Determination of boundaries between ranges of high and low gradient of beam profile

Abstract

The method of determining the boundaries by using the beam profile gradient can be extremely helpful during the commissioning of the treatment planning system for Intensity Modulated Radiation Therapy or for other techniques which require very small field sizes.

Using beam profile inflection point in process of treatment planning system verification

“…First, the field size was checked in terms of inflection points (treated as points designed the field size). In the next step, the renormalized profiles were compared, but the comparison was relativethe same parts of profiles using terms of the high and low dose gradient were compared [12]. To show the differences, two profiles for dmax and 20 cm depth with marked 50% intensity points and inflection points are presented in Figure 6.…”

“…For proper comparison of the measured open symmetric field with the calculated one, centering and renormalization of both were used [12] (Wendykier i inni, 2016). For this purpose, the x values for 50% intensity of the normalized to 100% beam profile need to be known.…”

“…The purpose of this step was to check if the inflection points could be characteristic points of the beam profile and useful for comparison purposes. Zeros of the first derivative were computed in two ways: using earlier designated boundaries between the high and low gradient [12] (Wendykier i inni, 2016) and the newly implemented method (fitting the first derivative peak points for the Gauss curve [14]. The Gaussian could be described as:…”

“…The main algorithm for off-axis and wedged beam profiles comparison remained similar to the case of open symmetrical fields [12]: normalization (to 100% for the point of maximum dose), computing the inflection points, designating differences between their abscissas and nominal field sizes for theoretical beam, centering and renormalization to nominal sizes and, finally, finding the boundary between regions of high and low gradient. Technical details of the comparison process are presented in [12].…”

“…Our experience in the field of dosimetric verification of the treatment planning systems (TPS) has been recently described [12]. That paper shows a method of designating boundaries between high and low dose gradient regions.…”