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A Dosimetric Comparison of 3D Conformal, IMRT, and MammoSite Partial Breast Radiation
S176
I. J. Radiation Oncology
● Biology ● Physics
Volume 63, Number 2, Supplement, 2005
dose (gEUD) equates a non-uniform dose distribution to a uniform one but does not account for fraction size. Equivalent uniform biologically effective dose (EUBED) combines the concepts of gEUD and BED, and accounts for the variation in fraction size throughout the dose distribution. This study is a case-based investigation using the EUBED formalism for the evaluation of the biological equivalence of the doses delivered to the area around the lumpectomy cavity with WB vs. APBI. Materials/Methods: CT datasets were acquired for five patients treated with APBI. Plans for multicatheter brachytherapy and standard tangents were created. The lumpectomy cavity was delineated on all datasets. Planning target volume definitions were based on the current NSABP/RTOG phase III protocol. The target was defined for brachytherapy as the lumpectomy cavity plus a 1.5 cm margin and for WB as the lumpectomy cavity plus a 2.5 cm margin. The most widely accepted fractionation regimens were examined. Brachytherapy was prescribed to 34 Gy delivered in 10 fractions and WB to 50 Gy in 25 fractions. Dose matrices and target structures were exported from the planning systems (Varian BrachyVision and Pinnacle) and analyzed with in-house written software. A 3D binary mask was created for each of the structures and applied over the dose matrix. The BED was calculated for each voxel. The most commonly reported values for ␣ and  were used (for tumor control: ␣/⫽10Gy and ␣⫽0.3Gy⫺1; for late effects/fibrosis: ␣/⫽2Gy, ␣⫽0.06 – 0.12Gy⫺1). Neither sublethal damage repair nor repopulation was considered. The EUBED was then calculated using an expression derived using only the linear component of the LQ formalism. For the gEUD, the power exponents used were a⫽⫺7.2 for breast local control and a⫽1 and 4.2 for normal tissue complications. Results: EUBEDs for the targets in each of the plans were calculated using the radiobiological parameters for local control. The values obtained were remarkably similar. For APBI and WB treatment, the mean EUBEDs were 47.3 and 47.8 Gy, respectively. When evaluating fibrosis as the end-point, the mean EUBED values for the area surrounding the lumpectomy cavity were also very similar for the two modalities: 98.9 –102.8 and 89.6 –98.24 Gy for APBI and WB treatment, respectively. If the entire breast is considered, the EUBEDs for fibrosis are markedly different. Since the standard treatment is the only one in which the whole breast is irradiated, the mean EUBED for WB is 46.46 –78.1 Gy whereas the value is 14.1–17.5 Gy for APBI. Conclusions: The standard doses used for multicatheter brachytherapy and WB radiotherapy are radiobiologically comparable when using a method which accounts not only for fractionation, but also for differences in dose distribution.
