Evaluation of respiratory gating – dose sparing and set-up

Strålbehandling kan användas för att behandla olika cancerdiagnoser. Man vill då kunna rikta strålningen mot tumören medan så lite frisk vävnad som möjligt bestrålas. Olika studier visar att för patienter som behandlas med strålbehandling för cancer i vänster bröst är förekomsten av och dödligheten i olika hjärtsjukdomar högre än för de som behandlas med strålbehandling för cancer i höger bröst. Detta beror på den ökade stråldosen till hjärtat vid behandling av cancer i vänster bröst till följd av att hjärtat är placerat närmare vänster bröst än höger bröst. Ett sätt att minska stråldosen till hjärtat vid behandling av bröstcancer i vänster bröst är att använda andningsanpassad strålbehandling. Då får patienten andas in djupare än normalt under behandlingen efter en röst som säger ”andas in” och ”andas ut”. Bestrålningen sker bara när patienten andats in. Då är avståndet mellan bröstet och hjärtat som störst och på så sätt kan stråldosen till hjärtat minskas. I denna studie visas att genom att behandla patienter med vänstersidig bröstcancer med andningsanpassad strålbehandling kan stråldosen till hjärtat minskas med 46 %, vilket resulterar i en minskning av sannolikheten att dö i hjärtsjukdomar för dessa kvinnor. Innan strålbehandlingen får patienten göra en datortomografiundersökning, vilket är en form av röntgenundersökning som ger snittbilder av patienten i tre dimensioner. I dessa bilder planerar man sedan hur strålfälten ska gå för att få så bra fördelning av stråldosen till det område som ska behandlas samtidigt som man minimerar stråldosen till den friska vävnaden. Det är viktigt att patienten ligger likadant vid behandling som under datortomografin. Ligger patienten annorlunda leder det till att stråldosen inte hamnar på det område som det var tänkt vilket kan leda till bestrålning av riskorgan och att delar av behandlingsområdet inte får den stråldos det var tänkt. På grund av uppläggningsproceduren för de patienter som behandlas med andningsanpassad strålbehandling kommer de att ligga lite annorlunda vid varje behandling. Denna avvikelse i positioneringen är systematisk och påverkar samtliga tillfällen patienten behandlas och kan korrigeras med en korrektionsstrategi. Genom att använda en korrektionsstrategi kan man uppskatta den systematiska avvikelsen och korrigera för den. Om man inte använder någon korrektionsstrategi introducerar man stora systematiska positioneringsavvikelser genom att använda andningsanpassad strålbehandling, vilket påverkar dosfördelningen till behandlingsområdet och hjärtat. Det är därför viktigt att korrigera för dessa systematiska avvikelser. Denna studie visar att den allmänt vedertagna korrektionsstrategin inte är den optimala för de patienter som behandlas med andningsanpassad strålbehandling. En justering av denna korrektionsstrategi, som resulterar i en bättre positionering, föreslås istället användas för denna patientgrupp.Purpose: To evaluate the benefits of using respiratory gating for left-sided breast cancer in the form of dose-sparing and biological effects to the heart and to investigate the set-up deviations for patients treated with respiratory gating in order to find an optimal correction strategy for this group of patients. Materials and methods: Nineteen patients treated with respiratory gating for left-sided breast cancer using the Real-time Position Management system (RPM, Varian Medical Systems, Inc., Palo Alto, CA) were retrospectively enrolled in this study. All patients had been treated with breast conserving surgery and no nodes were irradiated. Two CT-scans were performed for all patients treated with respiratory gating, one during deep breathing and one during normal free breathing. Since the patients had been treated with respiratory gating, structure delineation and treatment plans had already been made in the gated CT image set. For evaluation of the dose sparing and radiobiological effect, structure delineation was carried out and individually optimized treatment plans were created also for conventional treatment. Comparable target coverage was the main criteria when creating the treatment plans. The relative seriality model was used to calculate the cardiac mortality probability for the two treatment techniques. For evaluation of the set-up deviations, orthogonal kilovolt set-up images were acquired at every fraction for 18 patients treated with respiratory gating and 17 patients treated conventionally for comparison. In total, 659 images were acquired and manually matched with digitally reconstructed radiographs reconstructed from the CT image sets. Calculations of the set-up deviations were made both with no correction strategy applied and with the currently used correction strategy. The effect of the set-up deviation on the absorbed dose distribution was investigated by simulations in the treatment planning system (Eclipse version 10, Varian Medical Systems, Inc., Palo Alto, CA) and measurements with a biplanar diode array. Results: The mean absorbed dose to the heart was decreased for all patients in this study using respiratory gating. The average mean absorbed dose to the heart was 2.6 Gy for conventional treatment and 1.4 Gy for respiratory gating, a reduction of 46 %. For the left anterior descending (LAD) coronary artery the average mean absorbed dose was 13.9 Gy for conventional treatment and 4.2 Gy for respiratory gating, a reduction of 70 %. These reductions are statistically significant (p<0.01). The average mean absorbed dose to the left lung was 5.8 Gy for both conventional treatment and respiratory gating. As a result of the dose sparing for the heart the cardiac mortality probability could be reduced from 0.58 % for conventional treatment to 0.05 % for respiratory gating. An overall mean systematic deviation (moverall), calculated as the mean deviation for all patients and all treatment fractions, of 6.0 mm in the anterior direction and 8.1 mm in the cranial direction was present for the patients treated with respiratory gating if no correction strategy was applied. This set-up deviation results in increased absorbed dose to the organs at risk (OAR) and affects the absorbed dose distribution to the target. If the currently used correction strategy was applied to the deviations, moverall was reduced to 1.1 mm in the anterior direction and 3.3 mm in the cranial direction. moverall can be further reduced if the AML factor is excluded from the current correction strategy. If this was done, the moverall was 0.5 mm in the posterior direction and 1.0 mm in the cranial direction. No difference in the random set-up error was seen between the patients treated with conventional treatment and respiratory gating. Conclusions: Significant dose-sparing to the heart and LAD can be achieved using respiratory gating without compromising the target coverage. As a result of this dose sparing, the cardiac mortality probability can be reduced. This was comparable with earlier results [10, 13]. If no correction strategy is used for respiratory gating large systematic set-up deviations will be present which would increase the absorbed dose to the OARs and affect the dose distribution to the PTV. By excluding the AML factor from the currently used NAL correction strategy, the set-up deviations for the patients treated with respiratory gating will be minimized

