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EP-1823: DVH- and NTCP-based dosimetric comparison of different margins for VMAT-IMRT of esophageal cancer
S998 ESTRO 36 _______________________________________________________________________________________________
EP-1821 Air gap between patient surface and immobilization devices: dosimetric impact on H&N IMRT plans S. Moragues-Femenia1, M. Pozo-Massó2, J.F. CalvoOrtega2, J. Casals-Farran2 1 Moragues Femenia Sandra, HOSPITAL QUIRON BARCELONA- Radiotherapy, Barcelona, Spain 2 HOSPITAL QUIRON BARCELONA- Radiotherapy, HOSPITAL QUIRON BARCELONA- Radiotherapy, Barcelona, Spain Purpose or Objective In head and neck (H&N) treatments, there is an avoidable air gap between the typical mask-based immobilization device used and the patient surface ("air gap" from now on). Our aim is to evaluate the dosimetric effect of considering the "air gap" on the patient dose distribution on H&N IMRT plans. Material and Methods
A total of 5 H&N patients were selected. The "immobilization" device consisted of a thermoplastic mask covering the head, neck and shoulders, and attached to a board on the linac couch. Targets (PTVs) and organs-atrisks (OARs: spinal cord, brainstem, optic nerves, parotids and oral cavity) were outlined in Eclipse TPS. The posterior aspect of patient skin was also contoured. Two different approaches were proposed to define the "body structure": 1) the patient outer contour plus the immobilization device (Fig 1); and 2) as previous but also including the air gap between the immobilization device and the patient outer contour (Fig 2). Dose distributions were calculated using identical IMRT plans for each approach. The differences in the minimum (D98%), maximum (D2%) and mean (Dmean) doses to the PTVs and OARs as well as the skin mean doses were compared. Results Differences within ±1% were found in the dosimetric parameters analyzed for PTVs and OARs. Mean skin was up to 2% greater when the gap air between patient surface was considered. Conclusion Little dose differences were observed between the approaches of including or not the air gap existing between the immobilization device and the patient surface. EP-1822 Monitoring of parotid gland changes in radiotherapy of NPC with parapharyngeal space involvement W.C.V. Wu1, Y. Zhang2, C. Lin2, J. Wu2 1 Hong Kong Polytechnic University, HTI, Kowloon- Hong Kong- SAR, China 2 Sun Yat-sen University Cancer, Cancer Hospital, Guangzhou, China Purpose or Objective Parapharyngeal space (PPS) involvement is present in over 70% of nasopharyngeal carcinoma (NPC) patients. Since PPS is close to parotid gland, a radical course of radiotherapy for this group of patients may deliver high dose to this organ. The purpose of this study was to evaluate the parotid gland changes of NPC patients with PPS involvement during radiotherapy and up to 3 months after treatment.
Material and Methods Kilovoltage computed tomography (CT) scans of head and neck region of 39 NPC patients with PPS involvement recruited from Sun Yat-sen University Cancer Center between January 2011 and April 2013 were performed at pre-radiotherapy, 10th, 20th and 30th fractions, and 3 months after treatment. All patients were treated with intensity modulated radiotherapy using 6 MV photons with prescribed doses of 66-70 Gy to the target volume. The parotid glands were contoured in pre-radiotherapy planning CT scan and in subsequent scans. At each time interval, DICE similarity coefficient (DSC), percentage volume change and centroid movement between the planning CT and the subsequent CTs were obtained from the contouring software. In addition, the distance between medial and lateral borders of parotid glands from the midline at various time intervals were also measured. Results The ipsilateral parotid gland received a mean dose of about 5 Gy higher than the contralateral side (56.3±6.2 Gy vs 51.7±9.2 Gy). The mean DSC for ipsilateral parotid gland decreased to 0.63 at 30th fraction and returned to 0.74 at 3 months after treatment. Partial recovery was observed at 3 months after treatment. All differences between each pair of consecutive measurements (such as between 10th and 20th fractions and 20th and 30th fractions) were statistically significant (p < 0.05). The mean volume change for ipsilateral parotid gland decreased from 15.27% at 20th fraction to -37.49% at 30th fraction and partially recovered to -23.14% in 3 months. There were no significant differences between ipsilateral and contralateral groups despite the changes in the ipsilateral side being relatively greater. The centroid displacement followed a similar