Dosimetri og vurdering av algoritme for inversoptimalisert doseplanlegging for brachyterapi

Purpose Individual optimized treatment planning is recommended when creating treatment plans for brachytherapy of cervical cancer. Manual alteration of the dose distribution is time consuming and the treatment plan may be dependent on the person creating it. Inverse planning simulated anneahng (IPSA) is an algorithm that can optimize the dose distribution considering dose to several delineated structures. This algorithm, currently available in the treatment planning system Masterplan, has been evaluated for brachytherapy of cervical cancer. The Masterplan system simulates a source type from at different manufacturer than the type used for treatment at St. Olavs Hospital at the time being. The dose distribution from the two source types were evaluated to see if Masterplan an be used to simulate the source type used for treatment at St. Olavs Hospital. Methods and materials The dose distributions from the two source types were compared based on calcuations from two treatment planning systems (Masterplan and Plato) simulating each source type. Dose measurements of the source used at St. Olavs Hospital for brachytherapy treatment of cervical cancer were taken. These were compared with the dose distribution calculated by the two treatment planning systems. At St. Olavs Hospital treatment are executed using a Fletcher type applicator. MR-images are taken with the applicator in place. Target and organs at risk are delineated in the images before the treatment planning is performed. For 11 patients treated with brachytherapy of cervical cancer at St. Olavs Hospital, three different IPSA-plans with different dose constraints (IPSA1, IPSA2 and IPSA3) and one treatment plan with equal dwell times were made in retrospect. All IPSA-plans constrain the same dose to the target. IPSA1 and IPSA3 have the same constraints to organs at risk, while IPSA2 allow a higher dose to the organs at risk. IPSA3 sets a limit for maximum dose in target volume. For evaluation of the quality of the treatment plans, dose parameters of chnical relevance were extracted from dose volume histograms. Results Deviations in the calculated dose distribution up to 30% is found for the two source types in certain areas. These deviations are found close to the source and below the connector end of the source. For distances ≥ 4 mm from the source center along one axis, deviations of the calculations were ≤ 4%. This is in correspondance with the measured dose values. Target coverage for IPSA2 is 0.92. For IPSA1 and IPSA3 target coverage is 0.84 and 0.81 respectively. The number of treatment plans exceeding tolerance limit for one or more OAR is 82% for IPSA2, 55% for IPSA1 and 35% for IPSA3. The plan with equal dwell times have a target coverage of 0.66 and 45% of the treatment plans exceed the given tolerance limit for one or more organs at risk. Conclusion Deviations are found in the simulated dose distribution of the two source types tested, but only in clinical irrelevant areas for brachytherapy of cervical cancer. Masterplan can be used for simulating the dose distribution of the source used for treatment at St. Olavs Hospital. Using IPSA is better when it comes to improving target coverage and not violating tolerance limit for organs at risk, than a conservative treatment plan with equal dwell times. Due to too high doses to organs at risk, IPSA2 should be rejected. IPSA1 has better target coverage and IPSA3 have lower dose to the organs at risk. To avoid inhomogeneities in dwell time values, IPSA3 is probably the best suggestion.  Sammendrag Formål Det er anbefalt & lage individuelt optimaliserte plan når behandlingsplaner skal lages i forbindelse med brachyterapi av livmorhalskreft. Manuell endring av dosefordelingen er tidkrevende og resultatet kan bli preget av personen som lager planen. 'Iverse planning simulated anneahng' (IPSA) er en algoritme som kan optimalisere dosefordehngen slik at dose til flere skisserte strukturer blir tatt hensyn til. Denne algoritmen, tilgjengehg i doseplanleggingssystemet Masterplan, har blitt vurdert for brachyterapi av livmorhalskreft. Masterplan simulerer en kildetype fra en annen produsent enn den kildetypen som blir brukt til behandling på St. Olavs hospital i dag. Dosefordehngen til de to kildetypene har blitt vurdert for å se om Masterplan kan brukes til å simulere kildetypen brukt til behandling. Metode og utstyr Dosefordehngen fra de to kildetypene ble sammenlignet ved hjelp av doseberegninger fra to doseplanleggingssystemer (Masterplan og Plato) som simulerer hver sin kildetype. Det ble tatt målinger av dosen fra kilden brukt på St. Olavs hospital til brachyterapi av livmorhalskreft. Disse ble sammenlignet med dosefordelingen regnet ut av de to planleggingssystemene. På St. Olavs hospital blir en Fletcher type apphkator brukt til behandling. MR-bilder blir tatt etter at applikatoren er posisjonert. I bildene blir målvolum og risikooganer skissert før behandlingsplanleggingen gjennomføres. I denne studien har tre ulike IPSA-planer med forskjellig doserestriksjoner (IPSA1, IPSA2 and IPSA3) og en plan med lik liggetid i kildeposisjonene, blitt laget i ettertid for 11 pasienter behandlet for livmorhalskreft på St. Olavs hospital. IPSA-planene har samme doserestriksjoner til målvolum. IPSA1 og IPSA3 har samme begrensning til risikoorganer, mens IPSA2 tillater høyere dose til risikoorganer. IPSA3 har en begrensning for maksimum dose til volum for måvolumet. For vurdering av kvaliteten til planene ble klinisk relevante doseparametre funnet fra dosevolum-histogram. Resultat Det ble funnet avvik opp til 30% for beregnet dose i ulike punkt for de to kildetypene i visse omr&der. Disse avvikene ligger nærme kilden og rett under koblingsenden. For avstander ≥ 4 mm fra kildesenter transversalt på kilden er avvikene i beregningene ≤4%. Dosemålingene som ble tatt støtter dette. Dekning av målvolum er 0.92 for IPSA2. For IPSA1 og IPSA3 er denne dekninjen henholdsvis 0.84 og 0.81. Antall planer hvor en definert grense for dosen til et eller flere risikoorgan har blitt oversteget, er 82% for IPSA2, 55% for IPSA1 og 35% for IPSA3. Planen hvor liggetidene er fordelt likt har malvolumdekning på 0.66 og 45% av planene overstiger den definerte toleranse grensen for et eller flere risikoorgan. Konklusjon Det ble funnet avvik i de simulerte dosefordelingene mellom de to kildetypene, men kun i klinisk irrelevante områder for brachyterapi av livmorhalskreft. Masterplan kan bli brukt til å simulere dosefordelingen til kilden som blir brukt til behandling på St. Olavs hospital. Bruk av IPSA gir bedre resultater enn den konservative behandlingsplanen med lik liggetid ncir det gjelder dekning av målvolum og å overholde toleransegrensene som er satt for risikorganene. På grunn av for høye doser til risikoorganer burde IPSA2 forkastes. IPSA3 gir bedre dekning av måvolum mens IPSA3 gir lavere dose til risikoorganer. For å unngå store forskjeller mellom liggetidene i de ulike kildeposisjonene vil antagelig IPSA3 gi best utganspunkt for videre planlegging

