Three-Dimensional Dosimetry Using Magnetic Resonance Imaging of Polymer Gel / 대한방사선종양학회지

PURPOSE: Three-dimensional radiation dosimetry using magnetic resonance imaging of polymer gel was recently introduced. This dosimetry system is based on radiation induced chain polymerization of acrylic monomers in a muscle equivalent gel and provide accurate 3 dimensional dose distribution. We planned this study to evaluate the clinical value of this 3-dimensional dosimetry. MATERIALS AND METHODS: The polymer gel poured into a cylindrical glass flask and a spherical glass flask. The cylindrical test tubes were for dose response evaluation and the spherical flasks, which is comparable to the human head, were for isodose curves. T2 maps from MR images were calculated using software, IDL. Dose distributions have been displayed for dosimetry. The same spherical flask of gel and the same irradiation technique was used for film and TLD dosimetry and compared with each other. RESULTS: The R2 of the gel respond linearly with radiation doses in the range of 2 to 15 Gy. The repeated dosimetry of spherical gel showed the same isodose curves. These isodose curves were identical to dose distributions from treatment planning system especially high dose range. In addition, the gel dosimetry system showed comparable or superior results with the film and TLD dosimetry. CONCLUSION: The 3-dimensional dosimetry for conformal radiation therapy using MRI of polymer gel showed stable and accurate results. Although more studies are needed for convenient clinical application, it appears to be a useful tool for conformal radiation therapy.

CT Densitometry of Lung Mass: The Effect of Reconstruction Algorithm

PURPOSE: To evaluate the effect of reconstruction algorithms on the CT measurement of mean lung mass density and normal thoracic structures. MATERIALS AND METHODS: Forty-six patients with a 2-9cm-sized lung mass underwent thoracic CT examinations with intravenous contrast enhancement and using a CT HiSpeed Advantage scanner (GE Medical Systems). In each examination, the axial image of the lung mass was reconstructed using soft, standard, detail, and bone algorithms. The mean value and standard deviation of mass density in Hounsfield Units (HU) were measured using ROIs of three different sizes (50 mm2, 200 mm2, and 350 mm2 or more), and the same method was used to measure the density of normal lung, muscle, bone, and vessels. In 21 patients, mass density was also measured on unenhanced and delayed enhanced images and the degree of enhancement was calculated. RESULTS: The average maximum difference in mean mass density in the images of the four different algorithms was less than 1 (range, 0.1 -1.9) HU (ROI size, 350 mm2 or more), 0 -4.2 HU (200 mm 2), and 0.1 -3.6 HU (50mm2). The average maximum difference in the degree of lung mass enhancement was 0.5 -1.2 (range, 0 -1.6 )HU (ROI size, 350 mm2 or more). The mean density of the four normal thoracic structures was highest in images reconstructed with the bone algorithm, though there was no significant difference between the four different algorithms (p = 1.000). CONCLUSION: The measured mean CT density of a lung mass larger than 2 cm does not significantly change according to the reconstruction algorithm used. When using a small ROI, however, the density difference may increase.

Interstitial Vaginal Needle Implantation in Gynecological Tumors: Design and Construction of Applicator / 대한방사선종양학회지

PURPOSE: It is not a simple task to achieve the ideal isodose curve with a standard vaginal applicator or single plane needle impant in the paravaginal tissue when primary or recurrent gynecological neoplasms (cervical cancers, vaginal cancers and vulvar cancers) are treated as a boost following external beam radiotherapy. The authors introduce the development and construction of a simple, inexpensive, customized applicator for volume implant to maximize the radiation dose to the tumor while minimizing the dose to the rectum and the bladder. MATERIALS AND METHODS: Nine patients underwent Ir-192 transperineal interstitial implantation for either recurrent (5 cases) or primary (3 cases) cervical cancers or primary vaginal cancer (1 case) between August 1994 and February 1998 at Ajou university hospital. First 3 cases were performed with a single plane implant guided by digital palpation. Because of inadequate isodose coverage in the tumor volume in first 3 cases, we designed and constructed interstitial vaginal applicator for volume implant to improve tumor dose distribution and homogeneity while sparing the surrounding normal tissue. Our applicators consist of vaginal obturator and perineal template that made of the clear acrylamide and dental mold material (Provil ). The applicators were customized individually according to the tumor size and its location. Both HDR and LDR irradiation were given with these applicators accomodating 6 Fr needles (Microselectron, Nucletron). The pretreatment planning prior to actual implant was performed whenever possible. RESULTS: Needles can be inserted easily and evenly into the tumor volume through the holes of templates, requiring less efforts and time for the implant prodecure. Our applicators made of materials available from commercial vendors. These have an advantage that require easy procedure, and spend relatively short time to construct. Also it was possible to fabricate applicators to individualize according to the tumor size and its location and to achieve the ideal isodose coverage. We found an accurate needle arrangement and ideal dose distribution through the CT scan that was obtained in 3 cases after needle implant. Three patients with primary cervical and vaginal cancers were controlled locally at final follow up. But all recurrent cases failed to do so. CONCLUSION: The authors introduce inexpensive, simple interstitial vaginal templates which were self-designed and constructed using materials available from commercial vendors such as acrylamide and dental mold material (Provil ).

Interstitial Vaginal Needle Implantation in Gynecological Tumors: Design and Construction of Applicator / 대한방사선종양학회지

PURPOSE: It is not a simple task to achieve the ideal isodose curve with a standard vaginal applicator or single plane needle impant in the paravaginal tissue when primary or recurrent gynecological neoplasms (cervical cancers, vaginal cancers and vulvar cancers) are treated as a boost following external beam radiotherapy. The authors introduce the development and construction of a simple, inexpensive, customized applicator for volume implant to maximize the radiation dose to the tumor while minimizing the dose to the rectum and the bladder. MATERIALS AND METHODS: Nine patients underwent Ir-192 transperineal interstitial implantation for either recurrent (5 cases) or primary (3 cases) cervical cancers or primary vaginal cancer (1 case) between August 1994 and February 1998 at Ajou university hospital. First 3 cases were performed with a single plane implant guided by digital palpation. Because of inadequate isodose coverage in the tumor volume in first 3 cases, we designed and constructed interstitial vaginal applicator for volume implant to improve tumor dose distribution and homogeneity while sparing the surrounding normal tissue. Our applicators consist of vaginal obturator and perineal template that made of the clear acrylamide and dental mold material (Provil ). The applicators were customized individually according to the tumor size and its location. Both HDR and LDR irradiation were given with these applicators accomodating 6 Fr needles (Microselectron, Nucletron). The pretreatment planning prior to actual implant was performed whenever possible. RESULTS: Needles can be inserted easily and evenly into the tumor volume through the holes of templates, requiring less efforts and time for the implant prodecure. Our applicators made of materials available from commercial vendors. These have an advantage that require easy procedure, and spend relatively short time to construct. Also it was possible to fabricate applicators to individualize according to the tumor size and its location and to achieve the ideal isodose coverage. We found an accurate needle arrangement and ideal dose distribution through the CT scan that was obtained in 3 cases after needle implant. Three patients with primary cervical and vaginal cancers were controlled locally at final follow up. But all recurrent cases failed to do so. CONCLUSION: The authors introduce inexpensive, simple interstitial vaginal templates which were self-designed and constructed using materials available from commercial vendors such as acrylamide and dental mold material (Provil ).