pattern, which moved medially and superiorly by an average of 0.30 cm and 0.18 cm respectively at 30th fraction. The changes in ipsilateral gland were slightly greater than the contralateral side. Conclusion In radiotherapy of NPC patients with PPS involvement, the parotid gland shrank by about 1/3 towards the end of the treatment course. DSC and percentage volume changes of both ipsilateral and contralateral parotid glands decreased during the radiotherapy course and partially recovered in 3 months after treatment. This trend was also seen in the displacements of centroids and the medial and lateral borders of the gland. A re-planning was suggested at around 15th to 20th fraction so as to reduce the dose to the parotid gland due to the detected movement of this structure during the radiotherapy course. EP-1823 DVH- and NTCP-based dosimetric comparison of different margins for VMAT-IMRT of esophageal cancer S. Münch1, M. Oechsner1, S.E. Combs1,2, D. Habermehl1 1 Klinikum rechts der Isar- TU München, Radiation Oncology, München, Germany 2 Institute of innovative radiotherapy iRT, Hermholtz Zentrum, Oberschleißheim, Germany Purpose or Objective To cover the microscopic, longitudinal tumor spread in squamous cell carcinoma of the esophagus (SCC), longitudinal margins of 3-4 centimetres are used for neoadjuvant and definitive radiotherapy (RT) protocols. Therefore, RT of SCC is often done with large treatment volumes, which lead to high doses to the organs at risk (OAR). However, while the promising results of the CROSS-Trial, that used longitudinal margins of 4 cm, defined a new standard for neoadjuvant chemoradiation (CRT), a smaller margin of 3 cm might be reasonable, especially for early tumor stages.
S999 ESTRO 36 _______________________________________________________________________________________________
Purpose of this study was to compare the dose distribution to the organs at risk for different longitudinal margins using a DVH- and NTC-based approach. Material and Methods 10 patients with SCC of the middle or the lower third, who underwent CRT at our institution were retrospective selected. Three planning target volumes (PTV) were created for every patient, with an axial margin of 1.5 cm to the gross target volume (GTV) (primary tumor and PETpositive lymph nodes), analogous to the protocol of the CROSS-trial. The longitudinal margins were 4 cm, 3 cm and 2 cm, respectively. Contouring and treatment planning was performed with the Eclipse 13 planning system (Varian Medical Systems, Palo Alto, CA, USA). For every PTV, volumetric modulated arc therapy (VMAT) plans were optimized. Dose calculation was performed using the AAA algorithm (version 10.0.28) and heterogeneity correction. All plans were normalized to a median prescribed PTV dose of 41.4 Gy with a daily dose of 1.8 Gy. Dose to the lungs, heart and liver were evaluated and compared. Differences of dose parameters were tested for significance with ttest for paired samples. Results Median tumor length was 6 cm with a range of 3 to 10 cm and 8 of the 10 patients (80%) had lymph node metastasis. When using a longitudinal margin of 3 cm instead of 4 cm, all dose parameters (Dmin, Dmax, Dmean, Dmedian and V5-V35), except Dmax could be significantly reduced for the lungs. Regarding the heart, a significant reduction was seen for Dmean and V5, whereas no significant difference was seen for Dmin, Dmax, Dmedian and V10-V35. When comparing a longitudinal margin of 4 cm to a longitudinal margin of 2 cm, not only Dmin, Dmax, Dmean, Dmedian and V5-V35 for the lungs, but also Dmax, Dmin and V5-V35 for the heart were significantly reduced. Nevertheless, no difference was seen for the median heart dose. In addition, the risk of pneumonitis was significantly reduced by a margin reduction of 3 cm and 2 cm. Conclusion The reduction of the longitudinal margin from 4 cm to 3 cm can significantly reduce the dose to lungs, while the reduction to 2 cm can also reduce doses to the heart. Despite clinical benefit and oncologic outcome remain unclear, reduction of the longitudinal margins might provide the opportunity to reduce side effects of CRT for SCC in upcoming studies. EP-1824 Elective breast RT including level I & II lymph nodes: A planning study with the humeral head as PRV J. Van der Leer1, K. Surmann1, M. Van der Sangen1, M. Van Lieshout1, C.W. Hurkmans1 1 Catharina Ziekenhuis, Radiotherapy, Eindhoven, The Netherlands Purpose or Objective The aim of this planning study was to determine a new technique for elective breast radiotherapy and level I and II lymph nodes following the new ESTRO delineation consensus guidelines. According to these guidelines the humeral head should be spared by introducing a planning risk volume (PRV) of the humeral head and connective tissue 10 mm around it. Material and Methods We included ten left sided breast cancer patients in our planning study in Pinnacle3 v9.8. Each patient was planned with 16 x 2.66 Gy on the breast PTV (PTVp) and the elective level I and II lymph nodes (PTVn). We compared three treatment planning techniques: high tangential field (HTF), 6-field IMRT and VMAT. The HTF technique consisted of two open beams with extra segments and the cranial and posterior border was extended to include PTVn. Some of the leaves were closed
