Impact of in-homogenity corrected dose calculation of clinical brachytherapy sites

Abstract

To determine the impact of in-homogeneity corrected dose calculations for various clinical brachytherapy sites, and to quantify the variation between the two algorithms: TG- 43 & Grid based Boltzmann Solver(Acuros). Various disease sites with Ir-192-HDR brachytherapy implants have been investigated: surface mould of the nose, base of tongue-tonsil implant, soft tissue sarcoma of the chest wall, breast multi catheter APBI, lip cancer, Skin cancer of eyelid, and gynaecological applications which consisted of two applicators, namely Vienna and ring made up of polymer and stainless steel material respectively. After the implantation, CT scans were obtained, followed by reconstruction of the implant, dose calculation, optimization and treatment delivery. The clinical dose calculations were carried out using TG-43 algorithm, which were then re-calculated using Acuros (Eclipse v 10, VMS). The dose to the target, OARs were evaluated using the DVH parameters, volumes of various isodose levels (V300%, V200%, V100%, V50%) and isodose distribution. TG-43 overestimated the dose as compared to Acuros for all the implant types. Implants such as eyelid and lip had larger variation >10%, while implants of breast, soft-tissue sarcoma of the chest wall and base of tongue resulted in variation of the order of 5-10%. The gynaecological implants resulted with lowest variation of <5%. In surface mould of the nose, the mean dose to the ipsilateral eye resulted in a variation of 11%, while in tongue implant, the dose to the underlying bone resulted in a variation of 9%. In soft tissue sarcoma and breast implant, TG-43 over estimated the dose to the skin by 20 and 35 cGy while the dose to the lung was underestimated by 10cGy per fraction (prescription dose: 4Gy/fraction). The impact of in-homogeneity corrected dose calculations for various clinical brachytherapy sites, between the two algorithms, TG-43 & Acuros has been quantified.