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Feasibility of deep inspiration breath hold combined with intensity modulated radiation treatment delivery for left sided breast cancer
Proceedings
2064
Feasibility of deep inspiration breath hold combined delivery for left sided breast cancer
M. C. Aznar,’
291
of the 42nd Annual ASTRO Meeting
with intensity modulated
radiation
treatment
K. E. Sixel,‘,” Y. C. Ung’,’
‘Toronto-Sunnybrook
Regional Cancer Centre, Toronto, ON, ‘Universio
of Toronto, Toronto, ON, Canada
Purpose: To demonstrate that forward planned intensity modulated radiotherapy (IMRT) with a small number of beam segments provides a treatment delivery mechanism which is compatible with a deep inspiration breath hold (DIBH) technique for cardiac dose reduction in left sided breast cancer irradiation. Materials and Methods: DIBH applied in left sided breast radiation therapy can substantially reduce irradiated cardiac volumes in suitably selected patients. However, delivery of radiation with tangential wedged photon beams typically results in treatment times on the order of a few minutes, making patient compliance and practicality of breath hold application difficult. We explore alternative radiation delivery mechanisms such as forward planned IMRT which delivers a uniform dose distribution using a small number of beam segments as well as inverse planned IMRT. DIBH was achieved using the Active Breathing Control (ABC) device designed at William Beaumont Hospital, Michigan. In 5 left-sided breast cancer patients, breath holds were forced at a predefined, reproducible lung volume. Duration of breath hold was patient dependent, typically lasting 15 sec. For each patient CT scans were acquired with and without breath hold, and virtual simulation was performed for regular and wide tangent techniques. The dose distributions of tangential opposed beams were calculated and optimized using three means of beam modification: conventional wedges, forward planned IMRT using a limited number of segments, and inverse planned IMRT. A standard 3D planning system was used to calculate dose distributions for the first two scenarios, while a commercial inverse planning system determined field segments and ensuing dose distributions for the full IMRT trial. For each delivery modality, the resulting beam-on time was calculated and the feasibility of synchronizing radiation delivery with periods of forced breath hold was assessed. Results: Dose volume histogram analyses show that the use of deep inspiration breath hold can decrease the volume of irradiated heart from 6% to 1% if treating with regular tangents. and from 16% to 4% with wide tangents in the most significant case. All three delivery techniques were optimized to result in comparable distributions. However, total monitor units required to deliver the prescribed dose per fraction differed. On average, wedged fields required a beam on time of 500 MU per fraction. For forward planned IMRT fields, it was found that a uniform dose distribution could be obtained with 3 segments per tangential beam, resulting in a total of 6 segments, The resulting MU per fraction was typically 250. Finally, the inverse planned IMRT distribution required 20 segments in total, with a total delivery time of 1000 MU. Conclusions: Forward planned segment limited IMRT can result in a beam-on times compatible with deep inspiration breath hold for left sided breast irradiation. Typically, a total of six breath holds are required for dose delivery. These can easily be synchronized with each field segment, providing a means of realizing the benefits of DIBH in a practical and patient compliant manner. In contrast, wedged tangential fields or inverse planned IMRT beams require extensive beam-on times limiting their practicality with breath hold techniques.
