The breakpoint of fresh commercial meats and in vivo mice has been assessed using tissue temperature enhancement pattern. A 1 cm length and 0.1 cm diameter gold rod was implanted in fresh chicken breast, beef, fish, and in vivo Mus musculus white mice and was insonated with ultrasound. The temperature enhancement of gold rods was measured with a needle type thermistor over a temperature range from 35 to 50 °C. From these results the breakpoints were determined by plotting the gold rod temperature versus ultrasound exposure duration using the interception point of two curves fitted by a linear regression equations of thermal response above and below 43 °C. The linear correlation coefficients for all fitted curves lie within 0.985 and 0.997. The breakpoints were found to be 42.1 ± 1.1, 42.3 ± 0.9, 42.6 ± 0.8 and 43.5 ± 0.6 for fish, chicken breast, beef and in vivo Mus musculus white mice, respectively. The interception of the thermal response curves above and below 43 °C. Soft tissue temperature enhancement pattern has demonstrated to be a fast method to determine breakpoint. It denotes the temperature where cells may start to be destroyed and may be used to spot the startup point in dosimetry of hyperthermia cancer therapy.

Purpose:To determine the breakeven points in fresh commercial meat and in vivo mice using the tissue temperature enhancement pattern.Methods:A 1 cm length and 0.1 cm diameter gold rod were implanted in fresh chicken breast, beef, fish, in vivo Mus Musculus white mice (medial dorsal region) and insonated with ultrasound. The temperature enhancement of gold rods was measured with a needle type thermistor over a temperature range from 35–50 oC. From these results the breakeven points were determined by plotting the gold rod temperature versus ultrasound exposure time and determining the interception point of two curves fitted by a linear regression of thermal response above and below 43 °C.Results:The linear correlation coefficients for all fitted curves lie within 0.97 and 0.99. The breakeven points were found to be the same for all kinds of fresh meat (fish = 42.1 ±1.1, chicken breast = 42.3 ±0.9, beef = 42.6 ±0.8) and in vivo Mus Musculus white mice (43.3 ±0.6). These temperatures agree with the standardized value (e.g. equivalent minutes at 43 °C) for comparison of thermal treatments (Proc. SPIE Int. Soc. Opt. Eng. 2003 June 2; 4954: 37).Conclusion:The interception of the thermal response curves above and below 43 °C may be used as a fast method and useful dosimetric tool in clinical research.

A Paris system-based implant approach has been used to improve the bio-heat distribution from implanted gold rods in insonated tissues. Experiments with single-plane implants using parallel equidistant 1.018 ± 0.015 cm height and 0.136 ± 0.001 cm diameter 24-K gold rods) arranged in triangular and square shapes were performed in Mus musculus white mice (medial dorsal region). The mice were anesthetized and gold rods were implanted by means of a trocar needle and the implanted region was insonated with a 4-cm diameter transducer oscillating with a nominal frequency of 1 MHz and power of about 75 W. Intramuscular tissue temperature measurements were recorded using implantable needle type thermocouples affixed to a portable Fluke thermometer. Superficial tissue temperature profile was also measured with a FLIR infrared camera and thermographic analysis was performed using the ImageJ computer software. In both cases, the central implant planes have been assigned to that approximately bisects all the implanted rods. Measured with the needle type thermistor, for the triangular implant, the percentage deviation between the maximum and minimum temperature within the triangular plane was 5%. For a square shape, this percentage deviation was 6%. The thermographic analysis have shown a deviation of 3 and 5% for the triangular and square shapes, respectively. The Paris system-based implant approach for gold rods implanted in tissue and exposed to ultrasound may greatly improve the bio-heat propagation and sustain a constant temperature profile inside triangular and square patterns formed by gold rods implants. Additionally, the Paris system may minimize ablations areas and treatment length in hyperthermia if used in cancer tumor treatment with gold seeds and ultrasound.

