Is the in vivo dosimetry with the OneDosePlusTM system able to detect intra-fraction motion? A retrospective analysis of in vivo data from breast and prostate patients

Abstract

BackgroundThe OneDosePlusTM system, based on MOSFET solid-state radiation detectors and a handheld dosimetry reader, has been used to evaluate intra-fraction movements of patients with breast and prostate cancer.MethodsAn Action Threshold (AT), defined as the maximum acceptable discrepancy between measured dose and dose calculated with the Treatment Planning System (TPS) (for each field) has been determined from phantom data. To investigate the sensitivity of the system to direction of the patient movements, fixed displacements have been simulated in phantom. The AT has been used as an indicator to establish if patients move during a treatment session, after having verified the set-up with 2D and/or 3D images. Phantom tests have been performed matching different linear accelerators and two TPSs (TPS1 and TPS2).ResultsThe ATs have been found to be very similar (5.0% for TPS1 and 4.5% for TPS2). From statistical data analysis, the system has been found not sensitive enough to reveal displacements smaller than 1 cm (within two standard deviations). The ATs applied to in vivo treatments showed that among the twenty five patients treated for breast cancer, only four of them moved during each measurement session. Splitting data into medial and lateral field, two patients have been found to move during all these sessions; the others, instead, moved only in the second part of the treatment. Patients with prostate cancer have behaved better than patients with breast cancer. Only two out of twenty five moved in each measurement session.ConclusionsThe method described in the paper, easily implemented in the clinical practice, combines all the advantages of in vivo procedures using the OneDosePlusTM system with the possibility of detecting intra-fraction patient movements.

Standard or hypofractionated radiotherapy in the postoperative treatment of breast cancer: a retrospective analysis of acute skin toxicity and dose inhomogeneities

“…For each patient, the measurements were performed using one MOSFET for each field of the treatment plan (both medial and lateral fields). We calculated an Action Threshold (AT), defined as the maximum acceptable discrepancy between the dose measured with the detector and the dose calculated with the TPS for each single field from phantom data [12]. The AT was ± 5% within 2 Standard Deviations.…”

Characteristics of mobile MOSFET dosimetry system for megavoltage photon beams

“…In vivo dosimetry is routinely performed to estimate the radiation dose to validate the dose delivery to the patient organs such as the eye, [ 1 2 ] nasopharynx, [ 3 ] oropharynx, [ 3 ] breast, [ 4 5 ] and prostate. [ 4 6 7 ] Most of the in vivo dose measurements are either performed to measure the entrance and exit doses or the organs doses by intracavitary measurements.…”