TY - JOUR
T1 - Measured vs. calculated off-axis wedged dose distributions
AU - Sethi, Ani1
AU - Leybovich, Leonid
AU - Dogan, Nesrin
AU - Glasgow, Glenn
PY - 2000/1/1
Y1 - 2000/1/1
N2 - Wedge filters are frequently used in the clinic to improve target dose homogeneity. All physical wedges have a uniform thickness along the non-wedged direction. Therefore wedged field profiles show a "sagging effect" in this direction. Most treatment planning systems (TPS) assume an open field profile when calculating wedged dose distributions in the off-axis plane. Although this effect has been discussed in literature, a detailed analysis of calculated and measured dose distributions was not reported. Wedged dose distributions in the non-wedged direction were systematically measured for VARIAN 600CD 6MV photons for all available wedge angles and a range of off-axis distances. Measured results were compared against dose distributions calculated by 3d FOCUS TPS. It was found that, depending on the field size, wedge angle and off-axis distance, the difference between measured and planned calculated doses may exceed 10%. In planes close to the central axis, the TPS overestimated the delivered dose, whereas in the distant off-axis planes the delivered dose was underestimated. This may lead to an appreciable underdosing and/or overdosing in the peripheral regions of the PTV. A three dimensional "wedge compensator" (3DWC) was designed for each wedge angle to be used in conjunction with the wedge filters. This 3DWC was used for dose distribution calculations only. The shape of this "wedge compensator" was determined by analyzing differences between measured and calculated dose distributions. Wedged dose distributions were recalculated using 3DWC. Excellent agreement between calculated and measured dose distributions was achieved.
AB - Wedge filters are frequently used in the clinic to improve target dose homogeneity. All physical wedges have a uniform thickness along the non-wedged direction. Therefore wedged field profiles show a "sagging effect" in this direction. Most treatment planning systems (TPS) assume an open field profile when calculating wedged dose distributions in the off-axis plane. Although this effect has been discussed in literature, a detailed analysis of calculated and measured dose distributions was not reported. Wedged dose distributions in the non-wedged direction were systematically measured for VARIAN 600CD 6MV photons for all available wedge angles and a range of off-axis distances. Measured results were compared against dose distributions calculated by 3d FOCUS TPS. It was found that, depending on the field size, wedge angle and off-axis distance, the difference between measured and planned calculated doses may exceed 10%. In planes close to the central axis, the TPS overestimated the delivered dose, whereas in the distant off-axis planes the delivered dose was underestimated. This may lead to an appreciable underdosing and/or overdosing in the peripheral regions of the PTV. A three dimensional "wedge compensator" (3DWC) was designed for each wedge angle to be used in conjunction with the wedge filters. This 3DWC was used for dose distribution calculations only. The shape of this "wedge compensator" was determined by analyzing differences between measured and calculated dose distributions. Wedged dose distributions were recalculated using 3DWC. Excellent agreement between calculated and measured dose distributions was achieved.
KW - Compensators
KW - Off-axis dose distribution
KW - Wedge filters
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U2 - 10.1109/IEMBS.2000.901332
DO - 10.1109/IEMBS.2000.901332
M3 - Article
AN - SCOPUS:0034442584
VL - 4
SP - 2502
EP - 2505
JO - Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference
JF - Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference
SN - 1557-170X
ER -