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15 Quantifying the dose distribution homogeneity improvement for breast IMRT: what is the best parameter to evaluate plans?
S4 3-5 October 2003
cohorts. Conclusion: Postmastectomy radiotherapy for positive margins in the absence of advanced primary tumour stage or 4 or more positive nodes conferred modest absolute reductions in Iocoregional recurrence but no statistically significant impact in long-term relapse or survival was demonstrated. 13
Regional radiation of the axilla and supraclavicular fossa for adjuvant breast treatment: a comparison of four techniques C. Jephcott, S. Tyldesley, C.-L. Swift, V. LaPointe, W. Kwa British Columbia Cancer Agency, Vancouver Cancer Centre, Vancouver, British Columbia, Canada Back(]round: Adjuvant nodal radiotherapy is an important part of treatment for women with breast cancer. Three common techniques used to treat the axilla and supraclavicular nodes are a single anterior field (AP), an anterior to posterior parallel pair (AP:PA), and an anterior field with a posterior boost field to the axilla (AP:PAboost). Each of these techniques has a potential disadvantage: the AP may underdose the deeper nodes; the AP:PA unnecessarily irradiates the medial posterior neck; and the AP:PAboost produces an unnecessary anterior hotspot. We hypothesize that an AP:PA boost technique with customized MLC compensation of the anterior beam will minimize these disadvantages (APcomp:PAboost). Methods: CT data from 10 patients who had completed breast and regional radiotherapy with AP:PA boost were used for the analysis. The fields as previously planned by the oncologist were used as the standard fields for each patient. Axillary and supraclavicular nodal volumes, treated volume, and the brachial plexus were contoured. A plan for each of the 4 techniques (AP,AP:PA, AP:PA boost, APcomp:PAboost) were then generated for each of the 10 patients using CadPlan with modified Batho correction. Each plan was compared for total treated volume, nodal coverage, plexus dose, hotspot dose, and PTV coverage. Results: The AP plan gave poor PTV coverage in 70% of cases. The AP:PA provided good PTV coverage and minimal hotspots, but there was consistent unnecessary irradiation to the medial posterior neck. The AP:PAboost provided adequate PTV coverage and limited dose to the medial posterior neck, but produced hotspots in excess of 120% in 90% of cases. The APcomp:PAboost provided good PTV coverage, limited dose to the medial posterior neck and hotspots<115% in the majority of cases. Conclusion: In the majority of cases, the best plan in terms of PTV cover, acceptable hot spots, and limited irradiation of the medial posterior neck was produced with the APcomp:PAboost technique. 14
A dose-volume analysis of regional lymph nodes in breast tangent radiation K.D. Voduc, M. Keyes British Columbia Cancer Agency, University of British Columbia, Vancouver, British Columbia, Canada PurPose: To formulate a systematic method of contouring Level I, II, III axillary regions and internal mammary nodes on planning CT scan; and to then perform a dose-volume analysis of the nodal regions in breast cancer patients treated with standard breast tangents. Methods and Materials: Planning CT scans of 23 women invasive breast cancer were retrospectively reviewed. All patients were treated with breast conserving surgery, followed by adjuvant radiation with standard breast tangents. Level I, II, and III axillary node regions and the internal mammary nodes were contoured on SomaVision. Dose-volume histographs were then obtained from Cadplan. Endpoints were maximum dose, minimum dose, median dose, and standard deviation, as well as volume receiving 95% of the prescribed dose. Coverage was considered adequate if 95% of the target volume received 95% of the prescribed dose. Results: Axillary node regions were first defined in relation to anatomical stuctures. These regions were then located on planning CT scan and were reviewed with a diagnostic radiologist. In 0/23 of the patients studied were the level I axillary nodes adequately treated with the prescribed tangent fields. Only 5/23 patients had 40% or more of the level I axillary volume treated with 95% of the prescribed dose. Conclusions: The results of this study suggest that breast irradiation by standard tangent fields does not adequately treat the level t axilla. We can also suggest that regional lymph nodes be outlined on planning CT prior to the field placement, if treatment to these areas is intended.