to spare the humeral head + 10 mm around it (hh+10). For the IMRT technique we added four additional fields to the high tangential fields (gantry angle of 330, 30, 80 and 170 degrees) to ensure coverage of the cranial part of the breast and lymph nodes. The caudal border of these additional fields was set 1 cm below the attachment of the clavicle at the sternum. The third technique was a dual arc VMAT from 305 to 180 degrees. The plans were made by inverse planning, achieving a PTVp coverage of V95% ≥ 97% and a PTVn V90% ≥ 95%. Additionally, the dose to the lungs, heart and right breast (OARs) has been minimized. hh+10 was included with an objective of V40Gy < 1 cm3 for all three techniques. Results HTF resulted in an average PTVp V95% of 97.2% and an average PTVn V90% of 90.4% (see Table 1 and Figure 1). With the additional fields of the IMRT technique the coverage of PTVn increased significantly to on average 98% (p=0.01) while PTVp did not vary significantly (p=0.92). The dose to the OAR was comparable between the HTF and IMRT techniques. When using VMAT the coverage of the PTVn was on average 99.5% (p<0.01 compared to the HTF and p=0.19 compared to IMRT). The dose to the OARs however increased as well. The mean dose to the contralateral breast increased significantly from 0.6 Gy with HTF and IMRT to 2.3 Gy with VMAT (p<0.01 for both).
EP-1821 Air gap between patient surface and immobilization devices: dosimetric impact on H&N IMRT plans S. Moragues-Femenia1, M. Pozo-Massó2, J.F. CalvoOrtega2, J. Casals-Farran2 1 Moragues Femenia Sandra, HOSPITAL QUIRON BARCELONA- Radiotherapy, Barcelona, Spain 2 HOSPITAL QUIRON BARCELONA- Radiotherapy, HOSPITAL QUIRON BARCELONA- Radiotherapy, Barcelona, Spain Purpose or Objective In head and neck (H&N) treatments, there is an avoidable air gap between the typical mask-based immobilization device used and the patient surface ("air gap" from now on). Our aim is to evaluate the dosimetric effect of considering the "air gap" on the patient dose distribution on H&N IMRT plans. Material and Methods
A total of 5 H&N patients were selected. The "immobilization" device consisted of a thermoplastic mask covering the head, neck and shoulders, and attached to a board on the linac couch. Targets (PTVs) and organs-atrisks (OARs: spinal cord, brainstem, optic nerves, parotids and oral cavity) were outlined in Eclipse TPS. The posterior aspect of patient skin was also contoured. Two different approaches were proposed to define the "body structure": 1) the patient outer contour plus the immobilization device (Fig 1); and 2) as previous but also including the air gap between the immobilization device and the patient outer contour (Fig 2). Dose distributions were calculated using identical IMRT plans for each approach. The differences in the minimum (D98%), maximum (D2%) and mean (Dmean) doses to the PTVs and OARs as well as the skin mean doses were compared. Results Differences within ±1% were found in the dosimetric parameters analyzed for PTVs and OARs. Mean skin was up to 2% greater when the gap air between patient surface was considered. Conclusion Little dose differences were observed between the approaches of including or not the air gap existing between the immobilization device and the patient surface. EP-1822 Monitoring of parotid gland changes in radiotherapy of NPC with parapharyngeal space involvement W.C.V. Wu1, Y. Zhang2, C. Lin2, J. Wu2 1 Hong Kong Polytechnic University, HTI, Kowloon- Hong Kong- SAR, China 2 Sun Yat-sen University Cancer, Cancer Hospital, Guangzhou, China Purpose or Objective Parapharyngeal space (PPS) involvement is present in over 70% of nasopharyngeal carcinoma (NPC) patients. Since PPS is close to parotid gland, a radical course of radiotherapy for this group of patients may deliver high dose to this organ. The purpose of this study was to evaluate the parotid gland changes of NPC patients with PPS involvement during radiotherapy and up to 3 months after treatment.
