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Variable dose interplay effects across radiosurgical apparatus in treating multiple brain metastases.

Ma L, Nichol A, Hossain S, Wang B, Petti P, Vellani R, Higby C, Ahmad S, Barani I, Shrieve DC, Larson DA, Sahgal A - Int J Comput Assist Radiol Surg (2014)

Bottom Line: All treatment plans were developed at individual centers, and the results were centrally analyzed.We found that dose-volume constraints were satisfied by each apparatus with some differences noted in certain structures such as the lens.Treatment times were shortest with TrueBeam FFF.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiation Oncology, University of California, San Francisco, 505 Parnassus Avenue, Room L-08, San Francisco, CA , 94143, USA, lijunma@radonc.ucsf.edu.

ABSTRACT

Purpose: Normal brain tissue doses have been shown to be strongly apparatus dependent for multi-target stereotactic radiosurgery. In this study, we investigated whether inter-target dose interplay effects across contemporary radiosurgical treatment platforms are responsible for such an observation.

Methods: For the study, subsets ([Formula: see text] and 12) of a total of 12 targets were planned at six institutions. Treatment platforms included the (1) Gamma Knife Perfexion (PFX), (2) CyberKnife, (3) Novalis linear accelerator equipped with a 3.0-mm multi-leaf collimator (MLC), and the (4) Varian Truebeam flattening-filter-free (FFF) linear accelerator also equipped with a 2.5 mm MLC. Identical dose-volume constraints for the targets and critical structures were applied for each apparatus. All treatment plans were developed at individual centers, and the results were centrally analyzed.

Results: We found that dose-volume constraints were satisfied by each apparatus with some differences noted in certain structures such as the lens. The peripheral normal brain tissue doses were lowest for the PFX and highest for TrueBeam FFF and CyberKnife treatment plans. Comparing the volumes of normal brain receiving 12 Gy, TrueBeam FFF, Novalis, and CyberKnife were 180-290 % higher than PFX. The mean volume of normal brain-per target receiving 4-Gy increased by approximately 3.0 cc per target for TrueBeam, 2.7 cc per target for CyberKnife, 2.0 cc per target for Novalis, and 0.82 cc per target for PFX. The beam-on time was shortest with the TrueBeam FFF (e.g., 6-9 min at a machine output rate of 1,200 MU/min) and longest for the PFX (e.g., 50-150 mins at a machine output rate of 350 cGy/min).

Conclusion: The volumes of normal brain receiving 4 and 12 Gy were higher, and increased more swiftly per target, for Linac-based SRS platforms than for PFX. Treatment times were shortest with TrueBeam FFF.

No MeSH data available.


Linear plot of average normal brain isodose volumes per target versus increasing number of targets () for the four SRS modalities ( Gamma Knife Perfexion,  CyberKnife,  Novalis,  flattening filter free Truebeam). Note the significantly lower slope gradient and y-intercept values for the GK as compared with other linac-based modalities
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Fig7: Linear plot of average normal brain isodose volumes per target versus increasing number of targets () for the four SRS modalities ( Gamma Knife Perfexion, CyberKnife, Novalis, flattening filter free Truebeam). Note the significantly lower slope gradient and y-intercept values for the GK as compared with other linac-based modalities

Mentions: Finally, dose interplay effects, defined as the additional dose delivered to the normal brain surrounding each target as a result of irradiating the other targets, were measured in this study by examining the average peripheral isodose volumes (such as the dose enclosed by the isodose levels at the 20–80 % of the prescribed dose) per target versus increasing number of targets. Note that such a dose interplay effect was contributed by the scattering as well as the direct-hit photon beams. For example, when planning a three-target SRS case, irradiation of the first target from a large number of beams (e.g., 100–200) inevitably produced a variable dose background to the second and to the third target. However, when accounting for such a dose background, dose delivered to the second or to the third target will in return affect the dose to the first target in a reciprocal manner. As the number of the targets increases, such a dose interplay effect was found to vary among different SRS platforms. The results are illustrated in Fig. 7. Both the 12-Gy and the 4-Gy isodose volumes were plotted with increasing number of targets in Fig. 7. A rapid linear increase in the 4-Gy isodose volume per target, indicating greater interplay effects, was observed for linac-based modalities as compared to the Gamma Knife PFX. The dip for the Truebeam FFF curve at was from averaging the results from the two different treatment planning strategies (e.g., averaging the results between the 2-arc technique and the 3-arc technique), in contrast to those of 3-, 6-, 9-target treatment plans where all FFF treatment plans were created with a 2-arc technique. Significantly higher increase in the 12-Gy volume per target was also noted for the linac-based modalities as compared to the PFX, where no dependence in the 12-Gy volume per target with increasing number of targets was observed. This suggests that interplay effects significantly increase the 12-Gy peripheral isodose volume for the linac-based modalities, but less so for the Gamma Knife PFX.Fig. 7


Variable dose interplay effects across radiosurgical apparatus in treating multiple brain metastases.

