Friday, 20 October 2017
Thursday, 19 October 2017
PSA (prostate specific antigen) density
PSA density (ng/mL2 or ng/mL/cc) is calculated preoperatively during the biopsy procedure by using transrectal ultrasound by dividing the maximum preoperative PSA value and prostate volume [1]. The latter is calculated based on the ellipse dimension theory formula [2] (D1 × D2 × D3 × pi/6), where D1 is the maximum transverse diameter, D2 is the maximum anteroposterior diameter, D3 is the maximum longitudinal diameter, and pi is a mathematical constant approximately equal to 3.14.
A study of a large cohort of patients (1662 patients) found a significant trend of worsening pathological features as PSA density increases [3]. Other studies [4,5] found that PSA density (using a pathological weight of the surgical specimen) was a better predictor of extracapsular disease, positive surgical margins, seminal vesicle invasion, lymph node invasion and biochemical recurrence than PSA.
«A PSAD of >0.15 ng/mL/cm3 identifies men with a higher risk of detecting prostate cancer on a screening biopsy» [6].
«A PSAD of >0.15 ng/mL/cm3 identifies men with a higher risk of detecting prostate cancer on a screening biopsy» [6].
«It is used because an elevated PSA might not arouse suspicion in a man with a very enlarged prostate. The use of PSA density to interpret PSA results is controversial because prostate cancer might be overlooked in a man with an enlarged prostate» [7].
Bibliographic references:
[1] Sfoungaristos S, Perimenis P. Evaluating PSA Density as a Predictor of Biochemical Failure after Radical Prostatectomy: Results of a Prospective Study after a Median Follow-Up of 36 Months. ISRN Urol. 2013 May 16;2013:984951. Available at: https://doi.org/10.1155/2013/984951.
[2] Wolff JM, Boeckmann W, Mattelaer P, et al. Determination of prostate gland volume by transrectal ultrasound: correlation with radical prostatectomy specimens. Eur Urol. 1995;28(1):10-2. Available at: https://doi.org/10.1159/000475012.
[3] Kundu SD, Roehl KA, Yu X, et al. Prostate specific antigen density correlates with features of prostate cancer aggressiveness. J Urol. 2007 Feb;177(2):505-9. Available at: https://doi.org/10.1016/j.juro.2006.09.039.
[4] Freedland SJ, Wieder JA, Jack GS, et al. Improved risk stratification for biochemical recurrence after radical prostatectomy using a novel risk group system based on prostate specific antigen density and biopsy Gleason score. J Urol. 2002 Jul;168(1):110-5. Available at: http://dx.doi.org/10.1016/S0022-5347(05)64841-0.
[5] Sfoungaristos S, Perimenis P. PSA density is superior than PSA and Gleason score for adverse pathologic features prediction in patients with clinically localized prostate cancer. Can Urol Assoc J. 2012 Feb;6(1):46-50. Available at: https://doi.org/10.5489/cuaj.11079.
[6] Shah A. 53 - Low-Risk Prostate Cancer. In: Hristov B, Lin S, Christodouleas J. Radiation Oncology. 2nd ed. Philadelphia, USA: Wolters Klumer Health; 2015:366.
[7] Definition of PSA density. Phoenix5org. 2002. Available at: http://www.phoenix5.org/glossary/PSA_density.html. Accessed October 19, 2017.
[7] Definition of PSA density. Phoenix5org. 2002. Available at: http://www.phoenix5.org/glossary/PSA_density.html. Accessed October 19, 2017.
Biochemical failure in prostate cancer
«The definition of biochemical recurrence following radiation therapy is complicated by the incomplete ablation of all functioning prostatic epithelium, which creates difficulty in establishing a meaningful absolute nadir and the phenomenon of “prostate-specific antigen (PSA) bounce”» [4]. Biochemical failure after primary radiotherapy with or without hormonal therapy in men with clinically localized prostate cancer by 2005 RTOG-ASTRO Phoenix Consensus Conference is: 1) PSA rise by 2 ng/mL or more above the nadir PSA; and 2) a recurrence evaluation should be considered when PSA has been confirmed to be increasing after radiation even if the rise above nadir is not yet 2 ng/mL, especially in candidates for salvage local therapy who are young and healthy [1]. The rise has to be at least 25% over nadir [5]. «This definition accepts some limitation on sensitivity in the interest of increased specificity for detecting failures associated with clinical outcomes other than cure» [4].
Following radical prostatectomy, a cutoff of 0.2 ng/mL has been associated with a high likelihood of subsequent PSA progression [2]. More recently, 0.4 ng/mL and rising has been proposed as a definition associated more closely with the development of distant metastases [3]. However, according to the ASTRO/AUA (American Urological Association) guidelines [6], «biochemical (PSA) recurrence after surgery is defined as detection of PSA concentration at 0.2 ng/mL, with a second confirmatory level detected at 0.2 ng/mL.»
Following salvage radiotherapy, biochemical recurrence is «defined as a rise in PSA ≥ 0.2 ng/ml above the PSA nadir followed by a sequentially equal or higher value [7].»
