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Electron Arc Therapy for Bilateral Chest Wall Irradiation: Treatment Planning and Dosimetric Study
I. J. Radiation Oncology d Biology d Physics
S718
3192
Volume 75, Number 3, Supplement, 2009
Dosimetric Evaluation of Rotation of Contura Multi-lumen Balloon Applicator for Breast High Dose Rate Brachytherapy
Y. Kim, M. G. Trombetta Allegheny General Hospital, Pittsburgh, PA Purpose/Objective(s): Compared with a single lumen MammoSite applicator, four surrounding lumens with 5 mm offset from the central lumen in the Contura applicator can provide a potential to improve target coverage with better skin and rib sparing. However, if the Contura device rotates around the central lumen, the asymmetrical dose distribution may result in an inadvertent reduction of target coverage and/or dose increase to normal tissue. This study evaluates the dosimetric impact of rotation of the Contura multi-lumen balloon. Materials/Methods: A highly asymmetrical dose distribution was generated for a patient whose balloon was located in proximity to both skin and rib (balloon-skin distance = 5 mm; balloon-rib distance = 2 mm). The Contura rotation was simulated virtually in a treatment planning system (TPS). The position coordinates of applicator points for four offset lumens were extracted from the TPS and rotated every 10 degrees over a ±180 degree range with respect to the central lumen using a mathematically calculated rotational matrix. The computed new position coordinates were manually transferred to the TPS corresponding to each applicator point. Thirty-five rotated plans were produced and compared to the original multi-lumen plan as well as two single (central) lumen plans (single lumen, single dwell position; SLSD and single lumen multi-dwell position; SLMD). For plan comparison, the following dosimetric parameters were evaluated: PTV_EVAL coverage (V95), maximum dose (Dmax) of skin and rib relative to the prescribed dose (PD), and the breast tissue volume receiving 200% of PD (V200). Results: Compared to SLSD and SLMD plans, the multi-lumen plan resulted in better target coverage (V95 = 98.1% vs. 96.2 and 97.5%) and lower skin Dmax (126.1% of PD vs. 145.4 and 140.9%), rib Dmax (162.9% of PD vs. 186.9 and 180.7%) and breast V200 (8.1 cc vs. 8.6 and 8.9cc). At a 70 degree rotation, the dosimetric data of the rotated plan were inferior to the single lumen plans. The V95 was reduced to 95%. The critical structure dose was increased by 11.2% of PD for skin Dmax and 27.7% of PD for rib Dmax. The breast V200 was increased by 0.6 cc. For a small rotation angle of ±30 degree, the V95 value was reduced by 1.6% while increasing skin Dmax by 5.3% of PD and rib Dmax by 16.4% of PD. The breast V200 was increased by 0.4 cc. Conclusions: A significant rotation of the Contura balloon can outweigh the benefit of improved dose shaping capability from four additional offset lumens and make dosimetric data worse than single lumen plans. With rotational deviation as little as 30 degrees, the multi-lumen plan can be degraded similar to single lumen plans. The verification and correction of rotation is essential prior to delivery of each fraction. Author Disclosure: Y. Kim, None; M.G. Trombetta, None.