1054
A Dosimetric Comparison of 3D Conformal, IMRT, and MammoSite Partial Breast Radiation
A. Dickler, M. Kirk, A. Khan, P. Mehta, J. Chu, K. Griem, C. Nguyen Radiation Oncology, Rush University Medical Center, Chicago, IL Purpose/Objective: Accelerated partial breast irradiation (PBI) has been explored as an alternative to whole breast irradiation in selected patients after lumpectomy. Several methods of delivering PBI have been developed including 3D conformal partial breast irradiation (3DCRT), intensity modulated partial breast irradiation (IMRT), and PBI utilizing the MammoSite breast brachytherapy applicator. Limited information is available comparing the target volume coverage and doses of radiation delivered to the normal organs when using the different techniques of PBI. We present our results of a dosimetric analysis comparing 3DCRT, IMRT, and MammoSite PBI techniques Materials/Methods: The study population consisted of 15 patients with early stage breast cancer treated using the MammoSite device from September, 2004 to March, 2005. After lumpectomy and placement of the MammoSite catheter, each patient underwent CT scans of the balloon in both an inflated and deflated state. Based on the CT scans, each patient had a PBI plan developed using a 3DCRT, IMRT, and MammoSite technique. A prescription dose of 3400 cGy delivered in ten fractions was used. For both the 3DCRT and IMRT plans, normal tissue constraints and construction of the PTV were based upon guidelines from RTOG 0319. The 3DCRT and IMRT based plans utilized a four or a five field noncoplanar technique. For the MammoSite plans, dose was prescribed to a PTV located 1 cm from the surface. The mean V90 (percent of the PTV that received 90% of the prescription dose), V100 (percent of the PTV that received 100% of the prescription dose), PTV volume, ipsilateral breast V50 (percent of the ipsilateral normal breast that received 50% of the prescription dose), contralateral breast V3 (percent of the contralateral breast that received 3% of the prescription dose), ipsilateral lung V30 (percent of the ipsilateral lung that received 30% of the prescription dose), and, for those patients with left sided breast tumors, the heart V5 (percent of the heart that received 5% of the prescription dose) were determined for each patient using the three methods of PBI. Results: The mean V90 was 98.1% (SD ⫽ 3.1), 99.6% (SD ⫽ 0.7), and 99.7% (SD ⫽ 0.4), and the mean V100 was 93.0% (SD ⫽ 5.9), 84.8% (SD ⫽ 8.4), and 93.5% (SD ⫽ 9.3) for the MammoSite, 3DCRT, and IMRT techniques respectively. The mean ipsilateral breast V50 was 35.9% (SD ⫽ 14.8), 48.7% (SD ⫽ 19.5), and 34.3% (SD ⫽ 16.2) for the MammoSite, 3DCRT, and IMRT methods respectively. The mean contralateral breast V3 was 0% (SD ⫽ 0), 5.1% (SD ⫽ 13.3%), and 3.0% (SD ⫽ 8.1) for the MammoSite, 3DCRT, and IMRT methods respectively. The mean ipsilateral lung V30 was 5.4% (SD ⫽ 3.1), 6.0% (SD ⫽ 5.4), and 2.1% (SD ⫽ 2.8) for the MammoSite, 3DCRT, and IMRT methods respectively. For the 10 patients with left sided breast tumors, the mean heart V5 was 13.6% (SD ⫽ 16.9), 6.4% (SD ⫽ 12.1), and 1.8% (SD ⫽ 3.6) for the MammoSite, 3DCRT, and IMRT methods respectively. The mean PTV volume for the MammoSite technique was 107.4 cc (SD ⫽ 17.4) while the mean PTV volume for both the IMRT and 3DCRT plans was 160.5 cc (SD ⫽ 54.2). Conclusions: The MammoSite and IMRT based PBI techniques achieve superior target volume coverage compared with a 3DCRT based PBI technique. The MammoSite technique allows the greatest sparing of the contralateral breast, while IMRT achieves more sparing of the ipsilateral lung and heart.
