Evaluation of Elekta VMAT for Stereotactic Body Radiotherapy (SBRT ...

Proceedings of the 52nd Annual ASTRO Meeting

3411

Helical TomoTherapy Treatment Planning Utilizing Dynamic Jaws and Dynamic Couch for Cervical Cancer

J. Cates1, V. L. Rodriguez1, S. H. Endicott1, M. E. Michaletz-Lorenz1, S. Mutic1, P. W. Grigsby1, G. Olivera2, D. A. Low1, S. M. Goddu1 1

Washington University School of Medicine Department of Radiation Oncology, St. Louis, MO, 2TomoTherapy, Inc., Madison, WI

Purpose/Objective(s): Current helical tomotherapy (HT) treatments are limited to fixed jaw widths and constant couch speeds (FJCC) during delivery. With these restrictions, increased plan quality results in increased delivery time. The next generation HT delivery allows for dynamic jaw motion and dynamic couch speed, a treatment technique called Dynamic Jaw and Dynamic Couch (DJDC). This novel technique could potentially produce treatment plans (TPs) with significantly reduced treatment times that are of equal of greater quality than those produced by FJCC. The purpose of this study is to compare the quality of DJDC plans to FJCC plans for patients with cervical cancer. Total delivery times (TDTs) of the two techniques will be compared. Materials/Methods: In this study, ten clinical post-operative cervical or endometrial cancer patients, treated using FJCC technique on HT, were retrospectively planned on TomoTherapy’s research platform using DJDC technique. PTvs. and organs at risk (OARs) were contoured on CT simulations for each patient for treatment planning. The OARs of interest were the bladder, rectum, bowel, pelvic bones, vertebral column and femoral heads. The CT scans and contoured volumes used for the original FJCC plan were also used for the DJDC plans. Clinical treatment planning guidelines of our institution were followed. The optimization goals were to keep the OAR doses below their toxicity limits. Dose volume histograms of the FJCC and DJDC plans were evaluated and compared based on dose homogeneity in the PTV, OAR sparing, and average mean doses given to critical structures. Results: For the DJDC plans, on average the PTV minimum dose (D99%) was decreased by 0.29 ± 0.90 Gy, the PTV maximum dose (D1%) was increased by 1.47 ± 0.66 Gy, and the PTV mean dose was increased by 0.54 ± 0.54 Gy. The average Homogeneity Index (HI = (D1%-D99%)/DRx) of the PTV was increased by 0.03 ± 0.02 in the DJDC plans. In DJDC plans, mean dose to the bladder, bowel (for nine patients), and pelvic bones increased by 0.01 ± 2.18 Gy, 1.21 ± 2.39 Gy, and 2.39 ± 2.44 Gy, respectively; while mean dose to the rectum, left femoral head, and right femoral head decreased by 2.32 ± 2.29 Gy, 2.22 ± 3.19 Gy, and 2.29 ± 3.69 Gy, respectively. Dose sparing in DJDC plans was shown most notably in the bladder and rectum, where V45 was reduced by 4.72 ± 3.78% and 12.23 ± 6.51%, respectively. Average delivery times (DTs) for FJCC and DJDC techniques were 9.33 ± 1.1 minutes and 3.56 ± 0.42 minutes, respectively. Conclusions: While dosimetric accuracy of the DJDC technique was not validated, this treatment planning study shows that the DJDC technique can produce plans of comparable quality to and with significantly shorter treatment times than those of FJCC plans. Using DJDC, treatment delivery times were reduced on average by 62% from those of the FJCC plans. Author Disclosure: J. Cates, TomoTherapy, Inc., B. Research Grant; V.L. Rodriguez, TomoTherapy, Inc., B. Research Grant; S.H. Endicott, None; M.E. Michaletz-Lorenz, TomoTherapy, Inc., B. Research Grant; S. Mutic, None; P.W. Grigsby, None; G. Olivera, TomoTherapy, Inc., A. Employment; TomoTherapy, Inc., E. Ownership Interest; D.A. Low, None; S.M. Goddu, TomoTherapy, Inc., B. Research Grant.

