Conformal rotation therapy with central axis beam block is a feasible alternative to intensity-modulated radiotherapy for chordomas of the cervical spine.

AIMS: Paraspinal tumours, such as chordoma, represent a treatment challenge for oncologists, requiring high dose to the target volume without exceeding the tolerance dose of the spinal cord. Intensity-modulated radiotherapy (IMRT) is helpful in achieving sharp dose gradients and conformation of dose to the target volume. We present a simpler technique--conformal rotation therapy with a central axis beam block (CRT + BB), which can provide similar dose distributions. MATERIALS AND METHODS: A patient with a cervical chordoma developed postoperative recurrence and was treated with high-dose palliative radiotherapy. Treatment was delivered using CRT + BB, with three fixed beams and three coplanar arcs. A dose of 62 Gy in 31 fractions was delivered to the 100% isodose, giving a maximum spinal cord dose of 49.6 Gy. The patient relapsed 2 years later, and was re-treated using the same technique to a dose of 57 Gy in 30 fractions. Estimates of spinal cord repair rates in primates were used to determine the tolerance dose of the spinal cord for re-treatment. The patient remained well for a further 25 months before developing local recurrence, which was treated with palliative chemotherapy. RESULTS: Re-treatment plans using CRT + BB and IMRT were compared. Dose-volume histograms show equivalence of dose to the spinal cord, although the IMRT plan delivered a slightly higher dose to tumour and lower dose to surrounding soft tissues. CONCLUSION: Treatment using CRT + BB requires careful planning and discussion with neurosurgeons before surgery. The normal curvature of the cervical spine must be eliminated if possible, and the patient must be immobilised with the neck horizontal. If these geometric constraints can be satisfied, then CRT + BB can be used as a safe and effective alternative treatment to IMRT for tumours at this site.

A radiotherapy technique to improve dose homogeneity around bone prostheses.

Purpose. Following limb conserving surgery for bone or soft tissue sarcoma, patients may require post-operative radiotherapy to minimise the risk of local recurrence. In such circumstances the metal prosthesis reduces the dose in its shadow by approximately 10% when using opposed fields. We describe a technique to boost the underdosed area to overcome this problem.Patients or subjects. Seven sequential patients presenting between 1995 and 2001 had their treatment individualised because they had metal prosthesis in the treatment volume.Methods. To improve the target dose homogeneity we used a custom-made keyhole cutout to boost the area in the shadow of the prosthesis. The degree of attenuation caused by the metal prosthesis was estimated and a boost dose calculated. Exit thermoluminescent dosimetry (TLD) was used to confirm the estimates made.Results and discussion. Variation between patients was seen, demonstrating the need for exit TLD to individualise the treatment plan. The use of a boost field provides a method to overcome under-dosage in the shadow of a metal prosthesis. It improves dose homogeneity throughout the target volume and ensures adequate dose intensity around the prosthesis, the site most at risk of local recurrence.

Total body irradiation using a modified standing technique: a single institution 7 year experience.

We describe a simple standing technique for delivering total body irradiation (TBI) using large horizontal fields, made possible by the off-centre installation of a non-dedicated treatment unit in a pre-existing bunker. Patients are treated using anterior and posterior fields with customized lung compensators. This technique enables the dose to the lung to be accurately calculated and modified to avoid overdose and to minimize the risk of pneumonitis. From February 1991 to December 1997, 94 patients with a variety of haematological malignancies were given fractionated TBI using this technique prior to allogenic or autologous bone marrow transplantation. Patients received a total dose of 14.4 Gy given in eight fractions over 4 days, with at least 6 h between fractions. The prescribed dose to the lungs was reduced to 12 Gy in eight fractions. The technique was well tolerated, took less than 10 min to set up and did not disrupt the daily routine use of the machine. Doses to all measured points on the trunk and head were within +/-6% of the prescribed dose. Doses to the lungs were within +/-5% of the prescribed dose. There were no early respiratory deaths in the 37 autologous transplant patients. There were 10 (17%) respiratory deaths in the 57 allogeneic transplant patients, 3 of confirmed infectious aetiology.