Comparative study of treatment dose plans after the refinement of Leksell Gamma Knife single-beam dose profiles.

We investigated the amplification of discrepancy when using multiple shots of the same collimator size helmet, by comparing dose plans in the Leksell GammaPlan employing the default single-beam dose profiles and the Monte Carlo generated single-beam profiles. Four collimator helmets were studied. The results show that the largest amplification of discrepancy with multiple shots was found with the 8 mm collimator because of the largest discrepancy of its single-beam dose profile. The amplification of discrepancy is significant when tumor volumes increase but insignificant when the tumor volumes are in an elongated shape. Using close shot overlapping strategy (i.e., more shots close packed together) shows no observable increase in the amplification of discrepancy. For the best quality of Leksell Gamma Knife radiosurgery, it is suggested that the single-beam dose profiles should be refined, especially the 8 mm collimator, to prevent error amplification when using multiple collimator shots.

Prolonged survival in a subgroup of patients with brain metastases treated by gamma knife surgery.

OBJECT: The authors analyzed the factors involved in determining prolonged survival (> or = 24 months) in patients with brain metastases treated by gamma knife surgery (GKS). METHODS: Between 1995 and 2003, a total of 116 patients underwent 167 GKS procedures for brain metastases. There was no special case selection. Smaller and larger lesions were treated with different protocols. The mean patient age was 56.9 years, the mean number of initial lesions was 3.15, and the mean lesion volume was 10.45 cm.3 The mean follow-up time was 9.2 months. The median patient survival was 8.68 months. One-, 2-, 3-, 4-, and 5-year actuarial survival rates were 31.8%, 19.8%, 14.6%, 7.7%, and 6.9%, respectively. Patient age, number of lesions at presentation, and lesion volume had no influence on patient survival. Twenty-three (19.8%) patients survived for 24 months or more. Certain factors were associated with increased survival time. These were stable primary disease (21 of 23 patients), a long latency between diagnosis of the primary tumor and the occurrence of brain metastases (mean 28.4 months, median 16 months), absence of third-organ involvement, and repeated local procedures. Ten patients underwent repeated GKS (mean 3.4 per patient). Seven patients required open surgery for local treatment failures (recurrence or radiation necrosis). Two patients had both. Fifteen patients underwent repeated procedures. CONCLUSIONS: Aggressive local therapy with GKS, repeated GKS, and GKS plus surgery can achieve increased survival in a subgroup of patients with stable primary disease, no third-organ involvement, and long primary-brain secondary intervals.

Dose distribution close to metal implants in Gamma Knife Radiosurgery: a Monte Carlo study.

Materials with high atomic numbers favor the occurrence of the photoelectric effect when they are irradiated with gamma rays. Therefore, the photoelectric effects of metal implants within the target regions in Gamma Knife Radiosurgery are worth studying. In the present work, Monte Carlo simulations using EGS4 were employed to investigate the resulting dose enhancements. A dose enhancement as high as 10% was observed close to a platinum implant along the x and y axes, while no significant dose enhancements were observed for silver, stainless steel 301, and titanium ones. A dose enhancement as high as 20% was observed close to the platinum implant along the z axis at the superior position of the metal-phantom interface and was 10% higher for other metal implants.

Role of pituitary radiosurgery for the management of intractable pain and potential future applications.