3412

Prostate Brachytherapy using 20-gauge Needles: An Early Experience

1

R. Gutt , B. J. Moran2, T. A. Moran2, M. Braccioforte2 1

University of Chicago Hospitals and Clinics, Chicago, IL, 2Prostate Cancer Foundation of Chicago, Westmont, IL

Purpose/Objective(s): Prostate brachytherapy technique has evolved over the years to improve outcomes and reduce treatmentrelated toxicities. A 20-gauge (g) needle has been introduced to accommodate 125I isotopes. Technically, the 20g needle should present less mechanical trauma, minimize bleeding, minimize edema, and as a result, lower risk of urinary retention in comparison to 18g needles. The purpose of this study is to report an early experience with the 20g needle technique. Materials/Methods: From June to October 2009, 26 patients were treated at Chicago Prostate Center with low dose rate prostate brachytherapy as monotherapy, using preloaded 20g needles (Oncura, Inc, model 9011 ThinStrand). All patients had T1c-T2c disease, Gleason Score 6-7, with median pretreatment PSA 5.35 ng/mL. 16/26 (62%) patients had a pretreatment AUA score #7 (range, 2-19). Baseline prostate volume was\40cc in 50%, 41-60cc in 31%, and .60cc in 19% (range, 22.0-76.6 cc). The prescription dose was 144 Gy, with a median of 20 needles and 79 seeds per implant. Given increased flexibility of 20g needles, compared to18g needles, there were some modifications in brachytherapy technique. These included placement of the brachytherapy template directly against the perineum and stabilization of the needle with the contralateral hand while advancing along the z-axis to prevent needle bowing. Data was recorded on acute urinary toxicity, perineal pain, perineal bruising, day 0 dosimetric outcomes, and treatment time. Results: Only one patient (3.84%) required Foley catheterization postimplant secondary to acute urinary retention. This patient required the catheter for three weeks and now reports no trouble voiding. Our previously reported urinary retention rate using 18g needles is 7.5%. Day 0 dosimetry demonstrated median values of D90 147.3 Gy, V100 92.01%, and V150 46.55%. Less than 2cc of perineal bleeding was seen in all patients. There was no perineal pain or bruising reported. Despite difference in needle flexibility, requiring modifications in technique, implant time was similar to that of our experience with 18g needles, with median implant time of 17 minutes (range, 8-32 minutes). Conclusions: Results from our early experience demonstrate the feasibility of using 20g needles with favorable short-term morbidity and dosimetric measures. This is an example of a modification to current technique that could prove to be beneficial over time. Author Disclosure: R. Gutt, None; B.J. Moran, None; T.A. Moran, None; M. Braccioforte, None.

3413

Evaluation of Elekta VMAT for Stereotactic Body Radiotherapy (SBRT): Comparison with Helical TomoTherapy (HT), BrainLAB Dynamic Conformal Arc Therapy (DCAT), and Fixed Field Therapy

X. Qi1, A. Hu1, W. Dzingle2, K. Stuhr2, H. Rice1, Q. Diot1, F. Newman1 1

Univ. of Colorado Denver, Aurora, CO, 2Univ. of Colorado Hospital, Aurora, CO

Purpose/Objective(s): The objective of this study is to report our initial evaluation of SBRT using VMAT on plan quality, dose delivery efficiency and accuracy compared with other arc therapy modalities, including HT, DCAT and CMS XiO planned fixed field therapy.

S835

I. J. Radiation Oncology d Biology d Physics

S836

Volume 78, Number 3, Supplement, 2010

Materials/Methods: Ten SBRT cases were investigated retrospectively for various tumor sites, including lung, liver, spine, kidney and prostate with fraction doses ranging from 6 to 15 Gy. Single-arc (full-arc or partial arc) and/or two-arc VMAT plans were generated on CMS Monaco TPS (Version 2.03.01, CMS Inc., MO) using biologically based optimization with Monte Carlo dose calculation. HT plans were created on TomoTherapy Hi?ART planning station (Version 3.2.3.2, TomoTherapy Inc., WI) using a jaw size of 2.5 cm. DCAT plans were generated on BrainLAB radiotherapy treatment planning software (BrainSCAN, Version 5.31, Germany). Fixed field IMRT/conformal plans were developed on CMS XiO TPS (Version 4.4, CMS Inc., MO). Metrics used to evaluate the dosimetric plan quality include target coverage, heterogeneity index (HI), target mean/maximum/minimum doses, DVHs and patient mean dose. Evaluation of dose delivery efficiency and accuracy were performed using a cylindrical diode array detector system ArcCHECK (Sun Nuclear Corp., FL). Results: Both VMAT and HT are capable of providing more uniform target dose and better normal structure sparing compared to fixed field and DCAT plans. For lung SBRT, the PTV coverages are 95.9, 97 and 98.3% with HIs of 1.09, 1.08 and 1.13 respectively for the VMAT, HT and DCAT plans. For liver SBRT, the HI for HT plan is the lowest (1.04) compared to VMAT (1.06) and XiO (1.24). The target coverage of VMAT (99.6%) is slightly higher than the HT plan (97%). VMAT offers more efficient dose delivery than HT. Compared to HT treatment durations of 25, 17.9 and 7 min for the lung, liver and prostate cases, a reduction of 74%, 66% and 17% treatment times is measured for the VMAT plans. The estimated treatment time of DCAT for spine is reduced by 24.7% compared to VMAT plan, while for lung, liver and kidney cases, the treatment times of DCAT are comparable or shorter. The total MUs are 1594, 6100 and 857 for the VMAT, HT and DCAT plans for the lung SBRT; 2368, 5985 and 2921 MUs for prostate and 2864, 15360 and 1464 MUs for liver for the VMAT, HT and XiO plans respectively. Plan delivery accuracy for all the modalities was comparable with average passing rates greater than 95%. Conclusions: Single-arc VMAT improved target uniformity and normal tissue sparing compared to CMS XiO fixed field and BrainLAB DCAT plans for SBRT. In comparison to HT, VMAT demonstrates significantly reduced treatment time and fewer MUs to achieve comparable dosimetric plans. Author Disclosure: X. Qi, None; A. Hu, None; W. Dzingle, None; K. Stuhr, None; H. Rice, None; Q. Diot, None; F. Newman, None.

