SMARTARC FOR HEAD AND NECK PATIENTS, HOW MANY ARCS ARE NEEDED?

IMRT: R OTATIONAL THERAPIES

526 poster (Physics Track) SIMULTANEOUS INTEGRATED BOOST RADIOTHERAPY FOR BILATERAL BREAST CARCINOMA WITH RAPIDARC OR IMRT G. Nicolini1 , A. Fogliata Cozzi1 , L. Cozzi1 , E. Vanetti de Palma1 , A. Clivio1 1 O NCOLOGY I NSTITUTE OF S OUTHERN S WITZERLAND, Bellinzona, Switzerland

Purpose: A study was performed comparing volumetric modulated arcs with RapidArc and fixed field IMRT on patients with synchornous bilateral breast carcinoma Materials: Plans for IMRT and RapidArc, were optimised for 5 patients prescribing 50Gy to the breast (2.0Gy/fraction) and 60Gy to the tumour bed (2.4Gy/fraction). Objectives for PTV were: Dosemin>95%, Dosemax<107%. Mean lung dose MLD<15Gy, V20Gy<22%; heart involvement was to be minimised. DVH were evaluated. The MU and delivery time measured treatment efficiency. Pre-treatment dosimety was performed using EPID dosimetry (GLAaS method) and a 2D array, the PTW729 scoring results with the Gamma Agreement Index (GAI). Results: Target coverage and homogeneity improved with RapidArc (V90% increased from 93.9±2.5% to 97.1±1.2%, D5-D95 reduced from 3.3±0.2Gy to 2.5±0.4Gy for PTVII-PTVI (p<0.05). Conformity index was lower for RA: 1.19±0.1 vs. 1.24±0.1 for IMRT, External Index reduced from 8.3±3.1% to 3.4±1.6% (p<0.05) with RA. MLD resulted inferior to 9 Gy for all cases, V20Gy was 9.5±1.5Gy for RapidArc (left lung) and 11.3±1.6Gy for IMRT, similar for right lungs. Mean dose to heart was 4.3±1.7 Gy for RapidArc and 6.1±2.1Gy for IMRT, V10Gy was 4.3±3.0% and 11.6±7.2% respectively. MU resulted 1422±283 for IMRT and 784±114 for RapidArc; the average measured treatment time was 11.6±1.7 minutes for IMRT and 3.0±0.1 for RapidArc. GAI resulted 99.1±1.5% and 98.8±1.3% for IMRT and RapidArc respectively with GLAaS and 99.5±1.3 and 97.0±3.2 with PTW729 (3% and 3mm). Conclusions: RapidArc treatments showed improvements in conformal avoidance with respect to conventional IMRT, delivery parameters confirmed its logistical advantages, pre-treatment dosimetry proved its reliability. 527 poster (Physics Track) SINGLE ARC VMAT OF H&N CANCER A. Bertelsen1 , C. R. Hansen2 , J. Johansen3 , C. Brink1 1 U NIVERSITY OF S OUTHERN D ENMARK, Faculty of Health Sciences, Odense, Denmark 2 O DENSE U NIVERSITY H OSPITAL, Laboratory of Radiation Physics 3 O DENSE U NIVERSITY H OSPITAL, Odense, Denmark 4 O DENSE U NIVERSITETS H OSPITAL, Laboratory of Radiation Physics, Odense, Denmark

S 195

IMRT and VMAT radiation treatment plans delivered on an Elekta Synergy accelerator produced clinically acceptable geometric dose precision. 528 poster (Physics Track) SINGLE RAPIDARC TM IN HEAD AND NECK CANCER. PAROTID GLANDS RESULTS COMPARE WITH IMRT. N. Ailleres1 , F. Rat1 , P. Boisselier1 , S. Simeon1 , D. Azria1 , J. B. Dubois1 , P. Fenoglietto1 1 CRLC VAL D ’AURELLE - PAUL L AMARQUE, Montpellier, France

Purpose: Treatment of Head and Neck (H&N) cancers with intensity modulated radiotherapy (IMRT) allows increased total dose to the targeted volume while preserving critical organs such as parotid glands. However, treatment time is a limiting factor for some patients unable to stay immobilized for a long time during the IMRT fraction. RapidarcTM (RArIMRT) is capable to shorten the duration of beam delivery to the minute with a complete rotation around the patient. Nevertheless, dosimetric quality of the treatment plan is still an unresolved question. Materials: Treatments from five patients treated in our institution were optimized using the first clinical version 8.5 of Eclipse that only allows one arc by treatment plan. We selected different H&N tumors to be as exhaustive as possible (oropharynx, nasopharynx, mobile tongue and base of tongue). A RapidarcTM plan was generated using the final constraints obtained with the IMRT optimization. Another one attempted to decrease these constraints on parotids glands. Plans were normalized to obtain 95% of the dose (D95%) to the boost volume Results: Coverage of the various PTV and the protection of organs at risk were similar in the following three conditions (i) IMRT "procedure A", (ii) RArIMRT with IMRT constraints "procedure B", (iii) RArIMRT with modified IMRT constraints "procedure C". Homogeneity was slightly impaired in procedure C but always less than 1%. Mean dose difference delivered to the ipsilateral parotid was 4.4 Gy (range, 2.6-9.5) in favour of C compared to A. Regarding the controlateral parotid, this difference was 3 Gy (range, 0.1-5) again in favour of C. Concerning D50, these differences were 6.6 Gy (range, 2.9-13.8) and 4.1 Gy (range, 0.1-5.1) in favour of C in both cases. Conclusions: Treatment of H&N with IMRT using RapidarcTM reduces treatment time and the number of monitor units. The dose delivery to both parotids was significantly decreased even with the use of only one arc. 529 poster (Physics Track) SMARTARC FOR HEAD AND NECK PATIENTS, HOW MANY ARCS ARE NEEDED? D. Schuring1 , G. Meijer1 , F. van Aarle1 , J. Cassee1 , T. Scheenstra1 , I. Schmeets1 C ATHARINA H OSPITAL, Eindhoven, Netherlands

