Search

Purpose: To investigate the optimal treatment plan for stereotactically-guided conformal radiotherapy (SCRT) of sellar and parasellar lesions, with respect to sparing normal brain tissue, in the context of routine treatment delivery, based on dose volume histogram analysis., Methods and Materials: Computed tomography (CT) data sets for 8 patients with sellar- and parasellar-based tumors (6 pituitary adenomas and 2 meningiomas) have been used in this study. Treatment plans were prepared for 3-coplanar and 3-, 4-, 6-, and 30-noncoplanar-field arrangements to obtain 95% isodose coverage of the planning target volume (PTV) for each plan. Conformal shaping was achieved by customized blocks generated with the beams eye view (BEV) facility. Dose volume histograms (DVH) were calculated for the normal brain (excluding the PTV), and comparisons made for normal tissue sparing for all treatment plans at > or =80%, > or =60%, and > or =40% of the prescribed dose., Results: The mean volume of normal brain receiving > or =80% and > or =60% of the prescribed dose decreased by 22.3% (range 14.8-35.1%, standard deviation sigma = 7.5%) and 47.6% (range 25.8-69.1%, sigma = 13.2%), respectively, with a 4-field noncoplanar technique when compared with a conventional 3-field coplanar technique. Adding 2 further fields, from 4-noncoplanar to 6-noncoplanar fields reduced the mean normal brain volume receiving > or =80% of the prescribed dose by a further 4.1% (range -6.5-11.8%, sigma = 6.4%), and the volume receiving > or =60% by 3.3% (range -5.5-12.2%, sigma = 5.4%), neither of which were statistically significant. Each case must be considered individually however, as a wide range is seen in the volume spared when increasing the number of fields from 4 to 6. Comparing the 4- and 6-field noncoplanar techniques to a 30-field conformal field approach (simulating a dynamic arc plan) revealed near-equivalent normal tissue sparing., Conclusion: Four to six widely spaced, fixed-conformal fields provide the optimum class solution for the treatment of sellar and parasellar lesions, both in terms of normal brain tissue sparing and providing a relatively straightforward patient setup. Increasing the number of fields did not result in further significant sparing, with no clear benefit from techniques approaching dynamic conformal radiotherapy in the cases examined.

Stereotactically-guided conformal radiotherapy is a practical technique for irradiating irregular lesions in the brain. The shaping of the conformal fields may be achieved using lead alloy blocks, a conventional multi-leaf collimator (MLC) or a mini/micro-MLC. Although the former gives more precise shaping, it is labour intensive. The latter methods are more practical as both mould room and treatment room times are reduced, but the shaping is limited by the finite leaf-width. This study compares treatment plans, in terms of normal tissue doses and tumour coverage, for fields shaped using conformal blocks and a conventional MLC in two series of geometrical shapes and nine patient tumours. For the range of tumour sizes considered (volumes 14-264 cm3, minimum dimension 30 mm, maximum 102 mm), the MLC treats, on average, 14% (range 3-34%) and 17% (range 0-36%) more normal brain tissue than conformal blocks to >50% and >80% of the prescription dose, respectively. The large variability is due to strong dependence on tumour shape and the presence of partial leaf-widths in the MLC fit. It is therefore important to consider both of these effects when deciding whether the MLC is appropriate for a particular target volume.

Percutaneous nephrostomy can be used to resect transitional cell carcinoma (TCC) from the renal pelvis, to avoid nephrectomy in selected patients. This procedure carries a potential risk of tumour seeding along the nephrostomy track, which it is our policy to irradiate prophylactically. A total of 25 procedures on 23 patients have been carried out since 1982. The 18 males and five females had a median age of 64 years (range 46-81) at the time of treatment. Of the ten patients with only one functioning kidney, nine had undergone contralateral nephroureterectomy, seven for TCC, one for a non-functioning kidney, and one for renal tuberculosis; one patient had received radical radiotherapy for an inoperable contralateral renal tumour. The other 13 patients had asked for a conservative treatment approach to be adopted. From 1982-1989, low dose rate 192Ir wire was used in 13 patients to deliver a median dose of 45 Gy (range 40-50) to the full length of the track at the surface of nephrostomy tube. Since 1989, we have used a high dose rate (HDR) 192Ir microSelectron to treat 12 patients with a single fraction of 10-12 Gy, including two who had undergone previously 192Ir wire track irradiation of the same kidney. One patient required a nephroureterectomy after developing a non-healing renal pelvis leak following combined modality treatment. Otherwise, no early or late radiation-related morbidity has been seen, and no nephrostomy track recurrences have occurred during a median follow-up of 5 years (range 1-9). The HDR microSelection has enabled us to deliver this treatment quickly and simply during the standard postoperative stay in hospital following percutaneous nephrostomy.