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Dosimetric impact of reduced nozzle-to-isocenter distance in intensity-modulated proton therapy of intracranial tumors in combined proton-carbon fixed-nozzle treatment facilities.

Jelen U, Bubula ME, Ammazzalorso F, Engenhart-Cabillic R, Weber U, Wittig A - Radiat Oncol (2013)

Bottom Line: The resulting plans were compared in terms of dose distributions, dose-volume histograms and selected dosimetric indexes.With comparable target coverage, statistically significant normal tissue sparing was achieved through the reduction of the distance between nozzle and treatment isocenter.A reduced distance between nozzle and treatment isocenter leads to steeper lateral dose gradients and significantly reduces the volume of OARs adjacent to the target, which receives low to intermediate doses.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Radiotherapy and Radiation Oncology, Philipps-University of Marburg, Marburg, Baldingerstrasse 35043, Germany. andrea.wittig@med.uni-marburg.de.

ABSTRACT

Background: In combined proton-carbon fixed-nozzle treatment facilities with raster scanning delivery, the scattering of proton pencil beams caused by nozzle elements and the relatively large nozzle-to-isocenter distance cause a beam broadening. This may pose limitations to the achievable dose conformity. One way to counteract this effect is by delivering the treatment in a position closer to the nozzle than the room isocenter. Purpose of this study was to assess the potential dosimetric benefit of such solution, in terms of dose conformity and normal tissue sparing, in intensity-modulated proton therapy (IMPT) of intracranial tumors.

Material and methods: For 12 patients with intracranial lesions, IMPT-plans were created at two treatment positions: nozzle-to-treatment-isocenter distance: 100 cm (room isocenter) and nozzle-to-treatment-isocenter distance: 60 cm. The resulting plans were compared in terms of dose distributions, dose-volume histograms and selected dosimetric indexes.

Results: With comparable target coverage, statistically significant normal tissue sparing was achieved through the reduction of the distance between nozzle and treatment isocenter. The decrease in mean dose (Dmean) was 12.5% to the whole brain, 16.2% to the brainstem, 9.7% and 15.4% to the temporal lobes, 10.0% and 12.9% to the hippocampi, 11.8% and 12.5% to the optic nerves and 0.2% to the chiasm. The volume receiving at least 10% of the prescribed dose (V10%) was reduced by more than 10% for most organs at risk (OARs). The maximum dose (Dnear-max) values to most OARs remained without significant difference.

Conclusion: A reduced distance between nozzle and treatment isocenter leads to steeper lateral dose gradients and significantly reduces the volume of OARs adjacent to the target, which receives low to intermediate doses. Technical solutions shifting the treatment isocenter closer to the nozzle should be considered in clinical situations, where critical OARs are adjacent to the beam channel and where the integral dose should be minimized.

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Dose distribution in a representative axial CT slice of a selected patient for the IMPT plans created using two distances between nozzle and treatment isocenter: a) 100 cm (dISO) and b) 60 cm (dISO-40). The reduced distance between the nozzle and patient leads to a sharper lateral dose fall-off, hence to improved target conformation.
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Figure 2: Dose distribution in a representative axial CT slice of a selected patient for the IMPT plans created using two distances between nozzle and treatment isocenter: a) 100 cm (dISO) and b) 60 cm (dISO-40). The reduced distance between the nozzle and patient leads to a sharper lateral dose fall-off, hence to improved target conformation.

Mentions: Figure 2 and Figure 3 illustrate in an exemplary case that sparing of normal tissues was more effective at the treatment position closer to the nozzle. Dose-volume comparisons for the whole brain and selected OARs for all 12 patients are shown in Table 3. In all cases, improved sparing of OARs was achieved at the treatment isocenter position closer to the nozzle (dISO-40). Statistically significant reduction of the integral dose and substantial sparing of the OARs in terms of Dmean, V2%, V10%, V60% and V80% were achieved in the whole patient cohort owing to the decreased pencil beam widths.