Dosimetric effects of breathing motion in radiotherapy

The goal of radiotherapy is to deliver a homogeneous high dose of radiation to a tumour while minimising the dose to the surrounding healthy tissue. To achieve this, increasingly advanced treatment techniques, such as volumetric modulated arc therapy (VMAT) and proton therapy, have been developed. However, these treatment techniques are sensitive to patient motion, such as breathing, which may degrade the dose distribution to the tumour and healthy tissue. The simultaneous movement of the tumour and treatment delivery may cause unwanted heterogeneities in the dose distribution, so-called interplay effects. Treatment during deep inspiration (DI) could mitigate the motion and lead to favourable anatomical changes in the tumour position with respect to healthy tissue. The aim of the work presented in this thesis was to investigate various effects of breathing motion on the tumour and healthy tissue dose distribution in radiotherapy.Potential healthy tissue dose sparing using DI photon or proton therapy was investigated for left-sided breast cancer and mediastinal Hodgkin’s lymphoma (HL) by performing comparative treatment planning studies. The use of DI reduced the dose to healthy tissue for left-sided breast cancer patients. It also reduced the healthy tissue dose for most mediastinal HL patients, but the benefits were more patient specific due to large variations in the disease distribution. Protons reduced the dose to healthy tissue for both left-sided breast cancer and mediastinal HL patients compared to photons, regardless of the use of DI.A tool to simulate breathing-motion-induced interplay effects for VMAT was developed and used to investigate how interplay effects vary for different treatment scenarios. The tool was further adapted for use in a more clinical setting to investigate interplay effects for stereotactic VMAT treatment of liver metastases. Interplay effects were shown to negatively affect the dose distribution, resulting in underdosing part of the tumour. The extent of interplay effects depended on the tumour motion and treatment plan characteristics. In conclusion, major dosimetric effects of breathing motion on radiotherapy treatment were demonstrated by the work presented in this thesis. A beneficial effect of reduced healthy tissue dose was observed when the patient used controlled DI. Furthermore, by knowing the breathing-induced motion of the tumour, the treatment delivery parameters can be selected wisely to minimise unwanted interplay effects. Knowledge of the dosimetric effects of breathing motion is important to be able to individually optimise the radiotherapy treatment

The effect of systematic set-up deviations on the absorbed dose distribution for left-sided breast cancer treated with respiratory gating

The aim of this study was 1) to investigate interfraction set-up uncertainties for patients treated with respiratory gating for left-sided breast cancer, 2) to investigate the effect of the inter-fraction set-up on the absorbed dose-distribution for the target and organs at risk (OARs) and 3) optimize the set-up correction strategy. By acquiring multiple set-up images the systematic set-up deviation was evaluated. The effect of the systematic set-up deviation on the absorbed dose distribution was evaluated by 1) simulation in the treatment planning system and 2) measurements with a biplanar diode array. The set-up deviations could be decreased using a no action level correction strategy. Not using the clinically implemented adaptive maximum likelihood factor for the gating patients resulted in better set-up. When the uncorrected set-up deviations were simulated the average mean absorbed dose was increased from 1.38 to 2.21 Gy for the heart, 4.17 to 8.86 Gy to the left anterior descending coronary artery and 5.80 to 7.64 Gy to the left lung. Respiratory gating can induce systematic set-up deviations which would result in increased mean absorbed dose to the OARs if not corrected for and should therefore be corrected for by an appropriate correction strategy