Proceedings of the 47th Annual ASTRO Meeting
1055
A Comparison of Five External Beam 3D Conformal Partial Breast Radiotherapy 3D-PBRT Techniques with Standard Tangents Whole Breast Radiotherapy WBRT
L.R. Salter, I. Olivotto, W. Beckham, H. Kader, C. Popescu, V. Patenaude, A. Nichol Radiation Therapy, Vancouver Island Cancer Centre, Victoria, BC, Canada Purpose/Objective: To compare dosimetry for five 3D PBRT techniques and standard WBRT for adjuvant RT after lumpectomy. Materials/Methods: 30 patients treated with lumpectomy and WBRT with a range of laterality, quadrant location & seroma sizes had WBRT tangent 3D dosimetry calculated on a volumetric planning CT using Varian Eclipse software to deliver 50Gy in 25 fractions. Five 3D-PBRT techniques were tested: (i) partial breast tangents; (ii) 3fld photons; (iii) 3fld photon/electron; (iv) 4fld non-coplanar (lt & rt breast), (v) 5fld non-coplanar (lt breast only). Each PBRT technique was 3D planned with a dose of 36Gy in 10 fractions. Volumes of interest for dosimetric evaluation included: heart, ipsilateral lung (IL),contralateral lung (CL), contralateral breast (CB), ipsilateral breast (IL), clinical target volume (CTV⫽Seroma⫹1.5cm) & planning target volume (PTV⫽CTV⫹1cm). Results: For the 3D-PBRT techniques (i to v) & the standard WBRT(vi) the mean dose volume histogram (DVH) results are. Heart(V2): 2.3%; 50.20%; 13.3%; 2.7%; 4.9%; 4.1% IL(V11): 7.8%; 22.4%; 9.7%; 9.2%; 8.5%; 9.7% CL(V2): 0.1%; 34.9%; 1.4%; 2.2%; 1.8%; 0.1% CB(V5): 2.0%; 1.8%; 4.0%; 1.2%; 1.1%; 4.1% IB(V18): 66.6%; 62.3%; 63.6%; 60.3%; 62.2%; 98.5% IB(V34): 50.6%; 32.7%; 33.1%; 35.9%; 32.5%; 92.0% PTV homogeneity index: 0.95; 0.96; 0.86; 0.97; 0.97; 0.90 PTV conformity Index: 0.30; 0.60; 0.60; 0.60; 0.66; 0.20 Conclusions: The 3fld photon/electron technique and the 4- and 5-field non-coplanar techniques improved PTV conformity and sparing of IB tissue compared to standard WBRT tangents, while maintaining acceptable doses to the heart, lungs and CB. Partial breast tangents did not adequately spare uninvolved ipsilateral breast tissue. The 3-field photon technique delivered unacceptably high doses to the heart, lungs & CB. The time/resource implications of the 3fld photon/electron and non-coplanar techniques need to be considered to select an optimal class solution for 3D PBRT.
1056
A Dosimetric Comparison of Two External Beam Conformal Treatment Techniques for the Delivery of Accelerated Partial Breast Irradiation (APBI)
K.P. Doppke, K.R. Kozak, A. Katz, A.G. Taghian Radiation Oncology, Massachusetts General Hospital, Boston, MA Purpose/Objective: To compare the dosimetry of two different methods of 3D conformal radiation to deliver APBI. Materials/Methods: Twelve patients with early breast cancer underwent planning using two different methods for delivering APBI the first, a multiple noncoplanar photon field technique described in the NSABP B-39 / RTOG 0413 protocol and the second, a method consisting of photon minitangents and an en face electron field. Because of the depth of the PTV in one patient an additional photon beam was used. The excision cavity represented the CTV, which was expanded by 1.5–2.0 cm to create the planning target volume (PTV) and then edited so the PTV came no closer than 0.5 cm to the skin surface and no deeper than the anterior chest wall / pectoralis muscles. The beam weighting was adjusted so that the prescription dose would cover the PTV for all plans. Dosimetric comparisons were made between the two plans using paired t-tests. Results: Seven patients had left-sided and 5 patients had right-sided breast cancers. The median CTV was 26.2 cc (range 5.8 –54.0 cc), and the median PTV was 155 cc (range, 58 –273 cc). The mean percentage of the whole breast designated as PTV was 19% (range 11%–33%).The mean contribution of the electrons to the total dose for the minitangent plans was 21% (range, 13–28%). The doses delivered to the ipsilateral lung, contralateral lung, heart, nontarget breast (whole breast minus PTV) and whole breast, for both methods are listed in Table 1. Conclusions: Both 3D conformal APBI methods result in low doses to normal structures with good coverage of the tumor bed and comply with the dose constraints of the NSABP B-39 / RTOG 0413 trial randomizing patients between APBI and whole breast treatment. To achieve ideal dosimetry, the multiple noncoplanar photon beam technique may require beam arrangements that are not deliverable by some linear accelerators. In contrast, APBI employing minitangents with en face electrons can be delivered by any linear accelerator capable of delivering standard whole breast irradiation. This technique may permit more facilities to offer APBI to patients and participate in the NSABP B-39 / RTOG 0413 clinical trial.
