New multileaf collimator with a leaf width of 5 mm improves plan quality compared to 10 mm in step-and-shoot IMRT of HNC using integrated boost procedure.
OBJECTIVE
To investigate whether a new multileaf collimator with a leaf width of 5 mm (MLC-5) over the entire field size of 40 x 40 cm(2) improves plan quality compared to a leaf width of 10 mm (MLC-10) in intensity-modulated radiotherapy (IMRT) with integrated boost for head and neck cancer.


METHODS
A plan comparison was performed for ten patients with head and neck cancer. For each patient, seven plans were calculated: one plan with MLC-10 and nine beams, four plans with MLC-5 and nine beams (with different intensity levels and two-dimensional median filter sizes [2D-MFS]), and one seven-beam plan with MLC-5 and MLC-10, respectively. Isocenter, beam angles and planning constraints were not changed. Mean values of common plan parameters over all ten patients were estimated, and plan groups of MLC-5 and MLC-10 with nine and seven beams were compared.


RESULTS
The use of MLC-5 led to a significantly higher conformity index and an improvement of the 90% coverage of PTV1 (planning target volume) and PTV2 compared with MLC-10. This was noted in the nine- and seven-beam plans. Within the nine-beam group with MLC-5, a reduction of the segment number by up to 25% at reduced intensity levels and for increased 2D-MFS did not markedly worsen plan quality. Interestingly, a seven-beam IMRT with MLC-5 was inferior to a nine-beam IMRT with MLC-5, but superior to a nine-beam IMRT with MLC-10.


CONCLUSIONS
The use of an MLC-5 has significant advantages over an MLC-10 with respect to target coverage and protection of normal tissues in step-and-shoot IMRT of head and neck cancer.
Zwicker
Felix
F
Department of Radiation Oncology, University of Heidelberg, Germany. F.Zwicker@dkfz.de
Hauswald
Henrik
H
Nill
Simeon
S
Rhein
Bernhard
B
Thieke
Christian
C
Roeder
Falk
F
Timke
Carmen
C
Zabel-du Bois
Angelika
A
Debus
Jürgen
J
Huber
Peter E
PE
D000328:Adult; D000368:Aged; D002294:Carcinoma, Squamous Cell / Q000188:drug therapy / Q000532:radiotherapy* / Q000601:surgery; D017024:Chemotherapy, Adjuvant; D003131:Combined Modality Therapy; D004867:Equipment Design; D005260:Female; D006801:Humans; D015182:Lymphatic Irradiation; D008279:Magnetic Resonance Imaging / Q000295:instrumentation; D008297:Male; D008875:Middle Aged; D010039:Otorhinolaryngologic Neoplasms / Q000188:drug therapy / Q000532:radiotherapy* / Q000601:surgery; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation*; D018714:Radiotherapy, Adjuvant; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation*; D012984:Software; D014057:Tomography, X-Ray Computed / Q000295:instrumentation