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A novel implementation of mARC treatment for non-dedicated planning systems using converted IMRT plans.

Dzierma Y, Nuesken F, Licht N, Ruebe C - Radiat Oncol (2013)

Bottom Line: For all plans, the treatment time was noticeably reduced by conversion to mARC.We present the feasibility test for converting IMRT step-and-shoot plans from the RTP-output of any treatment planning system (Philips Pinnacle and Prowess Panther, in our case) into mARC plans.The feasibility and dosimetric equivalence is demonstrated for the examples of a prostate and a head-and-neck patient.

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ABSTRACT

Background: The modulated arc (mARC) technique has recently been introduced by Siemens as an analogue to VMAT treatment. However, up to now only one certified treatment planning system supports mARC planning. We therefore present a conversion algorithm capable of converting IMRT plans created by any treatment planning system into mARC plans, with the hope of expanding the availability of mARC to a larger range of clinical users and researchers. As additional advantages, our implementation offers improved functionality for planning hybrid arcs and provides an equivalent step-and-shoot plan for each mARC plan, which can be used as a back-up concept in institutions where only one linac is equipped with mARC.

Methods: We present a feasibility study to outline a practical implementation of mARC plan conversion using Philips Pinnacle and Prowess Panther. We present examples for three different kinds of prostate and head-and-neck plans, for 6 MV and flattening-filter-free (FFF) 7 MV photon energies, which are dosimetrically verified.

Results: It is generally more difficult to create good quality IMRT plans in Pinnacle using a large number of beams and few segments. We present different ways of optimization as examples. By careful choosing the beam and segment arrangement and inversion objectives, we achieve plan qualities similar to our usual IMRT plans. The conversion of the plans to mARC format yields functional plans, which can be irradiated without incidences. Absolute dosimetric verification of both the step-and-shoot and mARC plans by point dose measurements showed deviations below 5% local dose, mARC plans deviated from step-and-shoot plans by no more than 1%. The agreement between GafChromic film measurements of planar dose before and after mARC conversion is excellent. The comparison of the 3D dose distribution measured by PTW Octavius 729 2D-Array with the step-and-shoot plans and with the TPS is well above the pass criteria of 90% of the points falling within 5% local dose and 3 mm distance to agreement. For all plans, the treatment time was noticeably reduced by conversion to mARC.

Conclusions: We present the feasibility test for converting IMRT step-and-shoot plans from the RTP-output of any treatment planning system (Philips Pinnacle and Prowess Panther, in our case) into mARC plans. The feasibility and dosimetric equivalence is demonstrated for the examples of a prostate and a head-and-neck patient.

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Example dose distributions of prostate treatment plan. A standard prostate plan (irradiated for the patient) is shown on top, the dose distributions of plan versions a/b and c (6 MV) in the middle panel, with dose volume histogram (lower panel). In the DVH, thick lines correspond to the standard IMRT plan, thin lines to prostate plan version a/b (no noteable difference between the two plans), and dashed lines to prostate plan version c.
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Figure 3: Example dose distributions of prostate treatment plan. A standard prostate plan (irradiated for the patient) is shown on top, the dose distributions of plan versions a/b and c (6 MV) in the middle panel, with dose volume histogram (lower panel). In the DVH, thick lines correspond to the standard IMRT plan, thin lines to prostate plan version a/b (no noteable difference between the two plans), and dashed lines to prostate plan version c.

Mentions: Creation of plans with very few segments per beam is generally complicated in Pinnacle, even more so when flattening-filter-free beams are used. For the prostate patient, decent quality plans could be achieved with little difficulty using IMRT with either 19 beams or 30 beams and 35 segments; in both cases the flat 6 MV plan gave better dose distribution, so we present these two plans as compared with the clinically radiated plan for the same patient (Figure 3). The splitting of the beams did not introduce great changes in the plans, in particular the very symmetrical and conformal prostate plans. Prostate plans version a and b are virtually identical with respect to DVH and quality measures, only few slices show a slightly different dose distribution in several voxels, which is negligible. We therefore present prostate plan versions a/b combined without distinguishing between the two. All prostate 6 MV plans are acceptable according to our in-house standard in that the PTV is covered by the 95% isodose, although coverage is slightly reduced and the maximum slightly higher (i.e. homogeneity is effectively worse) than for the treated plan. The dose to the organs at risk is similar to the original plan, with a decrease in dose to the bladder for the arc plans. Depending on whether PTV homogeneity or dose to the bladder is weighted higher, the decision would be either for the arc plans or for the originally treated plan. The FFF 7 MV plans were discarded because although satisfying all the criteria (PTV coverage and dose to organs at risk), they had higher dose gradients close to the rectum, which would endanger the rectum in the case of positioning uncertainties or intra-fraction motion.


A novel implementation of mARC treatment for non-dedicated planning systems using converted IMRT plans.