3193
Early Clinical Experience with Minisavi APBI Applicator: A Unique Solution for Small Lumpectomy Cavities and Skin Distances
S. Morcovescu1, J. D. Morton2, K. Perry3 1
AROS LLC, Colleyville, TX, 2Texas Oncology Denton, Denton, TX, 3North Texas Hospital, Denton, TX
Purpose/Objective(s): The purpose of this study was to demonstrate that the miniSAVI multicatheter APBI applicator was the applicator of choice, anatomically and dosimetrically, in patients in whom the breast size, the size of the lumpectomy cavity and its proximity to the skin precluded treatment and the use of other available APBI balloon-type applicators (MammoSite or Contura). Materials/Methods: The study considered the first seven (7) patients who, because of the cavity size and/or inadequate skin distance, were not fit for treatment using other balloon-type devices. MammoSite-type and a Contura-type template plans were superimposed on the miniSAVI CT original planning scan and pertinent dosimetric comparison were performed. Results: The breast size and the size and location of the lumpectomy cavities demanded the use of a treatment device of dimensions not accommodated by ABPI balloon-type devices, generally inflated above the 35cc volume range. The use of any balloon-type devices would have been prone to cause extreme patient discomfort, skin overstretching and balloon deformations, due to limited cavity size and chest wall or rib cage proximity. Due to variance in PTV shape, from ellipsoidal (best approximation - for miniSAVI) to spherical (balloon applicators), comparison results of coverage indexes, D100, D95 and D90 are proven of minor relevance in this study. Instead, maximum skin and chest wall dose differences were of extreme relevance. Typical miniSAVI planning structure volumes, in the range of 8.0-10.0 cc, are the equivalent of 1.2 - 1.3 cm radius balloon-type applicators. Properly inflated balloon-type applicators have a radius of at least 2.0 cm. Only under-inflated, distorted and highly asymmetrical balloons would have been a fit for lumpectomy cavity sizes considered in this study. We demonstrated that the hypothetical use of such balloon-type applicators would have rendered prohibitive skin doses, 200% - 450% of the typical prescription dose of 34 Gy. An increase in the risk of fat tissue necrosis was observed, as higher V200 and V150 values were recorded as well. Conclusions: The miniSAVI multicatheter APBI applicator proved to be a unique surgical and dosimetrical solution for the cases considered for this study. Differential loading of the device catheters allowed reduced skin dose without compromising the planning target. The use of this device has the potential to increase the use of APBI in patients where the breast size, the cavity size and/ or skin distance would not allow the use of balloon-type devices. Author Disclosure: S. Morcovescu, None; J.D. Morton, None; K. Perry, CIANNA Medical, F. Consultant/Advisory Board.
3194
Electron Arc Therapy for Bilateral Chest Wall Irradiation: Treatment Planning and Dosimetric Study
P. K. Sharma, A. Munshi, A. Budrukkar, S. V. Jamema, C. M. Tambe, R. Jalali, R. Sarin, D. D. Deshpande, S. K. Shrivastava Tata Memorial Hospital, Mumbai, India Purpose/Objective(s): Treatment of patients with synchronous bilateral breast cancer is a challenge. Bilateral chest wall as planning target volume (PTV) with its varying thickness, curvature and proximity to Organ At Risk (OARs) are challenging
Proceedings of the 51st Annual ASTRO Meeting aspects for radiotherapy planning. We present the first report of dosimetric data of patients treated with electron arc (EA) therapy. Materials/Methods: Ten patients requiring bilateral chest wall irradiation for bilateral breast cancer were considered suitable for EA therapy. After positioning and immobilization, patients underwent CT scans from neck to upper abdomen. PTV included bilateral chest wall while OARs included bilateral lungs and heart. EA plans were generated using the PLATO RTS (V1.8.2 Nucletron) Treatment Planning System. Electron energy was chosen depending upon the depth and thickness of the PTV. Combinations of electron energies (6-9) MeV with bolus were used to account for differential chest wall thickness. For all patients, the arc angle ranged between 80-160 degrees. The source to skin distance remained between 80 -90cm. The electron applicator was designed to have a fixed field width of 5cm and varying field length depending on PTV. The aim was to cover the entire target with the 85% isodose line. Homogeneity Index (HI), Coverage Index (CI) and doses to OARs were evaluated. Patient specific dosimetry was carried out and output was measured in terms of MU/ Gy/degree. In addition, Thermoluminescence surface dosimetry (TLD) was done for all patients. The total planned dose to the PTV was 50Gy/25 fractions with a fraction size of 2Gy per fraction delivered over 5 fractions per week. Results: The mean PTV (± Standard Deviation) volume was 568.9 (±116) cc. Mean PTV coverage was 88(±5.8) % of the prescribed dose. The mean volume of right lung was 974 (±228.6) cc. The mean value of D1, D5, D10 and V20 were 46(±7.6) Gy, 36(±9) Gy and 29(±9) Gy and 28.4±10.5% respectively. The mean volume of left lung was 826(±220) cc. The mean value of D1, D5, D10 and V20 were 45.6(±7) Gy, 36(±9) Gy, 28(±8) Gy and 25.8±7.6% respectively. The mean volume of heart was 381(±78) cc. The mean value of D1, D5 and D10 were 24.6(±15) Gy, 16(±12) Gy and 11(±9) Gy respectively. Mean HI and CI of the PTV was found to be 24 (± 6.6) and 0.88(±0.05) respectively. The mean values of TLD at various pre specified locations on the chest wall surface (right, left, center, superior and inferior) were 1.83Gy, 1.82Gy, 1.85Gy, 1.89Gy and 1.78Gy respectively. Conclusions: EA technique for treating bilateral chest wall is a feasible and pragmatic technique. This technique has the twin advantages of adequate coverage of the target volume and sparing of adjacent normal structures. However, comparing with other techniques, it needs a firm quality assurance protocol for dosimetry and treatment delivery. Author Disclosure: P.K. Sharma, None; A. Munshi, None; A. Budrukkar, None; S.V. Jamema, None; C.M. Tambe, None; R. Jalali, None; R. Sarin, None; D.D. Deshpande, None; S.K. Shrivastava, None.
