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Surface application of a hdr afteriaading system
301
Proceedings of the 35th Annual ASTRO Meeting
1093 SURFACE
APPLICATIONOF A HDR AFTERIOADINGSYSTEM
H.C. Park, P.R. Almord ard D. Butler Universityof Louisvi:Lle, Brown Cancer Center, Louisville,KY
Significant problems are associated with the treatment of irregular surface fields. The use of surface mokl therapy for superficial tumors has been abandoned as a result of personnel radiation hazards, extended treatment times and the introdudion of electron beam therapy. The advent of high dose-rate afterloading systems (HDR) has ameliorated many of the drawbacks of conventional surface mold therapy. The purpose of the study was to combine HDR methods with conventional mold therapy in the clinical treatment of skin cancer. TLD methods were used to describe dosimetry of irregular surface tields. METHODS: The MicroSelectron HDR afterloading (Nucletron Corp.) was used to treat a patient with inguinal dermal metastases. A surface applicator was constructed 01 Supedlab (Mick Radio-Nuclear Instruments, Inc., New York) bolus material with seven catheter channels spaced 1 cm apart. The treatment field was 10 x 6 cm and the bolus thickness (0.5 cm) was selected to deliver a uniform superfidal dose. The patient received a prescribed dose to the skin surface of 4400 cGy with sixteen daily fractions of 275 cGy utilizing Iridium-192 HDR surface applicator. Thermoluminescent dosimetry was used to vettfy the prescribed surface dose. Computer generated isodose distributions were obtained for A/P lateral and cross-section views of the treatment area. RESULTS: The custom construction of a surface HDR applicator using Superflab bolus material provided excellent dose distribution over the treatment field. In this particular case, only three minutes was required to deliver the prescribed dose. The verification of dose was reproducible from day to day over the full course of treatments. CONCLUSIONS: The use of the MicroSelectron HDR afterloading system with surlace applicator provides an excellent method for treating lesions located in irregular surface areas. The advantages noted are the complete elimination of personnel radiation hazards. the reduction of treatment times from hours to minutes. and a high degree of reproducibility with excellent dose distributions.
1094 LIFFECTS OF DEVIATIONS T. Wu, Ph.D.,
IN ACTUAL
SEED PIACRB‘ENT ON
PRR-PLANNED
DOSES
PDR
PROSTATE
INPLANTS
J.E. Dswson, Ph.D., T. Roy, ll.D., H. Kim, M.D. J.Y. Qu, M.8.
Rsdistion Oncology Depsrtnent, St Louis University Purpose/Objective: Proper irradiation of the entire prostate is achieved when each qeed is implanted in the pre-planned (PRPLN) position. Multiplane trsnsrectsl ultrasound probes have been introduced to permit more precise seed positioning. Such equipment does not preclude the seeds from drifting at the time of implantation, a fact that can be observed by fluoroscopy. The effect of the random seed drifting on the ieodose curves must be considered before the implant. 6 Nethoder 'Variations of the prescribed dose at reference distancea between 5 and 10 mm from the periphery of a eerie8 of optimized implanted volumes were evaluated. Random numbers were used to generate different maximum deviations in the PRPLN poeitions (msx 2-6 mm). The isotopee studied were 1125, Pd103 and s mixed implant (42% of the prescribed dose contributed by Pd103 and 586 by 1125).
Msterislm
Results: Analysis of :!Ocylindrical I125 implants (48 seeds each, maximum deviation 4 mm per seed), resulted in maximum average underdosee (MAU) in the transverse plane of 149, 109, and S%, when the dose wse prescribed et 5, 7.5 and 10 mm, respectively, from the outermost seeds. For a similar arrangement of Pd103 Iseeds,MAU= 239 at 5 mm and for s mixed implant, MAU-18% at 5 mm. For 48 seeds if the of Pd103, s maximum deviation of only 2 mm in the PRPLN poeition resulted in s MAW138 reference points were defined at 5 mm from the outer surface of the implant. Conclusion: The resul.te indicate that random deviations from the PRPLN position affect the dose to the reference points. This effect ie very significant if the prescription points are defined at 5 mm of the outermost seede, snd if Pd-103 is ueed. Mixed implants, while reducing the errors associated with the lower energy of Palladium, may keep some of the advantages of its doee rate. dose Deviations in seed positioning muet be an integral part of PRPLN. Optimal distance for prescription and seed separation must be evaluated.
