Stephen Deboer - Academia.edu (original) (raw)
Papers by Stephen Deboer
Duplicating a tandem and ovoids distribution with intensity-modulated radiotherapy: a feasibility study
Journal of applied clinical medical physics / American College of Medical Physics, Jan 17, 2007
Brachytherapy plays an important role in the definitive treatment of cervical cancers by radiothe... more Brachytherapy plays an important role in the definitive treatment of cervical cancers by radiotherapy. In the present study, we investigated whether sliding-window intensity-modulated radiation therapy (IMRT) can achieve a pear-shaped distribution with a similar sharp dose falloff identical to that of brachytherapy. The computed tomography scans of a tandem and ovoid patient were pushed to both a high dose rate (HDR) and an IMRT treatment planning system (TPS) after the rectum, bladder, and left and right femoral heads had been outlined, ensuring identical structures in both planning systems. A conventional plan (7 Gy in 5 fractions, defined as the average dose to the left and right point A) was generated for HDR treatment. The 150%, 125%, 100%, 75%, 50%, and 25% isodose curves were drawn on each slice and then transferred to the IMRT TPS. The 100% isodose envelope from the HDR plan was the target for IMRT planning. A 7-field IMRT plan using 6-MV X-ray beams was generated and compar...
Journal of Applied Clinical Medical Physics, 2005
The maximum width of an intensity-modulated radiotherapy (IMRT) treatment field is usually smalle... more The maximum width of an intensity-modulated radiotherapy (IMRT) treatment field is usually smaller than the conventional maximum collimator opening because of design limitations inherent in some multileaf collimators (MLCs). To increase the effective field width, IMRT fluences can be split and delivered with multiple carriage positions. However, not all treatment-planning systems and MLCs support this technique, and if they do, the maximum field width in multiple carriage position delivery is still significantly less than the maximum collimator opening. For target volumes with dimensions exceeding the field size limit for multiple carriage position delivery, such as liver tumors or other malignancies in the abdominal cavity, IMRT treatment can be accomplished with multiple isocenters or with an extended treatment distance. To study dosimetric statistics of large field IMRT planning, an elliptical volume was chosen as a target within a cubic phantom centered at a depth of 7.5 cm. Multiple three-field plans (one AP and two oblique beams with 160° between them to avoid parallel opposed geometry) with constraints designed to give 100% dose to the elliptical target were developed. Plans were designed with a single anterior field with dual carriage positions, or with the anterior field split into two fields with separate isocenters 8 cm apart with the beams being forcibly matched at the isocenter or with a 1 cm, 2 cm, 3 cm, and 4 cm overlap. The oblique beams were planned with a single carriage position in all cases. All beams had a nominal energy of 6 MV. In the dual isocenter plans, jaws were manually fixed and dose constraints remained unaltered. Dosimetric statistics were studied for plans developed for treatment delivery using both dynamic leaf motion (sliding window) and multiple static segments (step and shoot) with the number of segments varying from 5 to 30. All plans were analyzed based on the dose homogeneity in the isocenter plane, 2 cm anterior and 2 cm posterior to it, along with their corresponding dose-volume histograms (DVHs). All the dual isocenter plans had slight underdosage anterior to the match point and slight overdosage posterior to it, while the dual carriage plan had a nice blending of the dose distribution without the accompanying hot or cold spots. Based on the dose statistics, it was noted that the dual isocenter plans can be clinically acceptable if they have at least a 3-cm overlap. In the case of step and shoot IMRT, the number of segments used in a dual carriage plan was found to affect the overall plan dosimetric indices.
