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Purpose: The potential of P-32 ophthalmic applicator irradiation after pterygium excision has been demonstrated as an alternative to Sr/Y-90 irradiation. This study aimed to provide the clinical dosimetry for this new applicator. Methods: The prototype of a cylindrical P-32 applicator was fabricated according to the Monte Carlo (MC)-based design study. At a nominal activity of 6 mCi (0.22 GBq), the absorbed dose rate at the front surface (i.e., reference dose rate) was measured by using an extrapolation ionization chamber (EC). The radiochromic film (RCF) was also used to measure the reference dose, axial depth dose distributions and transaxial dose profiles at various depths in water. Results: The reference dose rate was 3.89 ± 0.14 cGy/s for EC and 3.84 ± 0.25 cGy/s for RCF. The depth dose rate was reduced approximately by an order of magnitude for every 2 mm depth in water. Measured depth doses in depths of 0.5–2.5 mm agreed with Monte Carlo data within ±3%. Due to nonuniform absorption of P-32 into an absorbent disk, the dose profiles were not symmetric and decreased more rapidly toward the periphery than those predicted by the MC. The authors confirmed no leakage of P-32 activities and negligible exposure rate around the hand grip of the applicator. Conclusions : The P-32 applicator can delivertherapeuticdoses to the surface of the conjunctiva, while sparing the lens better than Sr/Y-90 applicators. The doses at any points from the P-32 applicator could be calculated by using the measured dosimetry data. They also confirmed no leakage of the source, reliable integrity of the applicator, and negligible exposure level around the hand grip of the applicator. However, due to a possibility of nonuniform distributions of P-32 in an absorbent disk, measuring dose profiles as well as the reference dose rate for every new applicator would be recommended.

The potential of P-32 ophthalmic applicator irradiation after pterygium excision has been demonstrated as an alternative to Sr∕Y-90 irradiation. This study aimed to provide the clinical dosimetry for this new applicator.The prototype of a cylindrical P-32 applicator was fabricated according to the Monte Carlo (MC)-based design study. At a nominal activity of 6 mCi (0.22 GBq), the absorbed dose rate at the front surface (i.e., reference dose rate) was measured by using an extrapolation ionization chamber (EC). The radiochromic film (RCF) was also used to measure the reference dose, axial depth dose distributions and transaxial dose profiles at various depths in water.The reference dose rate was 3.89 ± 0.14 cGy∕s for EC and 3.84 ± 0.25 cGy∕s for RCF. The depth dose rate was reduced approximately by an order of magnitude for every 2 mm depth in water. Measured depth doses in depths of 0.5-2.5 mm agreed with Monte Carlo data within ±3%. Due to nonuniform absorption of P-32 into an absorbent disk, the dose profiles were not symmetric and decreased more rapidly toward the periphery than those predicted by the MC. The authors confirmed no leakage of P-32 activities and negligible exposure rate around the hand grip of the applicator.The P-32 applicator can deliver therapeutic doses to the surface of the conjunctiva, while sparing the lens better than Sr∕Y-90 applicators. The doses at any points from the P-32 applicator could be calculated by using the measured dosimetry data. They also confirmed no leakage of the source, reliable integrity of the applicator, and negligible exposure level around the hand grip of the applicator. However, due to a possibility of nonuniform distributions of P-32 in an absorbent disk, measuring dose profiles as well as the reference dose rate for every new applicator would be recommended.

Purpose: Fourteen cases out of 150 IMRT DQA (dose quality assurance) plans showed measured dose differences of particular fields > ±10%. We investigated the relationship between potential setup errors, and dose gradients and dose differences. Method and Materials: A 0.125 cc ion‐chamber and a home‐made cylindrical phantom were used for verifying patient specific DQA plans of IMRT. We investigated dose gradients within ±3 mm from a verification point along x, y, z axes of 5 DQA plans where dose differences of any fields were within ±5% and of 14 DQA plans where at least one of fields had dose differences of > ±10% at planed delivery dose larger than 10 cGy. Reflecting potential setup errors, we moved the verification point along the axis of the steepest dose gradient and searched the point that dose differences of any fields were within ±10%. Results: For the DQA plans of dose differences ±10% was 1.6% (3.5 cGy), 1.2% (2.5 cGy), 0.8% (1.8 cGy), respectively. The correlation between those variations of the two groups was statistically significant (p‐value: 0.034). Except six cases of 14 DQA plans, all fields showed dose differences smaller than ±8% by shifting the ion‐chamber less than 3 mm from the original location. The average of all field dose differences was reduced from 4.7% to 3.6% after shifting. Conclusion: Due to steep dose gradients, small setup errors less than 3 mm significantly affect the measured doses of individual fields, of which dose differences could be larger than ±10%. Such a large difference at a particular field can occur, even the total dose difference is less than ±3%.