1

Purpose: A few radiation treatment planning systems are currently able to plan volumetric modulated arc therapy (VMAT). The VMAT algorithm in Pinnacle3 TM is called SmartArc. The capability of SmartArc to generate complex treatment plans for the head and neck (H&N) region was tested. Materials: This retrospective planning study includes patients with oropharyngeal or hypopharyngeal cancer previously treated with IMRT by utilization of the Pinnacle3 TM treatment planning system and Elekta Synergy accelerators. Doses between 50Gy and 68Gy were prescribed to individual Planning Target Volumes (PTV). The patients were re-planned with VMAT using the SmartArc algorithm in Pinnacle3 TM 8.9c (research version). A constraint for the re-planning was to use only one single arc to create deliverable plans. The objectives were to achieve identical or better target coverage and sparing of the organs at risk (OAR) using VMAT compared to IMRT. The comparison was made by evaluating of 1) dose-volume histograms (DVHs) of PTVs and OARs, 2) monitor units, 3) treatment time, and 4) treatment accuracy as delivered on Elekta Synergy accelerators Results: Preliminary results based on 11 patients showed that single arc VMAT plans satisfied all the re-planning objectives. The average maximum dose to the spinal cord was 42.1±0.7Gy and 43.4±0.5Gy for the VMAT and IMRT plans, respectively. V26 of the parotic glands was 45±4% with VMAT and 48±5% with IMRT. SmartArc generated VMAT treatment plans with an average conformity index (V95%/Vtarget) of 1.56±0.04 improving the conformity index of 1.71±0.07 by IMRT. This significantly reduced the size of high dose volumes (volumes which received more than 15Gy) in the surrounding normal tissues. VMAT reduced the number of MUs by 10% from mean 503±20MU to 449+/-22MU using IMRT and VMAT, respectively. Delivering the VMAT plans on an Elekta Synergy accelerator the mean treatment time was 250s which was a 40 percent reduction compared to IMRT. Dose measurements of the VMAT treatments with a Delta4 phantom (Scandidos) showed that 99.1±0.1% of the detector points - when corrected for offset in output - satisfied a gamma criterion of 3mm and 3% of 2Gy compared to 99.7±0.1% for IMRT. Conclusions: SmartArc generated single arc VMAT plans with improved target coverage and sparing of OARs compared to IMRT. The conformity was increased by VMAT compared to IMRT reducing high dose volumes in normal tissues. The VMAT plans used fewer MUs compared to the IMRT plans and reduced the treatment time by approximately 40% compared to IMRT. Both

Purpose: IMRT treatment plans of patients with advanced head and neck tumours belong to the most complex treatment plans in current radiotherapy due the convex shape of the target volume and the vicinity of various organs at risk. From this point of view it is not trivial whether volumetric intensity modulated arc therapies (VMAT) will result in adequate plan quality, because within a single arc only one segment per gantry is delivered.Purpose of this study is to evaluate the plan quality of VMAT plans with 1, 2 and 3 arcs compared to the plan quality of conventional step-and-shoot IMRT technique for patients with advanced head and neck tumours. Materials: In this study, we used the planning data of eight oropharynx patients with bilateral lymph node involvement that were treated with a DMPOTM IMRT technique (Pinnacle 8.0, Philips Medical Systems, Madison, US). All clinical step-and-shoot plans were generated with seven coplanar equidistant 6-MV beams typically with 60 segments. For each patient VMAT plan was generated with 1, 2 and 3 simultaneous optimized arcs using SmartArcTM as implemented in Pinnacle 8.9 with exactly the same objectives as the clinical plan. The plan quality was evaluated based on the following scoring parameters: the EUDs of the CTV, parotid glands and spinal cord (EUDCTV, EUDleft par, EUDright par and EUDspinal cord) the dose homogeneity for that part of the boost and elective PTV that is 7 mm below the skin surface (SDboost and SDelec) the conformity index for both the boost and elective dose level (CIboost and CIelec); the ratio of the 95% isodose volume and the PTV within this 95% isodose volume the total cost, i.e. the internal Pinnacle scoring parameter the total number of MUs the treatment time Results: The values of the scoring parameters averaged over all patients are displayed below:

S 196

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