CARO 2003
15
Quantifying the dose distribution homogeneity improvement for breast IMRT: what is the best parameter to evaluate plans? J..P. Pigno/, A. Mihai, K. Sixe/ Sunnybrook and Women's College Hea/th Sciences Centre, University of Toronto, Toronto, Ontario, Canada Purpose: Under breast IMRT a wide variety of techniques have been developed to compensate for missing tissue, ranging from 3D solid compensators to the use of multiple small field segments. Eventually, all these techniques improve the dose distribution homogeneity compared to conventional wedged technique (WT). The dosimetry benefits of these techniques were reported using a large range of parameter. Material and Method: A dosimetric study was performed on a cohort of 26 consecutive breast cancer patients referred at TSRCC for adjuvant breast irradiation. Breast WT and IMRT plans were generated for each patient following CT simulation using a Theraplan planning workstation. Dose distribution homogeneity was evaluated on a collection of parameters extracted from the dose distributions or Differential DVH: the maximum dose ('hotspot'), the DVH peak height, percentage of breast volume receiving 5% or 10% excess of dose compared to the prescribed dose, the dose gradient between the breast core and the infra-mammary fold (Sagittal Dose Gradient, SDG). Results: Averaging their values over the 26 patients, all parameters demonstrate that Breast IMRT improves dose distribution homogeneity compared to WT, although, the difference is generally small and statistically not significant: 112.5%+5 versus 113.4%+4 for the maximum, 11.7%--2.6 versus 15.4%±3.6 for the peak height, 2.3%±4.3 versus 3.9%±7 for the volume receiving dose >110%. Moreover, for about a third of the patients WT do better than IMRT. Only the SDG show strong consistent and statistically significant differences in favor of breast IMRT, 0.4% versus 10.7% (p=4.109). This parameter is also the most clinically relevant. Conclusion: Since November 2002, fourteen patients have received Breast IMRT at Sunnybrook. The plans are assessed on a sagittal and 3 horizontal dose distribution. In addition, the SDG is calculated to quantify the breast IMRT benefit. 16
Dosimetric comparison of 1251 and 103Pd seeds for a permanent breast implant as an adjuvant radiation technique J.-P. Pignol, B. Keller, E. Rakovitch, V. Benk, G. Morton, B. Curpen,. P. Causer, R. Sankreacha, W. Que Sunnybrook and Women's Health Sciences Centre, University of Toronto, Toronto, Ontario, Canada PurPose: Adjuvant radiation is used following Breast Conserving Surgery to achieve tumour local control. Radiation is generally delivered using external beam covering the whole breast and fractionated over a few weeks. Alternative approaches to deliver treatment to the tumour bed alone and using a shorter schedule have been recently suggested, including LDR and HDR brachytherapy. We propose using a single one hour procedure to do a permanent breast seed implant (PBI). This presentation compares 1251 and 103Pal BPI. Materials and Methods: CT scans of 10 early stage breast cancer patients were transferred to an MMS planning computer. The GTV plus a margin of 5 mm was implanted with seeds evenly spaced every lcm. The same implant geometry and the same number of seeds were used for both 1251 and 103Pd plans. The seed activity was adjusted so the Vl00 remained close to 100% for each isotope. Results: The target volume was small for the majority of the patients, 9cc (SD=4.4), translating into an implanted volume of 24cc. The average number of seeds was 28 (SD=8). The V200 was larger for 103Pd seeds (26%, SD=13.7%) than for 1251 seeds (13%, SD=6.6%), meaning that 103Pd yielded more hot spots than 1251. The D90 was roughly equivalent, 121% versus 128%. The skin dose was highly dependent on the distance to the skin, ranging from 1% to 55% for the 1251 seeds. Conclusion: The target volume was found to be small for the patient majority, translating into a small number of seeds required. Comparing 1251 and 103Pd, the D90 varies little suggesting that the coverage of the target volume is comparable. PBI appears feasible, may reduce acute skin side effects, and improve treatment compliance for women that live remotely from the cancer centre.