We have previously proposed a method of treating so lid tumors with a combination of gold macro-rods irradiated with ultrasound. Macro particle sized ro ds offer a greater circumferential treatment area o ver nanoparticle options. Experimental studies were con ducted to investigate the heat enhancement and the bio-heat transfer to breast chicken using gold macr o rod and ultrasound. An ultrasound, other than a focused ultrasound, may produce heat enough to coo k a chicken breast up to about 1 cm diameter if a single gold rod is placed on the superficial tissue . Simulations and experimental results will provide the means to evaluate the treatment, to better desi gn a patient-specific therapy to achieve maximum destruction of tumor and injury minimization of hea lthy tissue by controlling size, shape and location of gold seeds and ultrasound parameters.

Purpose: To develop a calibration phantom for Ir-192 high dose rate (HDR) brachytherapy units that renders possible the direct measurement of absorbed dose to water and verification of treatment planning system.Methods: A phantom, herein designated BrachyPhantom, consists of a Solid Water (TM) 8-cm high cylinder with a diameter of 14 cm cavity in its axis that allows the positioning of an A1SL ionization chamber with its reference measuring point at the midheight of the cylinder's axis. Inside the BrachyPhantom, at a 3-cm radial distance from the chamber's reference measuring point, there is a circular channel connected to a cylindrical-guide cavity that allows the insertion of a 6-French flexible plastic catheter from the BrachyPhantom surface. The PENELOPE Monte Carlo code was used to calculate a factor, P-sw(lw) to correct the reading of the ionization chamber to a full scatter condition in liquid water. The verification of dose calculation of a HDR brachytherapy treatment planning system was performed by inserting a catheter with a dummy source in the phantom channel and scanning it with a CT. The CT scan was then transferred to the HDR computer program in which a multiple treatment plan was programmed to deliver a total dose of 150 cGy to the ionization chamber. The instrument reading was then converted to absorbed dose to water using the N-gas formalism and the P-sw(lw) factor. Likewise, the absorbed dose to water was calculated using the source strength, S-k, values provided by 15 institutions visited in this work.Results: A value of 1.020 (0.09%, k = 2) was found for P-sw(lw). The expanded uncertainty in the absorbed dose assessed with the BrachyPhantom was found to be 2.12% (k = 1). To an associated S-k of 27.8 cGy m(2) h(-1), the total irradiation time to deliver 150 cGy to the ionization chamber point of reference was 161.0 s. The deviation between the absorbed doses to water assessed with the BrachyPhantom and those calculated by the treatment plans and using the S-k values did not exceed +/- 3% and +/- 1.6%, respectively.Conclusions: The BrachyPhantom may be conveniently used for quality assurance and/or verification of HDR planning system with a priori threshold level to spot problems of 2% and +/- 3%, respectively, and in the long run save time for the medical physicist. (C) 2013 American Association of Physicists in Medicine.