Dosimetry and evaluation of algorithm for inverseoptimized doseplanning for brachytherapy

Purpose Individual optimized treatment planning is recommended when creating treatment plans for brachytherapy of cervical cancer. Manual alteration of the dose distribution is time consuming and the treatment plan may be dependent on the person creating it. Inverse planning simulated anneahng (IPSA) is an algorithm that can optimize the dose distribution considering dose to several delineated structures. This algorithm, currently available in the treatment planning system Masterplan, has been evaluated for brachytherapy of cervical cancer. The Masterplan system simulates a source type from at different manufacturer than the type used for treatment at St. Olavs Hospital at the time being. The dose distribution from the two source types were evaluated to see if Masterplan an be used to simulate the source type used for treatment at St. Olavs Hospital. Methods and materials The dose distributions from the two source types were compared based on calcuations from two treatment planning systems (Masterplan and Plato) simulating each source type. Dose measurements of the source used at St. Olavs Hospital for brachytherapy treatment of cervical cancer were taken. These were compared with the dose distribution calculated by the two treatment planning systems. At St. Olavs Hospital treatment are executed using a Fletcher type applicator. MR-images are taken with the applicator in place. Target and organs at risk are delineated in the images before the treatment planning is performed. For 11 patients treated with brachytherapy of cervical cancer at St. Olavs Hospital, three different IPSA-plans with different dose constraints (IPSA1, IPSA2 and IPSA3) and one treatment plan with equal dwell times were made in retrospect. All IPSA-plans constrain the same dose to the target. IPSA1 and IPSA3 have the same constraints to organs at risk, while IPSA2 allow a higher dose to the organs at risk. IPSA3 sets a limit for maximum dose in target volume. For evaluation of the quality of the treatment plans, dose parameters of chnical relevance were extracted from dose volume histograms. Results Deviations in the calculated dose distribution up to 30% is found for the two source types in certain areas. These deviations are found close to the source and below the connector end of the source. For distances ≥ 4 mm from the source center along one axis, deviations of the calculations were ≤ 4%. This is in correspondance with the measured dose values. Target coverage for IPSA2 is 0.92. For IPSA1 and IPSA3 target coverage is 0.84 and 0.81 respectively. The number of treatment plans exceeding tolerance limit for one or more OAR is 82% for IPSA2, 55% for IPSA1 and 35% for IPSA3. The plan with equal dwell times have a target coverage of 0.66 and 45% of the treatment plans exceed the given tolerance limit for one or more organs at risk. Conclusion Deviations are found in the simulated dose distribution of the two source types tested, but only in clinical irrelevant areas for brachytherapy of cervical cancer. Masterplan can be used for simulating the dose distribution of the source used for treatment at St. Olavs Hospital. Using IPSA is better when it comes to improving target coverage and not violating tolerance limit for organs at risk, than a conservative treatment plan with equal dwell times. Due to too high doses to organs at risk, IPSA2 should be rejected. IPSA1 has better target coverage and IPSA3 have lower dose to the organs at risk. To avoid inhomogeneities in dwell time values, IPSA3 is probably the best suggestion. &nbsp