cohorts. Conclusion: Postmastectomy radiotherapy for positive margins in the absence of advanced primary tumour stage or 4 or more positive nodes conferred modest absolute reductions in Iocoregional recurrence but no statistically significant impact in long-term relapse or survival was demonstrated. 13
Regional radiation of the axilla and supraclavicular fossa for adjuvant breast treatment: a comparison of four techniques C. Jephcott, S. Tyldesley, C.-L. Swift, V. LaPointe, W. Kwa British Columbia Cancer Agency, Vancouver Cancer Centre, Vancouver, British Columbia, Canada Back(]round: Adjuvant nodal radiotherapy is an important part of treatment for women with breast cancer. Three common techniques used to treat the axilla and supraclavicular nodes are a single anterior field (AP), an anterior to posterior parallel pair (AP:PA), and an anterior field with a posterior boost field to the axilla (AP:PAboost). Each of these techniques has a potential disadvantage: the AP may underdose the deeper nodes; the AP:PA unnecessarily irradiates the medial posterior neck; and the AP:PAboost produces an unnecessary anterior hotspot. We hypothesize that an AP:PA boost technique with customized MLC compensation of the anterior beam will minimize these disadvantages (APcomp:PAboost). Methods: CT data from 10 patients who had completed breast and regional radiotherapy with AP:PA boost were used for the analysis. The fields as previously planned by the oncologist were used as the standard fields for each patient. Axillary and supraclavicular nodal volumes, treated volume, and the brachial plexus were contoured. A plan for each of the 4 techniques (AP,AP:PA, AP:PA boost, APcomp:PAboost) were then generated for each of the 10 patients using CadPlan with modified Batho correction. Each plan was compared for total treated volume, nodal coverage, plexus dose, hotspot dose, and PTV coverage. Results: The AP plan gave poor PTV coverage in 70% of cases. The AP:PA provided good PTV coverage and minimal hotspots, but there was consistent unnecessary irradiation to the medial posterior neck. The AP:PAboost provided adequate PTV coverage and limited dose to the medial posterior neck, but produced hotspots in excess of 120% in 90% of cases. The APcomp:PAboost provided good PTV coverage, limited dose to the medial posterior neck and hotspots<115% in the majority of cases. Conclusion: In the majority of cases, the best plan in terms of PTV cover, acceptable hot spots, and limited irradiation of the medial posterior neck was produced with the APcomp:PAboost technique. 14
A dose-volume analysis of regional lymph nodes in breast tangent radiation K.D. Voduc, M. Keyes British Columbia Cancer Agency, University of British Columbia, Vancouver, British Columbia, Canada PurPose: To formulate a systematic method of contouring Level I, II, III axillary regions and internal mammary nodes on planning CT scan; and to then perform a dose-volume analysis of the nodal regions in breast cancer patients treated with standard breast tangents. Methods and Materials: Planning CT scans of 23 women invasive breast cancer were retrospectively reviewed. All patients were treated with breast conserving surgery, followed by adjuvant radiation with standard breast tangents. Level I, II, and III axillary node regions and the internal mammary nodes were contoured on SomaVision. Dose-volume histographs were then obtained from Cadplan. Endpoints were maximum dose, minimum dose, median dose, and standard deviation, as well as volume receiving 95% of the prescribed dose. Coverage was considered adequate if 95% of the target volume received 95% of the prescribed dose. Results: Axillary node regions were first defined in relation to anatomical stuctures. These regions were then located on planning CT scan and were reviewed with a diagnostic radiologist. In 0/23 of the patients studied were the level I axillary nodes adequately treated with the prescribed tangent fields. Only 5/23 patients had 40% or more of the level I axillary volume treated with 95% of the prescribed dose. Conclusions: The results of this study suggest that breast irradiation by standard tangent fields does not adequately treat the level t axilla. We can also suggest that regional lymph nodes be outlined on planning CT prior to the field placement, if treatment to these areas is intended.