Proceedings of the 35th Annual ASTRO Meeting
1093 SURFACE
APPLICATIONOF A HDR AFTERIOADINGSYSTEM
H.C. Park, P.R. Almord ard D. Butler Universityof Louisvi:Lle, Brown Cancer Center, Louisville,KY
Significant problems are associated with the treatment of irregular surface fields. The use of surface mokl therapy for superficial tumors has been abandoned as a result of personnel radiation hazards, extended treatment times and the introdudion of electron beam therapy. The advent of high dose-rate afterloading systems (HDR) has ameliorated many of the drawbacks of conventional surface mold therapy. The purpose of the study was to combine HDR methods with conventional mold therapy in the clinical treatment of skin cancer. TLD methods were used to describe dosimetry of irregular surface tields. METHODS: The MicroSelectron HDR afterloading (Nucletron Corp.) was used to treat a patient with inguinal dermal metastases. A surface applicator was constructed 01 Supedlab (Mick Radio-Nuclear Instruments, Inc., New York) bolus material with seven catheter channels spaced 1 cm apart. The treatment field was 10 x 6 cm and the bolus thickness (0.5 cm) was selected to deliver a uniform superfidal dose. The patient received a prescribed dose to the skin surface of 4400 cGy with sixteen daily fractions of 275 cGy utilizing Iridium-192 HDR surface applicator. Thermoluminescent dosimetry was used to vettfy the prescribed surface dose. Computer generated isodose distributions were obtained for A/P lateral and cross-section views of the treatment area. RESULTS: The custom construction of a surface HDR applicator using Superflab bolus material provided excellent dose distribution over the treatment field. In this particular case, only three minutes was required to deliver the prescribed dose. The verification of dose was reproducible from day to day over the full course of treatments. CONCLUSIONS: The use of the MicroSelectron HDR afterloading system with surlace applicator provides an excellent method for treating lesions located in irregular surface areas. The advantages noted are the complete elimination of personnel radiation hazards. the reduction of treatment times from hours to minutes. and a high degree of reproducibility with excellent dose distributions.
1094 LIFFECTS OF DEVIATIONS T. Wu, Ph.D.,
IN ACTUAL
SEED PIACRB‘ENT ON
PRR-PLANNED
DOSES
PDR
PROSTATE
INPLANTS
J.E. Dswson, Ph.D., T. Roy, ll.D., H. Kim, M.D. J.Y. Qu, M.8.
Rsdistion Oncology Depsrtnent, St Louis University Purpose/Objective: Proper irradiation of the entire prostate is achieved when each qeed is implanted in the pre-planned (PRPLN) position. Multiplane trsnsrectsl ultrasound probes have been introduced to permit more precise seed positioning. Such equipment does not preclude the seeds from drifting at the time of implantation, a fact that can be observed by fluoroscopy. The effect of the random seed drifting on the ieodose curves must be considered before the implant. 6 Nethoder 'Variations of the prescribed dose at reference distancea between 5 and 10 mm from the periphery of a eerie8 of optimized implanted volumes were evaluated. Random numbers were used to generate different maximum deviations in the PRPLN poeitions (msx 2-6 mm). The isotopee studied were 1125, Pd103 and s mixed implant (42% of the prescribed dose contributed by Pd103 and 586 by 1125).
Msterislm
Results: Analysis of :!Ocylindrical I125 implants (48 seeds each, maximum deviation 4 mm per seed), resulted in maximum average underdosee (MAU) in the transverse plane of 149, 109, and S%, when the dose wse prescribed et 5, 7.5 and 10 mm, respectively, from the outermost seeds. For a similar arrangement of Pd103 Iseeds,MAU= 239 at 5 mm and for s mixed implant, MAU-18% at 5 mm. For 48 seeds if the of Pd103, s maximum deviation of only 2 mm in the PRPLN poeition resulted in s MAW138 reference points were defined at 5 mm from the outer surface of the implant. Conclusion: The resul.te indicate that random deviations from the PRPLN position affect the dose to the reference points. This effect ie very significant if the prescription points are defined at 5 mm of the outermost seede, snd if Pd-103 is ueed. Mixed implants, while reducing the errors associated with the lower energy of Palladium, may keep some of the advantages of its doee rate. dose Deviations in seed positioning muet be an integral part of PRPLN. Optimal distance for prescription and seed separation must be evaluated.