Display options
Cite
Piermattei A, Grimaldi L, D'Onofrio G, et al. In-vivo portal dosimetry by an ionization chamber. Phys Med. 2005;21(4):143-52doi: 10.1016/S1120-1797(05)80003-1.
Piermattei, A., Grimaldi, L., D'Onofrio, G., Cilla, S., Viola, P., Craus, M., Fidanzio, A., Azario, L., Deodato, F., Macchia, G., & Morganti, A. (2005). In-vivo portal dosimetry by an ionization chamber. Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Association of Biomedical Physics (AIFB), 21(4), 143-52. https://doi.org/10.1016/S1120-1797(05)80003-1
Piermattei, Angelo, et al. "In-vivo portal dosimetry by an ionization chamber." Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Association of Biomedical Physics (AIFB) vol. 21,4 (2005): 143-52. doi: https://doi.org/10.1016/S1120-1797(05)80003-1
Piermattei A, Grimaldi L, D'Onofrio G, Cilla S, Viola P, Craus M, Fidanzio A, Azario L, Deodato F, Macchia G, Morganti A. In-vivo portal dosimetry by an ionization chamber. Phys Med. 2005 October - December;21(4):143-52. doi: 10.1016/S1120-1797(05)80003-1. PMID: 18348857.
Copy Download .nbib Format: NLM
Share it on

Phys Med. 2005 October - December;21(4):143-52. doi: 10.1016/S1120-1797(05)80003-1.

In-vivo portal dosimetry by an ionization chamber.

Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Association of Biomedical Physics (AIFB)

Angelo Piermattei, Luca Grimaldi, Giuseppe D'Onofrio, Savino Cilla, Pietro Viola, Maurizio Craus, Andrea Fidanzio, Luigi Azario, Francesco Deodato, Gabriella Macchia, Alessio Morganti

Affiliations

  1. U.O. di Fisica Sanitaria, Centro di Ricerca ad Alta Tecnologia nelle Scienze Biomediche dell'Università Cattolica Sacro Cuore, Campobasso (Italy); Istituto di Fisica, Università Cattolica del Sacro Cuore, Roma (Italy).

PMID: 18348857 DOI: 10.1016/S1120-1797(05)80003-1

Abstract

As all methods for in-vivo dosimetry require special efforts many physicists are often discouraged in verifying the middle dose in a patient along the beam central axis. This work reports a practical method for the determination of the middle dose value, D(m), on the central beam axis, using a signal S(t), obtained by a small thimble ion-chamber positioned at the center of the electronic portal imaging device, and irradiated by the X-ray beam transmitted through the patient. The use of a stable ion-chamber reduces many of the disadvantages associated to the use of diodes as their periodic recalibration and time consuming positioning. The method makes use of a set of correlation functions obtained by the S(t) and D(m) ratios, determined by irradiating a water-equivalent phantom with 6 MV, 10 MV and 5 MV X-ray beams. Several tests were carried out in phantoms with asymmetric inhomogeneities. The method here proposed is based on the determination of the water-equivalent thickness of the patient, along the beam central axis, by the treatment planning system that makes use of the electron densities obtained by a computer tomography scanner, that works with calibrated Hounsfield numbers. This way, it is therefore possible to compare the dose, D(m, TPS), obtained by a treatment planning system, with the in-vivo dose D(m) value, both defined at density middle point (identified along the beam central axis, where the thick material, in terms of g cm(-2), above and below, is the same). The method has been applied for the in-vivo dosimetry of 30 patients, treated with conformed beams for pelvic tumor, checking: anterior-posterior or posterior-anterior irradiations and lateral-lateral irradiations. For every checked field at least five measurements were carried out. Applying a correct quality assurance program based on the tests of the patient set-up, machine settings and calculations, results showed that the method is able to verify agreements between the dose D(m,TPS) and the in-vivo dose value D(m), within 4% for 95% of the 240 measurements carried out in-vivo.

Publication Types