Following radical prostatectomy, a cutoff of 0.2 ng/mL has been associated with a high likelihood of subsequent PSA progression [2]. More recently, 0.4 ng/mL and rising has been proposed as a definition associated more closely with the development of distant metastases [3]. However, according to the ASTRO/AUA (American Urological Association) guidelines [6], «biochemical (PSA) recurrence after surgery is defined as detection of PSA concentration at 0.2 ng/mL, with a second confirmatory level detected at 0.2 ng/mL.»
Following salvage radiotherapy, biochemical recurrence is «defined as a rise in PSA ≥ 0.2 ng/ml above the PSA nadir followed by a sequentially equal or higher value [7].»
Bibliographic references:
[1] Roach M 3rd, Hanks G, Thames H Jr, et al. Defining biochemical failure following radiotherapy with or without hormonal therapy in men with clinically localized prostate cancer: recommendations of the RTOG-ASTRO Phoenix Consensus Conference. Int J Radiat Oncol Biol Phys. 2006 Jul 15;65(4):965-74. Available at: https://doi.org/10.1016/j.ijrobp.2006.04.029.
[2] Freedland SJ, Sutter ME, Dorey F, Aronson WJ. Defining the ideal cutpoint for determining PSA recurrence after radical prostatectomy. Prostate-specific antigen. Urology. 2003 Feb;61(2):365-9. Available at: http://dx.doi.org/10.1016/S0090-4295(02)02268-9.
[3] Amling CL, Bergstralh EJ, Blute ML, et al. Defining prostate specific antigen progression after radical prostatectomy: what is the most appropriate cut point? J Urol. 2001 Apr;165(4):1146-51. Available at: http://dx.doi.org/10.1016/S0022-5347(05)66452-X.
[4] Nielsen ME, Partin AW. The Impact of Definitions of Failure on the Interpretation of Biochemical Recurrence Following Treatment of Clinically Localized Prostate Cancer. Rev Urol. 2007 Spring;9(2):57-62.
[5] Lowrance WT, Roth BJ, Kirkby E, Murad MH, Cookson MS. Castration-Resistant Prostate Cancer: AUA Guideline Amendment 2015. J Urol. 2016 May;195(5):1444-52. Available at: https://doi.org/10.1016/j.juro.2015.10.086.
[6] Valicenti RK, Thompson I Jr, Albertsen P, et al. Adjuvant and salvage radiation therapy after prostatectomy: American Society for Radiation Oncology/American Urological Association guidelines. Int J Radiat Oncol Biol Phys. 2013 Aug 1;86(5):822-8. Available at: https://doi.org/10.1016/j.ijrobp.2013.05.029.
[7] Jackson WC, Suresh K, Tumati V, et al. Impact of Biochemical Failure After Salvage Radiation Therapy on Prostate Cancer-specific Mortality: Competition Between Age and Time to Biochemical Failure. Eur Urol Oncol. 2018 Sep;1(4):276-282. Available at: https://doi.org/10.1016/j.euo.2018.04.014.
[2] Freedland SJ, Sutter ME, Dorey F, Aronson WJ. Defining the ideal cutpoint for determining PSA recurrence after radical prostatectomy. Prostate-specific antigen. Urology. 2003 Feb;61(2):365-9. Available at: http://dx.doi.org/10.1016/S0090-4295(02)02268-9.
[3] Amling CL, Bergstralh EJ, Blute ML, et al. Defining prostate specific antigen progression after radical prostatectomy: what is the most appropriate cut point? J Urol. 2001 Apr;165(4):1146-51. Available at: http://dx.doi.org/10.1016/S0022-5347(05)66452-X.
[4] Nielsen ME, Partin AW. The Impact of Definitions of Failure on the Interpretation of Biochemical Recurrence Following Treatment of Clinically Localized Prostate Cancer. Rev Urol. 2007 Spring;9(2):57-62.
[5] Lowrance WT, Roth BJ, Kirkby E, Murad MH, Cookson MS. Castration-Resistant Prostate Cancer: AUA Guideline Amendment 2015. J Urol. 2016 May;195(5):1444-52. Available at: https://doi.org/10.1016/j.juro.2015.10.086.
[6] Valicenti RK, Thompson I Jr, Albertsen P, et al. Adjuvant and salvage radiation therapy after prostatectomy: American Society for Radiation Oncology/American Urological Association guidelines. Int J Radiat Oncol Biol Phys. 2013 Aug 1;86(5):822-8. Available at: https://doi.org/10.1016/j.ijrobp.2013.05.029.
[7] Jackson WC, Suresh K, Tumati V, et al. Impact of Biochemical Failure After Salvage Radiation Therapy on Prostate Cancer-specific Mortality: Competition Between Age and Time to Biochemical Failure. Eur Urol Oncol. 2018 Sep;1(4):276-282. Available at: https://doi.org/10.1016/j.euo.2018.04.014.