Journal of Applied Clinical Medical Physics, 2007
Brachytherapy plays an important role in the definitive treatment of cervical cancers by radiothe... more Brachytherapy plays an important role in the definitive treatment of cervical cancers by radiotherapy. In the present study, we investigated whether slidingwindow intensity-modulated radiation therapy (IMRT) can achieve a pear-shaped distribution with a similar sharp dose falloff identical to that of brachytherapy. The computed tomography scans of a tandem and ovoid patient were pushed to both a high dose rate (HDR) and an IMRT treatment planning system (TPS) after the rectum, bladder, and left and right femoral heads had been outlined, ensuring identical structures in both planning systems. A conventional plan (7 Gy in 5 fractions, defined as the average dose to the left and right point A) was generated for HDR treatment. The 150%, 125%, 100%, 75%, 50%, and 25% isodose curves were drawn on each slice and then transferred to the IMRT TPS. The 100% isodose envelope from the HDR plan was the target for IMRT planning. A 7-field IMRT plan using 6-MV X-ray beams was generated and compared with the HDR plan using isodose conformity to the target and 125% volume, dosevolume histograms, and integral dose. The resulting isodose distribution demonstrated good agreement between the HDR and IMRT plans in the 100% and 125% isodose range. The dose falloff in the HDR plan was much steeper than that in the IMRT plan, but it also had a substantially higher maximum dose. Integral dose for the target, rectum, and bladder were found to be 6.69 J, 1.07 J, and 1.02 J in the HDR plan; the respective values for IMRT were 3.47 J, 1.79 J, and 1.34 J. Our preliminary results indicate that the HDR dose distribution can be replicated using a standard sliding-window IMRT dose delivery technique for points lying closer to the three-dimensional isodose envelope surrounding point A. Differences in radiobiology and patient positioning between the two techniques merit further consideration. PACS: 87.53.Jw
International Journal of Radiation Oncology*Biology*Physics, 2008
ferrous ammonium sulphate, 0.060 g of sodium chloride and 22 ml of sulphuric acid. The center of ... more ferrous ammonium sulphate, 0.060 g of sodium chloride and 22 ml of sulphuric acid. The center of the balloon is filled with water, the shell is filled with FeSo4 solution and the whole balloon is placed in a water phantom. Five balloons were casted in two halves and glued. One of the balloons was left in parts in order to have all dimensions measured with a traceable micrometer. Measurements were conducted using the Nucletron microSelectron-HDR 192 Ir source previously calibrated by a well type chamber traceable to the UW-ADCL and the Nucletron TPS was used to calculate the dose at a specified depth. The irradiated solutions was transferred from the balloon to a quartz cuvette with a 5.00 cm light path length and the optical densities measured using a Micronal spectrophotometer at 304 nm UV light. Monte Carlo (PENELOPE) calculations were done to assess the magnitude of the attenuation and scatter in the PMMA walls, as well as the effect of the source anisotropy in the average dose measured. Results: As result of the Monte Carlo calculations performed dividing the balloon in 36 sectors, 12 sectors above and below the source were identified with anisotropy values varying from 3% to 10%. The calculated values for the wall attenuation have introduced a correction smaller than 1%.For doses of 10 Gy delivered at the center of the balloon shell, the deviation between the average dose measured and the dose calculated by the TPS was smaller than 1.5%. Conclusions: Chemical dosimetry using standard FeSO4 solution in a containing vessel with uniform geometry relative to the source has shown to be a promising absorbed dose standard for HDR I-192 source. The overall uncertainties involving the vessel dimensions, wall thicknesses, dose calculation, wall attenuation, UV light band, source anisotropy, G value and the source transit time is better than 2%.
Duplicating a tandem and ovoids distribution with intensity-modulated radiotherapy: a feasibility study
Journal of applied clinical medical physics / American College of Medical Physics, 2007
Brachytherapy plays an important role in the definitive treatment of cervical cancers by radiothe... more Brachytherapy plays an important role in the definitive treatment of cervical cancers by radiotherapy. In the present study, we investigated whether sliding-window intensity-modulated radiation therapy (IMRT) can achieve a pear-shaped distribution with a similar sharp dose falloff identical to that of brachytherapy. The computed tomography scans of a tandem and ovoid patient were pushed to both a high dose rate (HDR) and an IMRT treatment planning system (TPS) after the rectum, bladder, and left and right femoral heads had been outlined, ensuring identical structures in both planning systems. A conventional plan (7 Gy in 5 fractions, defined as the average dose to the left and right point A) was generated for HDR treatment. The 150%, 125%, 100%, 75%, 50%, and 25% isodose curves were drawn on each slice and then transferred to the IMRT TPS. The 100% isodose envelope from the HDR plan was the target for IMRT planning. A 7-field IMRT plan using 6-MV X-ray beams was generated and compar...