Dosimetri og vurdering av algoritme for inversoptimalisert doseplanlegging for brachyterapi

Purpose Individual optimized treatment planning is recommended when creating treatment plans for brachytherapy of cervical cancer. Manual alteration of the dose distribution is time consuming and the treatment plan may be dependent on the person creating it. Inverse planning simulated anneahng (IPSA) is an algorithm that can optimize the dose distribution considering dose to several delineated structures. This algorithm, currently available in the treatment planning system Masterplan, has been evaluated for brachytherapy of cervical cancer. The Masterplan system simulates a source type from at different manufacturer than the type used for treatment at St. Olavs Hospital at the time being. The dose distribution from the two source types were evaluated to see if Masterplan an be used to simulate the source type used for treatment at St. Olavs Hospital. Methods and materials The dose distributions from the two source types were compared based on calcuations from two treatment planning systems (Masterplan and Plato) simulating each source type. Dose measurements of the source used at St. Olavs Hospital for brachytherapy treatment of cervical cancer were taken. These were compared with the dose distribution calculated by the two treatment planning systems. At St. Olavs Hospital treatment are executed using a Fletcher type applicator. MR-images are taken with the applicator in place. Target and organs at risk are delineated in the images before the treatment planning is performed. For 11 patients treated with brachytherapy of cervical cancer at St. Olavs Hospital, three different IPSA-plans with different dose constraints (IPSA1, IPSA2 and IPSA3) and one treatment plan with equal dwell times were made in retrospect. All IPSA-plans constrain the same dose to the target. IPSA1 and IPSA3 have the same constraints to organs at risk, while IPSA2 allow a higher dose to the organs at risk. IPSA3 sets a limit for maximum dose in target volume. For evaluation of the quality of the treatment plans, dose parameters of chnical relevance were extracted from dose volume histograms. Results Deviations in the calculated dose distribution up to 30% is found for the two source types in certain areas. These deviations are found close to the source and below the connector end of the source. For distances ≥ 4 mm from the source center along one axis, deviations of the calculations were ≤ 4%. This is in correspondance with the measured dose values. Target coverage for IPSA2 is 0.92. For IPSA1 and IPSA3 target coverage is 0.84 and 0.81 respectively. The number of treatment plans exceeding tolerance limit for one or more OAR is 82% for IPSA2, 55% for IPSA1 and 35% for IPSA3. The plan with equal dwell times have a target coverage of 0.66 and 45% of the treatment plans exceed the given tolerance limit for one or more organs at risk. Conclusion Deviations are found in the simulated dose distribution of the two source types tested, but only in clinical irrelevant areas for brachytherapy of cervical cancer. Masterplan can be used for simulating the dose distribution of the source used for treatment at St. Olavs Hospital. Using IPSA is better when it comes to improving target coverage and not violating tolerance limit for organs at risk, than a conservative treatment plan with equal dwell times. Due to too high doses to organs at risk, IPSA2 should be rejected. IPSA1 has better target coverage and IPSA3 have lower dose to the organs at risk. To avoid inhomogeneities in dwell time values, IPSA3 is probably the best suggestion.  Sammendrag Formål Det er anbefalt & lage individuelt optimaliserte plan når behandlingsplaner skal lages i forbindelse med brachyterapi av livmorhalskreft. Manuell endring av dosefordelingen er tidkrevende og resultatet kan bli preget av personen som lager planen. 'Iverse planning simulated anneahng' (IPSA) er en algoritme som kan optimalisere dosefordehngen slik at dose til flere skisserte strukturer blir tatt hensyn til. Denne algoritmen, tilgjengehg i doseplanleggingssystemet Masterplan, har blitt vurdert for brachyterapi av livmorhalskreft. Masterplan simulerer en kildetype fra en annen produsent enn den kildetypen som blir brukt til behandling på St. Olavs hospital i dag. Dosefordehngen til de to kildetypene har blitt vurdert for å se om Masterplan kan brukes til å simulere kildetypen brukt til behandling. Metode og utstyr Dosefordehngen fra de to kildetypene ble sammenlignet ved hjelp av doseberegninger fra to doseplanleggingssystemer (Masterplan og Plato) som simulerer hver sin kildetype. Det ble tatt målinger av dosen fra kilden brukt på St. Olavs hospital til brachyterapi av livmorhalskreft. Disse ble sammenlignet med dosefordelingen regnet ut av de to planleggingssystemene. På St. Olavs hospital blir en Fletcher type apphkator brukt til behandling. MR-bilder blir tatt etter at applikatoren er posisjonert. I bildene blir målvolum og risikooganer skissert før behandlingsplanleggingen gjennomføres. I denne studien har tre ulike IPSA-planer med forskjellig doserestriksjoner (IPSA1, IPSA2 and IPSA3) og en plan med lik liggetid i kildeposisjonene, blitt laget i ettertid for 11 pasienter behandlet for livmorhalskreft på St. Olavs hospital. IPSA-planene har samme doserestriksjoner til målvolum. IPSA1 og IPSA3 har samme begrensning til risikoorganer, mens IPSA2 tillater høyere dose til risikoorganer. IPSA3 har en begrensning for maksimum dose til volum for måvolumet. For vurdering av kvaliteten til planene ble klinisk relevante doseparametre funnet fra dosevolum-histogram. Resultat Det ble funnet avvik opp til 30% for beregnet dose i ulike punkt for de to kildetypene i visse omr&der. Disse avvikene ligger nærme kilden og rett under koblingsenden. For avstander ≥ 4 mm fra kildesenter transversalt på kilden er avvikene i beregningene ≤4%. Dosemålingene som ble tatt støtter dette. Dekning av målvolum er 0.92 for IPSA2. For IPSA1 og IPSA3 er denne dekninjen henholdsvis 0.84 og 0.81. Antall planer hvor en definert grense for dosen til et eller flere risikoorgan har blitt oversteget, er 82% for IPSA2, 55% for IPSA1 og 35% for IPSA3. Planen hvor liggetidene er fordelt likt har malvolumdekning på 0.66 og 45% av planene overstiger den definerte toleranse grensen for et eller flere risikoorgan. Konklusjon Det ble funnet avvik i de simulerte dosefordelingene mellom de to kildetypene, men kun i klinisk irrelevante områder for brachyterapi av livmorhalskreft. Masterplan kan bli brukt til å simulere dosefordelingen til kilden som blir brukt til behandling på St. Olavs hospital. Bruk av IPSA gir bedre resultater enn den konservative behandlingsplanen med lik liggetid ncir det gjelder dekning av målvolum og å overholde toleransegrensene som er satt for risikorganene. På grunn av for høye doser til risikoorganer burde IPSA2 forkastes. IPSA3 gir bedre dekning av måvolum mens IPSA3 gir lavere dose til risikoorganer. For å unngå store forskjeller mellom liggetidene i de ulike kildeposisjonene vil antagelig IPSA3 gi best utganspunkt for videre planlegging