2065
Potential role of IMRT and protons in the treatment
of the breast and regional nodes
A. J. Lomax, L. Cella, D. C. Weber, J. M. Kurtz, R. Miralbell Paul Scherrer Institute,
Vi&en,
Switzerland,
ZUniver.sity Hospital,
Geneva, Switzerland
Purpose: To investigate, using comparative treatment planning, the potential improvements that could result through the use of IMRT and protons for the treatment of complex-target (i.e. breast and regional nodes) breast cancer. Materials & Methods: Using CT data from a breast cancer patient, treatment plans were computed using ‘standard‘ photon/electron, intensity modulated photon (IMRT), and forward planned proton techniques. The target volume consisted of the involved breast, internal mammary, supraclavicular and axillary nodes, The prescribed dose to the target was 50Gy. The standard plan was designed using 6 MV X-ray beams to the breast, axillary and supraclavicular areas and a mixture of 6 MV X-rays and 12 MeV electrons for the internal mammary nodes. IMRT plans were calculated for 9 evenly spaced beams using dose-volume constraints to the organs at risk. Precedence in the optimization was given to reducing dose in the lung as much as possible while preserving target dose homogeneity. The proton plan consisted of two oblique, energy modulated fields. Three criteria were considered in the analysis: target volume dose homogeneity. dose to the ipsilateral lung, and dose to the myocardium. Results: For the standard plan, DVHs to the target volumes revealed severe dose heterogeneity as a result of the patched photon and electron fields (e.g. 17% of PTV receives < 95% of the prescription dose). Target coverage for the IMRT and proton plans were comparable (8% and 6% underdosage at the 95% dose level, respectively). Lung DVHs for the standard and IMRT plans were also found to be comparable, while the proton plan showed the best sparing over all dose levels. Mean doses to the ipsilateral lung for the three plans were found to be 17Gy, 19Gy and 13Gy for the standard, IMRT and proton plans, respectively. For the myocardium, the IMRT plan delivered the highest mean dose (34Gy). reflecting the extra dose delivered through this organ in order to spare the lungs. This was significantly reduced in the standard plan (15Gy), with the best sparing being provided by the proton plan (6Gy). When the IMRT plan was re-optimized with precedence being given to the myocardium, the mean dose to the myocardium could be reduced to 30Gy, but at the cost of an increased mean dose to the lung (29~~). Conclusions: In comparison with the standard plan, IMRT photons have the potential to greatly improve the target dose homogeneity while providing a similar sparing of the ipsilateral lung. However, this can only be achieved at the cost of an increased integral dose to the myocardium. Of the plans analyzed here, only the two-field, energy modulated proton plan had the potential to preserve target dose homogeneity while simultaneously sparing the dose delivered to both the lung and myocardium.
2064
Feasibility of deep inspiration breath hold combined delivery for left sided breast cancer
M. C. Aznar,’
291
of the 42nd Annual ASTRO Meeting
with intensity modulated
radiation
treatment
K. E. Sixel,‘,” Y. C. Ung’,’
‘Toronto-Sunnybrook
Regional Cancer Centre, Toronto, ON, ‘Universio
of Toronto, Toronto, ON, Canada
Purpose: To demonstrate that forward planned intensity modulated radiotherapy (IMRT) with a small number of beam segments provides a treatment delivery mechanism which is compatible with a deep inspiration breath hold (DIBH) technique for cardiac dose reduction in left sided breast cancer irradiation. Materials and Methods: DIBH applied in left sided breast radiation therapy can substantially reduce irradiated cardiac volumes in suitably selected patients. However, delivery of radiation with tangential wedged photon beams typically results in treatment times on the order of a few minutes, making patient compliance and practicality of breath hold application difficult. We explore alternative radiation delivery mechanisms such as forward planned IMRT which delivers a uniform dose distribution using a small number of beam segments as well as inverse planned IMRT. DIBH was achieved using the Active Breathing Control (ABC) device designed at William Beaumont Hospital, Michigan. In 5 left-sided breast cancer patients, breath holds were forced at a predefined, reproducible lung volume. Duration of breath hold was patient dependent, typically lasting 15 sec. For each patient CT scans were acquired with and without breath hold, and virtual simulation was performed for regular and wide tangent techniques. The dose distributions of tangential opposed beams were calculated and optimized using three means of beam modification: conventional wedges, forward planned IMRT using a limited number