S177
I. J. Radiation Oncology
● Biology ● Physics
Volume 63, Number 2, Supplement, 2005
dose (gEUD) equates a non-uniform dose distribution to a uniform one but does not account for fraction size. Equivalent uniform biologically effective dose (EUBED) combines the concepts of gEUD and BED, and accounts for the variation in fraction size throughout the dose distribution. This study is a case-based investigation using the EUBED formalism for the evaluation of the biological equivalence of the doses delivered to the area around the lumpectomy cavity with WB vs. APBI. Materials/Methods: CT datasets were acquired for five patients treated with APBI. Plans for multicatheter brachytherapy and standard tangents were created. The lumpectomy cavity was delineated on all datasets. Planning target volume definitions were based on the current NSABP/RTOG phase III protocol. The target was defined for brachytherapy as the lumpectomy cavity plus a 1.5 cm margin and for WB as the lumpectomy cavity plus a 2.5 cm margin. The most widely accepted fractionation regimens were examined. Brachytherapy was prescribed to 34 Gy delivered in 10 fractions and WB to 50 Gy in 25 fractions. Dose matrices and target structures were exported from the planning systems (Varian BrachyVision and Pinnacle) and analyzed with in-house written software. A 3D binary mask was created for each of the structures and applied over the dose matrix. The BED was calculated for each voxel. The most commonly reported values for ␣ and  were used (for tumor control: ␣/⫽10Gy and ␣⫽0.3Gy⫺1; for late effects/fibrosis: ␣/⫽2Gy, ␣⫽0.06 – 0.12Gy⫺1). Neither sublethal damage repair nor repopulation was considered. The EUBED was then calculated using an expression derived using only the linear component of the LQ formalism. For the gEUD, the power exponents used were a⫽⫺7.2 for breast local control and a⫽1 and 4.2 for normal tissue complications. Results: EUBEDs for the targets in each of the plans were calculated using the radiobiological parameters for local control. The values obtained were remarkably similar. For APBI and WB treatment, the mean EUBEDs were 47.3 and 47.8 Gy, respectively. When evaluating fibrosis as the end-point, the mean EUBED values for the area surrounding the lumpectomy cavity were also very similar for the two modalities: 98.9 –102.8 and 89.6 –98.24 Gy for APBI and WB treatment, respectively. If the entire breast is considered, the EUBEDs for fibrosis are markedly different. Since the standard treatment is the only one in which the whole breast is irradiated, the mean EUBED for WB is 46.46 –78.1 Gy whereas the value is 14.1–17.5 Gy for APBI. Conclusions: The standard doses used for multicatheter brachytherapy and WB radiotherapy are radiobiologically comparable when using a method which accounts not only for fractionation, but also for differences in dose distribution.
1054
A Dosimetric Comparison of 3D Conformal, IMRT, and MammoSite Partial Breast Radiation
A. Dickler, M. Kirk, A. Khan, P. Mehta, J. Chu, K. Griem, C. Nguyen Radiation Oncology, Rush University Medical Center, Chicago, IL Purpose/Objective: Accelerated partial breast irradiation (PBI) has been explored as an alternative to whole breast irradiation in selected patients after lumpectomy. Several methods of delivering PBI have been developed including 3D conformal partial breast irradiation (3DCRT), intensity modulated partial breast irradiation (IMRT), and PBI utilizing the MammoSite breast brachytherapy applicator. Limited information is available comparing the target volume coverage and doses of radiation delivered to the normal organs when using the different techniques of PBI. We present our results of a dosimetric analysis comparing 3DCRT, IMRT, and MammoSite PBI techniques