Dosimetric evaluation of manually and inversely optimized treatment planning for high dose rate brachytherapy of cervical cancer

<div><p></p><p><b>Background.</b> To compare five inverse treatment planning methods with the conventional manually optimized planning approach for brachytherapy of cervical cancer with respect to dosimetric parameters.</p><p><b>Material and methods.</b> Eighteen cervical cancer patients treated with magnetic resonance imaging (MRI)-guided high dose rate (HDR) brachytherapy were included in this study. Six plans were created for each of the 4 HDR brachytherapy fractions for each patient: 1 manually optimized and 5 inversely planned. Three of these were based on inverse planning simulated annealing (IPSA) with and without extra constraints on maximum doses of the target volume, and different constraints on doses to the organs at risk (OARs). In addition there were two plans based on dose to target surface points. The resulting dose-volume histograms were analyzed and compared from the dosimetric point of view by quantifying specific dosimetric parameters, such as clinical target volume (CTV) D₉₀, CTV D₁₀₀, conformal index (COIN), and D_2cm3 for rectum, bladder and the sigmoid colon.</p><p><b>Results.</b> Manual optimization led to a mean target coverage of 78.3% compared to 87.5%, 91.7% and 82.5% with the three IPSA approaches (p < 0.001). Similar COIN values for manual and inverse optimization were found. The manual optimization led to better results with respect to the dose to the OARs expressed as D_2cm3. Overall, the best results were obtained with manual optimization and IPSA plans with volumetric constraints including maximum doses to the target volume.</p><p><b>Conclusions.</b> Dosimetric evaluation of manual and inverse optimization approaches is indicating the potential of IPSA for brachytherapy of cervical cancer. IPSA with constraints of maximum doses to the target volume is closer related to manual optimization than plans with constraints only to minimum dose to the target volume and maximum doses to OARs. IPSA plans with proper constraints performed better than those based on dose to target surface points and manually optimized plans.</p></div