Purpose/Objective(s)To determine the effect of the Leksell Gamma Knife (LGK) spectrum produced by the smallest and the largest radiation beams on the dose response of the Exradin A16 ion chamber.Materials/MethodsThe Monte Carlo simulations were performed with the PENELOPE code to obtain the photon spectrum of the LGK emerging from the 4-mm and 18-mm collimators (single beam) in the center of a 16-cm diameter spherical polystyrene phantom. The typical energy dependence of the micro chamber Exradin A16 and A12 between 40 keV x-rays and 1250 keV 60Co, in terms of air kerma provided by the Standard Imaging Inc., was used as the reference calibration coefficients. The photo-peaks and the portion of the Compton continuum scatter from the above radiation spectra were weighed over the response for both ion chambers to calculate the kermas in the center of the sphere.ResultsIn the range of energy between 40 and 1250 keV, the calibration coefficients from the A16 and A12 ion chambers change by a factor of 3.58 and 1.11, respectively. The ratio between integrated kermas calculated for the 18 and 4 mm collimators was 1.002 and 1.005 for A16 and A12 chambers respectively. The kerma calculated with the A12 ion chamber was 1.015 and 1.012 higher for the 18 mm and 4 mm collimators respectively when ,compared to the A16 chamber. The amount of Compton scatter produced by the 18 mm collimator was found to be of about 4% higher than that generated by the 4 mm collimator. Because the shape of the 18 and 4 mm spectra are similar and the degradation of the photopeaks into Compton radiation for the 18 mm collimator is higher than that observed for the 4 mm collimator, the integrated kerma doses calculated with the A16 ion chamber does not change significantly. However, the kerma in the center of the center of the polystyrene sphere with the 18 mm collimator has more Compton scatter, which may change the attenuation curves used for clinical purposes. The calculation done in this work was based in a single beam collimator. The 201 beams from the LGK results in a star-shaped radiation field which may change the amount o Compton radiation from both collimators. Additionally, ion chambers are calibrated in standardized laboratories using a teletherapy cobalt source. Based on the ASTM E1249 - 00 - 2005 data, the typical photon spectrum of such equipments may differ significantly from those calculated for the LGK. These effects are under consideration and are being investigated.ConclusionsThe high energy dependence of the A16 ion chamber may affect not only the reference dosimetry of the LGK but also its output factors relationship. Purpose/Objective(s)To determine the effect of the Leksell Gamma Knife (LGK) spectrum produced by the smallest and the largest radiation beams on the dose response of the Exradin A16 ion chamber. To determine the effect of the Leksell Gamma Knife (LGK) spectrum produced by the smallest and the largest radiation beams on the dose response of the Exradin A16 ion chamber. Materials/MethodsThe Monte Carlo simulations were performed with the PENELOPE code to obtain the photon spectrum of the LGK emerging from the 4-mm and 18-mm collimators (single beam) in the center of a 16-cm diameter spherical polystyrene phantom. The typical energy dependence of the micro chamber Exradin A16 and A12 between 40 keV x-rays and 1250 keV 60Co, in terms of air kerma provided by the Standard Imaging Inc., was used as the reference calibration coefficients. The photo-peaks and the portion of the Compton continuum scatter from the above radiation spectra were weighed over the response for both ion chambers to calculate the kermas in the center of the sphere. The Monte Carlo simulations were performed with the PENELOPE code to obtain the photon spectrum of the LGK emerging from the 4-mm and 18-mm collimators (single beam) in the center of a 16-cm diameter spherical polystyrene phantom. The typical energy dependence of the micro chamber Exradin A16 and A12 between 40 keV x-rays and 1250 keV 60Co, in terms of air kerma provided by the Standard Imaging Inc., was used as the reference calibration coefficients. The photo-peaks and the portion of the Compton continuum scatter from the above radiation spectra were weighed over the response for both ion chambers to calculate the kermas in the center of the sphere. ResultsIn the range of energy between 40 and 1250 keV, the calibration coefficients from the A16 and A12 ion chambers change by a factor of 3.58 and 1.11, respectively. The ratio between integrated kermas calculated for the 18 and 4 mm collimators was 1.002 and 1.005 for A16 and A12 chambers respectively. The kerma calculated with the A12 ion chamber was 1.015 and 1.012 higher for the 18 mm and 4 mm collimators respectively when ,compared to the A16 chamber. The amount of Compton scatter produced by the 18 mm collimator was found to be of about 4% higher than that generated by the 4 mm collimator. Because the shape of the 18 and 4 mm spectra are similar and the degradation of the photopeaks into Compton radiation for the 18 mm collimator is higher than that observed for the 4 mm collimator, the integrated kerma doses calculated with the A16 ion chamber does not change significantly. However, the kerma in the center of the center of the polystyrene sphere with the 18 mm collimator has more Compton scatter, which may change the attenuation curves used for clinical purposes. The calculation done in this work was based in a single beam collimator. The 201 beams from the LGK results in a star-shaped radiation field which may change the amount o Compton radiation from both collimators. Additionally, ion chambers are calibrated in standardized laboratories using a teletherapy cobalt source. Based on the ASTM E1249 - 00 - 2005 data, the typical photon spectrum of such equipments may differ significantly from those calculated for the LGK. These effects are under consideration and are being investigated. In the range of energy between 40 and 1250 keV, the calibration coefficients from the A16 and A12 ion chambers change by a factor of 3.58 and 1.11, respectively. The ratio between integrated kermas calculated for the 18 and 4 mm collimators was 1.002 and 1.005 for A16 and A12 chambers respectively. The kerma calculated with the A12 ion chamber was 1.015 and 1.012 higher for the 18 mm and 4 mm collimators respectively when ,compared to the A16 chamber. The amount of Compton scatter produced by the 18 mm collimator was found to be of about 4% higher than that generated by the 4 mm collimator. Because the shape of the 18 and 4 mm spectra are similar and the degradation of the photopeaks into Compton radiation for the 18 mm collimator is higher than that observed for the 4 mm collimator, the integrated kerma doses calculated with the A16 ion chamber does not change significantly. However, the kerma in the center of the center of the polystyrene sphere with the 18 mm collimator has more Compton scatter, which may change the attenuation curves used for clinical purposes. The calculation done in this work was based in a single beam collimator. The 201 beams from the LGK results in a star-shaped radiation field which may change the amount o Compton radiation from both collimators. Additionally, ion chambers are calibrated in standardized laboratories using a teletherapy cobalt source. Based on the ASTM E1249 - 00 - 2005 data, the typical photon spectrum of such equipments may differ significantly from those calculated for the LGK. These effects are under consideration and are being investigated. ConclusionsThe high energy dependence of the A16 ion chamber may affect not only the reference dosimetry of the LGK but also its output factors relationship. The high energy dependence of the A16 ion chamber may affect not only the reference dosimetry of the LGK but also its output factors relationship.

