Intensity modulation with photons for benign intracranial tumours: A planning comparison of volumetric single arc, helical arc and fixed gantry techniques

doi:10.1016/j.radonc.2008.07.021

Radiotherapy and Oncology

Volume 89, Issue 3, December 2008, Pages 254-262

https://doi.org/10.1016/j.radonc.2008.07.021 Get rights and content

Abstract

Background and purpose

The potential benefits and limitations of the new RapidArc treatment concept compared to Helical Tomotherapy and fixed gantry intensity modulation techniques have been assessed at treatment planning level on 12 patients presenting with ‘benign’ brain tumours.

Materials and methods

Plans for five acoustic neurinomas, five meningiomas and two pituitary adenomas were computed for an Helical Tomotherapy (HT) unit, for RapidArc delivery (RA) on a linac equipped with two types of MLC (RA_HD120 with the new High Definition MLC with 2.5 mm leaf width at isocentre and RA_M120 with the standard Millennium with 5 mm resolution) and for fixed beam IMRT with the High Definition MLC. Analysis was mostly performed on physical quantities derived from Dose–Volume Histograms (DVHs).

Results

Target coverage resulted basically equivalent among techniques. V_95% (in %) was higher than 99% for all techniques, minimum significant dose (D_99%) was 95.5 ± 1.4 for IMRT, 96.2 ± 1.4 and 97.0 ± 1.2 for the RA_HD120 and RA_M120 approaches and 96.8 ± 1.7 for HT, maximum significant dose (D_1%, in %) was 102.2 ± 0.8, 102.7 ± 0.5, 102.4 ± 0.5 and 103.0 ± 1.1, respectively, standard deviation (in %) was 1.4 ± 0.4, 1.3 ± 0.3, 1.1 ± 0.2 and 0.8 ± 0.3, respectively. Conformity Index (CI_95%) was 0.47 ± 0.12, 0.46 ± 0.12, 0.43 ± 0.11 and 0.38 ± 0.11, respectively. For organs at risk all techniques respected planning objectives. Concerning the healthy tissue: V_10Gy (in %) was 9.4 ± 5.5, 9.9 ± 6.1, 9.2 ± 6.1 and 12.1 ± 8.8, respectively. Integral dose measured on the healthy tissue was 7.5 ± 3.3, 9.7 ± 3.4, 8.7 ± 3.4, 10.4 ± 4.2 10³ Gy cm³, respectively.

Conclusions

For the class of tumours investigated in this report, HT and RA and IMRT proved to be adequate to properly treat patients. Further studies on more complex cases need to be investigated in order to assess the effectiveness of this new technique in a broader clinical perspective.

Section snippets

Materials and methods

Twelve patients with small “benign” brain tumours were randomly selected from the database of treated patients for comparative planning as described in [4]: five meningiomas, five acoustic neurinomas and two pituitary adenomas. Anatomical data were acquired on computed tomography (CT) with adjacent slices 3 mm thick. The mean volume for PTV was 4.22 cm³, median 2.37 cm³, minimum 0.49 cm³and maximum 14.32 cm³. Volumes of organs at risk (OAR: brain stem, chiasm, ipsi-lateral optic nerve and eye) were

Results

In Fig. 1, isodose distributions on axial and sagittal views are presented for all the techniques for a neurinoma and a meningioma case to provide a qualitative overview. Two medium-low isodoses are shown (30% and 60%) to illustrate also the differences present in healthy tissue irradiation among the techniques.

Fig. 2 shows, for an example case, the variation of Dose Rate and of Gantry Speed as a function of the Gantry Angular position during rotation. It can be seen, as intuitively apparent,

Discussion

Tumours of the base of skull are particularly complex to treat because of their proximity to organs at risk like brain stem, eyes, optic chiasm and optic nerves. In addition, ‘benign’ types like meningiomas, neurinomas or adenomas, leading to a long life expectancy for affected patients, require additional care in preserving structures at risk. Advanced solutions based on sophisticated photon delivery methods are becoming widely available, and have significant potential to benefit large numbers

Conclusion

For the class of tumours investigated in this report, coplanar modulated arc solutions as RapidArc or Helical Tomotherapy and non-coplanar fixed beam IMRT showed similar degrees of target coverage and sparing of organs at risk. Concerning conformity and sparing of healthy brain tissue, some differences were found to be statistically significant. Planning for the newly developed RapidArc technique on linacs showed promising results for this class of very small, benign indications, but further

Disclosure

Dr. L. Cozzi acts as Scientific Advisor to Varian Medical Systems managing the European Varian Science Circles and as Head of Research and Technological Development to Oncology Institute of Southern Switzerland, Bellinzona.

Acknowledgements

This study was conducted in strict cooperation with many persons at Varian Medical systems involved in the development of this novel technology. Among them we are particularly in debt for support and assistance to Martin Sabel and Yves Archambault for planning and to Jiri Bocanek for delivery issues.

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CNS treatment planningIntensity modulation with photons for benign intracranial tumours: A planning comparison of volumetric single arc, helical arc and fixed gantry techniques

Abstract

Background and purpose

Materials and methods

Results

Conclusions

Section snippets

Materials and methods

Results

Discussion

Conclusion

Disclosure

Acknowledgements

Int J Radiat Oncol Biol Phys

Radiother Oncol

Radiother Oncol

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Sem Rad Oncol

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Radiother Oncol

Int J Radiat Oncol Biol Phys

CNS treatment planning
Intensity modulation with photons for benign intracranial tumours: A planning comparison of volumetric single arc, helical arc and fixed gantry techniques