Dose painting
Dose painting with IMPT, helical tomotherapy and IMXT: A dosimetric comparison

https://doi.org/10.1016/j.radonc.2007.11.003Get rights and content

Abstract

Purpose

A planning study is presented in order to compare the suitability of intensity modulated photon radiotherapy (IMXT), helical tomotherapy (HTT) and intensity modulated protontherapy (IMPT) for dose painting.

Methods

For three HNC patients, nine different treatment plans were generated. Firstly, a uniform dose escalation (uniDE) of 10% was applied to the FDG PET positive region with step-and-shoot IMXT, HTT and IMPT. Secondly, dose painting by numbers (DPBN) was performed based on dose escalation maps determined from dynamic FMISO PET data for all three treatment modalities. Thirdly, the maximum PTV dose was not constrained while maximizing TCP, whereas the same organ at risk constraints as used for conventional IMXT had to be fulfilled. The dose distributions in spinal cord and parotids were optimized with equivalent uniform dose (EUD) constraints, expressing the risk of late reactions.

Results

The target coverage obtained with IMPT and HTT was more conformal regarding the inhomogeneous prescriptions than with IMXT for both uniDE and DPBN. IMPT allowed significantly higher levels of sparing normal tissues. In addition, the study showed that using IMXT, HTT or IMPT theoretically allows dose escalations of up to 50% under late reaction iso-toxicity conditions.

Conclusion

The quality of dose painting treatment plans created for IMXT, HTT and IMPT is comparable. More accurate target coverage can be reached with HTT and IMPT, whereas IMPT allows to significantly reduce the dose to normal tissues.

Section snippets

Methods and materials

A treatment planning study was conducted on three HNC patients. Patient #1 (59 y, T2N3M0) and Patient #3 (48 y, T2N2cM0) had both oropharynx tumors, whereas Patient #2 (66 y, T4N2cM0) suffered from larynx cancer.

Results

In Fig. 1, the DPBN dose distributions for IMXT (A), HTT (B) and IMPT (C) are presented exemplarily for patient #2. The comparison of these three plans shows that with HTT, higher local DEs can be reached than with IMXT, whereas IMPT is able to deliver even steeper dose gradients. In this case the superimposed DE map demands a very focused spot of higher dose. Here, with IMXT a DE of 1.11 could be reached, whereas HTT and IMPT could escalate the dose by a factor of 1.23 and 1.26, respectively.

Discussion

The present study revealed that for the application of different DE strategies in HNC novel treatment techniques such as HTT and IMPT allow a better target coverage in the case of inhomogeneous dose prescriptions. Tomotherapy showed even slightly better coverage than IMPT. Furthermore, approximately equivalent levels of sparing OARs and unspecified normal tissues were obtained by HTT and IMXT. In contrast, IMPT has the potential to significantly reduce the dose to critical structures while

Conclusion

Even though only three patients were included into this planning study, all three treatment modalities IMPT, HTT and IMXT seem to be suitable for DP. Nevertheless, the observable differences in this study appear small in the light of the geometrical and biological uncertainties of such a treatment in practice. The main potential of IMPT lies in a significantly higher level of sparing distant parts of OARs. The dose to the PTV could theoretically be escalated by approximately 50% under

Acknowledgements

This project was financially supported by the German Research Foundation (DFG), Grant Nos. AL 877/1 and NU 33/8. The authors thank the Radiopharmacy Department, University Hospital Tübingen, for FMISO and FDG production, Dr. SM Eschmann for PET examinations and Dr. F Paulsen for patient recruitment.

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