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THE EFFECT OF CONTROL POINT SPACING ON VMAT TREATMENTS OF PROSTATE AND PELVIC NODES
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IMRT: R OTATIONAL THERAPIES
The single arc VMAT plans were generally slightly inferior in terms of plan quality in relation to the clinical IMRT plans. However, the dual arc VMAT plans scored better for each patient at all parameters. The addition of a third arc did not improve the plan quality, but increased the treatment time to a duration longer then the clinical treatment. Conclusions: Dual arc VMAT plans are superior to a seven-beam step-andshoot IMRT plans, whereas the treatment time is potentially two minutes shorter. Therefore, dual arc VMAT irradiations might be the first choice of treatment in future radiotherapy for advanced head and neck cancers. 530 poster (Physics Track) THE DEVELOPMENT OF A VMAT PLANNING SOLUTION USING A COMMERCIALLY-AVAILABLE TREATMENT PLANNING SYSTEM C. Boylan1 , C. Golby1 , S. Smith1 , C. Rowbottom1 1
T HE C HRISTIE NHS F OUNDATION T RUST, North Western Medical Physics, Manchester, United Kingdom
Purpose: Volumetric Modulated Arc Therapy (VMAT) offers the potential of improved dose distributions and shorter treatment times, when compared to IMRT. A number of VMAT planning solutions for the Elekta platform are under development; the aim of this study was to investigate whether a current commercially-available treatment planning system can be used to produce a single arc prostate plan. Materials: Using Pinnacle 8.0h, 15 equally spaced beams were added to the CT scan of a patient previously treated for prostate cancer using IMRT. Direct machine parameter optimization (DMPO) was used to produce a plan consisting of 2 control points per beam. These control points were then externally sequenced into an arc of 30 equally spaced beams each with a single control point. The sequencing process took into account the linac delivery constraints (leaf and jaw speeds, gantry motion and dose rate) in order to maximize delivery efficiency. After re-optimisation in Pinnacle, interpolated beams were added externally to more accurately model the arc delivery of the linear accelerator. This ’step and shoot’ plan was then converted into a VMAT plan for delivery by an Elekta Synergy linac. Dosimetric verification was performed using film and an in-house phantom. Results: The VMAT plan produced was of comparable quality to a clinical IMRT plan consisting of 5 beams and approximately 40 control points. The generated VMAT arc file delivered successfully on an Elekta Synergy linear accelerator and is consistent over multiple deliveries. A 3%/3mm transverse film gamma analysis gave >95% of pixels with Γ<1 within the 50% isodose line. Conclusions: A commercially available treatment planning system has been used to produce a single arc VMAT plan with a dose distribution equivalent to a clinical IMRT plan. Successful delivery and verification of the plan has been demonstrated. Repeatability measurements have indicated that the solution is robust. 531 poster (Physics Track) THE EFFECT OF CONTROL POINT SPACING ON VMAT TREATMENTS OF PROSTATE AND PELVIC NODES J. Bedford1 , A. Warrington1 1 T HE I NSTITUTE OF C ANCER R ESEARCH AND T HE R OYAL M ARSDEN NHS F OUNDATION T RUST, Joint Department of Physics, Sutton, United Kingdom
Purpose: The optimum spacing of control points in VMAT planning and delivery is not yet fully understood. This retrospective study aims to evaluate plan quality and accuracy of delivery as a function of control point spacing. Materials: Plans were created using Pinnacle3 v8.9 (Philips Radiation Oncology Systems, Madison, WI) for treatment of prostate and pelvic nodes. Prescription dose was 60 Gy in 20 fractions to the prostate and base of seminal vesicles, and 47 Gy in 20 fractions to the pelvic lymph nodes. The treatment plan consisted of a single clockwise gantry arc from 181 deg to 179 deg, with control points spaced at 6 deg, 4 deg or 3 deg. The same objectives and constraints were specified in each case. Maximum delivery time was specified to be 360s and maximum leaf motion was specified as 0.66cm per degree.
