Impact of jaw position on sparing organs at risk in 3-dimensional conformal radiation therapy of pancreatic cancer
Purpose: The objective of this work is to investigate the impact of collimator jaw position on dose to organs at risk (OARs) during a 3-dimensional conformal radiotherapy (3DCRT) of pancreatic cancer and postulate a method to minimize OAR dose by proper positioning of the jaws.
Methods: Clinically delivered 3DCRT treatment plans for 10 patients optimized with multiple static beams using multileaf collimator (MLC) leaves conformed to a block margin around target, and collimator jaws aligned with outer extent of the block margin were selected. Subsequent plans were generated by displacing the collimator jaws outward in lateral, superior-inferior or both directions by 1 and 2 cm without altering the MLC position. Computed dose to OARs and target with unaltered dose normalization were compared against the corresponding dose obtained from the original plans.
Results: Outward displacement of the collimator jaws by 1 cm in lateral and/or superior-inferior direction resulted in a significant increase in mean dose to the studied OARs. The increase was found to be proportional to the outward displacement of the jaws. The increase in maximum dose to spinal cord was significant in a few patients while it was insignificant for all other OARs.
Conclusion: Collimator jaws aligned with outer extent of a block margin minimize dose to OARs. Any gap between the block margin and the collimator jaws can lead to an inadvertent delivery of higher dose to the OARs. Hence, the use of an optimal jaw position during treatment planning becomes important to all patient plans.
Pancreatic cancer projected to become second leading cause of cancer-related death in the United States by 2030; AACR News release, 2015 available from http://www.aacr.org/Newsroom/Pages/News-Release-Detail.aspx?ItemID=541#.Ve2ZYhFVhBc
Ghaneh P, Costello E, Neoptolemos JP. Biology and management of pancreatic cancer. Gut. 2007; 56: 1134-52.
Tempero MA, Arnoletti JP, Behrman S, et al. Pancreatic adenocarcinoma. J Natl Compr Canc Netw. 2010; 8(9): 972-1017.
Treatment of locally unresectable carcinoma of the pancreas: comparison of combined-modality therapy (chemotherapy plus radiotherapy) to chemotherapy alone. Gastrointestinal Tumor Study Group. J Natl Cancer Inst. 1988;80(10):751-5.
Roldan GE, Gunderson LL, Nagorney DM, et al. External beam versus intraoperative and external beam irradiation for locally advanced pancreatic cancer. Cancer. 1988; 61: 1110-6.
Klaassen DJ, MacIntyre JM, Catton GE, et al. Treatment of locally unresectable cancer of the stomach and pancreas: a randomized comparison of 5-fluorouracil alone with radiation plus concurrent and maintenance 5-fluorouracil--an Eastern Cooperative Oncology Group study. J Clin Oncol. 1985; 3: 373-8.
Ceha HM, van Tienhoven G, Gouma DJ, et al. Feasibility and efficacy of high dose conformal radiotherapy for patients with locally advanced pancreatic carcinoma. Cancer. 2000; 89: 2222-9.
Ling TC, Slater JM, Mifflin R, et al. Evaluation of normal tissue exposure in patients receiving radiotherapy for pancreatic cancer based on RTOG 0848. J Gastrointest Oncol. 2015; 6(2): 108-14.
Szpala S, Cao F, Kohli K. On using the dosimetric leaf gap to model the rounded leaf ends in VMAT/RapidArc plans. J Appl Clin Med Phys. 2014;15(2):4484.
Paudel N, Han E, Liang X, et al. Effect of jaw position on dose to critical structures in 3-D conformal radiotherapy treatment of pancreatic cancer. Med Phys. 2015;42(6):3413.
R Development Core Team. R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. ISBN 3-900051-07-0, 2008.
Han EY, Zhang X, Yah Y, et al. Static jaw collimation settings to minimize radiation dose to normal brain tissue during stereotactic radiosurgery. Med Dosim. 2012;37:391-5.
Ali MA, Babaiah M, Madhusudhan N, et al. Comparative dosimetric analysis of IMRT and VMAT (RapidArc) in brain, head and neck, breast and prostate malignancies. Int J Cancer Ther Oncol. 2015;3(1):03019.
Amoush A, Dalton A, Rabatic B, et al. Volumetric modulated arc therapy for spine SBRT patients to reduce treatment time and intrafractional motion. Int J Cancer Ther Oncol. 2015; 3(2):03026.
Eppinga W, Lagerwaard F, Verbakel W, et al. Volumetric modulated arc therapy for advanced pancreatic cancer. Strahlenther Onkol. 2010;186(7):382-7.
Nabavizadeh N, Simeonova AO, Waller JG, et al. Volumetric-modulated arc radiotherapy for pancreatic malignancies: dosimetric comparison with sliding-window intensity -modulated radiotherapy and 3-dimensional conformal radiotherapy. Med Dosim. 2014; 39(3):256-60.
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