Motion induced interplay effects for VMAT radiotherapy

The purpose of this study was to develop a method to simulate breathing motion induced interplay effects for volumetric modulated arc therapy (VMAT), to verify the proposed method with measurements, and to use the method to investigate how interplay effects vary with different patient- and machine specific parameters. VMAT treatment plans were created on a virtual phantom in a treatment planning system (TPS). Interplay effects were simulated by dividing each plan into smaller sub-arcs using an in-house developed software and shifting the isocenter for each sub-arc to simulate a sin6 breathing motion in the superior-inferior direction. The simulations were performed for both flattening-filter (FF) and flattening-filter free (FFF) plans and for different breathing amplitudes, period times, initial breathing phases, dose levels, plan complexities, CTV sizes, and collimator angles. The resulting sub-arcs were calculated in the TPS, generating a dose distribution including the effects of motion. The interplay effects were separated from dose blurring and the relative dose differences to 2% and 98% of the CTV volume (ΔD98% and ΔD2%) were calculated. To verify the simulation method, measurements were carried out, both static and during motion, using a quasi-3D phantom and a motion platform. The results of the verification measurements during motion were comparable to the results of the static measurements. Considerable interplay effects were observed for individual fractions, with the minimum ΔD98% and maximum ΔD2% being -16.7% and 16.2%, respectively. The extent of interplay effects was larger for FFF compared to FF and generally increased for higher breathing amplitudes, larger period times, lower dose levels, and more complex treatment plans. Also, the interplay effects varied considerably with the initial breathing phase, and larger variations were observed for smaller CTV sizes. In conclusion, a method to simulate motion induced interplay effects was developed and verified with measurements, which allowed for a large number of treatment scenarios to be investigated. The simulations showed large interplay effects for individual fractions and that the extent of interplay effects varied with the breathing pattern, FFF/FF, dose level, CTV size, collimator angle, and the complexity of the treatment plan

Comparison of doses and NTCP to risk organs with enhanced inspiration gating and free breathing for left-sided breast cancer radiotherapy using the AAA algorithm.

The purpose of this study was to investigate the potential dose reduction to the heart, left anterior descending (LAD) coronary artery and the ipsilateral lung for patients treated with tangential and locoregional radiotherapy for left-sided breast cancer with enhanced inspiration gating (EIG) compared to free breathing (FB) using the AAA algorithm. The radiobiological implication of such dose sparing was also investigated

Normal tissue sparing potential of scanned proton beams with and without respiratory gating for the treatment of internal mammary nodes in breast cancer radiotherapy

Proton therapy has shown potential for reducing doses to normal tissues in breast cancer radiotherapy. However data on the impact of protons when including internal mammary nodes (IMN) in the target for breast radiotherapy is comparatively scarce. This study aimed to evaluate normal tissue doses when including the IMN in regional RT with scanned proton beams, with and without respiratory gating. The study cohort was composed of ten left-sided breast patients CT-scanned during enhanced inspiration gating (EIG) and free-breathing (FB). Proton plans were designed for the target including or excluding the IMN. Targets and organs-at-risk were delineated according to RTOG guidelines. Comparison was performed between dosimetric parameters characterizing target coverage and OAR radiation burden. Statistical significance of differences was tested using a paired, two-tailed Student's t-test. Inclusion of the IMN in the target volume led to a small increase of the cardiopulmonary burden. The largest differences were seen for the ipsilateral lung where the mean dose increased from 6.1 to 6.6 Gy (RBE) (P < 0.0001) in FB plans and from 6.9 to 7.4 Gy (RBE) (P = 0.003) in EIG plans. Target coverage parameters were very little affected by the inclusion of IMN into the treatment target. Radiotherapy with scanned proton beams has the potential of maintaining low cardiovascular burden when including the IMN into the target, irrespective of whether respiratory gating is used or not

Sustainable practice change : Professionals’ experiences with a child health intervention programme in Sweden

Godkänd; 2010; 20111122 (rickg

Sustainable practice change : Professionals’ experiences with a child health intervention programme in Sweden

Godkänd; 2010; 20111122 (rickg

DiVA -Digitala Vetenskapliga Arkivet Sustainable practice change: Professionals&apos; experiences with a multisectoral child health promotion programme in Sweden

Abstract Background: New methods for prevention and health promotion and are constantly evolving; however, positive outcomes will only emerge if these methods are fully adopted and sustainable in practice. To date, limited attention has been given to sustainability of health promotion efforts. This study aimed to explore facilitators, barriers, and requirements for sustainability as experienced by professionals two years after finalizing the development and implementation of a multisectoral child health promotion programme in Sweden (the Salut programme). Initiated in 2005, the programme uses a &apos;Salutogenesis&apos; approach to support health-promoting activities in health care, social services, and schools