The potential of intensity-modulated proton radiotherapy to reduce swallowing dysfunction in the treatment of head and neck cancer: A planning comparative study.
BACKGROUND
Predictive models for swallowing dysfunction were developed previously and showed the potential of improved intensity-modulated radiotherapy to reduce the risk of swallowing dysfunction. Still the risk is high. The aim of this study was to determine the potential of swallowing-sparing (SW) intensity-modulated proton therapy (IMPT) in head and neck cancer (HNC) for reducing the risk of swallowing dysfunction relative to currently used photon therapy.


METHODS
Twenty-five patients with oropharyngeal (n = 21) and hypopharyngeal (n = 4) cancer received primary radiotherapy, including bilateral neck irradiation, using standard (ST) intensity-modulated photon therapy (IMRT). Prophylactic (54 Gy) and therapeutic (70 Gy) target volumes were defined. The dose to the parotid and submandibular glands was reduced as much as possible. Four additional radiotherapy plans were created for each patient: SW-IMRT, ST-IMPT, 3-beam SW-IMPT (3B-SW-IMPT) and 7-beam SW-IMPT (7B-SW-IMPT). All plans were optimized similarly, with additional attempts to spare the swallowing organs at risk (SWOARs) in the SW plans. Probabilities of swallowing dysfunction were calculated with recently developed predictive models.


RESULTS
All plans complied with standard HNC radiotherapy objectives. The mean parotid gland doses were similar for the ST and SW photon plans, but clearly lower in all IMPT plans (ipsilateral parotid gland ST-IMRT: 46 Gy, 7B-SW-IMPT: 29 Gy). The mean dose in the SWOARs was lowest with SW-IMPT, in particular with 7B-SW-IMPT (supraglottic larynx ST-IMRT: 60 Gy, 7B-SW-IMPT: 40 Gy). The observed dose reductions to the SWOARs translated into substantial overall reductions in normal tissue complication risks for different swallowing dysfunction endpoints. Compared with ST-IMRT, the risk of physician-rated grade 2-4 swallowing dysfunction was reduced on average by 8.8% (95% CI 6.5-11.1%) with SW-IMRT, and by 17.2% (95% CI: 12.7-21.7%) with 7B-SW-IMPT.


CONCLUSIONS
SWOAR-sparing with proton therapy has the potential to substantially reduce the risk of swallowing dysfunction compared to similar treatment with photons.
Department of Radiation Oncology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands. h.p.van.der.laan@umcg.nl
Hans Paul
HP
van der Laan
Tara A
TA
van de Water
Heleen E
HE
van Herpt
Miranda E M C
ME
Christianen
Hendrik P
HP
Bijl
Erik W
EW
Korevaar
Coen R
CR
Rasch
Aart A
AA
van 't Veld
Arjen
A
van der Schaaf
Cornelis
C
Schilstra
Johannes A
JA
Langendijk
D000293:Adolescent; D000328:Adult; D000368:Aged; D002277:Carcinoma / Q000453:epidemiology / Q000473:pathology / Q000532:radiotherapy*; D003680:Deglutition Disorders / Q000453:epidemiology / Q000209:etiology / Q000517:prevention & control*; D004307:Dose-Response Relationship, Radiation; D006258:Head and Neck Neoplasms / Q000453:epidemiology / Q000473:pathology / Q000532:radiotherapy*; D006801:Humans; D008875:Middle Aged; D009929:Organ Size; D011832:Radiation Injuries / Q000453:epidemiology / Q000209:etiology / Q000517:prevention & control*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects; D047368:Tumor Burden; D055815:Young Adult