3195
Dynamic Jaws and Dynamic Couch in Helical Tomotherapy 1
F. Sterzing , M. Uhl1, G. Sroka-Perez1, K. Schubert1, Y. Chen2, W. Lu2, T. R. Mackie2, J. Debus1, G. Oliveira2, K. Herfarth1 1
Department of Radiation Oncology, University of Heidelberg, Germany, 2Tomotherapy Inc., Madison, WI
Purpose/Objective(s): To investigate the next generation technique of helical tomotherapy delivery with dynamic jaw and dynamic couch movement. Materials/Methods: The new technique of dynamic jaws and dynamic couch movement is described and the prototype software planning station version 6.1 is used to do a comparative planning study. Ten nasopharyngeal cancer patients with skull base infiltration close to the optic pathways and lymph node metastases were chosen to analyze the characteristics of the longitudinal dose profile comparing regular tomotherapy delivery, running-start-stop treatment and dynamic jaw and dynamic couch delivery. Target coverage, conformity and homogeneity as well as organ at risk sparing, integral dose and radiation delivery time are evaluated for 5 different plans for each patient. Within a multifocal simultaneous integrated boost concept a median dose of 70.4 Gy to the primary tumor and involved lymph nodes and a median dose of 57.4 Gy to the bilateral cervical lymphatic drainage pathways were prescribed in 32 fractions. Results: Mean parotid dose for all different deliveries was between 24.8 and 26.1 Gy without significant differences. The mean integral dose was lowered by 6.3% using the dynamic jaw and dynamic couch technique in comparison with 2.5 cm field width regular delivery and by 16.7% in comparison with 5cm regular delivery. Dose to optic pathways, brain and lung was lowered significantly with the new technique. Using dynamic jaw and couch movement the calculated radiation time was reduced to 33% of the time required with regular delivery using 2.5cm field width (199 seconds vs. 595 seconds, p \ 0.001). Conclusions: The current delivery mode of helical tomotherapy produces excellent dose distributions with conformal avoidance of parotid glands, brain stem and spinal cord for this challenging patient group. The new technology with dynamic jaw and couch movement improves the plan quality by reducing the dose penumbra and by a reducing the integral dose. In addition, radiation time is reduced to 33% of the regular delivery and patient throughput can be increased. Author Disclosure: F. Sterzing, research collaboration with Tomotherapy Inc., B. Research Grant; speaker for tomotherapy, D. Speakers Bureau/Honoraria; M. Uhl, None; G. Sroka-Perez, None; K. Schubert, None; Y. Chen, employee of tomotherapy, A. Employment; W. Lu, employee of tomotherapy, A. Employment; T.R. Mackie, employee of tomotherapy, A. Employment; J. Debus, None; G. Oliveira, employee of tomotherapy, A. Employment; K. Herfarth, research collaboration, B. Research Grant.