Purpose: To determine the relationship between maximum and average doses in thin Fricke layers irradiated with soft x‐rays. Methods: The MC code PENELOPE was used to modeling a Fricke solution pillbox‐like volume 0.30 cm thick and 1.5 cm diameter embedded in the center and flushing the surface of a 0.50‐cm thick, 1125 cm3 solid water thank filled with water. The pillbox was covered with a 0.0030 cm thick polystyrene film and the reference point for the absorbed dose calculations was its geometric center for all the simulations performed at a source‐detector distance of 30.0 cm using the PTB (Physikalisch‐Technische Bundesanstalt‐Germany courtesy: R. Kramer) calibration therapy TW30 kV, TW50 kV TW 70kV and TW100 kV spectra. The same procedure was followed with pillbox thickness varying from 0.0010 to 0.40 cm. For each x‐ray quality, the average energy per unit mass (average dose) in the pillboxes were normalized for the 0.30 cm thick Fricke solution and their maximum average dose values were assigned as being the CPE region. The effect of the beam divergence on the average dose and the water/Fricke dose relationship are being investigated. Results: As the thickness of the pillbox increases, the average dose increases, reaching a maximum after descending due to attenuation in the solution. With an uncertainty of ±0.3%, a deviation between the maximum and average doses of 17.0% (0.010‐cm depth), 5.2% (0.025‐cm depth), 0.23% (0.15‐cm depth) and 0.00% (0.30‐cm depth) were observed for 30, 50, 70 and 100 kV, respectively. Conclusions: As expected, different thickness of Fricke solution are required to determine the absorbed dose under CPE condition. Nevertheless, the data provided in this work may serve for absolute calibration of the Fricke solution using a similar setup, radiation qualities and the calculated relationship between maximum and average dose presented herein.

Purpose: The dose changes in the buildup region and beam attenuation by several carbon fiber tabletops were investigated for 6 and 10 MV photon beams. Method and Materials: Measurements were performed for 3 × 3, 10 × 10, and 25 × 25 cm2 field sizes. The surface dose and percentage depth doses (PDD) were measured using a Markus parallel plate ionization chamber. A Farmer type ionization chamber with appropriate buildup caps have been used for attenuation measurement at several gantry angles (from 0° to 180°). Oncor's couch (Siemens schematic G5499), Primus' couch (MED-TEC model IL3005), and CT's couch (MED-TEC model IL3302) have been studied. Results: For a 6 MV beam Oncor couch increases the surface dose from 16.8% to 77.6% for small fields. Attenuation varies from 1% to 4.7% for 180° and 120° gantry angles. At 6 and 10 MV beams respectively, Siemen's couch increases the dose from 17.8% to 43.2% and from 10.0% to 28.5%, the beam attenuation varies from 0.1% to 8.6% and 0.2% to 3.1% for 180° and 120° gantry angles. The increase of the surface dose for the CT couch is from 17.5% to 77.8% and 9.6% to 58.9% for 6 and 10 MV beams respectively, and beam attenuation varies from 1% to 4.7% and 1% to 2.4% for 180° and 120° gantry angles. Conclusion: The carbon fiber tabletops significantly decrease the skin sparring effect. Our data show that the surface dose increase in the buildup region is about the same for the three couches. The dosimetric effect of the tabletop may be higher, especially for intensity-modulated radiation therapy depending on the beam orientation. Attenuation should be considered and corrected such as any material under the patient at the treatment planning stage. Keywords: Carbon fibre tabletops, Oncor, Primus, CT, PDD