RATIONALE: Two or three decades ago, cancer pain was treated by surgical/chemical hypophysectomy. In one report, the control of central pain (thalamic pain syndrome) was also approached with chemical hypophysectomy. Although in most of the patients these treatments resulted in a decrease in severe pain, concomitantly severe adverse effects (panhypopituitarism, diabetes insipidus and visual dysfunction) occurred in most patients. This historical evidence prompted us to perform Gamma Knife surgery (GKS) for this kind of intractable severe pain using a high irradiation dose to the pituitary stalk/gland. In the majority of patients, marked pain relief was achieved, surprisingly without any of the complications mentioned above. MATERIALS AND METHODS: A prospective multicenter study was conducted to evaluate the efficacy and safety in patients treated in Prague, Hong Kong and Tokyo. Indications of this treatment were: (1) failure of other effective treatment approaches prior to GKS, (2) good general patient condition (Karnofsky performance status >40%), (3) response to morphine for pain control (cancer pain), and (4) no previous radiotherapy of brain metastases (GKS/conventional radiotherapy). Eight patients with severe cancer pain due to bone metastasis and 12 patients with post-stroke thalamic pain syndrome were treated with GKS. The target was the border between the pituitary stalk and gland. Maximum dose was 160 Gy for cancer pain and 140 Gy for central pain. Follow-up included 6 patients (>1 month) with cancer pain and 8 patients (> 6 months) with thalamic pain syndrome. RESULTS: All patients (6/6) with cancer pain experienced significant pain reduction, and 87.5% (7/8) of the patients with thalamic pain had initially significant pain reduction. In some patients, pain reduction was delayed for several hours. Pain relief was noted within 7 days (median 2 days). No recurrence was observed in the patients with cancer pain. However, in 71.4% (5/7) of the patients with thalamic pain syndrome, disease recurred during the 6-month follow-up. Up to now, other complications have not been observed. CONCLUSION: Our clinical study protocol is only preliminary. Further clinical results on the management of thalamic pain are required to develop this treatment protocol. However, efficacy and safety have been shown in all our cases. In our opinion, this treatment has a potential to control severe pain, and GKS will play an important role in the management of intractable pain.

Choice of phantom materials for dosimetry of Leksell Gamma Knife unit: a Monte Carlo study.

In calculations for the Leksell Gamma Knife, GammaPlan employs a tissue equivalent material without the presence of a skull bone, while dosimetry work is based on a polystyrene phantom. The compatibility of these dose distributions is uncertain. The Monte Carlo technique was employed to determine the radial dose distributions from a single 14 mm collimator helmet in 160 mm diam phantoms with different materials. The materials studied were polystyrene, perspex, water, and water with skull bone. Results showed no significant differences among the radial doses in different phantom materials for the 14 mm collimator helmet. The Monte Carlo simulation was repeated with the inclusion of all 201 sources. Again, no significant differences were observed.

Gamma knife surgery for cancer pain-pituitary gland-stalk ablation: a multicenter prospective protocol since 2002.

OBJECT: The authors have treated intractable pain, particularly cancer pain related to bone metastasis, with various protocols. Cancer pain has been treated by gamma knife radiosurgery (GKS), targeted to the pituitary gland-stalk, as an alternative new pain control method. The purpose of this study was to investigate a prospective multicenter protocol to prove the efficacy and the safety of this treatment. METHODS: Indications for patient inclusion in this treatment protocol were: 1) pain related to bone metastasis; 2) no other effective pain treatment options; 3) general condition rated as greater than 40 on the Kamofsky Performance Scale; 4) morphine effective for pain control; and 5) no previous treatment with radiation (GKS or conventional radiotherapy) for brain metastasis. The authors at one institution have treated two patients, who suffered from severe cancer pain related to bone metastasis, by using GKS. The target was the pituitary gland. The maximum dose was 160 Gy with one isocenter of an 8-mm collimator, keeping the radiation dose to the optic nerve less than 8 Gy. At another institution two patients were treated in the same way; an additional five patients were treated similarly with targeting of the pituitary gland with two isocenters of 4-mm collimator. In all nine cases, pain resolved without significant complication. Pain relief was observed within several days, and this effect was prolonged until the day that they died. At a follow up of 1 to 24 months, no recurrences and no hormonal dysfunction were observed. CONCLUSIONS: Despite insufficient experience, the efficacy and the safety of GKS for intractable pain were demonstrated in nine patients. This treatment has the potential to ameliorate cancer-related pain, and GKS will play a more important role in the treatment of intractable pain. More experience and additional refined study protocols are needed to evaluate which parameters are important, to determine what treatment strategy is the best, and to clarify the safest option for patients with intractable cancer pain.