CARO 2003
15
Quantifying the dose distribution homogeneity improvement for breast IMRT: what is the best parameter to evaluate plans? J..P. Pigno/, A. Mihai, K. Sixe/ Sunnybrook and Women's College Hea/th Sciences Centre, University of Toronto, Toronto, Ontario, Canada Purpose: Under breast IMRT a wide variety of techniques have been developed to compensate for missing tissue, ranging from 3D solid compensators to the use of multiple small field segments. Eventually, all these techniques improve the dose distribution homogeneity compared to conventional wedged technique (WT). The dosimetry benefits of these techniques were reported using a large range of parameter. Material and Method: A dosimetric study was performed on a cohort of 26 consecutive breast cancer patients referred at TSRCC for adjuvant breast irradiation. Breast WT and IMRT plans were generated for each patient following CT simulation using a Theraplan planning workstation. Dose distribution homogeneity was evaluated on a collection of parameters extracted from the dose distributions or Differential DVH: the maximum dose ('hotspot'), the DVH peak height, percentage of breast volume receiving 5% or 10% excess of dose compared to the prescribed dose, the dose gradient between the breast core and the infra-mammary fold (Sagittal Dose Gradient, SDG). Results: Averaging their values over the 26 patients, all parameters demonstrate that Breast IMRT improves dose distribution homogeneity compared to WT, although, the difference is generally small and statistically not significant: 112.5%+5 versus 113.4%+4 for the maximum, 11.7%--2.6 versus 15.4%±3.6 for the peak height, 2.3%±4.3 versus 3.9%±7 for the volume receiving dose >110%. Moreover, for about a third of the patients WT do better than IMRT. Only the SDG show strong consistent and statistically significant differences in favor of breast IMRT, 0.4% versus 10.7% (p=4.109). This parameter is also the most clinically relevant. Conclusion: Since November 2002, fourteen patients have received Breast IMRT at Sunnybrook. The plans are assessed on a sagittal and 3 horizontal dose distribution. In addition, the SDG is calculated to quantify the breast IMRT benefit. 16
Dosimetric comparison of 1251 and 103Pd seeds for a permanent breast implant as an adjuvant radiation technique J.-P. Pignol, B. Keller, E. Rakovitch, V. Benk, G. Morton, B. Curpen,. P. Causer, R. Sankreacha, W. Que Sunnybrook and Women's Health Sciences Centre, University of Toronto, Toronto, Ontario, Canada PurPose: Adjuvant radiation is used following Breast Conserving Surgery to achieve tumour local control. Radiation is generally delivered using external beam covering the whole breast and fractionated over a few weeks. Alternative approaches to deliver treatment to the tumour bed alone and using a shorter schedule have been recently suggested, including LDR and HDR brachytherapy. We propose using a single one hour procedure to do a permanent breast seed implant (PBI). This presentation compares 1251 and 103Pal BPI. Materials and Methods: CT scans of 10 early stage breast cancer patients were transferred to an MMS planning computer. The GTV plus a margin of 5 mm was implanted with seeds evenly spaced every lcm. The same implant geometry and the same number of seeds were used for both 1251 and 103Pd plans. The seed activity was adjusted so the Vl00 remained close to 100% for each isotope. Results: The target volume was small for the majority of the patients, 9cc (SD=4.4), translating into an implanted volume of 24cc. The average number of seeds was 28 (SD=8). The V200 was larger for 103Pd seeds (26%, SD=13.7%) than for 1251 seeds (13%, SD=6.6%), meaning that 103Pd yielded more hot spots than 1251. The D90 was roughly equivalent, 121% versus 128%. The skin dose was highly dependent on the distance to the skin, ranging from 1% to 55% for the 1251 seeds. Conclusion: The target volume was found to be small for the patient majority, translating into a small number of seeds required. Comparing 1251 and 103Pd, the D90 varies little suggesting that the coverage of the target volume is comparable. PBI appears feasible, may reduce acute skin side effects, and improve treatment compliance for women that live remotely from the cancer centre.