Pinnacle Planning System Research Articles

Po-Thur Eve General-09: Dynamic evaluation for the treatment outcome incorporating prostate organ motion

This paper is to calculate the cumulative dose considering internal organ motion and patient repositioning of prostate patient using the one fractional treatment plan method for a specific phantom and patients. In the multi‐fractional radiation treatment, it is desirable to consider the internal organ motion from fraction to fraction. The PTV positional variations can be measured and expressed as the fractional equivalent uniform dose (FEUD) deviation by randomly picking up the FEUD using Monte Carlo method in every fraction. The average EUD deviations for PTV with hundreds of simulations are 3.3% for phantom and 1.8% for 5 prostate patients. The changes of rectal volume and position are also simulated by shifting the geometric center of the rectum and changing the rectal radius to model the rectal deformation using Pinnacle3 planning system and FEUD for rectum are estimated. The prostate margin, together with the inter‐fraction variations in rectal position and shape, affects the delivered dose to the rectum. The effect of the dose fluctuations is larger for the normal tissues than the target, and the change of rectal position would cause more complication compared to the rectal volume change. The method provides a simple way to estimate the tumor control probability and normal tissue complication probability dynamically with considering internal organ motion and repositioning errors throughout the whole treatment course. It is possible to test a treatment plan against a range of possible patterns of organ motion with this dynamic evaluation for the treatment outcome.

TU-D-ValA-03: Continuous Intensity Map Optimization (CIMO): A Novel Leaf-Sequencing Algorithm

Purpose: In IMRT planning, leaf-sequencing algorithms are used to translate optimized intensity maps into deliverable aperture shapes. We have developed a novel approach to leaf sequencing called continuous intensity map optimization (CIMO). The CIMO algorithm can significantly reduce the number of segments required for IMRT delivery. A unique feature of the CIMO algorithm is that it operates directly on continuous intensity maps. Consequently, the intensity maps do not need to be divided into discrete levels. Method and Materials: CIMO uses a simulated annealing algorithm to optimize the aperture shapes and weights with a goal of minimizing the discrepancies between the optimized and sequenced fluence maps. We have benchmarked the performance of the CIMO sequencer against the algorithms in the Pinnacle3 and Eclipse treatment planning systems. Results: When the CIMO sequencer was applied to 10 IMRT plans from the Pinnacle3 planning system, the average number of segments was reduced from 133 to 62 (a 54% reduction). The average number of monitor units was reduced from 646 to 555 (a 14% reduction). The CIMO algorithm also provided a 36% reduction in the average root mean square errors between the optimal and sequenced fluence maps. Additionally, the CIMO sequenced plans provided more uniform PTV coverage with comparable sparing of critical structures. The average standard deviation of the PTV dose distribution decreased from 9.6 to 7.4 cGy. When the CIMO algorithm was applied to 5 IMRT patients from the Eclipse planning system, the average number of segments was reduced by 46% and the average number of monitor units was cut by 31%. Equivalent plan quality was observed. Conclusion: As compared with both commercial systems, the CIMO algorithm resulted in equivalent or improved plan quality while providing a significant reduction in the required number of segments and monitor units.

SU‐FF‐T‐07: A Comparison Between Intensity Modulated Arc Therapy (IMAT) and Tomotherapy