Purpose: To construct and test a small 192Ir collimator for HDR brachytherapy dosimetry purposes. Material and methods: The device is made up of a cerrobend cube to produce a collimated beam when a catheter from an HDR 192Ir source is inserted in the center of the cube. The cube is mounted in a calibration bench which allows the positioning of a 15 × 15 × 15 cm3 water and/or solid water phantoms in the central axis of the radiation beam at a fixed distance. The field size at the fixed calibration distance of 10 cm is 5 cm diameter. The radiation beam profile at this distance was measured with a gafchromic film, ionization chamber and calculated with the PENELOPE Monte Carlo code. Such code was also used to determine the spectra of radiation in air and at 0.5-cm depth of both phantoms. Simulations were performed with 109 histories. Results: Calculated data have shown that both profiles (x and the z-axis which is along the source) at a distance 10 cm away from the source is flat within 0.7%. This beam flatness was confirmed with the measurements done with the ionization chamber and with the gaphchromic film as well. Within the statistical uncertainty of the calculations (0.4%), there was no observable change in the mean energy of the input photon spectra and at 0.5-cm depth in water phantom. Conclusion: The miniature irradiatior can be used for QA of HDR brachytherapy equipments. If the system is provided with a standard calibrated ionization chamber and appropriate phantoms, it can be used to calibrate HDR sources, TLDs films and to determine the Fricke chemical yield.

Invasive anal cancers are generally successfully treated by combined chemotherapy with radiation therapy (XRT). For those patients who locally fail this intervention many are salvaged by surgery which generally results in permanent colostomy. We examined the treatment and outcome of Photofrin based photodynamic therapy (PDT) in a cohort of patients with anal cancer who failed locally despite chemo-radiation (N=6) and two patients with positive margins of resection after excision of small T(1) squamous cell anal cancers who refused further surgery or chemo-radiation. PDT consisted of outpatient infusion of Photofrin at 1.2mg/kg followed 48 h later by outpatient illumination. Red light (630 nm) illumination was delivered by a 5 cm diffusing fiber, treating transphincterally at 300 J/cm followed by microlens illumination at 200 J/cm(2) to the perianal tumor bed with 2 cm margin. All patients completed PDT without incident and all have maintained local control of disease in the anal region for the length of follow up (18-48 months). PDT may serve as a new means to salvage local failures and perhaps could be employed as a primary treatment modality in select patients with early stage of disease.

Purpose: This study is aimed to develop a spreadsheet which allows fast determination of laser power and irradiation time for effective dose delivered in PDT intracavitary treatment. Calculations were based on treatment cavity diameter, cylindrical diffuser length, medical radiant exposure prescription (H), and adopted clinical irradiance range (E). Method and Materials: Irradiance profiles delivered by the diffusers were measured with a spherical sensor (2.0 mm diameter). A 630 nm PDT diode laser coupled with sets of different diffusers of 10, 20, 25, and 50 mm length was used as light source. Irradiance was measured from 2–25 mm source to detector distance (SDD). The reference point of measurement was the geometric center of the diffuser and the measurements normalized at its surface (1.59 mm diameter). Curves were fitted with a double exponential decay (0.9349≤r2≤0.9951). Simulations were performed to model experimental results and compared with experimental and clinical methods (calculated by the total irradiance divided by the cylinder area bounded by SDD). Results: Compared with the irradiance calculated clinically using the area bounded by a cylinder, the irradiance measured with spherical sensor differs by as much as −32% at 1.2 cm SDD for a 20 mm length diffuser. For this case, the irradiance calculated clinically is 99.52 mW/cm2 and the true irradiance is 67.78 mW/cm2. To obtain the prescribed radiant exposure, treatment time calculated by the clinical method is wrong by a factor of 1.46. Conclusion: Calculations using the spreadsheet developed in this work allows fast calculations of irradiance, with correct exposure time using the cylindrical diffusers.

