EFFECT OF WETNESS LEVEL ON THE SUITABILITY OF WET GAUZE AS A SUBSTITUTE FOR SUPERFLAB^® AS A BOLUS MATERIAL FOR USE WITH 6 MV PHOTONS

Abstract

Despite the availability of commercial tissue equivalent bolus material, wet gauze has an application in radiation therapy to provide superior conformance to irregular contours. Wet gauze bolus has the potential to reduce air gaps between the bolus and surface, which could decrease surface dose if sufficiently large to disrupt electronic equilibrium. Wet gauze bolus is often fabricated and wetness judged qualitatively. We assessed the effect of specific gauze wetness levels, quantified in terms of physical density, at various field sizes with respect to their effectiveness as bolus material compared with Superflab. For large fields, > 7 x 7 cm2 in this study, wet gauze sponges with a physical density of 1.02 g/cm3 performed essentially identical to Superflab; at a smaller field size the wet gauze was slightly less effective, likely due to the heterogeneity of the gauze-water matrix. Gauze that was wetter, with a physical density of 1.2 g/cm3, or less wet, with a physical density of 0.75 g/cm3 was not as effective either due to enhanced photon absorption in the wetter sponges, or less effective establishment of electronic equilibrium in the less wet sponges. The presence of an air gap under Superflab led to reduced surface dose, especially for small fields and large air gaps. Thus, if Superflab use leads to poor contact with the skin, wet gauze having a physical density of 1.02 g/cm3 can be used as a substitute. Judging the water content of wet gauze subjectively is not acceptable as over- or under wetness can lead to decreased effectiveness of the bolus material.

THE ELECTRON BEAM ATTENUATING PROPERTIES OF SUPERFLAB, PLAY‐DOH, AND WET GAUZE, COMPARED TO PLASTIC WATER

“…and Table ). The authors concluded that while wet gauze is a perfectly acceptable bolus material if carefully constructed and maintained, it should be avoided in the absence of sufficient quality control in order to avoid dosing errors, particularly with low‐energy electron beams …”

“…When wet gauze was used as substitute for SuperFlab with 6 MV photon treatments, dose buildup and absorption were similar at field sizes larger than 7 × 7 cm but at smaller field sizes, wet gauze was less effective as a bolus. Also, the water content of wet gauze needs to be controlled carefully to avoid either inadequate buildup or excessive photon absorption …”

On Presentation of Optimal Treatment Plan in Radiotherapy of Parotid Cancer: A Comparison of Nine Techniques in Three Dimensional Conformal Radiation Therapy (3DCRT)

“…Despite reports of many researchers who study mainly different treatment techniques and use of various radiation source (photons, electrons and a mixed beam) for this type of tumors, no unified study looking at impact of bolus in achieving an optimal treatment for parotid tumors [15,18,19,21,22,24,27,30,31].…”

“…The minimum treatment volume includes the ipsilateral parotid bed and the upper neck nodes [8,13]. Using of bolus is other method which is used in radiotherapy of these tumors [14][15][16][17][18]. Bolus is a tissue-equivalent material that is widely used in electron and photon radiation therapy to move or shift the buildup region [19,20].…”

“…According to the recommendations of AAPM Task Group 25 (American Association of Physicists in Medicine), bolus should designed in such a way that target Volume received at least 90 percent of prescribed doses but with internal inhomogeneity of tumor surface and non-uniformity of the dose with bolus observed that it would be the treatment of tumors of the parotid challengeable [15,18,19,[21][22][23][24][25][26][27].…”