Purpose: Intensity Modulated Arc Therapy (IMAT) has been proposed as an alternative to helical tomotherapy. IMAT can be delivered on a conventional linear accelerator and uses overlapping arcs to deliver a modulated intensity pattern from each beam direction. In this study, IMAT treatment plans were developed for ten patients previously treated with helical tomotherapy. The goal was to determine if IMAT could match the dosimetric capabilities of tomotherapy. Method and Materials: The IMAT planning process begins with an IMRT optimization performed using the Pinnacle3 planning system. In Pinnacle3, beams are placed at 10° increments along each arc path. After the optimization, an arc‐sequencing algorithm is applied to the optimized fluence maps to create a deliverable IMAT plan. The treatment sites in this study included lung, prostate, pancreas, brain, and head‐and‐neck. The IMAT plans were created under the assumption that the dose rate can vary from one beam angle to the next in each IMAT arc. Results: For coplanar delivery, the plan comparisons reveal that IMAT can generally provide equivalent plan quality as compared with tomotherapy. An average of 5 arcs and 692 MUs were used for these cases. In some cases improved critical structure sparing was observed in the IMAT plans at the expense of target dose uniformity. For three cases, noncoplanar IMAT plans were developed. The results demonstrate that for select cases the ability to incorporate noncoplanar arcs serves as a distinct advantage for IMAT. For example, in one case IMAT reduced the brainstem mean dose from 1866 to 606 cGy and the mean dose to the optic nerve from 388 to 95 cGy. Conclusion: When only axial coplaner arcs are used, IMAT plan can achieve as conformal dose distributions as tomotherapy plan. The IMAT plan, however, can provide a much better sparing to critical structures with non‐coplaner arcs.

SU‐FF‐T‐435: Tongue and Groove Effect in Direct Aperture Optimization IMRT Plans

Purpose: Direct Aperture Optimization (DAO) is a promising new IMRT technique whereby the MLC leaves and relative weights of the apertures are simultaneously optimized. Due to the stochastic nature of the simulated annealing optimization algorithm, MLC leaves can have positions that are significantly different from their neighboring leaves. Opposed adjacent leaves with these positions can lead to a “ripple” in the dose distribution due to tongue‐and‐groove effect (TGE). In this work, we attempt to quantify the magnitude of the effect and commission the Pinnacle planning system to account for it. Method and Materials: To quantify TGE, we generated a two‐segment beam: one segment with every other leaf on one side extending well past the central axis and the other with every other opposed adjacent leaf extending well past the central axis. Jaws set to 20×20 bound both segments and both had equal monitor units. This beam was delivered to a flat phantom with a film placed at 10cm depth.Newer versions of Pinnacle (7.4 or greater) take into account TGE. This is modeled in the physics tool with a tongue‐and‐groove step parameter. We systematically changed this parameter and compared the resulting dose distributions to the film measurement.We imported DAO IMRT plans into the Pinnacle planning system and compared the dose distributions with and without TGE. These were also compared with verification measurements. Results: The film displayed a 23% variation from minimum to maximum dose. The Pinnacle step parameter of 0.3cm reproduced the variation. If TGE is not accounted for in the planning, an underestimation of the absolute dose is observed for DAO IMRT plans. The magnitude of the underestimation is dependent upon the aperture shapes. Conclusions: TGE affects the dose distribution for DAO plans. Limiting the distance adjacent leaves may travel can reduce the effect of TGE.

A quantitative study of IMRT delivery effects in commercial planning systems for the case of oesophagus and prostate tumours

