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Determination of the reference air kerma rate for brachytherapy sources
S9 26 ROLE OF ERD IN THE RADIOTHERAPY AND CHEMORADI OTHERA~Y OF HEAD AND NECK CANCERS V.HEMA, 5.5 . SUPE, V.KANNAN, D.C. DOVAL, N.ANANTHA & S.J. SUPE*, KIDWAI MEMORIAL INSTITUTE OF ONCOLOGY , BANGALORE, * 17, SARAS BAUG, BOMBAY, INDIA. Extrapol<;tted Response Dose (ERD) concept was applJ.ed t o head and neck malignancies treated by radiotherapy (RT) alone (114 patients) and by cherno-radiotherapy (RT+CT) (115 patients). In the RT and RT+CT groups, the doses va ried from 40-77 Gy & 35-71 Gy respect ively. The chemotherapy (CT) (induction/ concurrent) drugs used were 5-FU, cisplatin, methotrexate either single or in combination. ERD values were evaluated with 0(/10 values of 10, 2.5 and 6 Gy for acute late comp~ications and tumour respons: respect1vely. The correlation of ERD with late complication, response and status a~ l<;ts~ follow up (NED) was stat istically s1gnJ.~1cant for both groups (p < 0.01). ~RD dJ.d not correlate with acute complicatidq 7n the RT group (p~O.Ol). From our analysis z n the RT + CT treatments of head and ~eck cancers, an ERD value of 69 Gy 1S suggested as t he limit for an acceptable 5% late complication rate.
THE USEOF A RADIOBIOLOGICAL MODEL IN RADIOSURGERY: PRELIMINARY RESULTS CONCERNING AVM TREATMENT B. LONGOBARDIo, L. VENTRELLA·, E. MOTTl., G.M. CATTANEO°
Servizio di Fisica Sanitaria", Divisione di Neurochirurgia-Gamma Knifes, Istituto Scientifico RS. Raffaele. Milano, Italy The ~m of radiosurgical techniques is to deliverhighdosesin a single fractlO? t~ small volumes, sparing healthy tissues as much as possible. 1.C: ~hckinger proposed a radiobiological model, using an integrated 108lslJ~ formula, for predicting complications, above all brain ~ecroSIS, when the ~ose distribution into treated volume is highly inhomogeneous. This model can also account for time and fractionation with an exponential or linear quadratic correction the probability of complications maybe calculated if dosedistributiondata (DVH)andthe fractionation schedule are known. A Leksell Gamma-Unit was installed at San Raffaele Hospital on december 1993, andto date over 200 patients havebeentreated. A new treatment planning system (LGP) has beenusedsincedecember 1994, the system is connected by network to diagnostic machines and hasthe possibilityof producingDYHdata. We have applied the integrated logistic formula to the treatment of arte~o-venous malformations (AVM) in order to better clarify the relation between dose, volume, diagnostic modalities and complicationprobability. Results show the usefulness of dose statistic parameters and radiobiological models in optimizing and evaluating treatment planning.
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THE CALffiRATION OF BRACHYTIIERAPY SOURCES: AN OVERVIEW OFTHE BIR/ IPSMRECOMMENDATIONS.
DETERMINATION OF THE REFERENCE AIR KERMA RATE FOR BRACHYTHERAPY SOURCES.
ColinH Jones, The Royal Marsden NHS Trust and The Institute of CancerResearch, Fulham Road, London SW3 611 The recommendations cover the specification of brachytherapy sources, the traceability of reference standards and descriptions of source calibration methods ( Aird et al 1993 ). The report deals principally with therapy sourcesof Co 60, Ra 226, Cs 137, Au 198 and IT 192: conversion factors for calculating absorbed doses in tissueare tabulated, as well as the coefficients recommended for use for oblique filtration corrections. Data are also provided which enable users to calculate absorbed doserates to water at points close to typical caesium needles and tubes: corresponding data are also provided for iridium wires of lengths from 10 to 60 em. More general recommendations are provided for localisation procedures, dose measurements in waterand in vivo. The underlying rationale of the report will be described and illustrated by reference to the calibration of low doserate and high doserate brachytherapy sources. The role of re-entrant ionisation chambers for quality assurance and calibration will be detailed. Intercomparison of source measurements made with different thimble ionisation chambers and re-entrant ion chambers shows that consistent calibrations can be achieved: for example, in-air doserate measurements of an iridium HDR sourcemade over a three month period of source decay made with a thimble chamber and a reentrantion chamber werefound to agreewithin 0.9 % Aird et ai, 1993. Reconunendations for Brachytherapy Dosimetry: Report of a Joint BIR/IPSM Working Party. British Institute of Radiology. ISBN0 905749 32 4
A. PIERMATTEr ISTITUTO 01 FISICA - UNIVERSITA' CATTOLICA S.C. ROMA - ITALY
The purposeof thispaperis to report the results obtained determining the reference air kerrna rate, Kr, for sources as Yb-169 and Cs-137 of lowdose ratesand Ir-192 sourcesof low and high dose rates, applying a standard formalism adopted by the "Cominato per la Dosimetria in Radioterapia" (CDR)of the Associazione Italiana di Fisica Biomedica (AIFB).Theformalism allows the evaluations ofKr by usingionization measurements in freeair,carried out at 1 meteror at different distances from the source. As well known this kind of measurement needs the determination of several correction factors to be applied to the ionchamber reading. The methods adopted to determine these corrections are examined in particular to determine: a) the collection efficiency at a lowdose rate as wellas other correction factors to obtain a standard measurement condition; b) the perturbation correction factors that take into account for the presence of scattered photons in the environment, the finite size of the ion-chamber and the presence of the air between the sourceand the detector. However,the method used to determine the calibration factor Nk (source) of the ion-chamber, implies an adequate choice of the number andqualitiesof the calibration beams. When an univocal dosimetric formalism was adopted in an Italian intercomparison of Ir-l92 (wire sources) Kr determinations, the average deviation between the Kr values obtained by the centers was 0.994withan extreme deviation of no morethan2%. Oncedetermined the Kr value, for the brachytherapysourcean indirect procedure to determine the Kr by using a well ionization chamber, calibrated at the hospital center, results the best suitable procedure for routine measurements requiredfor brachytherapy quality assurance.