Materials/Methods: The study population consisted of 15 patients with early stage breast cancer treated using the MammoSite device from September, 2004 to March, 2005. After lumpectomy and placement of the MammoSite catheter, each patient underwent CT scans of the balloon in both an inflated and deflated state. Based on the CT scans, each patient had a PBI plan developed using a 3DCRT, IMRT, and MammoSite technique. A prescription dose of 3400 cGy delivered in ten fractions was used. For both the 3DCRT and IMRT plans, normal tissue constraints and construction of the PTV were based upon guidelines from RTOG 0319. The 3DCRT and IMRT based plans utilized a four or a five field noncoplanar technique. For the MammoSite plans, dose was prescribed to a PTV located 1 cm from the surface. The mean V90 (percent of the PTV that received 90% of the prescription dose), V100 (percent of the PTV that received 100% of the prescription dose), PTV volume, ipsilateral breast V50 (percent of the ipsilateral normal breast that received 50% of the prescription dose), contralateral breast V3 (percent of the contralateral breast that received 3% of the prescription dose), ipsilateral lung V30 (percent of the ipsilateral lung that received 30% of the prescription dose), and, for those patients with left sided breast tumors, the heart V5 (percent of the heart that received 5% of the prescription dose) were determined for each patient using the three methods of PBI. Results: The mean V90 was 98.1% (SD ⫽ 3.1), 99.6% (SD ⫽ 0.7), and 99.7% (SD ⫽ 0.4), and the mean V100 was 93.0% (SD ⫽ 5.9), 84.8% (SD ⫽ 8.4), and 93.5% (SD ⫽ 9.3) for the MammoSite, 3DCRT, and IMRT techniques respectively. The mean ipsilateral breast V50 was 35.9% (SD ⫽ 14.8), 48.7% (SD ⫽ 19.5), and 34.3% (SD ⫽ 16.2) for the MammoSite, 3DCRT, and IMRT methods respectively. The mean contralateral breast V3 was 0% (SD ⫽ 0), 5.1% (SD ⫽ 13.3%), and 3.0% (SD ⫽ 8.1) for the MammoSite, 3DCRT, and IMRT methods respectively. The mean ipsilateral lung V30 was 5.4% (SD ⫽ 3.1), 6.0% (SD ⫽ 5.4), and 2.1% (SD ⫽ 2.8) for the MammoSite, 3DCRT, and IMRT methods respectively. For the 10 patients with left sided breast tumors, the mean heart V5 was 13.6% (SD ⫽ 16.9), 6.4% (SD ⫽ 12.1), and 1.8% (SD ⫽ 3.6) for the MammoSite, 3DCRT, and IMRT methods respectively. The mean PTV volume for the MammoSite technique was 107.4 cc (SD ⫽ 17.4) while the mean PTV volume for both the IMRT and 3DCRT plans was 160.5 cc (SD ⫽ 54.2). Conclusions: The MammoSite and IMRT based PBI techniques achieve superior target volume coverage compared with a 3DCRT based PBI technique. The MammoSite technique allows the greatest sparing of the contralateral breast, while IMRT achieves more sparing of the ipsilateral lung and heart.
Proceedings of the 47th Annual ASTRO Meeting
1055
A Comparison of Five External Beam 3D Conformal Partial Breast Radiotherapy 3D-PBRT Techniques with Standard Tangents Whole Breast Radiotherapy WBRT
L.R. Salter, I. Olivotto, W. Beckham, H. Kader, C. Popescu, V. Patenaude, A. Nichol Radiation Therapy, Vancouver Island Cancer Centre, Victoria, BC, Canada Purpose/Objective: To compare dosimetry for five 3D PBRT techniques and standard WBRT for adjuvant RT after lumpectomy. Materials/Methods: 30 patients treated with lumpectomy and WBRT with a range of laterality, quadrant location & seroma sizes had WBRT tangent 3D dosimetry calculated on a volumetric planning CT using Varian Eclipse software to deliver 50Gy in 25 fractions. Five 3D-PBRT techniques were tested: (i) partial breast tangents; (ii) 3fld photons; (iii) 3fld photon/electron; (iv) 4fld non-coplanar (lt & rt breast), (v) 5fld non-coplanar (lt breast only). Each PBRT technique was 3D planned with a dose of 36Gy in 10 fractions. Volumes of interest