Ma L, Nichol A, Hossain S, Wang B, Petti P, Vellani R, Higby C, Ahmad S, Barani I, Shrieve DC, Larson DA, Sahgal A - Int J Comput Assist Radiol Surg (2014)

Linear plot of average normal brain isodose volumes per target versus increasing number of targets () for the four SRS modalities ( Gamma Knife Perfexion,  CyberKnife,  Novalis,  flattening filter free Truebeam). Note the significantly lower slope gradient and y-intercept values for the GK as compared with other linac-based modalities
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4215114&req=5

Fig7: Linear plot of average normal brain isodose volumes per target versus increasing number of targets () for the four SRS modalities ( Gamma Knife Perfexion, CyberKnife, Novalis, flattening filter free Truebeam). Note the significantly lower slope gradient and y-intercept values for the GK as compared with other linac-based modalities
Mentions: Finally, dose interplay effects, defined as the additional dose delivered to the normal brain surrounding each target as a result of irradiating the other targets, were measured in this study by examining the average peripheral isodose volumes (such as the dose enclosed by the isodose levels at the 20–80 % of the prescribed dose) per target versus increasing number of targets. Note that such a dose interplay effect was contributed by the scattering as well as the direct-hit photon beams. For example, when planning a three-target SRS case, irradiation of the first target from a large number of beams (e.g., 100–200) inevitably produced a variable dose background to the second and to the third target. However, when accounting for such a dose background, dose delivered to the second or to the third target will in return affect the dose to the first target in a reciprocal manner. As the number of the targets increases, such a dose interplay effect was found to vary among different SRS platforms. The results are illustrated in Fig. 7. Both the 12-Gy and the 4-Gy isodose volumes were plotted with increasing number of targets in Fig. 7. A rapid linear increase in the 4-Gy isodose volume per target, indicating greater interplay effects, was observed for linac-based modalities as compared to the Gamma Knife PFX. The dip for the Truebeam FFF curve at was from averaging the results from the two different treatment planning strategies (e.g., averaging the results between the 2-arc technique and the 3-arc technique), in contrast to those of 3-, 6-, 9-target treatment plans where all FFF treatment plans were created with a 2-arc technique. Significantly higher increase in the 12-Gy volume per target was also noted for the linac-based modalities as compared to the PFX, where no dependence in the 12-Gy volume per target with increasing number of targets was observed. This suggests that interplay effects significantly increase the 12-Gy peripheral isodose volume for the linac-based modalities, but less so for the Gamma Knife PFX.Fig. 7

Bottom Line: All treatment plans were developed at individual centers, and the results were centrally analyzed.We found that dose-volume constraints were satisfied by each apparatus with some differences noted in certain structures such as the lens.Treatment times were shortest with TrueBeam FFF.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiation Oncology, University of California, San Francisco, 505 Parnassus Avenue, Room L-08, San Francisco, CA , 94143, USA, lijunma@radonc.ucsf.edu.

ABSTRACT

Purpose: Normal brain tissue doses have been shown to be strongly apparatus dependent for multi-target stereotactic radiosurgery. In this study, we investigated whether inter-target dose interplay effects across contemporary radiosurgical treatment platforms are responsible for such an observation.

Methods: For the study, subsets ([Formula: see text] and 12) of a total of 12 targets were planned at six institutions. Treatment platforms included the (1) Gamma Knife Perfexion (PFX), (2) CyberKnife, (3) Novalis linear accelerator equipped with a 3.0-mm multi-leaf collimator (MLC), and the (4) Varian Truebeam flattening-filter-free (FFF) linear accelerator also equipped with a 2.5 mm MLC. Identical dose-volume constraints for the targets and critical structures were applied for each apparatus. All treatment plans were developed at individual centers, and the results were centrally analyzed.

Results: We found that dose-volume constraints were satisfied by each apparatus with some differences noted in certain structures such as the lens. The peripheral normal brain tissue doses were lowest for the PFX and highest for TrueBeam FFF and CyberKnife treatment plans. Comparing the volumes of normal brain receiving 12 Gy, TrueBeam FFF, Novalis, and CyberKnife were 180-290 % higher than PFX. The mean volume of normal brain-per target receiving 4-Gy increased by approximately 3.0 cc per target for TrueBeam, 2.7 cc per target for CyberKnife, 2.0 cc per target for Novalis, and 0.82 cc per target for PFX. The beam-on time was shortest with the TrueBeam FFF (e.g., 6-9 min at a machine output rate of 1,200 MU/min) and longest for the PFX (e.g., 50-150 mins at a machine output rate of 350 cGy/min).

Conclusion: The volumes of normal brain receiving 4 and 12 Gy were higher, and increased more swiftly per target, for Linac-based SRS platforms than for PFX. Treatment times were shortest with TrueBeam FFF.

No MeSH data available.