Material and Methods Kilovoltage computed tomography (CT) scans of head and neck region of 39 NPC patients with PPS involvement recruited from Sun Yat-sen University Cancer Center between January 2011 and April 2013 were performed at pre-radiotherapy, 10th, 20th and 30th fractions, and 3 months after treatment. All patients were treated with intensity modulated radiotherapy using 6 MV photons with prescribed doses of 66-70 Gy to the target volume. The parotid glands were contoured in pre-radiotherapy planning CT scan and in subsequent scans. At each time interval, DICE similarity coefficient (DSC), percentage volume change and centroid movement between the planning CT and the subsequent CTs were obtained from the contouring software. In addition, the distance between medial and lateral borders of parotid glands from the midline at various time intervals were also measured. Results The ipsilateral parotid gland received a mean dose of about 5 Gy higher than the contralateral side (56.3±6.2 Gy vs 51.7±9.2 Gy). The mean DSC for ipsilateral parotid gland decreased to 0.63 at 30th fraction and returned to 0.74 at 3 months after treatment. Partial recovery was observed at 3 months after treatment. All differences between each pair of consecutive measurements (such as between 10th and 20th fractions and 20th and 30th fractions) were statistically significant (p < 0.05). The mean volume change for ipsilateral parotid gland decreased from 15.27% at 20th fraction to -37.49% at 30th fraction and partially recovered to -23.14% in 3 months. There were no significant differences between ipsilateral and contralateral groups despite the changes in the ipsilateral side being relatively greater. The centroid displacement followed a similar pattern, which moved medially and superiorly by an average of 0.30 cm and 0.18 cm respectively at 30th fraction. The changes in ipsilateral gland were slightly greater than the contralateral side. Conclusion In radiotherapy of NPC patients with PPS involvement, the parotid gland shrank by about 1/3 towards the end of the treatment course. DSC and percentage volume changes of both ipsilateral and contralateral parotid glands decreased during the radiotherapy course and partially recovered in 3 months after treatment. This trend was also seen in the displacements of centroids and the medial and lateral borders of the gland. A re-planning was suggested at around 15th to 20th fraction so as to reduce the dose to the parotid gland due to the detected movement of this structure during the radiotherapy course. EP-1823 DVH- and NTCP-based dosimetric comparison of different margins for VMAT-IMRT of esophageal cancer S. Münch1, M. Oechsner1, S.E. Combs1,2, D. Habermehl1 1 Klinikum rechts der Isar- TU München, Radiation Oncology, München, Germany 2 Institute of innovative radiotherapy iRT, Hermholtz Zentrum, Oberschleißheim, Germany Purpose or Objective To cover the microscopic, longitudinal tumor spread in squamous cell carcinoma of the esophagus (SCC), longitudinal margins of 3-4 centimetres are used for neoadjuvant and definitive radiotherapy (RT) protocols. Therefore, RT of SCC is often done with large treatment volumes, which lead to high doses to the organs at risk (OAR). However, while the promising results of the CROSS-Trial, that used longitudinal margins of 4 cm, defined a new standard for neoadjuvant chemoradiation (CRT), a smaller margin of 3 cm might be reasonable, especially for early tumor stages.
