Abstract
A practical and accurate generalized procedure to reconstruct the isocenter dose Diso for 3D conformal radiotherapy (3DCRT) has been developed for X‐ray open beams supplied by linacs of different manufacturers and equipped with aSi electronic portal imaging devices (aSi EPIDs). This paper reports an extension of the method, to be applied at the wedged X‐ray beams characterized by the wedge attenuation factor WAF.Using water‐equivalent solid phantoms (SPs) of different thicknesses, w, and photon square fields of sizes, L, the generalized midplane doses D0(WAF,w/2,L) and generalized transit signals st0(WAF,w,L) by 38 beams of six different linacs were determined. The generalized data were fitted by surface equations and used together with the information of the ‘record & verify’ network of the centers. In this manner, for every beam, the Diso reconstruction was obtained in about 25 seconds after the treatment.To test the in vivo dosimetric procedure, six pelvic treatments that used conformed wedged beams were carried out with three linacs of different manufacturers. For every beam, the comparison between the reconstructed Diso and the Diso,TPS computed by the TPS, resulted in an acceptable tolerance level of ±5%, estimated for this kind of treatment.Generally the in vivo dosimetry methods that use EPIDs require: (i) a special effort for the dosimetric commissioning with SPs of different thicknesses, and (ii) extra time for the analysis of the EPID signals. The proposed procedure simplifies the commissioning step and supplies for Varian, Elekta, and Siemens linacs equipped with the aSi EPIDs a quasi‐real time in vivo dosimetry for open and wedged 3DCRT fields.PACS number: 87.53Xd
Highlights
125 Piermattei et al.: In vivo dosimetry for wedged beams particular, the in vivo dosimetry could discover the discrepancies between the reconstructed and the expected doses due to pretreatment and intreatment errors
The in vivo dose verification is one of the major concerns in radiotherapy, and we believe it will become mandatory in many countries in the future.[2]. Some researchers have demonstrated the advantages of reconstructing the delivered dose during the treatment using a 2D array as the amorphous silicon electronic portal imaging device.[3]. The present authors have developed an in vivo dosimetry method for the 3D conformed radiotherapy technique (3DCRT) for open beams based on the ratios between the transit signals measured by aSi EPIDs, and the midplane doses of a water-equivalent solid phantom (SP).(4) The method has been applied to test head, thorax, pelvic, and breast tumors in radiotherapy treatments.[4,5]
This means that when the sr,t changes in time over this tolerance level, a new ks factor should be adopted to take into account the change of the EPID sensitivity
Summary
125 Piermattei et al.: In vivo dosimetry for wedged beams particular, the in vivo dosimetry could discover the discrepancies between the reconstructed and the expected doses due to pretreatment and intreatment errors. The in vivo dose verification is one of the major concerns in radiotherapy, and we believe it will become mandatory in many countries in the future.[2] Some researchers have demonstrated the advantages of reconstructing the delivered dose during the treatment using a 2D array as the amorphous silicon electronic portal imaging device (aSi EPID).(3) The present authors have developed an in vivo dosimetry method for the 3D conformed radiotherapy technique (3DCRT) for open beams based on the ratios between the transit signals measured by aSi EPIDs, and the midplane doses of a water-equivalent solid phantom (SP).(4) The method has been applied to test head, thorax, pelvic, and breast tumors in radiotherapy treatments.[4,5]. The authors have developed a generalized procedure for the in vivo dosimetric reconstruction at the isocenter point of the 3DCRT that used open photon beams of different linacs characterized by the TPR20,10 quality index ( named TPR). A dedicated software that uses the ‘record and verify’ (R&V) network of the center supplied the in vivo dosimetry tests in quasi-real time
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