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SU‐E‐T‐346: Effect of Jaw Position On Dose to Critical Structures in 3‐D Conformal Radiotherapy Treatment of Pancreatic Cancer
Author(s) -
Paudel N,
Han E,
Liang X,
Morrill S,
Zhang X,
Hardee M,
Penagaricano J,
Ratanatharathorn V
Publication year - 2015
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4924707
Subject(s) - truebeam , medicine , nuclear medicine , radiation therapy , dosimetry , radiation treatment planning , radiology , linear particle accelerator , physics , beam (structure) , optics
Purpose: Three‐dimensional conformal therapy remains a valid and widely used modality for pancreatic radiotherapy treatment. It usually meets dose constraints on critical structures. However, careful positioning of collimation jaws can reduce dose to the critical structures. Here we investigate the dosimetric effect of jaw position in MLC‐based 3‐D conformal treatment planning on critical structures. Methods: We retrospectively selected seven pancreatic cancer patients treated with 3‐D conformal radiotherapy. We started with treatment plans (Varian Truebeam LINAC, Eclipse TPS, AAA, 18MV) having both × and y jaws aligned with the farthest extent of the block outline (8mm around PTV). Then we subsequently moved either both x‐jaws or all × and y jaws outwards upto 3 cm in 1 cm increments and investigated their effect on average and maximum dose to neighboring critical structures keeping the same coverage to treatment volume. Results: Lateral displacement of both x‐jaws by 1cm each increased kidney and spleen mean dose by as much as 1.7% and 1.3% respectively and superior inferior displacement increased liver, right kidney, stomach and spleen dose by as much as 2.1%, 2%, 5.2% and 1.6% respectively. Displacement of all × and y‐jaws away by 1cm increased the mean dose to liver, right kidney, left kidney, bowels, cord, stomach and spleen by as much as 4.9%, 5.9%, 2.1%, 2.8%, 7.4%, 10.4% and 4.2% respectively. Percentage increase in mean dose due to 2 and 3cm jaw displacement increased almost linearly with the displaced distance. Changes in maximum dose were much smaller (mostly negligible) than the changes in mean dose. Conclusion: Collimation jaw position affects dose mostly to critical structures adjacent to it. Though treatment plans with MLCs conforming the block margin usually meet dose constraints to critical structures, keeping jaws all the way in, to the edge of the block reduces dose to the critical structures during radiation treatment.