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

Proton radiotherapy in the Management of extended conjunctival malignancies

Meeting Abstract

  • W. Sauerwein - Strahlenklinik, Universitätsklinikum Essen, Essen, Germany
  • A. Wittig - Strahlenklinik, Universitätsklinikum Essen, Essen, Germany
  • H. Westekemper - Abteilung für Erkrankungen des vorderen Augenabschnitts, Universitätsklinikum Essen, Essen, Germany
  • J. Herault - Cyclotron Biomédical, Centre Antoine-Lacassagne, Nice, France
  • H. Mammar - Cyclotron Biomédical, Centre Antoine-Lacassagne, Nice, France
  • L. Brualla - Strahlenklinik, Universitätsklinikum Essen, Essen, Germany
  • K.-P. Steuhl - Abteilung für Erkrankungen des vorderen Augenabschnitts, Universitätsklinikum Essen, Essen, Germany
  • N. Bornfeld - Abteilung für Erkrankungen des hinteren Augenabschnitts, Universitätsklinikum Essen, Essen, Germany

PTCOG 48. Meeting of the Particle Therapy Co-Operative Group. Heidelberg, 28.09.-03.10.2009. Düsseldorf: German Medical Science GMS Publishing House; 2009. Doc09ptcog176

DOI: 10.3205/09ptcog176, URN: urn:nbn:de:0183-09ptcog1762

Published: September 24, 2009

© 2009 Sauerwein et al.
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Outline

Text

Malignancies of the conjunctiva are rare and extended cases are extremely difficult to treat. The target volume is highly complex and includes most often the conjunctiva at the eyeball, as well as at the lids, from the surface to a depth of approximately1.5 cm. The immediate neighborhood of highly radiosensitive structures, such as the eye lens, the lachrymal gland, Meibohm’s glands, etc., adds a further degree of complexity. Furthermore, the conjunctiva itself has to be considered as an organ at risk (OAR), as the probability of severe dry eye syndrome increases with the irradiated volume and with the dose. On one hand there are different tumor entities to be considered, which need to be treated by different doses. On the other hand, no systematic dose finding study has been performed.

In a joint collaboration between the department of radiotherapy at the University Hospital Essen (Germany) and the Centre Antoine-Lacassagne in Nice (France) a technique has been developed and improved over the years to irradiate complex target volumes at the conjunctiva by protons, based on technical principles as follows: clips are inserted on the eye for localization of the target volume and repositioning purpose, a bolus is set-up to give a homogeneous flat entrance for the proton beam collimated to the size of target volume, the beam passes through a semi-spherical compensator to adapt the range of the proton beam to the shape of the inner sclera and let the protons irradiate lids (if necessary), conjunctiva and sclera. The compensator is individually customized from a Perspex block by a computerized milling machine. It results a homogeneous dose distribution to all parts of the conjunctiva, which have to be irradiated.

Malignant melanomas (MM) and squamous cell carcinomas (SCC) were treated using the same dose concept: a volume where microscopic disease was expected received 31.1 Gy in 6 fractions, a smaller "boost" volume at high risk was irradiated with additional 14 Gy in 2 fractions (assuming an RBE of 1.157, the biological weighted dose DB would be 36 Gy and 16 Gy respectively). In the case of a recurrent rhabdomyosarcoma the entire conjunctiva was irradiated in 24 fractions with 43.2 Gy (DB=50 Gy).

The latter case is under control with only mild dry eye symptoms. 30% of MM and SCC had a recurrent tumor, only 1 was observed in the area of the boost. 30% of the melanoma patients died within 3 years after the treatment for distant metastases, none of the SCC. Dry eye symptoms were observed in 85%, they were considered to be mild in 45% and strong in 40%.

Proton irradiation is a valid alternative to exenteration for extended malignancies of the conjunctiva. A biological weighted dose DB of 52 Gy seems to be sufficient to control locally MM and SCC. Increasing the number of fractions may help to reduce the side effects.