Abstract
The purpose of this work is to investigate if the change in plan quality with the finer leaf resolution and lower leakage of the 160 MLC would be dosimetrically significant for head and neck intensity‐modulated radiation therapy (IMRT) treatment plans. The 160 MLC consisting of 80 leaves of 0.5 cm on each bank, a leaf span of 20 cm, and leakage of less than 0.37% without additional backup jaws was compared against the 120 Millennium MLC with 60 leaves of 0.5 and 1.0 cm, a leaf span of 14.5 cm, and leakage of 2.0%. CT image sets of 16 patients previously treated for stage III and IV head and neck carcinomas were replanned on Prowess 5.0 and Eclipse 11.0 using the 160 MLC and the 120 MLC. IMRT constraints for both sets of 6 MV plans were identical and based on RTOG 0522. Dose‐volume histograms (DVHs), minimum dose, mean dose, maximum dose, and dose to 1 cc to the organ at risks (OAR) and the planning target volume, as recommended by QUANTEC 2010, were compared. Both collimators were able to achieve the target dose to the PTVs. The dose to the organs at risk (brainstem, spinal cord, parotids, and larynx) were 1%–12% (i.e., 0.5–8 Gy for a 70 Gy prescription) lower with the 160 MLC compared to the 120 MLC, depending on the proximity of the organ to the target. The large field HN plans generated with the 160 MLC were dosimetrically advantageous for critical structures, especially those located further away from the central axis, without compromising the target volume.PACS number: 87.55 D‐
Highlights
The use of intensity-modulated radiation therapy (IMRT) in the treatment of head and neck squamous cell carcinoma (HNSCC) is prevalent in today’s radiation oncology practice
The differences in the minimum, maximum, and mean dose for the planning target volumes (PTV) for 160 MLC and the 120 MLC were statistically insignificant for both the planning systems
The critical structure doses were lower with the 160 MLC compared to the 120 MLC, and this difference is shown to be statistically significant for both planning systems
Summary
The use of intensity-modulated radiation therapy (IMRT) in the treatment of head and neck squamous cell carcinoma (HNSCC) is prevalent in today’s radiation oncology practice. The multileaf collimator is a common tool which is used to modulate these IMRT treatment beams, and the plan quality and delivery of treatments are dependent on the dosimetric and mechanical properties of the MLC. Dosimetric properties such as leakage, penumbra, tongue and groove, and leaf resolution directly affect plan quality, whereas the leaf span and MLC leaf speed affect efficiency and duration of treatments. Besides the finer leaf resolution,(3) a much lower overall leaf leakage and transmission are attributed to this MLC The advantage of this finer resolution MLC for the entire field size can only be manifested if the IMRT field utilizes these leaves. A common site where large field IMRT is typically employed and these outer leaves are used for modulation is head and neck
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