Journal of Applied Clinical Medical Physics, 2014
This investigation studies the use of volumetric-modulated arc therapy (VMAT) to deliver the foll... more This investigation studies the use of volumetric-modulated arc therapy (VMAT) to deliver the following conceptual gynecological brachytherapy (BT) dose distributions: Type 1, traditional pear-shaped dose distribution with substantial dose gradients; Type 2, homogeneous dose distribution throughout PTV (BT prescription volume); and Type 3, increased dose to PTV without organ-at-risk (OAR) overdose. A tandem and ovoid BT treatment plan, with the prescription dose of 6 Gy to point A, was exported into the VMAT treatment planning system (TPS) and became the baseline for comparative analysis. The 200%, 150%, 130%, 100%, 75%, and 50% dose volumes were converted into structures for optimization and evaluation purposes. The 100% dose volume was chosen to be the PTV. Five VMAT plans (Type 1) were created to duplicate the Ir-192 tandem and ovoid inhomogeneous dose distribution. Another five VMAT plans (Type 2) were generated to deliver a homogeneous dose of 6 Gy to the PTV. An additional five VMAT plans (Type 3) were created to increase the dose to the PTV with a homogeneous dose distribution. In the first set of plans, the dose given to 99% of the 200%-100% dose volumes agreed within 2% of the BT plan on average. Additionally, it was found that the 75% dose volumes agreed within 5% of the BT plan and the 50% dose volumes agreed within 6.4% of the BT plan. In the second set of comparative analyses, the 100% dose volume was found to be within 1% of the original plan. Furthermore, the maximum increase of dose to the PTV in the last set of comparative analyses was 8 Gy with similar doses to OARs as the other VMAT plans. The maximum increase of dose was 2.50 Gy to the rectum and the maximum decrease of dose was 0.70 Gy to the bladder. Henceforth, VMAT was successful at reproducing brachytherapy dose distributions demonstrating that alternative dose distributions have the potential to be used in lieu of brachytherapy. It should also be noted that differences in radiobiology need to be further investigated.
Journal of Applied Clinical Medical Physics, 2005
The maximum width of an intensity-modulated radiotherapy (IMRT) treatment field is usually smalle... more The maximum width of an intensity-modulated radiotherapy (IMRT) treatment field is usually smaller than the conventional maximum collimator opening because of design limitations inherent in some multileaf collimators (MLCs). To increase the effective field width, IMRT fluences can be split and delivered with multiple carriage positions. However, not all treatment-planning systems and MLCs support this technique, and if they do, the maximum field width in multiple carriage position delivery is still significantly less than the maximum collimator opening. For target volumes with dimensions exceeding the field size limit for multiple carriage position delivery, such as liver tumors or other malignancies in the abdominal cavity, IMRT treatment can be accomplished with multiple isocenters or with an extended treatment distance. To study dosimetric statistics of large field IMRT planning, an elliptical volume was chosen as a target within a cubic phantom centered at a depth of 7.5 cm. Multiple three-field plans (one AP and two oblique beams with 160° between them to avoid parallel opposed geometry) with constraints designed to give 100% dose to the elliptical target were developed. Plans were designed with a single anterior field with dual carriage positions, or with the anterior field split into two fields with separate isocenters 8 cm apart with the beams being forcibly matched at the isocenter or with a 1 cm, 2 cm, 3 cm, and 4 cm overlap. The oblique beams were planned with a single carriage position in all cases. All beams had a nominal energy of 6 MV. In the dual isocenter plans, jaws were manually fixed and dose constraints remained unaltered. Dosimetric statistics were studied for plans developed for treatment delivery using both dynamic leaf motion (sliding window) and multiple static segments (step and shoot) with the number of segments varying from 5 to 30. All plans were analyzed based on the dose homogeneity in the isocenter plane, 2 cm anterior and 2 cm posterior to it, along with their corresponding dose-volume histograms (DVHs). All the dual isocenter plans had slight underdosage anterior to the match point and slight overdosage posterior to it, while the dual carriage plan had a nice blending of the dose distribution without the accompanying hot or cold spots. Based on the dose statistics, it was noted that the dual isocenter plans can be clinically acceptable if they have at least a 3-cm overlap. In the case of step and shoot IMRT, the number of segments used in a dual carriage plan was found to affect the overall plan dosimetric indices.