THE USEOF A RADIOBIOLOGICAL MODEL IN RADIOSURGERY: PRELIMINARY RESULTS CONCERNING AVM TREATMENT B. LONGOBARDIo, L. VENTRELLA·, E. MOTTl., G.M. CATTANEO°
Servizio di Fisica Sanitaria", Divisione di Neurochirurgia-Gamma Knifes, Istituto Scientifico RS. Raffaele. Milano, Italy The ~m of radiosurgical techniques is to deliverhighdosesin a single fractlO? t~ small volumes, sparing healthy tissues as much as possible. 1.C: ~hckinger proposed a radiobiological model, using an integrated 108lslJ~ formula, for predicting complications, above all brain ~ecroSIS, when the ~ose distribution into treated volume is highly inhomogeneous. This model can also account for time and fractionation with an exponential or linear quadratic correction the probability of complications maybe calculated if dosedistributiondata (DVH)andthe fractionation schedule are known. A Leksell Gamma-Unit was installed at San Raffaele Hospital on december 1993, andto date over 200 patients havebeentreated. A new treatment planning system (LGP) has beenusedsincedecember 1994, the system is connected by network to diagnostic machines and hasthe possibilityof producingDYHdata. We have applied the integrated logistic formula to the treatment of arte~o-venous malformations (AVM) in order to better clarify the relation between dose, volume, diagnostic modalities and complicationprobability. Results show the usefulness of dose statistic parameters and radiobiological models in optimizing and evaluating treatment planning.
27
28
THE CALffiRATION OF BRACHYTIIERAPY SOURCES: AN OVERVIEW OFTHE BIR/ IPSMRECOMMENDATIONS.
DETERMINATION OF THE REFERENCE AIR KERMA RATE FOR BRACHYTHERAPY SOURCES.
ColinH Jones, The Royal Marsden NHS Trust and The Institute of CancerResearch, Fulham Road, London SW3 611 The recommendations cover the specification of brachytherapy sources, the traceability of reference standards and descriptions of source calibration methods ( Aird et al 1993 ). The report deals principally with therapy sourcesof Co 60, Ra 226, Cs 137, Au 198 and IT 192: conversion factors for calculating absorbed doses in tissueare tabulated, as well as the coefficients recommended for use for oblique filtration corrections. Data are also provided which enable users to calculate absorbed doserates to water at points close to typical caesium needles and tubes: corresponding data are also provided for iridium wires of lengths from 10 to 60 em. More general recommendations are provided for localisation procedures, dose measurements in waterand in vivo. The underlying rationale of the report will be described and illustrated by reference to the calibration of low doserate and high doserate brachytherapy sources. The role of re-entrant ionisation chambers for quality assurance and calibration will be detailed. Intercomparison of source measurements made with different thimble ionisation chambers and re-entrant ion chambers shows that consistent calibrations can be achieved: for example, in-air doserate measurements of an iridium HDR sourcemade over a three month period of source decay made with a thimble chamber and a reentrantion chamber werefound to agreewithin 0.9 % Aird et ai, 1993. Reconunendations for Brachytherapy Dosimetry: Report of a Joint BIR/IPSM Working Party. British Institute of Radiology. ISBN0 905749 32 4
A. PIERMATTEr ISTITUTO 01 FISICA - UNIVERSITA' CATTOLICA S.C. ROMA - ITALY
The purposeof thispaperis to report the results obtained determining the reference air kerrna rate, Kr, for sources as Yb-169 and Cs-137 of lowdose ratesand Ir-192 sourcesof low and high dose rates, applying a standard formalism adopted by the "Cominato per la Dosimetria in Radioterapia" (CDR)of the Associazione Italiana di Fisica Biomedica (AIFB).Theformalism allows the evaluations ofKr by usingionization measurements in freeair,carried out at 1 meteror at different distances from the source. As well known this kind of measurement needs the determination of several correction factors to be applied to the ionchamber reading. The methods adopted to determine these corrections are examined in particular to determine: a) the collection efficiency at a lowdose rate as wellas other correction factors to obtain a standard measurement condition; b) the perturbation correction factors that take into account for the presence of scattered photons in the environment, the finite size of the ion-chamber and the presence of the air between the sourceand the detector. However,the method used to determine the calibration factor Nk (source) of the ion-chamber, implies an adequate choice of the number andqualitiesof the calibration beams. When an univocal dosimetric formalism was adopted in an Italian intercomparison of Ir-l92 (wire sources) Kr determinations, the average deviation between the Kr values obtained by the centers was 0.994withan extreme deviation of no morethan2%. Oncedetermined the Kr value, for the brachytherapysourcean indirect procedure to determine the Kr by using a well ionization chamber, calibrated at the hospital center, results the best suitable procedure for routine measurements requiredfor brachytherapy quality assurance.