The impact of dose calculatıon algorıthms for perıpheral dose dıstrıbutıons of enhanced dynamıc and physıcal wedges
Internatuinal Journal of Radiation Research
In radia on therapy, the peripheral dose is important when anatomical structures with very low dose tolerances are involved. In this study, the two available calcula on algorithms of the Varian Eclipse 8.6 treatment planning system(TPS), the anisotropic analy c algorithm (AAA) and pencil-beam convolu on (PBC) was used to compare measured and calculated peripheral dose distribu on of physical wedged (PW) and enhanced dynamic wedged fields (EDW). Materials and Methods: Peripheral dose
... al dose measurements were carried out for 6 and 18 MV photons using a 0.6cc Farmer-type ioniza on chamber in the slab phantom. Measurements were performed using 15°, 30°, 45° and 60° PW and EDW for three different field sizes at d max and up to a maximum distance of 50 cm beyond the field edges. peripheral dose was further computed using two different algorithms of a TPS. The measured and calculated datas were then compared to find which algorithm calculates peripheral dose distribu on more accurately. Results: Both algorithms from the TPS adequately model the peripheral dose distribu on up to 45 degrees. For large field sizes with 60 0 EDW, the largest devia on between calculated and measured dose distribu on is less than 3.5% using the AAA, but can increase up to 9.7% of the distribu on using PBC. Conclusion: The AAA models wedged peripheral dose distribu ons more accurately than the PBC does for all studied condi ons; the difference between the algorithms are more significant for large wedge angles and large field sizes. It must be emphasized that the use of PBC for planning large-field treatments with 60 0 EDW could lead to inaccuracies of clinical significance.