of segments, and inverse planned IMRT. A standard 3D planning system was used to calculate dose distributions for the first two scenarios, while a commercial inverse planning system determined field segments and ensuing dose distributions for the full IMRT trial. For each delivery modality, the resulting beam-on time was calculated and the feasibility of synchronizing radiation delivery with periods of forced breath hold was assessed. Results: Dose volume histogram analyses show that the use of deep inspiration breath hold can decrease the volume of irradiated heart from 6% to 1% if treating with regular tangents. and from 16% to 4% with wide tangents in the most significant case. All three delivery techniques were optimized to result in comparable distributions. However, total monitor units required to deliver the prescribed dose per fraction differed. On average, wedged fields required a beam on time of 500 MU per fraction. For forward planned IMRT fields, it was found that a uniform dose distribution could be obtained with 3 segments per tangential beam, resulting in a total of 6 segments, The resulting MU per fraction was typically 250. Finally, the inverse planned IMRT distribution required 20 segments in total, with a total delivery time of 1000 MU. Conclusions: Forward planned segment limited IMRT can result in a beam-on times compatible with deep inspiration breath hold for left sided breast irradiation. Typically, a total of six breath holds are required for dose delivery. These can easily be synchronized with each field segment, providing a means of realizing the benefits of DIBH in a practical and patient compliant manner. In contrast, wedged tangential fields or inverse planned IMRT beams require extensive beam-on times limiting their practicality with breath hold techniques.
2065
Potential role of IMRT and protons in the treatment
of the breast and regional nodes
A. J. Lomax, L. Cella, D. C. Weber, J. M. Kurtz, R. Miralbell Paul Scherrer Institute,
Vi&en,
Switzerland,
ZUniver.sity Hospital,
Geneva, Switzerland
Purpose: To investigate, using comparative treatment planning, the potential improvements that could result through the use of IMRT and protons for the treatment of complex-target (i.e. breast and regional nodes) breast cancer. Materials & Methods: Using CT data from a breast cancer patient, treatment plans were computed using ‘standard‘ photon/electron, intensity modulated photon (IMRT), and forward planned proton techniques. The target volume consisted of the involved breast, internal mammary, supraclavicular and axillary nodes, The prescribed dose to the target was 50Gy. The standard plan was designed using 6 MV X-ray beams to the breast, axillary and supraclavicular areas and a mixture of 6 MV X-rays and 12 MeV electrons for the internal mammary nodes. IMRT plans were calculated for 9 evenly spaced beams using dose-volume constraints to the organs at risk. Precedence in the optimization was given to reducing dose in the lung as much as possible while preserving target dose homogeneity. The proton plan consisted of two oblique, energy modulated fields. Three criteria were considered in the analysis: target volume dose homogeneity. dose to the ipsilateral lung, and dose to the myocardium. Results: For the standard plan, DVHs to the target volumes revealed severe dose heterogeneity as a result of the patched photon and electron fields (e.g. 17% of PTV receives < 95% of the prescription dose). Target coverage for the IMRT and proton plans were comparable (8% and 6% underdosage at the 95% dose level, respectively). Lung DVHs for the standard and IMRT plans were also found to be comparable, while the proton plan showed the best sparing over all dose levels. Mean doses to the ipsilateral lung for the three plans were found to be 17Gy, 19Gy and 13Gy for the standard, IMRT and proton plans, respectively. For the myocardium, the IMRT plan delivered the highest mean dose (34Gy). reflecting the extra dose delivered through this organ in order to spare the lungs. This was significantly reduced in the standard plan (15Gy), with the best sparing being provided by the proton plan (6Gy). When the IMRT plan was re-optimized with precedence being given to the myocardium, the mean dose to the myocardium could be reduced to 30Gy, but at the cost of an increased mean dose to the lung (29~~). Conclusions: In comparison with the standard plan, IMRT photons have the potential to greatly improve the target dose homogeneity while providing a similar sparing of the ipsilateral lung. However, this can only be achieved at the cost of an increased integral dose to the myocardium. Of the plans analyzed here, only the two-field, energy modulated proton plan had the potential to preserve target dose homogeneity while simultaneously sparing the dose delivered to both the lung and myocardium.