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407 poster MULTI-OBJECTIVE SBRT TREATMENT PLANNING USING PARETO
W EDNESDAY, M AY 11, 2011
ture, and the calculated dose distributions are compared to ion chamber and radiochromic film measurements. Results: With 36 non-coplanar arcs and a dynamic dose shaping feature, the GammaPodTM can deliver uniform doses to targets of up to 8.0 cm with good conformity. Spatial accuracy of the unit itself is less than 0.05 cm. Localization accuracy for breast lesions are also evaluated and reported to be less than 0.2 cm. Figure 1 shows the dosimetric profiles achieved with two sizes of collimators; 1.5 and 2.5 cm. The single shot penumbra (80% to 20% isodose line) for 1.5 and 2.5 cm collimators were 0.8 and 1.1 cm respectively in xz coronal plane and 0.6 and 0.9 cm in the y-z sagittal plane. Verifications of dose profiles using single shot distributions demonstrated agreement with the spatial accuracy specifications of the unit.
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based on the statistical correlation function between the three-dimensional dose distribution and the PTV while the OAR fitness function is based on the volume-weighted normalized dose computed from the dose-volume histogram (DVH). Results: PARETO treatment plans (DVHs and dose distributions) using coplanar beams will be presented for a spine tumour case containing several OARs. A trend of improved dose conformity to the PTV with an increasing number of optimized beams is apparent until a threshold is reached beyond which changes in the PTV dose conformity are small (Figure 1). The degree of OAR sparing will be compared between plans with a varying number of optimized beams.
Conclusions: Thus, from many Pareto-optimal plans, the clinician may select the plan which they decide is the most appropriate multi-objective compromise for a particular patient. 408 poster
Conclusions: The dosimetric potential of the GammaPodTM stereotactic breast radiotherapy device is characterized. The agreement between the MC based calculations and dosimetric measurements is reported for a single shot irradiation, as well as for treatments implementing dynamic dose shaping techniques. 407 poster MULTI-OBJECTIVE SBRT TREATMENT PLANNING USING PARETO P. Potrebko1 , J. Fiege2 , B. McCurdy3 , H. Champion2 , A. Cull2 1 W INNIPEG H EALTH S CIENCES C ENTRE, Research, Winnipeg, Canada 2 U NIVERSITY OF M ANITOBA, Physics and Astronomy, Winnipeg, Manitoba, Canada 3 C ANCER C ARE M ANITOBA, Medical Physics, Winnipeg, Manitoba, Canada Purpose: Stereotactic body radiation therapy (SBRT) treatment planning is fundamentally a multiobjective global optimization problem because clinical objectives are invariably in conflict and compromises are necessary. We propose a novel and powerful beam number and orientation optimization package for radiotherapy optimization, called PARETO (Pareto-Aware Radiotherapy Evolutionary Treatment Optimization), which consists of a multi-objective genetic algorithm capable of optimizing several objective functions simultaneously and mapping the structure of their trade-off surface efficiently and in detail. Given one or more objective functions for each region-of-interest (ROI), a Pareto-optimal treatment plan is one for which there does not exist another plan that is strictly better in at least one objective function while being no worse in every other ROI objective. PARETO generates a database of Pareto-optimal solutions and allows the graphical exploration of trade-offs between multiple planning objectives during IMRT treatment planning. Materials: Multiobjective beam number and orientation optimization is achieved through a genetic algorithm called Ferret, part of the Qubist global optimization package which is a third party global optimization toolbox for MATLAB, available from nQube Technical Computing Corporation. The current version of PARETO utilizes ray-tracing methods to calculate the primary dose, including divergence, attenuation, and inverse-square law effects, which is then convolved with a scattering kernel to simulate patient scatter. Rays are assumed to be conformal to the projection of the PTV in the beam’s-eye-view plane, and are modulated by a parameterized fluence pattern at each beam angle. In this work, the fluence pattern is modeled by an inverse cosine transform whose coefficients are treated as free parameters and optimized using multiobjective fitness functions, that robustly encode the attributes of the dose distribution, by PARETO. The PTV fitness function is
