The advantages of collimator optimization for intensity modulated radiation therapy

Brian E Doozan, Farrah Mohamed, Erika Nourishirazi, Silvia Pella, Theodora Leventouri


Purpose: The goal of this study was to improve dosimetry for pelvic, head and neck and other cancers with aspherical planning target volumes (PTV) using collimator optimization for intensity modulated radiation therapy (IMRT).

Methods: A retroactive study on the effects of collimator optimization of 20 patients was done by comparing collimator angles from optimized plans in Eclipse version 11.0. Keeping all other parameters equal, plans were created with four collimator techniques: CA0, all fields have collimators set to 0°, CA­E, using the Eclipse collimator optimization, CAA­, minimizing the area of the jaws around the PTV, and CAX, minimizing the x-jaw gap. The minimum area and the minimum x-jaw angles were found by evaluating each field beam’s eye view of the PTV with ImageJ and finding the desired parameters with a custom script. The evaluation of the plans included the monitor units (MU), the maximum dose of the plan, the maximum dose to organs at risk (OAR), the conformity index (CI) and the number of split fields.

Results: Compared to the CA0 plans, the monitor units decreased on average by 6% for the CAX with a p-value of 0.01 from an ANOVA test. The average maximum dose stayed within 1.1% between all four methods with the lowest being CAX. The maximum dose to the most at risk organ was best spared by the CAA, which decreased by 0.62% from the CA0. Minimizing the x-jaws significantly reduced the number of split field from 61 to 37.

Conclusion: In every field tested the CAX optimization produced as good or superior results than the other three techniques. For aspherical PTVs, CAX on average reduced the number of split fields, the maximum dose, minimized the dose to the surrounding OAR, and reduced the MU all while achieving the same control of the PTV.


Dosimetry, Collimator optimization, Radiation planning, IMRT, Monitor units, Split fields

Full Text:



Comprehensive Cancer Information. National Cancer Institute. Retrieved on August 1, 2016.

Maceira Rozas Mdel C, Rey Liste T, García Caeiro AL, et al. Recommendations for treatment with IMRT for prostate and head-neck cancer. Axencia de Avaliación de Tecnoloxías Sanitarias de Galicia. Clin Transl Oncol. 2006;8(4):262-5.

Carlson RH. Large, prospective study shows less toxicity with IMRT in locally advanced NSCLC. Oncol Times. 2015;37(24):6.

Badusha MA, Mcgarry CK. Practical collimator optimization in the management of prostate IMRT planning: A feasibility study. J Radiother Pract. 2011;11(02):107-15.

Shapiro CL, Recht A. Side effects of adjuvant treatment of breast cancer. N Engl J Med. 2001;344(26):1997-2008.

Glatstein E, Morrow M. Five-year outcomes after prostatectomy or radiotherapy for prostate cancer: The prostate cancer outcomes study. Yearbook of Oncology. 2006(2006): 146-9.

Provencio M, Isla D, Sánchez A, et al. Inoperable stage III non-small cell lung cancer: Current treatment and role of vinorelbine. J Thorac Dis. 2011;3(3):197-204.

Peñagarícano JA, Ratanatharathorn V, Papanikolaou N, et al. Intensity-modulated radiation therapy reduces the dose to normal tissue in T2N0M0squamous cell carcinoma of the glottic larynx. Med Dosim. 2004;29(4): 254-7.

Bucci MK, Bevan A, Roach M 3rd. Advances in radiation therapy: conventional to 3D, to IMRT, to 4D, and beyond. CA Cancer J Clin. 2005;55(2) :117-34.

Agarwal J, Rathod S, Murthy V, et al. Improved quality of Life (QOL) outcomes in patients with head-and-neck squamous cell carcinoma (HNSCC) treated with Intensity Modulated Radiation Therapy (IMRT) compared to 3-dimensional Conformal Radiation Therapy (3D-CRT): Evidence from a prospective randomized study. Int J Radiat Oncol Biol Phys. 2012;84(3).

Young CD, Speight JL, Akazawa PF, et al. Improved conformal coverage of the prostate with an IMRT potency-sparing technique. Int J Radiat Oncol Biol Phys. 2000;48(3):351.

Vergeer, MR, Doornaert PA, Rietveld DH, et al. Significant reduction of radiation-induced xerostomia in head and neck cancer with Intensity Modulated Radiotherapy (IMRT) compared to conventional 3D-Conformal Radiotherapy (3D-CRT). Int J Radiat Oncol Biol Phys. 2007;69(3).

Luxton G, Hancock SL, Boyer AL. Dosimetry and radiobiologic model comparison of IMRT and 3D conformal radiotherapy in treatment of carcinoma of the prostate. Int J Radiat Oncol Biol Phys. 2004;59(1):267-84.

Gunderson, Leonard L, Joel E. Tepper. Clinical Radiation Oncology. Philadelphia, PA: Elsevier Churchill Livingstone. 2007;293-4.

Kataria T, Rawat S, Sinha SN, et al. Intensity modulated radiotherapy in abdominal malignancies: our experience in reducing the dose to normal structures as compared to the gross tumor. J Cancer Res Ther. 2006;2(4): 161-5.

Chapek J, Tobler M, Toy BJ, et al. Optimization of collimator parameters to reduce rectal dose in intensity-modulated prostate treatment planning. Med Dosim. 2005;30(4):205-12.


Creative Commons License
This work is licensed under a Creative Commons Attribution 3.0 License.


International Journal of Cancer Therapy and Oncology (ISSN 2330-4049)

© International Journal of Cancer Therapy and Oncology (IJCTO)

To make sure that you can receive messages from us, please add the '' domain to your e-mail 'safe list'. If you do not receive e-mail in your 'inbox', check your 'bulk mail' or 'junk mail' folders.


Number of visits since October, 2013