Physics in Medicine and Biology

Our medical research library holds 5 studies published in Physics in Medicine and Biology (1987–2020). Each entry links to the study's record on PubMed and, where there is one, to the publisher's page and a free full text. 5 have an abstract, the authors' own summary as PubMed records it: open "Abstract" to read it.

About the journal

• Publisher: IOP Publishing
• Published: 1956 to the present, England
• Language: English
• ISSN: 0031-9155 (print), 1361-6560 (electronic)
• Its record in the NLM Catalog

2020s

• Infrared navigation system for light dosimetry during pleural photodynamic therapy. M.M. Kim, T.C. Zhu, Y.H. Ong, et al. 2020;65(7):075006. PubMed · Publisher · Free full text

  Abstract

  Pleural photodynamic therapy (PDT) is performed intraoperatively for the treatment of microscopic disease in patients with malignant pleural mesothelioma. Accurate delivery of light dose is critical to PDT efficiency. As a standard of care, light fluence is delivered to the prescribed fluence using eight isotropic detectors in pre-determined discrete locations inside the pleural cavity that is filled with a dilute Intralipid solution. An optical infrared (IR) navigation system was used to monitor reflective passive markers on a modified and improved treatment delivery wand to track the position of the light source within the treatment cavity during light delivery. This information was used to calculate the light dose, incorporating a constant scattered light dose and using a dual correction method. Calculation methods were extensively compared for eight detector locations and seven patient case studies. The light fluence uniformity was also quantified by representing the unraveled three-dimensional geometry on a two-dimensional plane. Calculated light fluence at the end of treatment delivery was compared to measured values from isotropic detectors. Using a constant scattered dose for all detector locations along with a dual correction method, the difference between calculated and measured values for each detector was within 15%. Primary light dose alone does not fully account for the light delivered inside the cavity. This is useful in determining the light dose delivered to areas of the pleural cavity between detector locations, and can serve to improve treatment delivery with implementation in real-time in the surgical setting. We concluded that the standard deviation of light fluence uniformity for this method of pleural PDT is 10%.

2010s

• PDT dose dosimetry for Photofrin-mediated pleural photodynamic therapy (pPDT). Y.H. Ong, M.M. Kim, J.C. Finlay, et al. 2017;63(1):015031. PubMed · Publisher · Free full text

  Abstract

  Photosensitizer fluorescence excited by photodynamic therapy (PDT) treatment light can be used to monitor the in vivo concentration of the photosensitizer and its photobleaching. The temporal integral of the product of in vivo photosensitizer concentration and light fluence is called PDT dose, which is an important dosimetry quantity for PDT. However, the detected photosensitizer fluorescence may be distorted by variations in the absorption and scattering of both excitation and fluorescence light in tissue. Therefore, correction of the measured fluorescence for distortion due to variable optical properties is required for absolute quantification of photosensitizer concentration. In this study, we have developed a four-channel PDT dose dosimetry system to simultaneously acquire light dosimetry and photosensitizer fluorescence data. We measured PDT dose at four sites in the pleural cavity during pleural PDT. We have determined an empirical optical property correction function using Monte Carlo simulations of fluorescence for a range of physiologically relevant tissue optical properties. Parameters of the optical property correction function for Photofrin fluorescence were determined experimentally using tissue-simulating phantoms. In vivo measurements of photosensitizer fluorescence showed negligible photobleaching of Photofrin during the PDT treatment, but large intra- and inter-patient heterogeneities of in vivo Photofrin concentration are observed. PDT doses delivered to 22 sites in the pleural cavity of 8 patients were different by 2.9 times intra-patient and 8.3 times inter-patient.

• Proton energy optimization and reduction for intensity-modulated proton therapy. W. Cao, G. Lim, L. Liao, et al. 2014;59(21):6341-54. PubMed · Publisher · Free full text

  Abstract

  Intensity-modulated proton therapy (IMPT) is commonly delivered via the spot-scanning technique. To 'scan' the target volume, the proton beam is controlled by varying its energy to penetrate the patient's body at different depths. Although scanning the proton beamlets or spots with the same energy can be as fast as 10-20 m s(-1), changing from one proton energy to another requires approximately two additional seconds. The total IMPT delivery time thus depends mainly on the number of proton energies used in a treatment. Current treatment planning systems typically use all proton energies that are required for the proton beam to penetrate in a range from the distal edge to the proximal edge of the target. The optimal selection of proton energies has not been well studied. In this study, we sought to determine the feasibility of optimizing and reducing the number of proton energies in IMPT planning. We proposed an iterative mixed-integer programming optimization method to select a subset of all available proton energies while satisfying dosimetric criteria. We applied our proposed method to six patient datasets: four cases of prostate cancer, one case of lung cancer, and one case of mesothelioma. The numbers of energies were reduced by 14.3%-18.9% for the prostate cancer cases, 11.0% for the lung cancer cases and 26.5% for the mesothelioma case. The results indicate that the number of proton energies used in conventionally designed IMPT plans can be reduced without degrading dosimetric performance. The IMPT delivery efficiency could be improved by energy layer optimization leading to increased throughput for a busy proton center in which a delivery system with slow energy switch is employed.

1990s

• The relationship between integrating sphere and diffusion theory calculations of fluence rate at the wall of a spherical cavity. W.M. Star. 1995;40(1):1-8. PubMed · Publisher

  Abstract

  The radiant energy fluence rate has been calculated at the wall of a spherical cavity, filled with a non-scattering and non-absorbing material, in a scattering and absorbing infinite medium, illuminated by an isotropic point light source at the centre. Two methods have been used: first, diffusion theory for a spherical geometry; second, integrating sphere theory using reflection factors obtained from diffusion theory for a plane semi-infinite medium illuminated by either a broad collimated perpendicularly incident beam or a broad diffuse incident beam. The two methods give identical results if the condition for the validity of the diffusion approximation is satisfied, that is mu(a) << mu(s) (mu(a) = optical absorption coefficient, mu(s) = scattering coefficient) and if also mu(eff)r1 >> 1, where r1 is the radius of the cavity and mu(eff) is the effective optical attenuation coefficient of the medium. Under the same conditions, the two methods also give identical results when the refractive index of the medium is larger than the refractive index of the material in the cavity. A numerical estimate using optical properties of human bladder indicates that the conditions for validity of the integrating sphere approach are nearly satisfied in whole-bladder photodynamic therapy.

1980s

• A Mössbauer-effect study of autopsied lung tissue of asbestos workers. G. Stroink, D. Lim, R.A. Dunlap. 1987;32(2):203-11. PubMed · Publisher

  Abstract

  A 57Fe Mössbauer-effect study of autopsied lung tissue from Canadian asbestos mine workers is presented. The spectra typically show large quantities of iron storage protein. This exhibits a quadrupole-split doublet at room temperature and both a doublet and a Zeeman-split sextet at 4.2 K, due to a distribution of particle sizes. A comparison is made with Mössbauer spectra of lung tissue from an individual not occupationally exposed to respirable asbestos, and with spectra of respirable chrysotile asbestos taken from Canadian mines.

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