CLINICAL AND RADIOLOGICAL OUTCOMES OF STEREOTACTIC RADIOTHERAPY WITH TOMOTHERAPY FOR PATIENTS WITH OLIGOMETASTATIC BRAIN LESIONS M. Galeandro1 , P. Ciammella1 , E. Donini1 , N. D Abbiero1 , A. Muraglia1 , E. Cagni2 , A. Botti2 , C. Iotti1 1 A RCISPEDALE S. M ARIA N UOVA, Radiation Oncology, Reggio Emilia, Italy 2 A RCISPEDALE S. M ARIA N UOVA, Medical Physics, Reggio Emilia, Italy Purpose: A significant proportion of adults with cancer will develop brain metastases. The outcome for these patients is generally poor, with a median survival following whole brain radiotherapy alone of only 3-4 months regardless of primary tumor histology. These results have shed light on the possibility of improving outcomes, in terms of local control, overall survival and quality of life, by using high-dose local radiotherapy in the treatment of brain oligometastases. The aim of the present study was to retrospectively evaluate the dosimetric parameters and the radiological response rate of stereotactic radiation therapy (SRT) for patients affected by brain oligometastases. Materials: Twenthy one patients with 1-3 brain metastases, treated between January 2009 and December 2010 with stereotactic radiation therapy, using Tomotherapy Hi-ART, were analyzed. The most common histology of the metastatic lesion was non small cell lung cancer (9), followed by breast cancer(6), renal cancer (2), rectal cancer (2) and melanoma (2). To be eligible for SRT, patients had to have a Karnofsky performance status greater than 70% and have stable systemic disease. Any patients had received prior brain radiotherapy.At the time of brain metastases diagnosis, 6 patients had an inoperable single brain lesion and 15 patients had 2-3 lesions, measuring less than 3 cm in maximum diameter and producing minimal mass effect. All patients, immobilized by a thermoshell in supine position, underwent computed tomography (CT) scan for radiotherapy planning. Magnetic resonance imaging (MRI) scan with Gadolinium contrast was performed in all patients and fused with CT images to draw the macroscopic (gross) tumour volume (GTV) and the organs at risk (OAR) (eyes, lens, optical nerves, chiasma, brainstem). A 3 mm margin was added to the GTV to create the planning target volume (PTV). A total dose of 24 Gy, prescribed to the 70% isodose line, was administered in three consecutive fractions. Plans were optimized for conformity and target coverage with maximum OAR sparing. A Tomotherapy megavoltage computed tomography (MVCT) was performed every day to verify and correct the patient set-up.Patients were seen 6-8 weeks after SRT completion and the local tumour response was evaluate with MRI, using the McDonald Criteria. Any toxicity was recorded according to the National Cancer Institute Common Terminology Criteria for Adverse Events (CTCAE vs 3.0). Results: Twenthy one patients (median age 67 years, range 50-87 yrs) with a total of 41 lesions (with mean diameter 1.68 cm, range 0.7-2.8 cm) were analyzed. The mean GTV volume was 4.73 cc and the mean PTV was 13.10 cm3 Dosimetric results were as follows: the mean conformity number was 0.85 + 0.1 with a median target coverage of 0.98 + 0.01. Intralesional dose
ture, and the calculated dose distributions are compared to ion chamber and radiochromic film measurements. Results: With 36 non-coplanar arcs and a dynamic dose shaping feature, the GammaPodTM can deliver uniform doses to targets of up to 8.0 cm with good conformity. Spatial accuracy of the unit itself is less than 0.05 cm. Localization accuracy for breast lesions are also evaluated and reported to be less than 0.2 cm. Figure 1 shows the dosimetric profiles achieved with two sizes of collimators; 1.5 and 2.5 cm. The single shot penumbra (80% to 20% isodose line) for 1.5 and 2.5 cm collimators were 0.8 and 1.1 cm respectively in xz coronal plane and 0.6 and 0.9 cm in the y-z sagittal plane. Verifications of dose profiles using single shot distributions demonstrated agreement with the spatial accuracy specifications of the unit.
P OSTER
S 161
based on the statistical correlation function between the three-dimensional dose distribution and the PTV while the OAR fitness function is based on the volume-weighted normalized dose computed from the dose-volume histogram (DVH). Results: PARETO treatment plans (DVHs and dose distributions) using coplanar beams will be presented for a spine tumour case containing several OARs. A trend of improved dose conformity to the PTV with an increasing number of optimized beams is apparent until a threshold is reached beyond which changes in the PTV dose conformity are small (Figure 1). The degree of OAR sparing will be compared between plans with a varying number of optimized beams.