This study focuses on understanding the impact of intensity-modulated radiotherapy (IMRT) delivery effects when applied to plans generated by commercial treatment-planning systems such as Pinnacle (ADAC Laboratories Inc.) and CadPlan/Helios (Varian Medical Systems). These commercial planning systems have had several version upgrades (with improvements in the optimization algorithm), but the IMRT delivery effects have not been incorporated into the optimization process. IMRT delivery effects include head-scatter fluence from IMRT fields, transmission through leaves and the effect of the rounded shape of the leaf ends. They are usually accounted for after optimization when leaf sequencing the "optimal" fluence profiles, to derive the delivered fluence profile. The study was divided into two main parts: (a) analysing the dose distribution within the planning-target volume (PTV), produced by each of the commercial treatment-planning systems, after the delivered fluence had been renormalized to deliver the correct dose to the PTV; and (b) studying the impact of the IMRT delivery technique on the surrounding critical organs such as the spinal cord, lungs, rectum, bladder etc. The study was performed for tumours of (i) the oesophagus and (ii) the prostate and pelvic nodes. An oesophagus case was planned with the Pinnacle planning system for IMRT delivery, via multiple-static fields (MSF) and compensators, using the Elekta SL25 with a multileaf collimator (MLC) component. A prostate and pelvic nodes IMRT plan was performed with the Cadplan/Helios system for a dynamic delivery (DMLC) using the Varian 120-leaf Millennium MLC. In these commercial planning systems, since IMRT delivery effects are not included into the optimization process, fluence renormalization is required such that the median delivered PTV dose equals the initial prescribed PTV dose. In preparing the optimum fluence profile for delivery, the PTV dose has been "smeared" by the IMRT delivery techniques. In the case of the oesophagus, the critical organ, spinal cord, received a greater dose than initially planned, due to the delivery effects. The increase in the spinal cord dose is of the order of 2-3 Gy. In the case of the prostate and pelvic nodes, the IMRT delivery effects led to an increase of approximately 2 Gy in the dose delivered to the secondary PTV, the pelvic nodes. In addition to this, the small bowel, rectum and bladder received an increased dose of the order of 2-3 Gy to 50% of their total volume. IMRT delivery techniques strongly influence the delivered dose distributions for the oesophagus and prostate/pelvic nodes tumour sites and these effects are not yet accounted for in the Pinnacle and the CadPlan/Helios planning systems. Currently, they must be taken into account during the optimization stage by altering the dose limits accepted during optimization so that the final (sequenced) dose is within the constraints.

Sci‐AM2 Sat ‐ 03: Anatomy‐based MLC field optimization for the treatment of gynecologic malignancies

To evaluate the use of a new inverse planning system with anatomy‐based field segmentation, as an alternative between “4‐field box” and beamlet‐based IMRT, to treat whole pelvis of women with resected gynecologic malignancies. A class solution has been elaborated with the assistance of an in‐house optimization tool named Ballista. This inverse planning system can generate anatomy‐based MLC fields and simultaneously optimize their orientation and weight. The selected geometry consists of 7 coplanar and 2 noncoplanar incidences. For 10 patients planned to receive 45Gy for resected endometrial or cervix neoplasia, target volume and organ at risk (bowel, region “at risk to find bowel” (B‐RAR), bladder, rectum, bone marrow) were delineated. Using the Pinnacle3 planning system, four plans were generated for each patient: conventional 4‐field, enlarged 4‐field (aperture shaped to PTV),“step‐and‐shoot” IMRT and Ballista plans. Dose‐volume histograms, number of segments and monitor units (MU) were analyzed. Statistical significance is based on Student's paired t‐test. The mean volume of B‐RAR receiving 45Gy was: 4‐field, 49.7±7.1%; enlarged 4‐field, 63.4±5.8%; IMRT, 26.4±3.1%; Ballista, 29.0±3.0%. No statistical difference was noted between the ability of IMRT and Ballista to spare bowel (p=0.14), while both plans were better than 4‐field (p<0.001). The mean number of segments for Ballista was 33.3±2.3 vs 128.6±2.6 for IMRT and the mean number of MU was 325.0±11.8 vs 731.5±25.0. Weight optimization, with anatomy‐based MLC fields, is a good alternative between manual planning and IMRT for the treatment of gynecologic malignancies. Clinical results of treatment tolerance will follow.

SU‐FF‐T‐62: Anatomy‐Based MLC Field Optimization for the Treatment of Gynecologic Malignancies