Purpose: To investigate the effect of solid water vessel in contact with the fricke dosimeter yield in terms of surface to volume ratio and storage time. Material and methods: Fricke solution was made up with the highest pure commercial available chemicals. The optical density was measured using the Varian Cary 400 UV‐Vis spectrophotometer provided with a temperature controller. Three set of ten cylindrical containers (internal radius of 0.5 cm and height 3.5 cm) were made of solid water, polystyrene, and PMMA. Containers have been filled with fricke solution of 4.3, 4.5, and 5 cm−1 surface to volume ration, and sealed with Mylar material. Optical density readings at 304 nm were performed in 120 minutes time interval, 30 minute step. The effects of solid water material on the Fricke dosimeter yield (surface to volume ratio and storage time) were compared against those values obtained for polystyrene and PMMA materials. Results: The deviation of the optical density for a surface to volume ratio ranging from 4.3 to 5 cm−1 was 0.01%, 0.01%, and 0.02% for PMMA, Polystyrene, and solid water, respectively. The maximum deviation among the different materials in the same surface to volume ratio range did not exceed 0.04%. Within the uncertainty of measurement (0.06%) no effect of solid water, polystyrene, and PMMA containers was observed on the Fricke dosimeter yield during the storage time interval of 120 minutes. Conclusion: Solid water plastic can be used to store Fricke solution and can still be comparable to polystyrene and PMMA. It has the advantage to have physical properties very close to water. Keywords: Surface to volume ratio, PMMA, Fricke dosimeter yield, solid water

Purpose: To determine the absolute dose at the reference point using measurement with Fricke dosimeter at various transverse bisector distances. Method and Materials: In a previous work we showed how the absolute dose from a source can be measured using a Fricke dosimeter. Ring shaped fricke volume of 1 mm width and 3 mm height was used to determine the absolute dose. AlphaOmega HDR source was located at the center of the ring which was 1 cm away from the source, the uncertainty at this point was too high ( k=7 %). In another second study we demonstrated that there is a size detector dependence and source positioning uncertainty when doing the measurement. We did dose profile measurements along and away from a source using four different detectors (two ionization chambers and two diodes). We showed that the detector size effect goes from 1.3% at 1 cm to 0.2% at 2.5 cm. Therefore PENELOPE Monte Carlo simulations for several radii have been used to determine conversion factors to the reference point. Results: We show in this work that the absorbed dose at various distances away from the source does not have an inverse square law behavior. Therefore, factors have been determined to convert the dose at measured point to the dose at the reference point recommended by AAPM TG‐43. These conversion factors are 4.454, 7.609, 11.288 and 16.003 for the distances 1.5, 2.0, 2.5, and 3.0 cm respectively. Conclusion: Feasibility of determining the absorbed dose using a Fricke dosimeter at the reference point (1 cm distance) was demonstrated in a previous work, however the uncertainty was too high (7%). Measurement at distances greater than 1 cm was demonstrated to lower the uncertainty. PENELOPE MC code was used to obtain the conversion factors at various radii to the reference point.

Purpose: To quantitatively evaluate current clinical dose calculations delivered by cylindrical diffusers used in superficial Photodynamic Therapy (PDT) treatments. Method and Materials: A setup was developed to investigate light irradiance patterns in air ranging from 2–50mm of Source to Detector Distances (SDD), distances customarily used in superficial PDT treatments. A 630 nm PDT diode laser light source was used in junction with diffusers ranging from: 10, 20, 25, and 50 mm. The detector was mounted on an optical bench along varying SDDs. The irradiance was then measured using a spherical optical fiber detector (1.8‐mm diameter), which was calibrated against a 1cm×1cm window photodiode detector (Ophir PD300‐3W traceable to NIST) connected to a power meter. Finally, sets of predicted irradiance values were calculated under typical clinical conditions by dividing the total power by the cylinder area bounded by the SDD. Results: The measured and predicted values were plotted and compared. For the 10mm diffuser, at approximately 50mm SDD, the predicted value was nearly fourteen times greater than that of the measured. For the larger diffusers, the disparity between the predicted and measured results narrowed. For example, the 50mm diffuser, at the same distance as that of the 10mm, predicted an intensity of only two times greater than that of the measured. Conclusion: Agreement between measured and predicted irradiance values is expected to occur for a hypothetical infinite length diffuser or for small SDD. The results however, revealed that at large distances from the source, with respect to the diffuser size, the theoretical results diverge from those obtained experimentally. Therefore, the current dose calculation should be reviewed for clinical PDT, as the understanding of the irradiance in air is paramount for the correct calculation of light dose delivered in PDT treatments.