Dosimetric impact of reduced nozzle-to-isocenter distance in intensity-modulated proton therapy of intracranial tumors in combined proton-carbon fixed-nozzle treatment facilities.

Jelen U, Bubula ME, Ammazzalorso F, Engenhart-Cabillic R, Weber U, Wittig A - Radiat Oncol (2013)

Dose distribution in a representative axial CT slice of a selected patient for the IMPT plans created using two distances between nozzle and treatment isocenter: a) 100 cm (dISO) and b) 60 cm (dISO-40). The reduced distance between the nozzle and patient leads to a sharper lateral dose fall-off, hence to improved target conformation.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3852283&req=5

Figure 2: Dose distribution in a representative axial CT slice of a selected patient for the IMPT plans created using two distances between nozzle and treatment isocenter: a) 100 cm (dISO) and b) 60 cm (dISO-40). The reduced distance between the nozzle and patient leads to a sharper lateral dose fall-off, hence to improved target conformation.
Mentions: Figure 2 and Figure 3 illustrate in an exemplary case that sparing of normal tissues was more effective at the treatment position closer to the nozzle. Dose-volume comparisons for the whole brain and selected OARs for all 12 patients are shown in Table 3. In all cases, improved sparing of OARs was achieved at the treatment isocenter position closer to the nozzle (dISO-40). Statistically significant reduction of the integral dose and substantial sparing of the OARs in terms of Dmean, V2%, V10%, V60% and V80% were achieved in the whole patient cohort owing to the decreased pencil beam widths.

Bottom Line: The resulting plans were compared in terms of dose distributions, dose-volume histograms and selected dosimetric indexes.With comparable target coverage, statistically significant normal tissue sparing was achieved through the reduction of the distance between nozzle and treatment isocenter.A reduced distance between nozzle and treatment isocenter leads to steeper lateral dose gradients and significantly reduces the volume of OARs adjacent to the target, which receives low to intermediate doses.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Radiotherapy and Radiation Oncology, Philipps-University of Marburg, Marburg, Baldingerstrasse 35043, Germany. andrea.wittig@med.uni-marburg.de.

ABSTRACT

Background: In combined proton-carbon fixed-nozzle treatment facilities with raster scanning delivery, the scattering of proton pencil beams caused by nozzle elements and the relatively large nozzle-to-isocenter distance cause a beam broadening. This may pose limitations to the achievable dose conformity. One way to counteract this effect is by delivering the treatment in a position closer to the nozzle than the room isocenter. Purpose of this study was to assess the potential dosimetric benefit of such solution, in terms of dose conformity and normal tissue sparing, in intensity-modulated proton therapy (IMPT) of intracranial tumors.

Material and methods: For 12 patients with intracranial lesions, IMPT-plans were created at two treatment positions: nozzle-to-treatment-isocenter distance: 100 cm (room isocenter) and nozzle-to-treatment-isocenter distance: 60 cm. The resulting plans were compared in terms of dose distributions, dose-volume histograms and selected dosimetric indexes.

Results: With comparable target coverage, statistically significant normal tissue sparing was achieved through the reduction of the distance between nozzle and treatment isocenter. The decrease in mean dose (Dmean) was 12.5% to the whole brain, 16.2% to the brainstem, 9.7% and 15.4% to the temporal lobes, 10.0% and 12.9% to the hippocampi, 11.8% and 12.5% to the optic nerves and 0.2% to the chiasm. The volume receiving at least 10% of the prescribed dose (V10%) was reduced by more than 10% for most organs at risk (OARs). The maximum dose (Dnear-max) values to most OARs remained without significant difference.

Conclusion: A reduced distance between nozzle and treatment isocenter leads to steeper lateral dose gradients and significantly reduces the volume of OARs adjacent to the target, which receives low to intermediate doses. Technical solutions shifting the treatment isocenter closer to the nozzle should be considered in clinical situations, where critical OARs are adjacent to the beam channel and where the integral dose should be minimized.

Show MeSH
Related in: MedlinePlus