Wednesday, 18 October 2017
Sunday, 15 October 2017
Electromagnetic tracking system (EMTS)
Image-guided therapy relies on the localization of the equipment with respect to the patient. This localization in three-dimensional space is referred to as tracking and is a key enabling technology for computer-assisted interventions. Electromagnetic (EM) tracking has emerged as the method of choice that enables localization of small EM sensors in a given EM field without the requirement for line-of-sight [3]. The introduction of continuous EM tracking has allowed the intrafraction motion to be measured and corrected in real-time during treatment [2]. When a receiving sensor moving in space, an EMTS can accurately calculate its position and orientation, it can provide dynamic, real-time measuring position and orientation angle [1].
«The term “electromagnetic” to describe the tracking phenomenon arises from the fact that electromagnets are responsible for producing changing or quasi-static magnetic fields, which induce currents in solenoids or fluxgate sensors embedded in the detectors. The phenomenon responsible for the operation of these tracking systems relies solely on magnetic induction rather than any strict electromagnetic effect. Nevertheless, while this technology is referred to by both the terms “magnetic tracking” (MT) and “electromagnetic tracking” (EMT), the latter has become the more common, having been adopted by the manufacturers of these devices, (...) [3].»
«The term “electromagnetic” to describe the tracking phenomenon arises from the fact that electromagnets are responsible for producing changing or quasi-static magnetic fields, which induce currents in solenoids or fluxgate sensors embedded in the detectors. The phenomenon responsible for the operation of these tracking systems relies solely on magnetic induction rather than any strict electromagnetic effect. Nevertheless, while this technology is referred to by both the terms “magnetic tracking” (MT) and “electromagnetic tracking” (EMT), the latter has become the more common, having been adopted by the manufacturers of these devices, (...) [3].»
Bibliographic references:
[1] Zhang Z, Liu G. The Design and Analysis of Electromagnetic Tracking System. Journal of Electromagnetic Analysis and Applications. 2013;5:85-9. Available at: http://dx.doi.org/10.4236/jemaa.2013.52014.
[2] Litzenberg DW, Gallagher I, Masi KJ, et al. A measurement technique to determine the calibration accuracy of an electromagnetic tracking system to radiation isocenter. Med Phys. 2013 Aug;40(8):081711. Available at: https://doi.org/10.1118/1.4813910.
[3] Franz AM, Haidegger T, Birkfellner W, et al. Electromagnetic tracking in medicine - a review of technology, validation, and applications. IEEE Trans Med Imaging. 2014 Aug;33(8):1702-25. Available at: https://doi.org/10.1109/TMI.2014.2321777.
SPECT (single photon emission computed tomography)
SPECT, or less commonly, SPET [3], is a medical imaging technique that is based on conventional nuclear medicine imaging, using gamma rays, and tomographic reconstruction methods. It is «performed by using a gamma camera to acquire multiple two-dimensional (2D) images from multiple angles» [4]. «The images reflect functional information about patients similar to that obtained with positron emission tomography (PET). Both SPECT and PET (...) give information based on the spatial concentration of injected radiopharmaceuticals» [1]. It «is a type of nuclear imaging test that shows how blood flows to tissues and organs» [2]. It is very similar to conventional nuclear medicine planar imaging using a gamma camera (that is, scintigraphy), but, it is able to provide true three-dimensional (3D) information [3]. A computer is used to apply a tomographic reconstruction algorithm to the multiple 2D projections, yielding a 3D dataset. «This dataset may then be manipulated to show thin slices along any chosen axis of the body» [4]. SPECT can be used to complement any gamma imaging study, where a true 3D representation can be helpful, (e.g., tumor imaging, infection (leukocyte) imaging, thyroid imaging or bone scintigraphy). Because SPECT permits accurate localization in 3D space, it can be used to provide information about the localized function in internal organs, such as functional cardiac or brain imaging [3].
Bibliographic references:
[1] National Research Council (US) and Institute of Medicine (US) Committee on the Mathematics and Physics of Emerging Dynamic Biomedical Imaging. Mathematics and Physics of Emerging Biomedical Imaging. Washington (DC): National Academies Press (US); 1996. Chapter 5, Single Photon Emission Computed Tomography. Available at: https://www.ncbi.nlm.nih.gov/books/NBK232492/. Accessed October 15, 2017.
[2] SPECT (single photon emission computed tomography) scan. Mayfield Brain & Spine. 2016. Available at: https://www.mayfieldclinic.com/PE-SPECT.htm. Accessed October 15, 2017.
[3] Single-photon emission computed tomography. Enwikipediaorg. 2017. Available at: https://en.wikipedia.org/wiki/Single-photon_emission_computed_tomography. Accessed October 15, 2017.
[4] Hricak H, Akin O, Vargas HA. (2013). C. In: L. Brady and T. Yaeger, ed., Encyclopedia of Radiation Oncology, 1st ed. Springer-Verlag Berlin Heidelberg, pp.790.
[4] Hricak H, Akin O, Vargas HA. (2013). C. In: L. Brady and T. Yaeger, ed., Encyclopedia of Radiation Oncology, 1st ed. Springer-Verlag Berlin Heidelberg, pp.790.
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