Compensator-based intensity-modulated radiation therapy for malignant pleural mesothelioma post extrapleural pneumonectomy
Friday, November 21st, 2008.
Journal of Applied Clinical Medical Physics. 2008 Oct 29;9(4):2799. [Link]
Javedan K, Stevens CW, Forster K.
Radiation Oncology,1 H. Lee Moffitt Cancer Center and Research Institute, Tampa, Florida, USA. khosrow.javedan@moffitt.org
Abstract
The present work investigated the potential of compensator-based intensity-modulated radiation therapy (CB-IMRT) as an alternative to multileaf collimator (MLC)-based intensity-modulated radiation therapy (IMRT) to treat malignant pleural mesothelioma (MPM) post extrapleural pneumonectomy. Treatment plans for 4 right-sided and 1 left-sided MPM post-surgery cases were generated using a commercial treatment planning system, XIO/CMS (Computerized Medical Systems, St. Louis, MO). We used a 7-gantry-angle arrangement with 6 MV beams to generate these plans. The maximum required field size was 30 x 40 cm. We evaluated IMRT plans with brass compensators (.Decimal, Sanford, FL) by examining isodose distributions, dose-volume histograms, metrics to quantify conformal plan quality, and homogeneity. Quality assurance was performed for one of the compensator plans. Conformal dose distributions were achieved with CB-IMRT for all 5 cases, the average planning target volume (PTV) coverage being 95.1% of the PTV volume receiving the full prescription dose. The average lung V20 (volume of lung receiving 20 Gy) was 1.8%, the mean lung dose was 6.7 Gy, and the average contralateral kidney V15 was 0.6%. The average liver dose V30 was 34.0% for the right-sided cases and 10% for the left-sided case. The average monitor units (MUs) per fraction were 980 MUs for the 45-Gy prescriptions (mean: 50 Gy) and 1083 MUs for the 50-Gy prescriptions (mean: 54 Gy). Post surgery, CB-IMRT for MPM is a feasible IMRT technique for treatment with a single isocenter. Compensator plans achieved dose objectives and were safely delivered on a Siemens Oncor machine (Siemens Medical Solutions, Malvern, PA). These plans showed acceptably conformal dose distributions as confirmed by multiple measurement techniques. Not all linear accelerators can deliver large-field MLC-based IMRT, but most can deliver a maximum conformal field of 40 x 40 cm. It is possible and reasonable to deliver IMRT with compensators for fields this size with most conventional linear accelerators.
Glossary
- therapy
- any of the measures taken to treat a disease. Unproven therapy is any therapy that has not been scientifically tested and approved. Use of an unproven therapy instead of standard (proven) therapy is called alternative therapy. Some alternative therapies have dangerous or even life-threatening side effects. For others, the main danger is that a patient may lose the opportunity to benefit from standard therapy. Complementary therapy, on the other hand, refers to therapies used in addition to standard therapy. Some complementary therapies may help relieve certain symptoms of cancer, relieve side effects of standard cancer therapy, or improve a patient's sense of well-being. The ACS recommends that patients considering use of any alternative or complementary therapy discuss this with their health care team.
- radiation therapy
- treatment with radiation to destroy cancer cells. This type of treatment may be used to reduce the size of a cancer before surgery, to destroy any remaining cancer cells after surgery, or, in some cases, as the main treatment.
- oncology
- (on-call-o-jee) the branch of medicine concerned with the diagnosis and treatment of cancer.
- cancer
- malignancy; a group of diseases typified by abnormal, generally out-of-control, cell growth.
- mesothelioma
- a tumor derived from mesothelial tissue, such as the peritoneum (lining the abdomen) or pleura (lining the lungs). More on mesothelioma.
- IMRT
- (intensity-modulated radiation therapy) an advanced mode of high-precision radiotherapy that utilizes computer-controlled x-ray accelerators to deliver thin beams of radiation of different strengths (beams of modulating intensity) directly to the tumor from many angles. Higher and more effective radiation doses can safely be delivered to tumors with fewer side effects as compared to conventional radiotherapy techniques. Even when doses are not increased, IMRT can potentially reduce treatment toxicity.
- extrapleural pneumonectomy
- (EPP) surgery to remove the pleura, diaphragm, pericardium, and entire lung involved with the tumor. You can view a web cast from Brigham and Women's Hospital in Boston of this procedure being done by Dr. David Sugarbaker: see the extrapleural pneumonectomy (EPP) web cast here.