Journal of Applied Clinical Medical Physics, 2007
Brachytherapy plays an important role in the definitive treatment of cervical cancers by radiothe... more Brachytherapy plays an important role in the definitive treatment of cervical cancers by radiotherapy. In the present study, we investigated whether slidingwindow intensity-modulated radiation therapy (IMRT) can achieve a pear-shaped distribution with a similar sharp dose falloff identical to that of brachytherapy. The computed tomography scans of a tandem and ovoid patient were pushed to both a high dose rate (HDR) and an IMRT treatment planning system (TPS) after the rectum, bladder, and left and right femoral heads had been outlined, ensuring identical structures in both planning systems. A conventional plan (7 Gy in 5 fractions, defined as the average dose to the left and right point A) was generated for HDR treatment. The 150%, 125%, 100%, 75%, 50%, and 25% isodose curves were drawn on each slice and then transferred to the IMRT TPS. The 100% isodose envelope from the HDR plan was the target for IMRT planning. A 7-field IMRT plan using 6-MV X-ray beams was generated and compared with the HDR plan using isodose conformity to the target and 125% volume, dosevolume histograms, and integral dose. The resulting isodose distribution demonstrated good agreement between the HDR and IMRT plans in the 100% and 125% isodose range. The dose falloff in the HDR plan was much steeper than that in the IMRT plan, but it also had a substantially higher maximum dose. Integral dose for the target, rectum, and bladder were found to be 6.69 J, 1.07 J, and 1.02 J in the HDR plan; the respective values for IMRT were 3.47 J, 1.79 J, and 1.34 J. Our preliminary results indicate that the HDR dose distribution can be replicated using a standard sliding-window IMRT dose delivery technique for points lying closer to the three-dimensional isodose envelope surrounding point A. Differences in radiobiology and patient positioning between the two techniques merit further consideration. PACS: 87.53.Jw
International Journal of Radiation Oncology*Biology*Physics, 2008
ferrous ammonium sulphate, 0.060 g of sodium chloride and 22 ml of sulphuric acid. The center of ... more ferrous ammonium sulphate, 0.060 g of sodium chloride and 22 ml of sulphuric acid. The center of the balloon is filled with water, the shell is filled with FeSo4 solution and the whole balloon is placed in a water phantom. Five balloons were casted in two halves and glued. One of the balloons was left in parts in order to have all dimensions measured with a traceable micrometer. Measurements were conducted using the Nucletron microSelectron-HDR 192 Ir source previously calibrated by a well type chamber traceable to the UW-ADCL and the Nucletron TPS was used to calculate the dose at a specified depth. The irradiated solutions was transferred from the balloon to a quartz cuvette with a 5.00 cm light path length and the optical densities measured using a Micronal spectrophotometer at 304 nm UV light. Monte Carlo (PENELOPE) calculations were done to assess the magnitude of the attenuation and scatter in the PMMA walls, as well as the effect of the source anisotropy in the average dose measured. Results: As result of the Monte Carlo calculations performed dividing the balloon in 36 sectors, 12 sectors above and below the source were identified with anisotropy values varying from 3% to 10%. The calculated values for the wall attenuation have introduced a correction smaller than 1%.For doses of 10 Gy delivered at the center of the balloon shell, the deviation between the average dose measured and the dose calculated by the TPS was smaller than 1.5%. Conclusions: Chemical dosimetry using standard FeSO4 solution in a containing vessel with uniform geometry relative to the source has shown to be a promising absorbed dose standard for HDR I-192 source. The overall uncertainties involving the vessel dimensions, wall thicknesses, dose calculation, wall attenuation, UV light band, source anisotropy, G value and the source transit time is better than 2%.
Using an EPID for patient-specific VMAT quality assurance
Medical Physics, 2011
A patient-specific quality assurance (QA) method was developed to verify gantry-specific individu... more A patient-specific quality assurance (QA) method was developed to verify gantry-specific individual multileaf collimator (MLC) apertures (control points) in volumetric modulated arc therapy (VMAT) plans using an electronic portal imaging device (EPID). VMAT treatment plans were generated in an Eclipse treatment planning system (TPS). DICOM images from a Varian EPID (aS1000) acquired in continuous acquisition mode were used for pretreatment QA. Each cine image file contains the grayscale image of the MLC aperture related to its specific control point and the corresponding gantry angle information. The TPS MLC file of this RapidArc plan contains the leaf positions for all 177 control points (gantry angles). In-house software was developed that interpolates the measured images based on the gantry angle and overlays them with the MLC pattern for all control points. The 38% isointensity line was used to define the edge of the MLC leaves on the portal images. The software generates graphs and tables that provide analysis for the number of mismatched leaf positions for a chosen distance to agreement at each control point and the frequency in which each particular leaf mismatches for the entire arc. Seven patients plans were analyzed using this method. The leaves with the highest mismatched rate were found to be treatment plan dependent. This in-house software can be used to automatically verify the MLC leaf positions for all control points of VMAT plans using cine images acquired by an EPID.
