Management of brain metastases by whole brain radiotherapy; IMRT versus conventional RT: early results

ABSTRACT

The conventional whole brain radiotherapy is usually associated with radiation induced toxicity as alopecia, hearing deficit and neurocogenitive problems. Any effort to decrease the treatment toxicity might result in compromised target coverage with conventional therapy, thus increasing the risk of local recurrence. Intensity-modulated radiotherapy [IMRT] is a more advanced form of three-dimensional conformal radiotherapy [3D-CRT]. This approach has been demonstrated to improve tumor coverage while decreasing the dose to critical structures in the head and neck and other sites. At present there is very little clinical or dosimetric data regarding the dose distribution and outcomes from IMRT in the treatment of metastatic brain disease. This initial study was to introduce and evaluate the WBRT-IMRT as a new technique for treatment of brain metastases and to reduce the incidence and severity of radiation morbidities. The study included thirteen, consecutive adult patients with multiple brain metastases who referred to the Radiation Oncology Department in the University of Alabama at Birmingham [UAB], Birmingham, AL; USA from October 2005 till December 2005. The entry criteria were, the patients' age was 65 years or less, with Karnofesky score 70 or more, their primary malignant tumor were controlled and no evidence of extracranial disease, [eg; RTOG class I] and no definite lesions by brain MRI in the frontal or temporal lobes. The number of metastases were more than three because the department protocol was treating three or less brain metastases by streotactic radiosurgery +/- WBRT. These patients randomized between two arms. Arm A included 15 patients were treated by conventional whole brain radiation therapy [C-WBRT]. Arm B included 15 patients were treated by WB-IMRT. The conventional WBRT was given by two opposing equally weighted lateral portals by using beam eye view and multi-leaf collimator [MLC] with skin flash to protect the eyes. For the WB-IMRT plans were done using several trials of beam numbers and arrangements to get the best and most acceptable plan. The parameters for optimization included the specified dose to the PTV, the dose limits for each of the critical structures, and the respective penalties for deviation from these criteria. The PTV dose was 100% +/- 5% at the isocenter and 100% of the prescribed dose to the >99% of the CTV. The lenses were restricted at <5 Gy and also to 50% of the volume of the other OARs at 25 Gy as upper constrains. The comparison of the two plans as regard the average relative median dose to both the target volumes and the organs at risk, table 4 showed that there were no significant statistical differences between the two plans except for the scalp dose in favor of the WB-IMRT [p=0.04] while the lenses dose was lower in the C-WBRT but did not reach a significant level [p=0.06]. The radiation induced toxicity were statistically insignificant between the two treatment groups except for the frequency and severity of the alopecia which it was significantly lower in the WB-IMRT versus the conventional treatment [p-value=0.006]. The treatment outcomes in both groups were statistically insignificant and at the end of follow up period of six months progression free and overall survival were statistically insignificant [p=0.653 and 0.862 respectively]. IMRT by five field arrangement is feasible for palliative management of multiple brain metastases. An image guided approach is necessary to spare the scalp and other critical structures and to treat a reduced -margin PTV. The treatment is well tolerated and appears clinically efficient. Patients lose much less, or not at all, hair with this technique. This could have a good impact on the quality of life