Intensity-modulated radiotherapy of nasopharyngeal carcinoma: a comparative treatment planning study of photons and protons.
BACKGROUND
The aim of this treatment planning study was to investigate the potential advantages of intensity-modulated (IM) proton therapy (IMPT) compared with IM photon therapy (IMRT) in nasopharyngeal carcinoma (NPC).


METHODS
Eight NPC patients were chosen. The dose prescriptions in cobalt Gray equivalent (GyE) for gross tumor volumes of the primary tumor (GTV-T), planning target volumes of GTV-T and metastatic (PTV-TN) and elective (PTV-N) lymph node stations were 72.6 GyE, 66 GyE, and 52.8 GyE, respectively. For each patient, nine coplanar fields IMRT with step-and-shoot technique and 3D spot-scanned three coplanar fields IMPT plans were prepared. Both modalities were planned in 33 fractions to be delivered with a simultaneous integrated boost technique. All plans were prepared and optimized by using the research version of the inverse treatment planning system KonRad (DKFZ, Heidelberg).


RESULTS
Both treatment techniques were equal in terms of averaged mean dose to target volumes. IMPT plans significantly improved the tumor coverage and conformation (P < 0.05) and they reduced the averaged mean dose to several organs at risk (OARs) by a factor of 2-3. The low-to-medium dose volumes (0.33-13.2 GyE) were more than doubled by IMRT plans.


CONCLUSIONS
In radiotherapy of NPC patients, three-field IMPT has greater potential than nine-field IMRT with respect to tumor coverage and reduction of the integral dose to OARs and non-specific normal tissues. The practicality of IMPT in NPC deserves further exploration when this technique becomes available on wider clinical scale.
Taheri-Kadkhoda
Zahra
Z
Göteborg University and Department of Oncology, Sahlgrenska University Hospital, Göteborg, Sweden. zahra.taheri-kadkhoda@vgregion.se
Björk-Eriksson
Thomas
T
Nill
Simeon
S
Wilkens
Jan J
JJ
Oelfke
Uwe
U
Johansson
Karl-Axel
KA
Huber
Peter E
PE
Münter
Marc W
MW
D000465:Algorithms; D003198:Computer Simulation; D006801:Humans; D009303:Nasopharyngeal Neoplasms / Q000532:radiotherapy*; D017785:Photons / Q000627:therapeutic use*; D061766:Proton Therapy; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects / Q000379:methods*; D011522:Protons
D011522:Protons