Purpose: To design the device improving the setup reproducibility of prostate cancer patients during radiation therapy.Method and Materials: A customized device made of polyurethane was designed to immobilize patient's knee, thigh and foot. It was composed of ‘Foot rest supine’, ‘Knee rest supine’ and ‘Knee rest prone’. 61 patients with prostate cancer were selected and divided into two groups to examine the performance of the devices; patients in one group used immobilization device and patients in the other group did not use that. The setup error was measured with respect to bony landmark in the three axes; medial‐lateral (ML), anterior‐posterior (AP) and cranial‐caudal (CC). 1) The difference between digitally reconstructed radiograph(DRR) and simulation film, 2) the difference between DRR and portal film, and 3) the standard deviation among portal films are measured to evaluate the reproducibility. The setup error over 3 mm and 5 mm were measured. Finally, the results were analyzed statistically by using standard t‐test. Results: Without immobilization device, the ML, AP and CC error between DRR and simulation film were 1.5±0.9 mm, 3.6±3.6 mm and 1.6±0.9 mm respectively and between DRR and portal film were 1.6±1.2 mm, 4.0±4.1 mm, and 4.2±5.5 mm respectively. The standard deviations along each axis among the portal films were 1.1 mm, 2.1 mm and 1.0 mm. With immobilization device, the ML, AP and CC error were 1.3±1.9 mm, 1.8±1.5 mm and 1.1±1.1 mm respectively between DRR and simulation film and 1.0±1.8 mm, 1.2±0.9 mm, and 1.2±0.8 mm respectively between DRR and portal film. The standard deviations were 0.9 mm, 1.6 mm and 0.8 mm. The percentage set up error greater than 3 mm and 5 mm were reduced by using immobilization device. The data were statistically significant. Conclusion: The immobilization device improved setup reproducibility and reduced critical set up error.

Purpose: New plate is devised to determine the geometrical information such as gantry and collimator rotations in weekly port films in routine radiation therapy.Method and Materials: : The plate consists of a base plate, an orientation marker, and scales. The base plate is made of 2cm acrylic plate and is inserted into the blocking tray slots of linear accelerators. It has three unique features: (1) two‐step wedges are implemented on one side of the plate, thus, making easy inserting and removing the plate into or from blocking tray slot. (2) Special geometrical structures of 4 major axis and vertical/horizontal lines (1mm wide * 18mm long) are made in grooves in the base plate and the Lipowitz metal is injected into the grooves with the use of high ‐pressure pump. (3) The orientation maker is made of two cylinders , and one cylinder is situated on top of the other. The volumes of two cylinders are exactly the same, but the central portion of one cylinder is blocked. The half of two cylinders is filled with mercury or fine lead grains mixed with saline water. Results: : The plate can be positioned with the uncertainty of < 0.2mm with 2 set‐wedge structures. Because of the gravity effect, the shadow of the orientation marker has very unique shapes in the port film for various gantry and collimator rotation. The geometrical relationships between the marker and the various lines are unambiguously analyzed and provide the mechanical information such as gantry and collimator rotations, which are very critical in radiation delivery of 3D CFRT Conclusion: : This plate has been used for weekly port film for several years. It is very effective tool as a port film QA in routine RT, 3D CFRT as well as mechanical QA for multi‐lead collimators.

Purpose: To analyze patient motions as well as patient positioning during conventional radiation therapy, a radio frequency (RF)‐based CCTV system with semi‐beam's eye views (BEV's) is to verify patient setup. Method and Materials: In order to capture patient images in semi‐beam's eye views, 4 small cameras are installed in the blocking tray, which is mounted in the treatment head of linear accelerators: right, left, superior, and inferior oblique angles towards the isocenter of the linear accelerator. Each camera has its own 2.7GHz RF module (minimize the cross‐talk interference between RF source of linear accelerator and the CCTV system), and transmits the signal to the receivers, which are placed in the wall of the treatment room. The semi‐BEV images are monitored before and during irradiations and saved in the computer. The CCTV images and port films taken and analyzed in the first day, then are used as reference images. Also, a special laser with a point and a circle is attached in the tray to make a reference point for 4 cameras and a magnification factor (can be used as SSD meter) Results: The CCTV images are captured in semi‐BEV's, thus very useful to compare the room lasers, cross hairs, and anatomical landmarks in patient contours. Because of wide dynamic range of the video amplifier, it can provide the patient images as well as room laser, and light field with room lights off. The radiation effects appear as a pepper and salt noise, which can be eliminated by employing averaging kernel in the computer. Conclusion: This CCTV system will be expanded to correlate with CT images in future and under progress. Also, the CCTV‐based images will be connected to the internet, so that the doctors can be able to monitor patient setup in remote site.

Purpose: A computerized dosimetric system with air-tight ion chambers and on-board electrometer has been devised to measure daily output checks of 4/6/10/15 MV X-ray of linear accelerators. It can be inserted into the blocking tray or can be setup on the treatment table of the linear accelerators. Method and Materials: The dosimetric systems consists of three parts : (1) air-tight plane-parallel ionization chamber, (2) on-board electrometer, (3) computer interface. The ionization chambers (10mm diameter * 2mm width) are implemented on printed circuit boards (PCB) with acrylic plates. Three electrodes are fabricated using approximately 100um thick gold/lead/cupper coating on the PCB board. The buildup plates ranging from 1cm to 3cm depending upon x-ray or electrons. The electrometer is designed using a typical current-to-voltage converter (ACF2101, Burbrown, USA) with 20-bit ADC circuits (ADC1210, Burbrown, USA), (3) The ADC output is transmitted via RS-232 interface to a personal computer. The power from rechargeable battery is supplied all the time to the electrometer, thus eliminating warm-up time. Results: The short and long term stabilities of the ion chamber are found to be less than 0.2% (one standard deviation) with reference of standard dosimetric system. Also, it is extended to be a 9-channel dosimetric system as a QA device of implementing transit dosimetry (±/−3% agreements between expected and measured values) to determine the overall performances of radiation therapy for the head/neck and breast treatments. Conclusion: The daily QA devices of measuring the output of linear accelerators (6EX and 21EX of Varian linear accelerators) are proven to be very effective. It will be modified to measure the output and the PDD (in a step of 1cm) of the electron beams as a weekly QA.