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Does electron and proton therapy reduce the risk of radiation induced cancer after spinal irradiation for childhood medulloblastoma? A comparative treatment planning study
Umeå University, Faculty of Medicine, Department of Radiation Sciences, Oncology.
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2005 (English)In: Acta Oncologica, ISSN 0284-186X, E-ISSN 1651-226X, Vol. 44, no 6, 554-562 p.Article in journal (Refereed) Published
Abstract [en]

The aim of this treatment planning comparison study was to explore different spinal irradiation techniques with respect to the risk of late side-effects, particularly radiation-induced cancer. The radiotherapy techniques compared were conventional photon therapy, intensity modulated x-ray therapy (IMXT), conventional electron therapy, intensity/energy modulated electron therapy (IMET) and proton therapy (IMPT).CT images for radiotherapy use from five children, median age 8 and diagnosed with medulloblastoma, were selected for this study. Target volumes and organs at risk were defined in 3-D. Treatment plans using conventional photon therapy, IMXT, conventional electron therapy, IMET and IMPT were set up. The probability of normal tissue complication (NTCP) and the risk of cancer induction were calculated using models with parameters-sets taken from published data for the general population; dose data were taken from dose volume histograms (DVH). Similar dose distributions in the targets were achieved with all techniques but the absorbed doses in the organs-at-risk varied significantly between the different techniques. The NTCP models based on available data predicted very low probabilities for side-effects in all cases. However, the effective mean doses outside the target volumes, and thus the predicted risk of cancer induction, varied significantly between the techniques. The highest lifetime risk of secondary cancers was estimated for IMXT (30%). The lowest risk was found with IMPT (4%). The risks associated with conventional photon therapy, electron therapy and IMET were 20%, 21% and 15%, respectively. This model study shows that spinal irradiation of young children with photon and electron techniques results in a substantial risk of radiation-induced secondary cancers. Multiple beam IMXT seems to be associated with a particularly high risk of secondary cancer induction. To minimise this risk, IMPT should be the treatment of choice. If proton therapy is not available, advanced electron therapy may provide a better alternative.

Place, publisher, year, edition, pages
2005. Vol. 44, no 6, 554-562 p.
URN: urn:nbn:se:umu:diva-14100DOI: 10.1080/02841860500218819PubMedID: 16165914OAI: diva2:153771
Available from: 2007-02-26 Created: 2007-02-26 Last updated: 2010-08-19Bibliographically approved
In thesis
1. Clinical application of intensity and energy modulated radiotherapy with photon and electron beams
Open this publication in new window or tab >>Clinical application of intensity and energy modulated radiotherapy with photon and electron beams
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In modern, advanced radiotherapy (e.g. intensity modulated photon radiotherapy, IMXT) the delivery time for each fraction becomes prolonged to 10-20 minutes compared with the conventional, commonly 2-5 minutes. The biological effect of this prolongation is not fully known.

The large number of beam directions in IMXT commonly leads to a large integral dose in the patient. Electrons would reduce the integral dose but are not suitable for treating deep-seated tumour, due to their limited penetration in tissues. By combining electron and photon beams, the dose distributions may be improved compared with either used alone. One obstacle for using electron beams in clinical routine is that there is no available treatment planning systems that optimise electron beam treatments in a similar way as for IMXT. Protons have an even more pronounced dose fall-off, larger penetration depth and less penumbra widening than electrons and are therefore more suitable for advanced radiotherapy. However, proton facilities optimised for advanced radiotherapy are not commonly available. In some instances electron beams may be an acceptable surrogate.

The first part of this study is an experimental in vitro study where the situation in a tumour during fractionated radiotherapy is simulated. The effect of the prolonged fraction time is compared with the predictions by radiobiological models. The second part is a treatment planning study to analyse the mixing of electron and photon beams for at complex target volume in comparison with IMXT. In the next step a research version of an electron beam optimiser was used for the improvement of treatment plans. The aim was to develop a method for translating crude energy and intensity matrices for optimised electrons into a deliverable treatment plan without destroying the dose distribution. In the final part, different methods of treating the spinal canal in medulloblastoma were explored in a treatment planning study that was evaluated with biological models for estimating risks for late radiation effects.

The effect on cell survival of prolonging fraction time at conventional doses/fraction is significant in an in vitro system. This effect is underestimated by biological models. Prolonging the fraction time will spare tissues with a fast DNA repair. Thus, there is a risk for sparing tumours. The mixed electron and photon beam technique has the potential to treat deep-seated tumours. Compared with IMXT the number of beams can be reduced and as a consequence, the time for each fraction could be kept shorter. The integral dose in the patient will also be lower. The mixed beam technique could potentially be further improved if automatic optimisation for electrons was available. The results suggest that optimisation and segmentation can be automated, and a deliverable treatment plan can be obtained with simple procedures without destroying the quality of the dose distribution. The integral dose in patients may lead to late radiation side effects. In childhood cancers the risk for development of radiation induced cancers is a reality and the integral dose outside the target volume should be minimised. Based on models for cancer induction, protons show the lowest risk while electrons have some benefit compared with different photon techniques. All methods are able to similarly well treat the target volume.

Place, publisher, year, edition, pages
Umeå: Strålningsvetenskaper, 2005. 42 p.
Umeå University medical dissertations, ISSN 0346-6612 ; 939
Oncology, Radiotherapy, IMXT, IMET, IMPT, proton beams, electron beams, treatment planning, cancer induction, side-effects, fraction time, intensity modulated radiotherapy, Onkologi
National Category
Cancer and Oncology
Research subject
urn:nbn:se:umu:diva-443 (URN)91-7305-793-2 (ISBN)
Public defence
2005-02-25, Sal 244, by 7, Norrlands universitetssjukhus, Umeå, 10:00 (English)
Available from: 2005-02-07 Created: 2005-02-07 Last updated: 2009-11-25Bibliographically approved

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