Potential benefits of scanned intensity-modulated proton therapy versus advanced photon therapy with regard to sparing of the salivary glands in oropharyngeal cancer.
OBJECTIVE
To test the hypothesis that scanned intensity-modulated proton therapy (IMPT) results in a significant dose reduction to the parotid and submandibular glands as compared with intensity-modulated radiotherapy with photons (IMRT) and three-dimensional conformal radiotherapy (3D-CRT) for oropharyngeal cancer. In addition, we investigated whether the achieved dose reductions would theoretically translate into a reduction of salivary dysfunction and xerostomia.


METHODS
Ten patients with N0 oropharyngeal carcinoma were used. The intensity-modulated plans delivered simultaneously 70 Gy to the boost planning target volume (PTV2) and 54 Gy to the elective nodal areas (PTV1). The 3D-CRT technique delivered sequentially 70 Gy and 46 Gy to PTV2 and PTV1, respectively. Normal tissue complication probabilities were calculated for salivary dysfunction and xerostomia.


RESULTS
Planning target volume coverage results were similar for IMPT and IMRT. Intensity-modulated proton therapy clearly improved the conformity. The 3D-CRT results were inferior to these results. The mean dose to the parotid glands by 3D-CRT (50.8 Gy), IMRT (25.5 Gy), and IMPT (16.8 Gy) differed significantly. For the submandibular glands no significant differences between IMRT and IMPT were found. The dose reductions obtained with IMPT theoretically translated into a significant reduction in normal tissue complication probability.


CONCLUSIONS
Compared with IMRT and 3D-CRT, IMPT improved sparing of the organs at risk, while keeping similar target coverage results. The dose reductions obtained with IMPT vs. IMRT and 3D-CRT varied widely per individual patient. Intensity-modulated proton therapy theoretically translated into a clinical benefit for most cases, but this requires clinical validation.
van de Water
Tara A
TA
Department of Radiation Oncology, University Medical Center Groningen/University of Groningen, Groningen, The Netherlands. t.a.van.de.water@rt.umcg.nl
Lomax
Antony J
AJ
Bijl
Hendrik P
HP
de Jong
Marije E
ME
Schilstra
Cornelis
C
Hug
Eugen B
EB
Langendijk
Johannes A
JA
D006801:Humans; D058958:Organs at Risk / Q000528:radiation effects*; D009959:Oropharyngeal Neoplasms / Q000532:radiotherapy*; D010306:Parotid Gland / Q000528:radiation effects*; D017785:Photons / Q000627:therapeutic use; D061766:Proton Therapy; D011832:Radiation Injuries / Q000517:prevention & control*; D011879:Radiotherapy Dosage; D020266:Radiotherapy, Conformal / Q000009:adverse effects / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects / Q000379:methods*; D013363:Submandibular Gland / Q000528:radiation effects; D014987:Xerostomia / Q000209:etiology / Q000517:prevention & control*; D011522:Protons
D011522:Protons