Dzierma Y, Nuesken F, Licht N, Ruebe C - Radiat Oncol (2013)

Example dose distributions of prostate treatment plan. A standard prostate plan (irradiated for the patient) is shown on top, the dose distributions of plan versions a/b and c (6 MV) in the middle panel, with dose volume histogram (lower panel). In the DVH, thick lines correspond to the standard IMRT plan, thin lines to prostate plan version a/b (no noteable difference between the two plans), and dashed lines to prostate plan version c.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3750816&req=5

Figure 3: Example dose distributions of prostate treatment plan. A standard prostate plan (irradiated for the patient) is shown on top, the dose distributions of plan versions a/b and c (6 MV) in the middle panel, with dose volume histogram (lower panel). In the DVH, thick lines correspond to the standard IMRT plan, thin lines to prostate plan version a/b (no noteable difference between the two plans), and dashed lines to prostate plan version c.
Mentions: Creation of plans with very few segments per beam is generally complicated in Pinnacle, even more so when flattening-filter-free beams are used. For the prostate patient, decent quality plans could be achieved with little difficulty using IMRT with either 19 beams or 30 beams and 35 segments; in both cases the flat 6 MV plan gave better dose distribution, so we present these two plans as compared with the clinically radiated plan for the same patient (Figure 3). The splitting of the beams did not introduce great changes in the plans, in particular the very symmetrical and conformal prostate plans. Prostate plans version a and b are virtually identical with respect to DVH and quality measures, only few slices show a slightly different dose distribution in several voxels, which is negligible. We therefore present prostate plan versions a/b combined without distinguishing between the two. All prostate 6 MV plans are acceptable according to our in-house standard in that the PTV is covered by the 95% isodose, although coverage is slightly reduced and the maximum slightly higher (i.e. homogeneity is effectively worse) than for the treated plan. The dose to the organs at risk is similar to the original plan, with a decrease in dose to the bladder for the arc plans. Depending on whether PTV homogeneity or dose to the bladder is weighted higher, the decision would be either for the arc plans or for the originally treated plan. The FFF 7 MV plans were discarded because although satisfying all the criteria (PTV coverage and dose to organs at risk), they had higher dose gradients close to the rectum, which would endanger the rectum in the case of positioning uncertainties or intra-fraction motion.

Bottom Line: For all plans, the treatment time was noticeably reduced by conversion to mARC.We present the feasibility test for converting IMRT step-and-shoot plans from the RTP-output of any treatment planning system (Philips Pinnacle and Prowess Panther, in our case) into mARC plans.The feasibility and dosimetric equivalence is demonstrated for the examples of a prostate and a head-and-neck patient.

View Article: PubMed Central - HTML - PubMed

ABSTRACT

Background: The modulated arc (mARC) technique has recently been introduced by Siemens as an analogue to VMAT treatment. However, up to now only one certified treatment planning system supports mARC planning. We therefore present a conversion algorithm capable of converting IMRT plans created by any treatment planning system into mARC plans, with the hope of expanding the availability of mARC to a larger range of clinical users and researchers. As additional advantages, our implementation offers improved functionality for planning hybrid arcs and provides an equivalent step-and-shoot plan for each mARC plan, which can be used as a back-up concept in institutions where only one linac is equipped with mARC.

Methods: We present a feasibility study to outline a practical implementation of mARC plan conversion using Philips Pinnacle and Prowess Panther. We present examples for three different kinds of prostate and head-and-neck plans, for 6 MV and flattening-filter-free (FFF) 7 MV photon energies, which are dosimetrically verified.

Results: It is generally more difficult to create good quality IMRT plans in Pinnacle using a large number of beams and few segments. We present different ways of optimization as examples. By careful choosing the beam and segment arrangement and inversion objectives, we achieve plan qualities similar to our usual IMRT plans. The conversion of the plans to mARC format yields functional plans, which can be irradiated without incidences. Absolute dosimetric verification of both the step-and-shoot and mARC plans by point dose measurements showed deviations below 5% local dose, mARC plans deviated from step-and-shoot plans by no more than 1%. The agreement between GafChromic film measurements of planar dose before and after mARC conversion is excellent. The comparison of the 3D dose distribution measured by PTW Octavius 729 2D-Array with the step-and-shoot plans and with the TPS is well above the pass criteria of 90% of the points falling within 5% local dose and 3 mm distance to agreement. For all plans, the treatment time was noticeably reduced by conversion to mARC.

Conclusions: We present the feasibility test for converting IMRT step-and-shoot plans from the RTP-output of any treatment planning system (Philips Pinnacle and Prowess Panther, in our case) into mARC plans. The feasibility and dosimetric equivalence is demonstrated for the examples of a prostate and a head-and-neck patient.

Show MeSH
Related in: MedlinePlus