3196
A Prospective Trial of Helical Tomotherapy (HT) in Patients with Head and Neck Cancer (HNC): Results of Dosimetric Comparisons with Three-Dimensional Conformal Radiotherapy (3D-CRT)
A. Haddad, S. El-Sayed, R. Zohr, J. Belec, L. Eapen, B. Esche, L. Grimard The Ottawa Hospital Cancer Centre, Ottawa, ON, Canada Purpose/Objective(s): Intensity-modulated radiotherapy (IMRT) has been shown to provide better sparing of organs at risk (OAR), especially the parotid glands, when treating patients with head and neck malignancies. Using HT inverse planning, we set out to quantify the differences in the dose distribution to multiple target volumes, OAR and to integral dose. Materials/Methods: OTT 05-06 is an ongoing single institution study looking to prospectively evaluate toxicity patterns, quality of life (QoL) and tumor control in 80 patients with HNC treated with IMRT using HT. Patients received 50Gy to an initial low-risk volume and a boost of 20Gy to gross disease, for a total of 35 fractions. This 2-phase approach was used to allow for a more appropriate comparison with previous 3D-CRT outcomes. The plans for an initial 19 patients were selected and parallel 3D-CRT
S719
S718
3192
Volume 75, Number 3, Supplement, 2009
Dosimetric Evaluation of Rotation of Contura Multi-lumen Balloon Applicator for Breast High Dose Rate Brachytherapy
Y. Kim, M. G. Trombetta Allegheny General Hospital, Pittsburgh, PA Purpose/Objective(s): Compared with a single lumen MammoSite applicator, four surrounding lumens with 5 mm offset from the central lumen in the Contura applicator can provide a potential to improve target coverage with better skin and rib sparing. However, if the Contura device rotates around the central lumen, the asymmetrical dose distribution may result in an inadvertent reduction of target coverage and/or dose increase to normal tissue. This study evaluates the dosimetric impact of rotation of the Contura multi-lumen balloon. Materials/Methods: A highly asymmetrical dose distribution was generated for a patient whose balloon was located in proximity to both skin and rib (balloon-skin distance = 5 mm; balloon-rib distance = 2 mm). The Contura rotation was simulated virtually in a treatment planning system (TPS). The position coordinates of applicator points for four offset lumens were extracted from the TPS and rotated every 10 degrees over a ±180 degree range with respect to the central lumen using a mathematically calculated rotational matrix. The computed new position coordinates were manually transferred to the TPS corresponding to each applicator point. Thirty-five rotated plans were produced and compared to the original multi-lumen plan as well as two single (central) lumen plans (single lumen, single dwell position; SLSD and single lumen multi-dwell position; SLMD). For plan comparison, the following dosimetric parameters were evaluated: PTV_EVAL coverage (V95), maximum dose (Dmax) of skin and rib relative to the prescribed dose (PD), and the breast tissue volume receiving 200% of PD (V200). Results: Compared to SLSD and SLMD plans, the multi-lumen plan resulted in better target coverage (V95 = 98.1% vs. 96.2 and 97.5%) and lower skin Dmax (126.1% of PD vs. 145.4 and 140.9%), rib Dmax (162.9% of PD vs. 186.9 and 180.7%) and breast V200 (8.1 cc vs. 8.6 and 8.9cc). At a 70 degree rotation, the dosimetric data of the rotated plan were inferior to the single lumen plans. The V95 was reduced to 95%. The critical structure dose was increased by 11.2% of PD for skin Dmax and 27.7% of PD for rib Dmax. The breast V200 was increased by 0.6 cc. For a small rotation angle of ±30 degree, the V95 value was reduced by 1.6% while increasing skin Dmax by 5.3% of PD and rib Dmax by 16.4% of PD. The breast V200 was increased by 0.4 cc. Conclusions: A significant rotation of the Contura balloon can outweigh the benefit of improved dose shaping capability from four additional offset lumens and make dosimetric data worse than single lumen plans. With rotational deviation as little as 30 degrees, the multi-lumen plan can be degraded similar to single lumen plans. The verification and correction of rotation is essential prior to delivery of each fraction. Author Disclosure: Y. Kim, None; M.G. Trombetta, None.
3193
Early Clinical Experience with Minisavi APBI Applicator: A Unique Solution for Small Lumpectomy Cavities and Skin Distances
S. Morcovescu1, J. D. Morton2, K. Perry3 1
AROS LLC, Colleyville, TX, 2Texas Oncology Denton, Denton, TX, 3North Texas Hospital, Denton, TX
Purpose/Objective(s): The purpose of this study was to demonstrate that the miniSAVI multicatheter APBI applicator was the applicator of choice, anatomically and dosimetrically, in patients in whom the breast size, the size of the lumpectomy cavity and its proximity to the skin precluded treatment and the use of other available APBI balloon-type applicators (MammoSite or Contura). Materials/Methods: The study considered the first seven (7) patients who, because of the cavity size and/or inadequate skin distance, were not fit for treatment using other balloon-type devices. MammoSite-type and a Contura-type template plans were superimposed on the miniSAVI CT original planning scan and pertinent dosimetric comparison were performed. Results: The breast size and the size and location of the lumpectomy cavities demanded the use of a treatment device of dimensions not accommodated by ABPI balloon-type devices, generally inflated above the 35cc volume range. The use of any balloon-type devices would have been prone to cause extreme patient discomfort, skin overstretching and balloon deformations, due to limited cavity size and chest wall or rib cage proximity. Due to variance in PTV shape, from ellipsoidal (best approximation - for miniSAVI) to spherical (balloon applicators), comparison results of coverage indexes, D100, D95 and D90 are proven of minor relevance in this study. Instead, maximum skin and chest wall dose differences were of extreme relevance. Typical miniSAVI planning structure volumes, in the range of 8.0-10.0 cc, are the equivalent of 1.2 - 1.3 cm radius balloon-type applicators. Properly inflated balloon-type applicators have a radius of at least 2.0 cm. Only under-inflated, distorted and highly asymmetrical balloons would have been a fit for lumpectomy cavity sizes considered in this study. We demonstrated that the hypothetical use of such balloon-type applicators would have rendered prohibitive skin doses, 200% - 450% of the typical prescription dose of 34 Gy. An increase in the risk of fat tissue necrosis was observed, as higher V200 and V150 values were recorded as well. Conclusions: The miniSAVI multicatheter APBI applicator proved to be a unique surgical and dosimetrical solution for the cases considered for this study. Differential loading of the device catheters allowed reduced skin dose without compromising the planning target. The use of this device has the potential to increase the use of APBI in patients where the breast size, the cavity size and/ or skin distance would not allow the use of balloon-type devices. Author Disclosure: S. Morcovescu, None; J.D. Morton, None; K. Perry, CIANNA Medical, F. Consultant/Advisory Board.