The short and long term stability of the Diomed 630 PDT laser with attached fiberoptic microlens was evaluated by means of integrating sphere, power meter and a calorimetric system. The calorimeter system was designed as a thermal mug with absorbing media (dye and water). Both the tip of the irradiation fiber and the detection probe of a thermocouple thermometer were positioned inside the dye solution and stirred during the measurements. The calorimetric system yielded measurement results consistent with the other two methods, and similar long term variations were observed by all methods. With an indicated laser power of 1 W, the detectors' readings ranged from 0.66 to 1.29 W. For short term stability study, the deviation of laser output assessed by integrating sphere, power meter and calorimetric system were 0.3%, 0.1% and 2.8% with long term deviations of 13%, 7% and 9% respectively. This wide variation in the laser output implies the needs to establish quality control procedures involving measurements pre and post PDT procedures. The calorimetric system has been demonstrated to be a powerful tool for clinical laser QA and maintenance of the calibration factor of the detectors used in this work.

Quantitative evaluation of in vivo local tissue optical properties including scattering coefficient (μs), absorption coefficient (μa) and anisotropy (g) is often important in both photodiagnosis and phototherapy. In this study, a reflectance based fast technique was developed to determine the optical properties of turbid media using a linear‐array fiber bundle probe. Five 200 um collection fibers were linearly set along from the 200 um illumination fiber with center‐to‐center separation of 350 um. Spatial reflectance values were sequentially measured by spectrometer connected to a fiber‐switch. A model that relates the reflectance profiles to optical properties of a turbid medium was developed based on Monte Carlo simulations and phantom experiments. Simulation results at wavelength of 633 nm showed that μs′ (2∼40 cm−1) and μa (0∼5 cm−1) can be determined by reflectance spatial profiles. Intralipid and Nigrosin were used to simulate different reduced scattering coefficient (μs′) and absorption coefficient (μa) values within the same range as Monte Carlo simulation. Preliminary results show good correlation between known optical properties in tissue phantom and the measured optical properties, the average error for μs′ and μa was 7.8% and 6.6%, respectively. With same reduced scattering coefficient (μs′), changes in the absorption coefficient (μa) could be measured within 0.1 cm−1. Accurate extraction of tissue optical properties from in vivo measurements could have potential application in noninvasively superficial (pre)cancer detection and phototherapy planning.

Multifocal recurrence of in-situ squamous cell cancer of the oral cavity, pharynx and vocal cord following surgical failure can be a therapeutic dilemma. Salvage surgery or radiation may be an option but morbidity can be significant. We evaluated the potential role of low dose Photofrin (R) (1.2mg/Kg) Photodynamic Therapy for this cohort of patients.A total of 25 patients with multifocal recurrent in-situ squamous cell cancer of the oral cavity, pharynx and vocal cord who had failed local resection, and where additional surgery or radiation therapy would likely result in permanent morbidity, were offered Photodynamic Therapy. PDT consisted of off label infusion of Photofrin (R) (1.2mg/kg) followed 48 hours later by illumination at 630nm employing a light diffuser (300J) and/or microlens (150Jcm(2)).All patients completed their prescribed PDT and no patient has been lost to follow up (minimum 1 year). No photosensitivity reactions were noted. No significant morbidity was seen. All patients were able to maintain oral nutrition. Procedure related pain was well controlled by one week of oral narcotics. At one month post PDT all patients were biopsy negative in the treatment region and no failures within the treatment region have been noted. No fibrosis or permanent PDT morbidity has been seen with follow up to three years. Vocal cord and voice function were excellent.Three patients developed new regions of in-situ disease outside the PDT fields, two underwent additional PDT and one had laser resection.Low dose Photofrin (R) PDT offers excellent palliation and durable local control of recurrent in-situ squamous cell cancers of the oral cavity, pharynx and true cords. This is a well tolerated therapy. Low dose Photofrin (R) appears to improve selectivity and minimize normal tissue injury. It should be tested in a larger patient population.