Conclusions: Thus, from many Pareto-optimal plans, the clinician may select the plan which they decide is the most appropriate multi-objective compromise for a particular patient. 408 poster
Conclusions: The dosimetric potential of the GammaPodTM stereotactic breast radiotherapy device is characterized. The agreement between the MC based calculations and dosimetric measurements is reported for a single shot irradiation, as well as for treatments implementing dynamic dose shaping techniques. 407 poster MULTI-OBJECTIVE SBRT TREATMENT PLANNING USING PARETO P. Potrebko1 , J. Fiege2 , B. McCurdy3 , H. Champion2 , A. Cull2 1 W INNIPEG H EALTH S CIENCES C ENTRE, Research, Winnipeg, Canada 2 U NIVERSITY OF M ANITOBA, Physics and Astronomy, Winnipeg, Manitoba, Canada 3 C ANCER C ARE M ANITOBA, Medical Physics, Winnipeg, Manitoba, Canada Purpose: Stereotactic body radiation therapy (SBRT) treatment planning is fundamentally a multiobjective global optimization problem because clinical objectives are invariably in conflict and compromises are necessary. We propose a novel and powerful beam number and orientation optimization package for radiotherapy optimization, called PARETO (Pareto-Aware Radiotherapy Evolutionary Treatment Optimization), which consists of a multi-objective genetic algorithm capable of optimizing several objective functions simultaneously and mapping the structure of their trade-off surface efficiently and in detail. Given one or more objective functions for each region-of-interest (ROI), a Pareto-optimal treatment plan is one for which there does not exist another plan that is strictly better in at least one objective function while being no worse in every other ROI objective. PARETO generates a database of Pareto-optimal solutions and allows the graphical exploration of trade-offs between multiple planning objectives during IMRT treatment planning. Materials: Multiobjective beam number and orientation optimization is achieved through a genetic algorithm called Ferret, part of the Qubist global optimization package which is a third party global optimization toolbox for MATLAB, available from nQube Technical Computing Corporation. The current version of PARETO utilizes ray-tracing methods to calculate the primary dose, including divergence, attenuation, and inverse-square law effects, which is then convolved with a scattering kernel to simulate patient scatter. Rays are assumed to be conformal to the projection of the PTV in the beam’s-eye-view plane, and are modulated by a parameterized fluence pattern at each beam angle. In this work, the fluence pattern is modeled by an inverse cosine transform whose coefficients are treated as free parameters and optimized using multiobjective fitness functions, that robustly encode the attributes of the dose distribution, by PARETO. The PTV fitness function is
CLINICAL AND RADIOLOGICAL OUTCOMES OF STEREOTACTIC RADIOTHERAPY WITH TOMOTHERAPY FOR PATIENTS WITH OLIGOMETASTATIC BRAIN LESIONS M. Galeandro1 , P. Ciammella1 , E. Donini1 , N. D Abbiero1 , A. Muraglia1 , E. Cagni2 , A. Botti2 , C. Iotti1 1 A RCISPEDALE S. M ARIA N UOVA, Radiation Oncology, Reggio Emilia, Italy 2 A RCISPEDALE S. M ARIA N UOVA, Medical Physics, Reggio Emilia, Italy Purpose: A significant proportion of adults with cancer will develop brain metastases. The outcome for these patients is generally poor, with a median survival following whole brain radiotherapy alone of only 3-4 months regardless of primary tumor histology. These results have shed light on the possibility of improving outcomes, in terms of local control, overall survival and quality of life, by using high-dose local radiotherapy in the treatment of brain oligometastases. The aim of the present study was to retrospectively evaluate the dosimetric parameters and the radiological response rate of stereotactic radiation therapy (SRT) for patients affected by brain oligometastases. Materials: Twenthy one patients with 1-3 brain metastases, treated between January 2009 and December 2010 with stereotactic radiation therapy, using Tomotherapy Hi-ART, were analyzed. The most common histology of the metastatic lesion was non small cell lung cancer (9), followed by breast cancer(6), renal cancer (2), rectal cancer (2) and melanoma (2). To be eligible for SRT, patients had to have a Karnofsky performance status greater than 70% and have stable systemic disease. Any patients had received prior brain radiotherapy.At the time of brain metastases diagnosis, 6 patients had an inoperable single brain lesion and 15 patients had 2-3 lesions, measuring less than 3 cm in maximum diameter and producing minimal mass effect. All patients, immobilized by a thermoshell in supine position, underwent computed tomography (CT) scan for radiotherapy planning. Magnetic resonance imaging (MRI) scan with Gadolinium contrast was performed in all patients and fused with CT images to draw the macroscopic (gross) tumour volume (GTV) and the organs at risk (OAR) (eyes, lens, optical nerves, chiasma, brainstem). A 3 mm margin was added to the GTV to create the planning target volume (PTV). A total dose of 24 Gy, prescribed to the 70% isodose line, was administered in three consecutive fractions. Plans were optimized for conformity and target coverage with maximum OAR sparing. A Tomotherapy megavoltage computed tomography (MVCT) was performed every day to verify and correct the patient set-up.Patients were seen 6-8 weeks after SRT completion and the local tumour response was evaluate with MRI, using the McDonald Criteria. Any toxicity was recorded according to the National Cancer Institute Common Terminology Criteria for Adverse Events (CTCAE vs 3.0). Results: Twenthy one patients (median age 67 years, range 50-87 yrs) with a total of 41 lesions (with mean diameter 1.68 cm, range 0.7-2.8 cm) were analyzed. The mean GTV volume was 4.73 cc and the mean PTV was 13.10 cm3 Dosimetric results were as follows: the mean conformity number was 0.85 + 0.1 with a median target coverage of 0.98 + 0.01. Intralesional dose