3194
Electron Arc Therapy for Bilateral Chest Wall Irradiation: Treatment Planning and Dosimetric Study
P. K. Sharma, A. Munshi, A. Budrukkar, S. V. Jamema, C. M. Tambe, R. Jalali, R. Sarin, D. D. Deshpande, S. K. Shrivastava Tata Memorial Hospital, Mumbai, India Purpose/Objective(s): Treatment of patients with synchronous bilateral breast cancer is a challenge. Bilateral chest wall as planning target volume (PTV) with its varying thickness, curvature and proximity to Organ At Risk (OARs) are challenging
Proceedings of the 51st Annual ASTRO Meeting aspects for radiotherapy planning. We present the first report of dosimetric data of patients treated with electron arc (EA) therapy. Materials/Methods: Ten patients requiring bilateral chest wall irradiation for bilateral breast cancer were considered suitable for EA therapy. After positioning and immobilization, patients underwent CT scans from neck to upper abdomen. PTV included bilateral chest wall while OARs included bilateral lungs and heart. EA plans were generated using the PLATO RTS (V1.8.2 Nucletron) Treatment Planning System. Electron energy was chosen depending upon the depth and thickness of the PTV. Combinations of electron energies (6-9) MeV with bolus were used to account for differential chest wall thickness. For all patients, the arc angle ranged between 80-160 degrees. The source to skin distance remained between 80 -90cm. The electron applicator was designed to have a fixed field width of 5cm and varying field length depending on PTV. The aim was to cover the entire target with the 85% isodose line. Homogeneity Index (HI), Coverage Index (CI) and doses to OARs were evaluated. Patient specific dosimetry was carried out and output was measured in terms of MU/ Gy/degree. In addition, Thermoluminescence surface dosimetry (TLD) was done for all patients. The total planned dose to the PTV was 50Gy/25 fractions with a fraction size of 2Gy per fraction delivered over 5 fractions per week. Results: The mean PTV (± Standard Deviation) volume was 568.9 (±116) cc. Mean PTV coverage was 88(±5.8) % of the prescribed dose. The mean volume of right lung was 974 (±228.6) cc. The mean value of D1, D5, D10 and V20 were 46(±7.6) Gy, 36(±9) Gy and 29(±9) Gy and 28.4±10.5% respectively. The mean volume of left lung was 826(±220) cc. The mean value of D1, D5, D10 and V20 were 45.6(±7) Gy, 36(±9) Gy, 28(±8) Gy and 25.8±7.6% respectively. The mean volume of heart was 381(±78) cc. The mean value of D1, D5 and D10 were 24.6(±15) Gy, 16(±12) Gy and 11(±9) Gy respectively. Mean HI and CI of the PTV was found to be 24 (± 6.6) and 0.88(±0.05) respectively. The mean values of TLD at various pre specified locations on the chest wall surface (right, left, center, superior and inferior) were 1.83Gy, 1.82Gy, 1.85Gy, 1.89Gy and 1.78Gy respectively. Conclusions: EA technique for treating bilateral chest wall is a feasible and pragmatic technique. This technique has the twin advantages of adequate coverage of the target volume and sparing of adjacent normal structures. However, comparing with other techniques, it needs a firm quality assurance protocol for dosimetry and treatment delivery. Author Disclosure: P.K. Sharma, None; A. Munshi, None; A. Budrukkar, None; S.V. Jamema, None; C.M. Tambe, None; R. Jalali, None; R. Sarin, None; D.D. Deshpande, None; S.K. Shrivastava, None.