Duplicating a tandem and ovoids distribution with intensity-modulated radiotherapy: a feasibility study
Journal of applied clinical medical physics / American College of Medical Physics, Jan 17, 2007
Brachytherapy plays an important role in the definitive treatment of cervical cancers by radiothe... more Brachytherapy plays an important role in the definitive treatment of cervical cancers by radiotherapy. In the present study, we investigated whether sliding-window intensity-modulated radiation therapy (IMRT) can achieve a pear-shaped distribution with a similar sharp dose falloff identical to that of brachytherapy. The computed tomography scans of a tandem and ovoid patient were pushed to both a high dose rate (HDR) and an IMRT treatment planning system (TPS) after the rectum, bladder, and left and right femoral heads had been outlined, ensuring identical structures in both planning systems. A conventional plan (7 Gy in 5 fractions, defined as the average dose to the left and right point A) was generated for HDR treatment. The 150%, 125%, 100%, 75%, 50%, and 25% isodose curves were drawn on each slice and then transferred to the IMRT TPS. The 100% isodose envelope from the HDR plan was the target for IMRT planning. A 7-field IMRT plan using 6-MV X-ray beams was generated and compar...
Journal of Applied Clinical Medical Physics, 2005
The maximum width of an intensity-modulated radiotherapy (IMRT) treatment field is usually smalle... more The maximum width of an intensity-modulated radiotherapy (IMRT) treatment field is usually smaller than the conventional maximum collimator opening because of design limitations inherent in some multileaf collimators (MLCs). To increase the effective field width, IMRT fluences can be split and delivered with multiple carriage positions. However, not all treatment-planning systems and MLCs support this technique, and if they do, the maximum field width in multiple carriage position delivery is still significantly less than the maximum collimator opening. For target volumes with dimensions exceeding the field size limit for multiple carriage position delivery, such as liver tumors or other malignancies in the abdominal cavity, IMRT treatment can be accomplished with multiple isocenters or with an extended treatment distance. To study dosimetric statistics of large field IMRT planning, an elliptical volume was chosen as a target within a cubic phantom centered at a depth of 7.5 cm. Multiple three-field plans (one AP and two oblique beams with 160° between them to avoid parallel opposed geometry) with constraints designed to give 100% dose to the elliptical target were developed. Plans were designed with a single anterior field with dual carriage positions, or with the anterior field split into two fields with separate isocenters 8 cm apart with the beams being forcibly matched at the isocenter or with a 1 cm, 2 cm, 3 cm, and 4 cm overlap. The oblique beams were planned with a single carriage position in all cases. All beams had a nominal energy of 6 MV. In the dual isocenter plans, jaws were manually fixed and dose constraints remained unaltered. Dosimetric statistics were studied for plans developed for treatment delivery using both dynamic leaf motion (sliding window) and multiple static segments (step and shoot) with the number of segments varying from 5 to 30. All plans were analyzed based on the dose homogeneity in the isocenter plane, 2 cm anterior and 2 cm posterior to it, along with their corresponding dose-volume histograms (DVHs). All the dual isocenter plans had slight underdosage anterior to the match point and slight overdosage posterior to it, while the dual carriage plan had a nice blending of the dose distribution without the accompanying hot or cold spots. Based on the dose statistics, it was noted that the dual isocenter plans can be clinically acceptable if they have at least a 3-cm overlap. In the case of step and shoot IMRT, the number of segments used in a dual carriage plan was found to affect the overall plan dosimetric indices.
