances that improve conformity and precision of radiation delivery have been employed to decrease side effects in this patient population. The questions that bear asking are "what have we gained from these advancements in the last 30 years and what are the next steps?"