TPS peripheral dose calculation control with in vivo dosimetry

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Introduction In the clinical context of a treatment of a left thigh's rhabdomyosarcoma for a young male patient (16y-o), we have been brought to measure the peripheral dose received at the testis with In-Vivo Dosimetry (IVD) in order to verify the pertinence of the out-of-field dose calculation of the treatment planning station (TPS). Material and methods Planning: Treatment plan of 23 fractions of 1.8 Gy with 3 oblique fields, realized with the Pinnacle V8.0 m TPS for an accelerator Elekta Synergy. Dosimeters: out-of-field calibration, at 12 cm of the beam axis, of two dosimeters for the IVD, MOSFETs (BMC) and thermoluminescent dosimeters LiF (TLD)(GR200A, Fimel), with an ionization chamber (IC) (CC13, IBA). Phantom measurements: – Received dose at the testis evaluation in a water equivalent phantom (RW3 polystyrene slab) for the same plan treatment. – Comparisons between the IC and dosimeters measurements. In-vivo measurements: Ten measurements have been performed during the whole treatment. Results Dose estimation in a phantom: Measured dose by the reference IC: 7.0 cGy (σ = ±0.1%) Measured dose by the TLDs: 8.1 cGy (±7.7%) Measured dose by the MOSFETs: 6.4 cGy (±8.2%) Mean dose calculated by the TPS: 6.5 cGy (±10.7%) In-vivo measurements. Mean recieved dose by the TLDs: 9.7 cGy (±34%) Mean recieved dose by the MOSFETs: 9.3 cGy (±70%) Mean dose calculated by the TPS: 9.1 cGy (±21.6%) Conclusion A relative agreement has been found between measurements and the TPS calculation for the specific condition of this treatment, considering the order of magnitude and the standard deviation. Nevertheless, these results cannot generalize the validation of the TPS calculation for all the peripheral doses. However, this case allowed us to create a protocol in order to measure accurately peripheral doses at the testis, in a context of a hospital with an important pediatric activity.