The plans were then delivered using a Synergy accelerator with RTDesktop v7.01 and Mosaiq v1.6 (Elekta Ltd, Crawley, UK) and verified using a Delta4 phantom (Scandidos, Uppsala, Sweden). The total delivery time and percentage of detectors measuring within 3% and 3 mm of the planned dose were recorded. Results: Decreasing the control point spacing from 6 deg to 3 deg resulted in the volume of the primary PTV covered by 95% dose increasing from 96% to 97%, and the volume of the nodal PTV covered by 95% dose increasing from 95% to 97%. Meanwhile, the volume of rectum irradiated to 50 Gy remained constant at 40% and the volume of bladder irradiated to 50 Gy decreased from 54% to 51%. Volume of bowel irradiated to 40 Gy remained constant at 28%. Delivery time was 180s for 6 deg control point spacing, 180s for 4 deg spacing and 210s for 3 deg spacing. A gamma criterion of 3% and 3 mm was satisfied by 93.5% of Delta4 detectors for 6 deg spacing, 91.3% for 4 deg spacing and 88.7% for 3 deg spacing. Conclusions: Decreasing the control point spacing from 6 deg to 3 deg produces a small increase in plan quality for this treatment site. Meanwhile, the time for delivery increases slightly and agreement of the planned dose and measured dose drops. Overall, control point spacing of 4-6 deg is concluded to be optimal for this treatment site. We are grateful to Elekta Ltd and Philips Radiation Oncology Systems for their collaboration in this project. 532 poster (Physics Track) TREATMENT OF ANAL CANAL CANCER. A PLANNING STUDY TO COMPARE BONE MARROW SPARING WITH RAPIDARC OR SLIDING WINDOW IMRT. J. B. Dubois1 , S. Vieillot1 , C. Llacer-Moscardo1 , C. Lemanski1 , S. Gourgou1 , D. Azria1 , P. Fenoglietto1 1 CRLC VAL D ’AURELLE - PAUL L AMARQUE, Montpellier, France
Purpose: Radiotherapy of pelvic disease is still a challenge considering the toxicity. IMRT provide a big improvement in organ at risk preservation but take time to be delivered. Rotational techniques open a new way by keeping a high plan quality and decreasing the time compare to conventional plans. Materials: Ten patients with anal canal carcinoma previously treated with IMRT were selected for this analysis. Using the treatment planning CT scan, three plans were generated for each patient: a fixed beam IMRT plan, single (RA1), and double (RA2) modulated arc therapy with the RapidArc technique. The treatment plan was designed to deliver in a single phase process with simultaneous integrated boost (SIB) a total dose of 59.4 Gy to the planning target volume based on gross disease (PTV2) in 1.8 Gy-daily fractions, 5 days a week. At the same time, 49.5 Gy were delivered to the PTV at risk for subclinical disease (PTV1) in 1.5 Gy-daily fractions.Dose-volume histograms (DVH) for the target volume and the organs at risk (bowel, bladder, iliac crests, femoral heads, genitalia/perineum, and healthy tissue) were compared for these techniques. Monitor units (MU) and delivery treatment time were also reported. Results: All plans achieved fulfilled objectives. Both IMRT and RA2 resulted in superior coverage of PTV than RA1 which was slightly inferior for conformity and homogeneity (p<0.05).Conformity index (CI95%) for the PTV2 was 1.15 ± 0.15 (RA2), 1.28 ± 0.22 (IMRT), and 1.79 ± 0.5 (RA1). Homogeneity (D5%-D 95%) for PTV2 was: 3.21 Gy ± 1.16 (RA2), 2.98 Gy ± 0.7 (IMRT), and 4.3 Gy ± 1.3 (RA1).IMRT and RapidArc showed to be similar in terms of organ at risk sparing. For bowel, the mean dose was reduced by 4 Gy with RA2 compared to IMRT. Similar trends were observed for bladder, femoral heads and genitalia. The DVH of bone marrow and healthy tissue resulted in comparable sparing for the low doses (V10 and V20). Mean MUs delivered for each fraction was significantly reduced by RapidArc compared to IMRT (p=0.0002) and therefore reduce treatment time by a factor of 6. Conclusions: For patients with anal canal cancer, RapidArc with 2 arcs was able to deliver equivalent treatment plan to IMRT in terms of PTV coverage and organ at risk sparing. It provided significant reductions in MU and treatment time per fraction. These improvements should reduce patient discomfort, allow more quality control, and may increase treatment acceptance compared to IMRT. 533 poster (Physics Track) VALIDATION OF A VOLUMETRIC MODULATED ARC THERAPY (VMAT) TREATMENT PLANNING APPROACH A. Perez-Rozos1 , M. Lobato Munoz1 , I. Jerez Sainz1 , J. A. Medina2 , J. L. Carrasco Rodríguez1 1 H OSPITAL V IRGEN DE LA V ICTORIA, Radiofísica y Protección Radiológica, Málaga, Spain 2 H OSPITAL V IRGEN DE LA V ICTORIA, Oncologia Radioterapica, Málaga, Spain