Following the general trends of modern dosimetry the quantity absorbed dose in water is the one mostly needed in clinical practice. A few attempts have been reported to establish this quantity for HDR brachytherapy and potential good results of two novel techniques have been reported, firstly by Sarfehnia et al (2007) using a water based calorimeter and secondly by Austerlitz et al (2008) both with uncertainties still high, 5% and 8% respectively and deAlmeida et al (2008) with uncertainties smaller than 3% both using ferrous sulphate-Fricke dosimeter.

To develop a new standard for absorbed dose based on chemical dosimetry for HDR Ir-192 brachytherapy sources. A molded double walled spherical balloon was made with 5.540 cm of outer and 4.500 cm inner diameters intercalated by a shell of 0.293 cm fitted with a 0.106 cm sleeve all made of PMMA. The FeSo4 solution was made of 0.392 g of ferrous ammonium sulphate, 0.060 g of sodium chloride and 22 ml of sulphuric acid. The center of the balloon is filled with water, the shell is filled with FeSo4 solution and the whole balloon is placed in a water phantom. Five balloons were casted in two halves and glued. One of the balloons was left in parts in order to have all dimensions measured with a traceable micrometer. Measurements were conducted using the Nucletron microSelectron-HDR 192 Ir source previously calibrated by a well type chamber traceable to the UW-ADCL and the Nucletron TPS was used to calculate the dose at a specified depth. The irradiated solutions was transferred from the balloon to a quartz cuvette with a 5.00 cm light path length and the optical densities measured using a Micronal spectrophotometer at 304 nm UV light. Monte Carlo (PENELOPE) calculations were done to assess the magnitude of the attenuation and scatter in the PMMA walls, as well as the effect of the source anisotropy in the average dose measured. As result of the Monte Carlo calculations performed dividing the balloon in 36 sectors, 12 sectors above and below the source were identified with anisotropy values varying from 3% to 10%. The calculated values for the wall attenuation have introduced a correction smaller than 1%.For doses of 10 Gy delivered at the center of the balloon shell, the deviation between the average dose measured and the dose calculated by the TPS was smaller than 1.5%. Chemical dosimetry using standard FeSO4 solution in a containing vessel with uniform geometry relative to the source has shown to be a promising absorbed dose standard for HDR I-192 source. The overall uncertainties involving the vessel dimensions, wall thicknesses, dose calculation, wall attenuation, UV light band, source anisotropy, G value and the source transit time is better than 2%.

Purpose: Bronchial stents are devices to keep an airway open when it has been obstruct by extrinsic or intrinsic tumor compression. Such device may be in use in a patient undergoing photodynamic therapy (PDT). The magnitude of the light attenuation by commercially available stents is unknown. To study the attenuation properties of four different kinds of commercially available bronchial stents that may be used in PDT. Method and Materials: The stents were a Nitinol mesh, a polyester mesh, a solid silicone and an opaque solid silicone, all manufactured by Boston Scientific. These stents were cut longitudinally so that each could be sandwiched in a 10 × 10 PMMA holder. For each measurement, the holder with and without the stent was positioned between a PDT laser beams (630 nm, 100 mW) and a laser power/energy monitor. The attenuation was obtained by the ratio of the light intensity that reaches the detector after traverse the PMMA with and without stent, respectively. Results: The Nitinol stent attenuated the light beam by 30.7%, the polyester stent by 51.1%, the transparent silicone stent by 7.83% and the opaque silicone stent by 80.8%. Conclusion: Bronchial stents can great attenuate the light in PDT, so that attenuation of a particular kind of stent should be evaluated, taking into account also treatment time and light intensity, before its use in a patient undergoing PDT.