Purpose: To evaluate the use of a new inverse planning system with anatomy‐based field segmentation, as an alternative between “4‐field box” and beamlet‐based IMRT, to treat whole pelvis of women with resected gynecologic malignancies. Method and Materials: A solution has been elaborated with the assistance of an in‐house optimization tool named Ballista. This inverse planning system can generate anatomy‐based MLC fields and simultaneously optimize their orientation and weight. The selected geometry consists of 7 coplanar and 2 noncoplanar incidences. For 10 patients planned to receive 45 Gy for resected endometrial or cervix neoplasia, target volume and organ at risk (bowel, region “at risk to find bowel” (B RAR), bladder, rectum, bone marrow) were delineated. Using the Pinnacle3 planning system, four plans were generated for each patient: conventional 4‐field, enlarged 4‐field (aperture shaped to PTV), “step‐and‐shoot” IMRT and Ballista plans. Dose‐volume histograms, number of segments and monitor units (MU) were analyzed. Results: Planning target volume (PTV) coverage was similar for enlarged 4‐field, IMRT and Ballista plans, and follows the ICRU standard recommendations. Only 77.5 ± 1.9% (mean ± SEM) of PTV received the prescription dose if conventional plans were applied (p<0.001). The mean volume of B RAR receiving 45 Gy was: 4‐field, 49.7 ± 7.1%; enlarged 4‐field, 63.4 ± 5.8%; IMRT, 26.4 ± 3.1%; Ballista, 29.0 ± 3.0%. No statistical difference was noted between the ability of IMRT and Ballista to spare bowel (p=0.14), while Ballista plans were better than 4‐field (p<0.001). The mean number of segments for Ballista was 33.3 ± 2.3 vs 128.6 ± 2.6 for IMRT and the mean number of MU was 325.0 ± 11.8 vs 731.5 ± 25.0. Conclusion: Weight optimization, with anatomy‐based MLC fields, is a good alternative between manual planning and IMRT for the treatment of gynecologic malignancies. Clinical results of treatment tolerance will follow.

SU-FF-J-72: The Effect of MV Cone-Beam CT Cupping Artifacts On Dose Calculation Accuracy

Purpose: MV cone‐beam (CB) CTimaging can be used to position the patient prior to external‐beam radiotherapy. If calibrated, these images may also be used in dose calculations, opening the possibility to reconstruct the delivered dose or re‐optimize the treatment plan before delivery. This study investigates the effect of imaging artifacts on dosimetric accuracy. Method and Materials: Two water cylinders of 13 cm and 22.5 cm diameters were imaged using A) a MV CBCT system integrated with a Siemens accelerator and B) a conventional kV CTimager. Cupping trends observed in the MV CBCT were imposed on the kV CTimages to create artificial data with simulated artifacts. Using the Phillips Pinnacle planning system, a 6 MV 10 × 16 cm2 field was applied to 1) the original kV CT of the smaller cylinder and 2) the kV CT with simulated artifacts. Similarly, a 18 × 18 cm2 field was applied to the original and artificial kV CT of the larger cylinder. Results: For the smaller cylinder, the MV CBCTwater signal relative to air at the cylinder center differs from the radial and axial extremities by approximately 14% and 17% respectively. For the larger cylinder, the differences are 38% and 20% in radial and axial directions. The dose distributions for the artificial images show a systematic deviation which increases with depth. In the high‐dose, low‐gradient regions, the largest deviation for the smaller cylinder is 1% of the maximum delivered dose. For the larger cylinder, the largest deviation is 4%. Conclusion: Cupping artifacts in water phantoms produce dosimetric errors much smaller in magnitude than the cupping trend itself but as large as 4% for large phantoms. These results suggest that rough correction of MV CBCT artifacts may be sufficient for dosimetric accuracy. Conflict of Interest: Research supported by Siemens OCS.

Do differences in target volume definition in prostate cancer lead to clinically relevant differences in normal tissue toxicity?