Purpose: A treatment planning approach for volumetric modulated arc therapy (VMAT), using a commercial treatment planning system with usual IMRT optimization options, is presented. Materials: VMAT delivery is approximated by 36 fixed gantry positions conventional fields simulating a single arc from 0 to 359. The dose from each field
IMRT: R OTATIONAL THERAPIES
The single arc VMAT plans were generally slightly inferior in terms of plan quality in relation to the clinical IMRT plans. However, the dual arc VMAT plans scored better for each patient at all parameters. The addition of a third arc did not improve the plan quality, but increased the treatment time to a duration longer then the clinical treatment. Conclusions: Dual arc VMAT plans are superior to a seven-beam step-andshoot IMRT plans, whereas the treatment time is potentially two minutes shorter. Therefore, dual arc VMAT irradiations might be the first choice of treatment in future radiotherapy for advanced head and neck cancers. 530 poster (Physics Track) THE DEVELOPMENT OF A VMAT PLANNING SOLUTION USING A COMMERCIALLY-AVAILABLE TREATMENT PLANNING SYSTEM C. Boylan1 , C. Golby1 , S. Smith1 , C. Rowbottom1 1
T HE C HRISTIE NHS F OUNDATION T RUST, North Western Medical Physics, Manchester, United Kingdom
Purpose: Volumetric Modulated Arc Therapy (VMAT) offers the potential of improved dose distributions and shorter treatment times, when compared to IMRT. A number of VMAT planning solutions for the Elekta platform are under development; the aim of this study was to investigate whether a current commercially-available treatment planning system can be used to produce a single arc prostate plan. Materials: Using Pinnacle 8.0h, 15 equally spaced beams were added to the CT scan of a patient previously treated for prostate cancer using IMRT. Direct machine parameter optimization (DMPO) was used to produce a plan consisting of 2 control points per beam. These control points were then externally sequenced into an arc of 30 equally spaced beams each with a single control point. The sequencing process took into account the linac delivery constraints (leaf and jaw speeds, gantry motion and dose rate) in order to maximize delivery efficiency. After re-optimisation in Pinnacle, interpolated beams were added externally to more accurately model the arc delivery of the linear accelerator. This ’step and shoot’ plan was then converted into a VMAT plan for delivery by an Elekta Synergy linac. Dosimetric verification was performed using film and an in-house phantom. Results: The VMAT plan produced was of comparable quality to a clinical IMRT plan consisting of 5 beams and approximately 40 control points. The generated VMAT arc file delivered successfully on an Elekta Synergy linear accelerator and is consistent over multiple deliveries. A 3%/3mm transverse film gamma analysis gave >95% of pixels with Γ<1 within the 50% isodose line. Conclusions: A commercially available treatment planning system has been used to produce a single arc VMAT plan with a dose distribution equivalent to a clinical IMRT plan. Successful delivery and verification of the plan has been demonstrated. Repeatability measurements have indicated that the solution is robust. 531 poster (Physics Track) THE EFFECT OF CONTROL POINT SPACING ON VMAT TREATMENTS OF PROSTATE AND PELVIC NODES J. Bedford1 , A. Warrington1 1 T HE I NSTITUTE OF C ANCER R ESEARCH AND T HE R OYAL M ARSDEN NHS F OUNDATION T RUST, Joint Department of Physics, Sutton, United Kingdom
Purpose: The optimum spacing of control points in VMAT planning and delivery is not yet fully understood. This retrospective study aims to evaluate plan quality and accuracy of delivery as a function of control point spacing. Materials: Plans were created using Pinnacle3 v8.9 (Philips Radiation Oncology Systems, Madison, WI) for treatment of prostate and pelvic nodes. Prescription dose was 60 Gy in 20 fractions to the prostate and base of seminal vesicles, and 47 Gy in 20 fractions to the pelvic lymph nodes. The treatment plan consisted of a single clockwise gantry arc from 181 deg to 179 deg, with control points spaced at 6 deg, 4 deg or 3 deg. The same objectives and constraints were specified in each case. Maximum delivery time was specified to be 360s and maximum leaf motion was specified as 0.66cm per degree.
