gms | German Medical Science

48th Meeting of the Particle Therapy Co-Operative Group

Particle Therapy Co-Operative Group (PTCOG)

28.09. - 03.10.2009, Heidelberg

Comparison of treatment planning of NSCLC with photon radiosurgery and particle radiotherapy using different lung fixation techniques

Meeting Abstract

  • M. Siebler - Department of Radiotherapy, University Hospital Giessen and Marburg, Marburg
  • U. Jelen - Department of Radiotherapy, University Hospital Giessen and Marburg, Marburg
  • F. Ammazzalorso - Department of Radiotherapy, University Hospital Giessen and Marburg, Marburg
  • B. Vogel - Department of Radiotherapy, University Hospital Giessen and Marburg, Marburg
  • F. Rose - Department of Radiotherapy, University Hospital Giessen and Marburg, Marburg
  • R. Engenhart-Cabillic - Department of Radiotherapy, University Hospital Giessen and Marburg, Marburg

PTCOG 48. Meeting of the Particle Therapy Co-Operative Group. Heidelberg, 28.09.-03.10.2009. Düsseldorf: German Medical Science GMS Publishing House; 2009. Doc09ptcog186

DOI: 10.3205/09ptcog186, URN: urn:nbn:de:0183-09ptcog1868

Published: September 24, 2009

© 2009 Siebler et al.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by-nc-nd/3.0/deed.en). You are free: to Share – to copy, distribute and transmit the work, provided the original author and source are credited.


Outline

Text

Background: Although surgical resection is a standard method for the treatment of early stage non-small-cell lung cancer (NSCLC), many patients, due to age, tumour inoperability or comorbidities, undergo non-surgical treatment. A commonly used alternative approach is hypofractionated stereotactic irradiation (1-5 fractions), e.g. stereotactic radiosurgery (ST-RS).

Such cases represent likely therapeutic indications for particle therapy, potentially benefiting from its high conformity and from the advantage of increased radiobiological efficacy (RBE) in the case of carbon ions. On the other hand the increased risk of target miss due to organ motion and deformation, must be specifically addressed in particle therapy.

The purpose of this planning study was 1) to acquire initial experience with particle therapy planning for lungs and 2) to compare the dosimetric quality of photon ST-RS and proton/carbon ion plans assuming different scenarios for lung fixation.

Material and methods: For 19 patients with stage I/II NSCLC or lung metastases (mean CTV volume 40 ml, 11 left and 8 right side), who underwent photon radiosurgery at our institution (planned with the Helax-TMS TPS), proton and carbon ion plans (absorbed dose only) were calculated, using the TRiP software.

For particle planning two different lung fixation methods, Active-Breathing-Control (ABC) and Jet-Ventilation (JET), were simulated at contouring level, using different CTV-to-PTV margins derived from the clinical experience. For ABC a 10 mm and for JET a 2 mm isotropic margin was used.

The quality of the plans was evaluated based on target coverage and OAR sparing.

Results: For all three modalities and both fixation techniques the average V95 for the CTV was more than 99.0%. Only for the JET technique, in cases with very small tumour volume, lower values were observed.

In terms of normal tissue sparing both modalities and both planning approaches were superior to photon therapy. The involvement of homolateral lung was significantly reduced (V30 = 20% for photons vs. 11% for 12C-ABC and 6% for 12C-JET). In the majority of the cases tumours were localized close to the thorax wall, resulting in hot spots for photon plans not present in ion plans. In centrally located tumours instead, significant reduction of the Dmax was observed (down to 30%), especially for plans with 2 mm margin (JET). Maximum doses to other OARs were reduced from around 20% for photon RS to 2–10% for particle therapy (no significant difference between ABC and JET) and V10 often down to zero (except for two patients with tumours located centrally in contact with trachea, aorta, left bronchus, heart and pulmonary artery).

Conclusion: Multiple treatment plans for proton and carbon ions were prepared with different beam setups and planning margin scenarios for a variety of NSCLC cases. Our analysis shows that particle therapy has the potential to reduce the extent of low dose regions (lung tissue) and almost completely spare other organs (heart, large blood vessels, bronchi, trachea, spine etc.). No statistically significant difference in terms of OAR sparing was observed between ABC and JET plans.

Further work will aim at assessment of the influence of the residual organ movement on the dosimetric quality of plans for various lung fixation scenarios. Figure 1 [Fig. 1].