Premium
Sci‐Thur PM Therapy‐01: 6MV Photon dMLC IMRT: Near Surface Dose with Oblique Incidence
Author(s) -
Popescu C,
Beckham W,
Bush K
Publication year - 2006
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 - 10.1118/1.2244615
Subject(s) - monte carlo method , ionization chamber , radiation treatment planning , percentage depth dose curve , nuclear medicine , incidence (geometry) , dosimetry , optics , monitor unit , physics , materials science , medicine , mathematics , radiation therapy , radiology , ionization , statistics , ion , quantum mechanics
The purpose of the study was to investigate absorbed dose in the build up region for oblique intensity modulated 6MV beams. For locally advanced breast carcinoma using multi‐field IMRT it is imperative to know with good precision the dose at the surface. This study intended to determine the effect of IMRT on the surface dose compared with open beams, to benchmark our Monte Carlo algorithm (BEAMnrc) in the build up region for clinical implementation and to characterize the dose calculation accuracy of our treatment planning system (Eclipse ™ 7.3) at the surface and depths up to d max . Measurements were performed in solid water using a parallel plate ionization chamber for a 10 × 10 cm 2 open field, 1 cm slit and a typical breast IMRT treatment field, both delivered with sliding window technique at 0 0° , 35 0° and 70 0° angles of incidence. Compared with the open field the 1cm gap sliding window decreased the surface dose up to 10% for normal incidence and up to 5% for 70° incidence. The measured depth‐dose curves along the central axis are in excellent agreement within 2% of the Monte Carlo simulations. The TPS using the pencil beam algorithm overestimates the dose at the surface by a factor of 3 at normal incidence for both open and IMRT fields. The TPS does not take into account the increase in the surface dose due to oblique incidence. Monte Carlo can be used to calculate with accuracy the surface dose for a clinical multi‐ field IMRT plan.