3195
Dynamic Jaws and Dynamic Couch in Helical Tomotherapy 1
F. Sterzing , M. Uhl1, G. Sroka-Perez1, K. Schubert1, Y. Chen2, W. Lu2, T. R. Mackie2, J. Debus1, G. Oliveira2, K. Herfarth1 1
Department of Radiation Oncology, University of Heidelberg, Germany, 2Tomotherapy Inc., Madison, WI
Purpose/Objective(s): To investigate the next generation technique of helical tomotherapy delivery with dynamic jaw and dynamic couch movement. Materials/Methods: The new technique of dynamic jaws and dynamic couch movement is described and the prototype software planning station version 6.1 is used to do a comparative planning study. Ten nasopharyngeal cancer patients with skull base infiltration close to the optic pathways and lymph node metastases were chosen to analyze the characteristics of the longitudinal dose profile comparing regular tomotherapy delivery, running-start-stop treatment and dynamic jaw and dynamic couch delivery. Target coverage, conformity and homogeneity as well as organ at risk sparing, integral dose and radiation delivery time are evaluated for 5 different plans for each patient. Within a multifocal simultaneous integrated boost concept a median dose of 70.4 Gy to the primary tumor and involved lymph nodes and a median dose of 57.4 Gy to the bilateral cervical lymphatic drainage pathways were prescribed in 32 fractions. Results: Mean parotid dose for all different deliveries was between 24.8 and 26.1 Gy without significant differences. The mean integral dose was lowered by 6.3% using the dynamic jaw and dynamic couch technique in comparison with 2.5 cm field width regular delivery and by 16.7% in comparison with 5cm regular delivery. Dose to optic pathways, brain and lung was lowered significantly with the new technique. Using dynamic jaw and couch movement the calculated radiation time was reduced to 33% of the time required with regular delivery using 2.5cm field width (199 seconds vs. 595 seconds, p \ 0.001). Conclusions: The current delivery mode of helical tomotherapy produces excellent dose distributions with conformal avoidance of parotid glands, brain stem and spinal cord for this challenging patient group. The new technology with dynamic jaw and couch movement improves the plan quality by reducing the dose penumbra and by a reducing the integral dose. In addition, radiation time is reduced to 33% of the regular delivery and patient throughput can be increased. Author Disclosure: F. Sterzing, research collaboration with Tomotherapy Inc., B. Research Grant; speaker for tomotherapy, D. Speakers Bureau/Honoraria; M. Uhl, None; G. Sroka-Perez, None; K. Schubert, None; Y. Chen, employee of tomotherapy, A. Employment; W. Lu, employee of tomotherapy, A. Employment; T.R. Mackie, employee of tomotherapy, A. Employment; J. Debus, None; G. Oliveira, employee of tomotherapy, A. Employment; K. Herfarth, research collaboration, B. Research Grant.
3196
A Prospective Trial of Helical Tomotherapy (HT) in Patients with Head and Neck Cancer (HNC): Results of Dosimetric Comparisons with Three-Dimensional Conformal Radiotherapy (3D-CRT)
A. Haddad, S. El-Sayed, R. Zohr, J. Belec, L. Eapen, B. Esche, L. Grimard The Ottawa Hospital Cancer Centre, Ottawa, ON, Canada Purpose/Objective(s): Intensity-modulated radiotherapy (IMRT) has been shown to provide better sparing of organs at risk (OAR), especially the parotid glands, when treating patients with head and neck malignancies. Using HT inverse planning, we set out to quantify the differences in the dose distribution to multiple target volumes, OAR and to integral dose. Materials/Methods: OTT 05-06 is an ongoing single institution study looking to prospectively evaluate toxicity patterns, quality of life (QoL) and tumor control in 80 patients with HNC treated with IMRT using HT. Patients received 50Gy to an initial low-risk volume and a boost of 20Gy to gross disease, for a total of 35 fractions. This 2-phase approach was used to allow for a more appropriate comparison with previous 3D-CRT outcomes. The plans for an initial 19 patients were selected and parallel 3D-CRT
S719