Journal of Applied Clinical Medical Physics, 2007
Brachytherapy plays an important role in the definitive treatment of cervical cancers by radiothe... more Brachytherapy plays an important role in the definitive treatment of cervical cancers by radiotherapy. In the present study, we investigated whether slidingwindow intensity-modulated radiation therapy (IMRT) can achieve a pear-shaped distribution with a similar sharp dose falloff identical to that of brachytherapy. The computed tomography scans of a tandem and ovoid patient were pushed to both a high dose rate (HDR) and an IMRT treatment planning system (TPS) after the rectum, bladder, and left and right femoral heads had been outlined, ensuring identical structures in both planning systems. A conventional plan (7 Gy in 5 fractions, defined as the average dose to the left and right point A) was generated for HDR treatment. The 150%, 125%, 100%, 75%, 50%, and 25% isodose curves were drawn on each slice and then transferred to the IMRT TPS. The 100% isodose envelope from the HDR plan was the target for IMRT planning. A 7-field IMRT plan using 6-MV X-ray beams was generated and compared with the HDR plan using isodose conformity to the target and 125% volume, dosevolume histograms, and integral dose. The resulting isodose distribution demonstrated good agreement between the HDR and IMRT plans in the 100% and 125% isodose range. The dose falloff in the HDR plan was much steeper than that in the IMRT plan, but it also had a substantially higher maximum dose. Integral dose for the target, rectum, and bladder were found to be 6.69 J, 1.07 J, and 1.02 J in the HDR plan; the respective values for IMRT were 3.47 J, 1.79 J, and 1.34 J. Our preliminary results indicate that the HDR dose distribution can be replicated using a standard sliding-window IMRT dose delivery technique for points lying closer to the three-dimensional isodose envelope surrounding point A. Differences in radiobiology and patient positioning between the two techniques merit further consideration. PACS: 87.53.Jw
International Journal of Radiation Oncology*Biology*Physics, 2008
ferrous ammonium sulphate, 0.060 g of sodium chloride and 22 ml of sulphuric acid. The center of ... more ferrous ammonium sulphate, 0.060 g of sodium chloride and 22 ml of sulphuric acid. The center of the balloon is filled with water, the shell is filled with FeSo4 solution and the whole balloon is placed in a water phantom. Five balloons were casted in two halves and glued. One of the balloons was left in parts in order to have all dimensions measured with a traceable micrometer. Measurements were conducted using the Nucletron microSelectron-HDR 192 Ir source previously calibrated by a well type chamber traceable to the UW-ADCL and the Nucletron TPS was used to calculate the dose at a specified depth. The irradiated solutions was transferred from the balloon to a quartz cuvette with a 5.00 cm light path length and the optical densities measured using a Micronal spectrophotometer at 304 nm UV light. Monte Carlo (PENELOPE) calculations were done to assess the magnitude of the attenuation and scatter in the PMMA walls, as well as the effect of the source anisotropy in the average dose measured. Results: As result of the Monte Carlo calculations performed dividing the balloon in 36 sectors, 12 sectors above and below the source were identified with anisotropy values varying from 3% to 10%. The calculated values for the wall attenuation have introduced a correction smaller than 1%.For doses of 10 Gy delivered at the center of the balloon shell, the deviation between the average dose measured and the dose calculated by the TPS was smaller than 1.5%. Conclusions: Chemical dosimetry using standard FeSO4 solution in a containing vessel with uniform geometry relative to the source has shown to be a promising absorbed dose standard for HDR I-192 source. The overall uncertainties involving the vessel dimensions, wall thicknesses, dose calculation, wall attenuation, UV light band, source anisotropy, G value and the source transit time is better than 2%.
Duplicating a tandem and ovoids distribution with intensity-modulated radiotherapy: a feasibility study
Journal of applied clinical medical physics / American College of Medical Physics, 2007
Brachytherapy plays an important role in the definitive treatment of cervical cancers by radiothe... more Brachytherapy plays an important role in the definitive treatment of cervical cancers by radiotherapy. In the present study, we investigated whether sliding-window intensity-modulated radiation therapy (IMRT) can achieve a pear-shaped distribution with a similar sharp dose falloff identical to that of brachytherapy. The computed tomography scans of a tandem and ovoid patient were pushed to both a high dose rate (HDR) and an IMRT treatment planning system (TPS) after the rectum, bladder, and left and right femoral heads had been outlined, ensuring identical structures in both planning systems. A conventional plan (7 Gy in 5 fractions, defined as the average dose to the left and right point A) was generated for HDR treatment. The 150%, 125%, 100%, 75%, 50%, and 25% isodose curves were drawn on each slice and then transferred to the IMRT TPS. The 100% isodose envelope from the HDR plan was the target for IMRT planning. A 7-field IMRT plan using 6-MV X-ray beams was generated and compar...
