Surface buildup dose dependence on photon field delivery technique for IMRT

Abstract

The more complex delivery techniques required for implementation of intensity‐modulated radiotherapy (IMRT) based on inverse planning optimization have changed the relationship between dose at depth and dose at buildup regions near the surface. Surface buildup dose is dependent on electron contamination primarily from the unblocked view of the flattening filter and secondarily from air and collimation systems. To evaluate the impact of beam segmentation on buildup dose, measurements were performed with 10×10 cm2 fields, which were delivered with 3 static 3.5×10 cm2 or 3×10 cm2 strips, 5 static 2×10 cm2 strips, 10 static 1×10 cm2 strips, and 1.1×10 cm2 dynamic delivery, compared with a 10×10 cm2 open field. Measurements were performed in water and Solid Water using parallel plate chambers, a stereotactic diode, and thermoluminescent dosimeters (TLDs) for a 6 MV X‐ray beam. Depth doses at 2 mm depth (relative to dose at 10 cm depth) were lower by 6%, 7%, 11%, and 10% for the above field delivery techniques, respectively, compared to the open field. These differences are most influenced by differences in multileaf collimator (MLC) transmission contributing to the useful beam. An example IMRT field was also studied to assess variations due to delivery technique (static vs. dynamic) and intensity level. Buildup dose is weakly dependent on the multileaf delivery technique for efficient IMRT fields.PACS numbers: 87.53.‐j, 87.53.Dq

Dosimetry of a 6 MV flattening filter-free small photon beam using various detectors

“…These results are consistent with those of previous studies using radiochromic films, ionization chambers, and diodes [40,41]. The energy spectrum, electron contamination from collimator assembly and air, and lateral scattering falling off in FFF photon beams are the reasons behind the variations in the surface doses with field sizes [42,43]. It can be seen from figure 9 that for small field sizes of 0.6 cm×0.6 cm to 6 cm×6 cm, the SNC125c showed the highest value for D S , whereas the lowest value was obtained with the EBT3.…”

Clinical evaluation of a deep learning model for segmentation of target volumes in breast cancer radiotherapy

“…Technological advances in radiotherapy offer increasingly conformal dose distribution, leading to a steeper dose fall-off outside target volumes (TVs) and resulting in decreased radiation doses to organs at risk (OARs) while maintaining or improving target coverage [4][5][6][7]. Inversely, erroneous segmentation of TVs could potentially cancel the advantage of increased conformity due to unwanted dose deposition in OARs, resulting in a surplus of toxicity and decreased local control [6].…”

The Effect of Denser Material than Air in Front of Clinical Radiotherapy X-Ray Beam

“…Therapy field accessories such as trays and wedges [7][8][9] and oblique incidence of the beam [10] also affect the surface dose. Lee et al [11] reported surface buildup dose measurements for IMRT that included effects of the patient mask material and oblique incidence [12].…”