3414

A Validating Study of ABAS: An Atlas-based Auto-Segmentation Program for Delineation of Target Volumes in Breast and Anorectal Cancer

L. Anders, F. Stieler, K. Siebenlist, J. Schaefer, F. Wenz, F. Lohr Department of Radiation Oncology of the University Medical Center Mannheim, Medical Faculty Mannheim of the University of Heidelberg, Mannheim, Germany Purpose/Objective(s): Rising numbers of patients in the field of radiation therapy require an optimization of the efficiency and automatism of the work process. One approach is the computer-assisted segmentation with atlas-based segmentation programs (ABAS) of clinical target volumes (CTV) and organs at risk (OAR), which automatically generate an estimate of CTV and OAR. We tested and evaluated the quality of those delineated volumes in context of treatment planning for breast and anorectal cancer. Materials/Methods: The algorithm used (Electa Software, St. Louis, MO) is based on the principle that an atlas with defined CTV serves as a template case to delineate automatically target volumes of sample patient cases. Automatic delineation results are compared with CTV‘s of breast and anorectal cancer, which are contoured manually according to guidelines of the Radio Therapy Oncology Group (RTOG). Results are quantified by analyzing the Dice Similarity Index (DSC), the logit Dice transformation (logitDSC) and Percent Overlap (PO). Dice Indices . 0.84 and logDSC . 0.750 are defined to be acceptable. Furthermore this study introduces an additional feature of the software, Staple, which is designed to improve the delineation outcome. Results: ABAS produced good results for the CTV of the breast and the rectum. However, delineations of the inguinal lymphatic flow were dissatisfying. Average DSC for CTV of the breast were between 0.86 and 0.9056 (Range [0,1]), of the average logit(DSC) between 0.7944 and 0.9889 (Range [-inf,inf]) and of the average PO between 75.5% and 82.89%. For anorectal cancer average DSC lied in between 0.7917 and 0.8467, average logit(DSC) in between 0.6083 and 0.7667 and average PO in between 68% and 73.67%. Conclusions: Generally ABAS produced satisfactory and time-saving results for the clinical target volumes of breast and anorectal cancer. In addition the introduction of Staple succeeded in enhancing the contouring outcome. Small target volumes with inaccurate definition of boundary layers are yet to be delineated manually. Author Disclosure: L. Anders, None; F. Stieler, None; K. Siebenlist, None; J. Schaefer, None; F. Wenz, None; F. Lohr, None.

3415

A Study on Conventional IMRTand RapidArc Treatment Planning Techniques for Head and Neck Cancers

S. Kumar1,2, P. Sriram1, K. Saranya1, N. Bhuvaneswari1, N. Vivekanandan1 1

Cancer Institute, Chennai, India, 2Cancer Institute, Chennai, India

Purpose/Objective(s): To evaluate the performance of volumetric arc modulation with Rapid Arc against conventional IMRT for head and neck cancers. Materials/Methods: Five patients treated with IMRT for advanced tumors of naso-, oro-, hypopharynx were selected for the planning comparison study. PTV was delineated for two different dose levels and planning has been done by means of a simultaneously integrated boost technique. A total dose of 70 Gy has been delivered to the boost volume (PTVboost) and 57.7 Gy to the elective PTV (PTVelective) in 35 equal treatment fractions. PTVboost consisted of the gross tumor volume and lymph nodes containing visible macroscopic tumor or biopsy-proven positive lymph nodes whereas the PTVelective consisted of elective nodal regions. Planning has been done for IMRT using 9 fields and RapidArc with single arc, double arc. Beam has been equally placed for IMRT plans. Single arc RapidArc plan utilizes full 360 degree gantry rotation and double arc consists of 2 co-planar arcs of 360 degree in clockwise and counter clockwise direction. Collimator was rotated from 35 to 45 degree to cover entire tumor which