Journal of Applied Clinical Medical Physics, 2014
This investigation studies the use of volumetric-modulated arc therapy (VMAT) to deliver the foll... more This investigation studies the use of volumetric-modulated arc therapy (VMAT) to deliver the following conceptual gynecological brachytherapy (BT) dose distributions: Type 1, traditional pear-shaped dose distribution with substantial dose gradients; Type 2, homogeneous dose distribution throughout PTV (BT prescription volume); and Type 3, increased dose to PTV without organ-at-risk (OAR) overdose. A tandem and ovoid BT treatment plan, with the prescription dose of 6 Gy to point A, was exported into the VMAT treatment planning system (TPS) and became the baseline for comparative analysis. The 200%, 150%, 130%, 100%, 75%, and 50% dose volumes were converted into structures for optimization and evaluation purposes. The 100% dose volume was chosen to be the PTV. Five VMAT plans (Type 1) were created to duplicate the Ir-192 tandem and ovoid inhomogeneous dose distribution. Another five VMAT plans (Type 2) were generated to deliver a homogeneous dose of 6 Gy to the PTV. An additional five VMAT plans (Type 3) were created to increase the dose to the PTV with a homogeneous dose distribution. In the first set of plans, the dose given to 99% of the 200%-100% dose volumes agreed within 2% of the BT plan on average. Additionally, it was found that the 75% dose volumes agreed within 5% of the BT plan and the 50% dose volumes agreed within 6.4% of the BT plan. In the second set of comparative analyses, the 100% dose volume was found to be within 1% of the original plan. Furthermore, the maximum increase of dose to the PTV in the last set of comparative analyses was 8 Gy with similar doses to OARs as the other VMAT plans. The maximum increase of dose was 2.50 Gy to the rectum and the maximum decrease of dose was 0.70 Gy to the bladder. Henceforth, VMAT was successful at reproducing brachytherapy dose distributions demonstrating that alternative dose distributions have the potential to be used in lieu of brachytherapy. It should also be noted that differences in radiobiology need to be further investigated.
Journal of Applied Clinical Medical Physics, 2005
The maximum width of an intensity-modulated radiotherapy (IMRT) treatment field is usually smalle... more The maximum width of an intensity-modulated radiotherapy (IMRT) treatment field is usually smaller than the conventional maximum collimator opening because of design limitations inherent in some multileaf collimators (MLCs). To increase the effective field width, IMRT fluences can be split and delivered with multiple carriage positions. However, not all treatment-planning systems and MLCs support this technique, and if they do, the maximum field width in multiple carriage position delivery is still significantly less than the maximum collimator opening. For target volumes with dimensions exceeding the field size limit for multiple carriage position delivery, such as liver tumors or other malignancies in the abdominal cavity, IMRT treatment can be accomplished with multiple isocenters or with an extended treatment distance. To study dosimetric statistics of large field IMRT planning, an elliptical volume was chosen as a target within a cubic phantom centered at a depth of 7.5 cm. Multiple three-field plans (one AP and two oblique beams with 160° between them to avoid parallel opposed geometry) with constraints designed to give 100% dose to the elliptical target were developed. Plans were designed with a single anterior field with dual carriage positions, or with the anterior field split into two fields with separate isocenters 8 cm apart with the beams being forcibly matched at the isocenter or with a 1 cm, 2 cm, 3 cm, and 4 cm overlap. The oblique beams were planned with a single carriage position in all cases. All beams had a nominal energy of 6 MV. In the dual isocenter plans, jaws were manually fixed and dose constraints remained unaltered. Dosimetric statistics were studied for plans developed for treatment delivery using both dynamic leaf motion (sliding window) and multiple static segments (step and shoot) with the number of segments varying from 5 to 30. All plans were analyzed based on the dose homogeneity in the isocenter plane, 2 cm anterior and 2 cm posterior to it, along with their corresponding dose-volume histograms (DVHs). All the dual isocenter plans had slight underdosage anterior to the match point and slight overdosage posterior to it, while the dual carriage plan had a nice blending of the dose distribution without the accompanying hot or cold spots. Based on the dose statistics, it was noted that the dual isocenter plans can be clinically acceptable if they have at least a 3-cm overlap. In the case of step and shoot IMRT, the number of segments used in a dual carriage plan was found to affect the overall plan dosimetric indices.