for dosimetric evaluation included: heart, ipsilateral lung (IL),contralateral lung (CL), contralateral breast (CB), ipsilateral breast (IL), clinical target volume (CTV⫽Seroma⫹1.5cm) & planning target volume (PTV⫽CTV⫹1cm). Results: For the 3D-PBRT techniques (i to v) & the standard WBRT(vi) the mean dose volume histogram (DVH) results are. Heart(V2): 2.3%; 50.20%; 13.3%; 2.7%; 4.9%; 4.1% IL(V11): 7.8%; 22.4%; 9.7%; 9.2%; 8.5%; 9.7% CL(V2): 0.1%; 34.9%; 1.4%; 2.2%; 1.8%; 0.1% CB(V5): 2.0%; 1.8%; 4.0%; 1.2%; 1.1%; 4.1% IB(V18): 66.6%; 62.3%; 63.6%; 60.3%; 62.2%; 98.5% IB(V34): 50.6%; 32.7%; 33.1%; 35.9%; 32.5%; 92.0% PTV homogeneity index: 0.95; 0.96; 0.86; 0.97; 0.97; 0.90 PTV conformity Index: 0.30; 0.60; 0.60; 0.60; 0.66; 0.20 Conclusions: The 3fld photon/electron technique and the 4- and 5-field non-coplanar techniques improved PTV conformity and sparing of IB tissue compared to standard WBRT tangents, while maintaining acceptable doses to the heart, lungs and CB. Partial breast tangents did not adequately spare uninvolved ipsilateral breast tissue. The 3-field photon technique delivered unacceptably high doses to the heart, lungs & CB. The time/resource implications of the 3fld photon/electron and non-coplanar techniques need to be considered to select an optimal class solution for 3D PBRT.
1056
A Dosimetric Comparison of Two External Beam Conformal Treatment Techniques for the Delivery of Accelerated Partial Breast Irradiation (APBI)
K.P. Doppke, K.R. Kozak, A. Katz, A.G. Taghian Radiation Oncology, Massachusetts General Hospital, Boston, MA Purpose/Objective: To compare the dosimetry of two different methods of 3D conformal radiation to deliver APBI. Materials/Methods: Twelve patients with early breast cancer underwent planning using two different methods for delivering APBI the first, a multiple noncoplanar photon field technique described in the NSABP B-39 / RTOG 0413 protocol and the second, a method consisting of photon minitangents and an en face electron field. Because of the depth of the PTV in one patient an additional photon beam was used. The excision cavity represented the CTV, which was expanded by 1.5–2.0 cm to create the planning target volume (PTV) and then edited so the PTV came no closer than 0.5 cm to the skin surface and no deeper than the anterior chest wall / pectoralis muscles. The beam weighting was adjusted so that the prescription dose would cover the PTV for all plans. Dosimetric comparisons were made between the two plans using paired t-tests. Results: Seven patients had left-sided and 5 patients had right-sided breast cancers. The median CTV was 26.2 cc (range 5.8 –54.0 cc), and the median PTV was 155 cc (range, 58 –273 cc). The mean percentage of the whole breast designated as PTV was 19% (range 11%–33%).The mean contribution of the electrons to the total dose for the minitangent plans was 21% (range, 13–28%). The doses delivered to the ipsilateral lung, contralateral lung, heart, nontarget breast (whole breast minus PTV) and whole breast, for both methods are listed in Table 1. Conclusions: Both 3D conformal APBI methods result in low doses to normal structures with good coverage of the tumor bed and comply with the dose constraints of the NSABP B-39 / RTOG 0413 trial randomizing patients between APBI and whole breast treatment. To achieve ideal dosimetry, the multiple noncoplanar photon beam technique may require beam arrangements that are not deliverable by some linear accelerators. In contrast, APBI employing minitangents with en face electrons can be delivered by any linear accelerator capable of delivering standard whole breast irradiation. This technique may permit more facilities to offer APBI to patients and participate in the NSABP B-39 / RTOG 0413 clinical trial.
S177