S999 ESTRO 36 _______________________________________________________________________________________________
Purpose of this study was to compare the dose distribution to the organs at risk for different longitudinal margins using a DVH- and NTC-based approach. Material and Methods 10 patients with SCC of the middle or the lower third, who underwent CRT at our institution were retrospective selected. Three planning target volumes (PTV) were created for every patient, with an axial margin of 1.5 cm to the gross target volume (GTV) (primary tumor and PETpositive lymph nodes), analogous to the protocol of the CROSS-trial. The longitudinal margins were 4 cm, 3 cm and 2 cm, respectively. Contouring and treatment planning was performed with the Eclipse 13 planning system (Varian Medical Systems, Palo Alto, CA, USA). For every PTV, volumetric modulated arc therapy (VMAT) plans were optimized. Dose calculation was performed using the AAA algorithm (version 10.0.28) and heterogeneity correction. All plans were normalized to a median prescribed PTV dose of 41.4 Gy with a daily dose of 1.8 Gy. Dose to the lungs, heart and liver were evaluated and compared. Differences of dose parameters were tested for significance with ttest for paired samples. Results Median tumor length was 6 cm with a range of 3 to 10 cm and 8 of the 10 patients (80%) had lymph node metastasis. When using a longitudinal margin of 3 cm instead of 4 cm, all dose parameters (Dmin, Dmax, Dmean, Dmedian and V5-V35), except Dmax could be significantly reduced for the lungs. Regarding the heart, a significant reduction was seen for Dmean and V5, whereas no significant difference was seen for Dmin, Dmax, Dmedian and V10-V35. When comparing a longitudinal margin of 4 cm to a longitudinal margin of 2 cm, not only Dmin, Dmax, Dmean, Dmedian and V5-V35 for the lungs, but also Dmax, Dmin and V5-V35 for the heart were significantly reduced. Nevertheless, no difference was seen for the median heart dose. In addition, the risk of pneumonitis was significantly reduced by a margin reduction of 3 cm and 2 cm. Conclusion The reduction of the longitudinal margin from 4 cm to 3 cm can significantly reduce the dose to lungs, while the reduction to 2 cm can also reduce doses to the heart. Despite clinical benefit and oncologic outcome remain unclear, reduction of the longitudinal margins might provide the opportunity to reduce side effects of CRT for SCC in upcoming studies. EP-1824 Elective breast RT including level I & II lymph nodes: A planning study with the humeral head as PRV J. Van der Leer1, K. Surmann1, M. Van der Sangen1, M. Van Lieshout1, C.W. Hurkmans1 1 Catharina Ziekenhuis, Radiotherapy, Eindhoven, The Netherlands Purpose or Objective The aim of this planning study was to determine a new technique for elective breast radiotherapy and level I and II lymph nodes following the new ESTRO delineation consensus guidelines. According to these guidelines the humeral head should be spared by introducing a planning risk volume (PRV) of the humeral head and connective tissue 10 mm around it. Material and Methods We included ten left sided breast cancer patients in our planning study in Pinnacle3 v9.8. Each patient was planned with 16 x 2.66 Gy on the breast PTV (PTVp) and the elective level I and II lymph nodes (PTVn). We compared three treatment planning techniques: high tangential field (HTF), 6-field IMRT and VMAT. The HTF technique consisted of two open beams with extra segments and the cranial and posterior border was extended to include PTVn. Some of the leaves were closed
to spare the humeral head + 10 mm around it (hh+10). For the IMRT technique we added four additional fields to the high tangential fields (gantry angle of 330, 30, 80 and 170 degrees) to ensure coverage of the cranial part of the breast and lymph nodes. The caudal border of these additional fields was set 1 cm below the attachment of the clavicle at the sternum. The third technique was a dual arc VMAT from 305 to 180 degrees. The plans were made by inverse planning, achieving a PTVp coverage of V95% ≥ 97% and a PTVn V90% ≥ 95%. Additionally, the dose to the lungs, heart and right breast (OARs) has been minimized. hh+10 was included with an objective of V40Gy < 1 cm3 for all three techniques. Results HTF resulted in an average PTVp V95% of 97.2% and an average PTVn V90% of 90.4% (see Table 1 and Figure 1). With the additional fields of the IMRT technique the coverage of PTVn increased significantly to on average 98% (p=0.01) while PTVp did not vary significantly (p=0.92). The dose to the OAR was comparable between the HTF and IMRT techniques. When using VMAT the coverage of the PTVn was on average 99.5% (p<0.01 compared to the HTF and p=0.19 compared to IMRT). The dose to the OARs however increased as well. The mean dose to the contralateral breast increased significantly from 0.6 Gy with HTF and IMRT to 2.3 Gy with VMAT (p<0.01 for both).