Many studies have described the quantitated differences between clinicians in target volume definition in prostate cancer. However, few studies have looked at the clinical effects of this. We aimed to assess the relevance and sequelae of such differences. Five experienced radiation oncologists were given the clinical details of 5 patients with early-stage prostate cancer and asked to define the clinical target volume, consisting of the prostate and seminal vesicles (CTV1) and the prostate alone (CTV2), on specified planning CT scans of the pelvis. Planning target volumes (PTV1) were generated by automatic expansion of the CTV1 by a 1-cm margin. The PTV2 was defined as the CTV2. The rectum and bladder were defined by a single experienced clinician for each plan without knowledge of the involved clinician marking the CTVs. The Pinnacle planning system was used to generate the plans, using four-field conformal radiotherapy, to deliver 64 Gy in 32 fractions to the PTV1 followed by a boost of 10 Gy to the PTV2 (Medical Research Council RT01 trial protocol). Dose-volume histograms were generated for the whole bladder and rectum for each plan and the volume receiving a specific percentage of the dose (e.g., V(90)) calculated for 74 Gy, followed by estimates of normal tissue complication probabilities (NTCPs) for the bladder and rectum. Statistically significant differences were found in the CTV1 and CTV2 and, consequently, the PTV1 among the 5 clinicians (p < 0.0005). Most of the discrepancies occurred at the delineation of the prostatic apex and seminal vesicles, with the smallest variance noted at the rectum-prostate and bladder-prostate interfaces. No statistically significant differences were found among clinicians for the rectal V(90), V(85), V(80), V(70), or V(50) or for the bladder V(85), V(80), V(70), or V(50). A difference was noted among consultants for the bladder V(90) (p = 0.015), although no correlation was found between the bladder V(90) and the size of the outlined volumes. No statistically significant differences were found between the estimates of bladder (p = 0.1) and rectal (p = 0.09) NTCPs. The statistically significant difference in outlined volumes of the CTV1, CTV2, and PTV1 among the 5 clinicians is in keeping with the findings of previous studies. However, the interclinician variability did not result in clinically relevant outcomes with respect to the irradiated volume of rectum and bladder or NTCP. This may have been because the outlined areas in which interclinician differences were smallest (the rectal-prostate and prostate-bladder interfaces) are the areas that have the greatest effect on normal tissue toxicity. For the areas in which the interclinician correlation was lowest (the prostatic apex and distal seminal vesicles), the effects on normal tissue toxicity are smallest. The results of this study suggest that interclinician outlining differences in prostate cancer may have less clinical relevance than was previously thought.

Intensity-modulated radiotherapy versus conventional three-dimensional conformal radiotherapy for boost or salvage treatment of nasopharyngeal carcinoma

Purpose : To compare intensity-modulated radiotherapy (IMRT) and conventional three-dimensional conformal radiotherapy (3D-CRT) for the boost treatment of new-onset nasopharyngeal carcinoma (NPC) or the salvage treatment of locally recurrent NPC. Methods and Materials : Between January 14 and February 23, 2000, 5-field 3D-CRT treatment plans were generated for 14 consecutive NPC patients using the ADAC Pinnacle planning system in Chang Gung Memorial Hospital, Kaohsiung, Taiwan. The planning data of these patients were later transferred to Memorial Sloan-Kettering Cancer Center, where new IMRT plans, also using 5–7 radiation fields were created for each patient using an inverse treatment planning system. The IMRT and 3D-CRT plans were compared for all 14 patients. The relationship between the anatomic shapes and locations of targets and the results of different plans were studied. Results : Target doses were more homogeneous in IMRT plans. The average maximal brainstem dose (D 05, the dose received by 5% of the brainstem volume) decreased from 30.9% of the prescription dose with 3D-CRT to 15.3% and 14.7% with 5- and 7-field IMRT, respectively ( p = 0.004 and 0.003, respectively, compared with 3D-CRT, paired Student’s t test). Five anatomic factors were found that predicted greater benefits with IMRT. These factors were ( 1) vertical length of target >7 cm, ( 2) minimal distance between target and brainstem <0.1 cm, ( 3) maximal AP overlap of target and brainstem >0.6 cm, ( 4) maximal AP overlap of target and spinal cord >1 cm, and ( 5) vertical overlap of target and eyes >0 cm. For the 7 patients with at least 1 of these 5 anatomic factors, the benefits achieved by IMRT planning would have been greater than the benefits for the other 7 patients ( p = 0.005, Fisher’s exact test). Conclusion : For boost or salvage treatment of NPC, lower normal tissue doses and more homogeneous target doses were achieved with IMRT plans. For NPC patients with at least 1 of the 5 anatomic factors, IMRT is highly recommended.

39 oral The use of Monte Carlo generated accelerator data in the photon model of the Pinnacle planning system

39 oral The use of Monte Carlo generated accelerator data in the photon model of the Pinnacle planning system