The plans were then delivered using a Synergy accelerator with RTDesktop v7.01 and Mosaiq v1.6 (Elekta Ltd, Crawley, UK) and verified using a Delta4 phantom (Scandidos, Uppsala, Sweden). The total delivery time and percentage of detectors measuring within 3% and 3 mm of the planned dose were recorded. Results: Decreasing the control point spacing from 6 deg to 3 deg resulted in the volume of the primary PTV covered by 95% dose increasing from 96% to 97%, and the volume of the nodal PTV covered by 95% dose increasing from 95% to 97%. Meanwhile, the volume of rectum irradiated to 50 Gy remained constant at 40% and the volume of bladder irradiated to 50 Gy decreased from 54% to 51%. Volume of bowel irradiated to 40 Gy remained constant at 28%. Delivery time was 180s for 6 deg control point spacing, 180s for 4 deg spacing and 210s for 3 deg spacing. A gamma criterion of 3% and 3 mm was satisfied by 93.5% of Delta4 detectors for 6 deg spacing, 91.3% for 4 deg spacing and 88.7% for 3 deg spacing. Conclusions: Decreasing the control point spacing from 6 deg to 3 deg produces a small increase in plan quality for this treatment site. Meanwhile, the time for delivery increases slightly and agreement of the planned dose and measured dose drops. Overall, control point spacing of 4-6 deg is concluded to be optimal for this treatment site. We are grateful to Elekta Ltd and Philips Radiation Oncology Systems for their collaboration in this project. 532 poster (Physics Track) TREATMENT OF ANAL CANAL CANCER. A PLANNING STUDY TO COMPARE BONE MARROW SPARING WITH RAPIDARC OR SLIDING WINDOW IMRT. J. B. Dubois1 , S. Vieillot1 , C. Llacer-Moscardo1 , C. Lemanski1 , S. Gourgou1 , D. Azria1 , P. Fenoglietto1 1 CRLC VAL D ’AURELLE - PAUL L AMARQUE, Montpellier, France
Purpose: Radiotherapy of pelvic disease is still a challenge considering the toxicity. IMRT provide a big improvement in organ at risk preservation but take time to be delivered. Rotational techniques open a new way by keeping a high plan quality and decreasing the time compare to conventional plans. Materials: Ten patients with anal canal carcinoma previously treated with IMRT were selected for this analysis. Using the treatment planning CT scan, three plans were generated for each patient: a fixed beam IMRT plan, single (RA1), and double (RA2) modulated arc therapy with the RapidArc technique. The treatment plan was designed to deliver in a single phase process with simultaneous integrated boost (SIB) a total dose of 59.4 Gy to the planning target volume based on gross disease (PTV2) in 1.8 Gy-daily fractions, 5 days a week. At the same time, 49.5 Gy were delivered to the PTV at risk for subclinical disease (PTV1) in 1.5 Gy-daily fractions.Dose-volume histograms (DVH) for the target volume and the organs at risk (bowel, bladder, iliac crests, femoral heads, genitalia/perineum, and healthy tissue) were compared for these techniques. Monitor units (MU) and delivery treatment time were also reported. Results: All plans achieved fulfilled objectives. Both IMRT and RA2 resulted in superior coverage of PTV than RA1 which was slightly inferior for conformity and homogeneity (p<0.05).Conformity index (CI95%) for the PTV2 was 1.15 ± 0.15 (RA2), 1.28 ± 0.22 (IMRT), and 1.79 ± 0.5 (RA1). Homogeneity (D5%-D 95%) for PTV2 was: 3.21 Gy ± 1.16 (RA2), 2.98 Gy ± 0.7 (IMRT), and 4.3 Gy ± 1.3 (RA1).IMRT and RapidArc showed to be similar in terms of organ at risk sparing. For bowel, the mean dose was reduced by 4 Gy with RA2 compared to IMRT. Similar trends were observed for bladder, femoral heads and genitalia. The DVH of bone marrow and healthy tissue resulted in comparable sparing for the low doses (V10 and V20). Mean MUs delivered for each fraction was significantly reduced by RapidArc compared to IMRT (p=0.0002) and therefore reduce treatment time by a factor of 6. Conclusions: For patients with anal canal cancer, RapidArc with 2 arcs was able to deliver equivalent treatment plan to IMRT in terms of PTV coverage and organ at risk sparing. It provided significant reductions in MU and treatment time per fraction. These improvements should reduce patient discomfort, allow more quality control, and may increase treatment acceptance compared to IMRT. 533 poster (Physics Track) VALIDATION OF A VOLUMETRIC MODULATED ARC THERAPY (VMAT) TREATMENT PLANNING APPROACH A. Perez-Rozos1 , M. Lobato Munoz1 , I. Jerez Sainz1 , J. A. Medina2 , J. L. Carrasco Rodríguez1 1 H OSPITAL V IRGEN DE LA V ICTORIA, Radiofísica y Protección Radiológica, Málaga, Spain 2 H OSPITAL V IRGEN DE LA V ICTORIA, Oncologia Radioterapica, Málaga, Spain
Purpose: A treatment planning approach for volumetric modulated arc therapy (VMAT), using a commercial treatment planning system with usual IMRT optimization options, is presented. Materials: VMAT delivery is approximated by 36 fixed gantry positions conventional fields simulating a single arc from 0 to 359. The dose from each field