Journal of Applied Clinical Medical Physics, 2007
Brachytherapy plays an important role in the definitive treatment of cervical cancers by radiothe... more Brachytherapy plays an important role in the definitive treatment of cervical cancers by radiotherapy. In the present study, we investigated whether slidingwindow intensity-modulated radiation therapy (IMRT) can achieve a pear-shaped distribution with a similar sharp dose falloff identical to that of brachytherapy. The computed tomography scans of a tandem and ovoid patient were pushed to both a high dose rate (HDR) and an IMRT treatment planning system (TPS) after the rectum, bladder, and left and right femoral heads had been outlined, ensuring identical structures in both planning systems. A conventional plan (7 Gy in 5 fractions, defined as the average dose to the left and right point A) was generated for HDR treatment. The 150%, 125%, 100%, 75%, 50%, and 25% isodose curves were drawn on each slice and then transferred to the IMRT TPS. The 100% isodose envelope from the HDR plan was the target for IMRT planning. A 7-field IMRT plan using 6-MV X-ray beams was generated and compared with the HDR plan using isodose conformity to the target and 125% volume, dosevolume histograms, and integral dose. The resulting isodose distribution demonstrated good agreement between the HDR and IMRT plans in the 100% and 125% isodose range. The dose falloff in the HDR plan was much steeper than that in the IMRT plan, but it also had a substantially higher maximum dose. Integral dose for the target, rectum, and bladder were found to be 6.69 J, 1.07 J, and 1.02 J in the HDR plan; the respective values for IMRT were 3.47 J, 1.79 J, and 1.34 J. Our preliminary results indicate that the HDR dose distribution can be replicated using a standard sliding-window IMRT dose delivery technique for points lying closer to the three-dimensional isodose envelope surrounding point A. Differences in radiobiology and patient positioning between the two techniques merit further consideration. PACS: 87.53.Jw
International Journal of Radiation Oncology*Biology*Physics, 2008
ferrous ammonium sulphate, 0.060 g of sodium chloride and 22 ml of sulphuric acid. The center of ... more ferrous ammonium sulphate, 0.060 g of sodium chloride and 22 ml of sulphuric acid. The center of the balloon is filled with water, the shell is filled with FeSo4 solution and the whole balloon is placed in a water phantom. Five balloons were casted in two halves and glued. One of the balloons was left in parts in order to have all dimensions measured with a traceable micrometer. Measurements were conducted using the Nucletron microSelectron-HDR 192 Ir source previously calibrated by a well type chamber traceable to the UW-ADCL and the Nucletron TPS was used to calculate the dose at a specified depth. The irradiated solutions was transferred from the balloon to a quartz cuvette with a 5.00 cm light path length and the optical densities measured using a Micronal spectrophotometer at 304 nm UV light. Monte Carlo (PENELOPE) calculations were done to assess the magnitude of the attenuation and scatter in the PMMA walls, as well as the effect of the source anisotropy in the average dose measured. Results: As result of the Monte Carlo calculations performed dividing the balloon in 36 sectors, 12 sectors above and below the source were identified with anisotropy values varying from 3% to 10%. The calculated values for the wall attenuation have introduced a correction smaller than 1%.For doses of 10 Gy delivered at the center of the balloon shell, the deviation between the average dose measured and the dose calculated by the TPS was smaller than 1.5%. Conclusions: Chemical dosimetry using standard FeSO4 solution in a containing vessel with uniform geometry relative to the source has shown to be a promising absorbed dose standard for HDR I-192 source. The overall uncertainties involving the vessel dimensions, wall thicknesses, dose calculation, wall attenuation, UV light band, source anisotropy, G value and the source transit time is better than 2%.
Using an EPID for patient-specific VMAT quality assurance
Medical Physics, 2011
A patient-specific quality assurance (QA) method was developed to verify gantry-specific individu... more A patient-specific quality assurance (QA) method was developed to verify gantry-specific individual multileaf collimator (MLC) apertures (control points) in volumetric modulated arc therapy (VMAT) plans using an electronic portal imaging device (EPID). VMAT treatment plans were generated in an Eclipse treatment planning system (TPS). DICOM images from a Varian EPID (aS1000) acquired in continuous acquisition mode were used for pretreatment QA. Each cine image file contains the grayscale image of the MLC aperture related to its specific control point and the corresponding gantry angle information. The TPS MLC file of this RapidArc plan contains the leaf positions for all 177 control points (gantry angles). In-house software was developed that interpolates the measured images based on the gantry angle and overlays them with the MLC pattern for all control points. The 38% isointensity line was used to define the edge of the MLC leaves on the portal images. The software generates graphs and tables that provide analysis for the number of mismatched leaf positions for a chosen distance to agreement at each control point and the frequency in which each particular leaf mismatches for the entire arc. Seven patients plans were analyzed using this method. The leaves with the highest mismatched rate were found to be treatment plan dependent. This in-house software can be used to automatically verify the MLC leaf positions for all control points of VMAT plans using cine images acquired by an EPID.