Proton Based Stereotactic Radiotherapy for Skull Base Patients: Dosimetric Comparison to 4 Modern Radiation Treatment Modalities

PURPOSE/OBJECTIVE(S)

Re-irradiation with ablative doses to a smaller target volume and strict critical structure constraint is a challenge for modern radiation planning and delivery systems. Several advanced radiation treatment techniques can be used for fractionated stereotactic ablative radiosurgery (FSRS) in select patients with unresectable recurrent head and neck tumors. In this study, in order to better understand the dosimetry advantage of each technique, we compare the stereotactic treatment plans of our new small spot size Hitachi proton treatment unit to those of CyberKnife stereotactic radiosurgery (CK), Gamma Knife radiosurgery (GK), volumetric modulated arc therapy (VMAT), and MR Linac radiotherapy (MRL).

MATERIALS/METHODS

Ten FSRS skull base patients treated at our institution using VMAT (n = 5) or GK (n = 5) techniques. Intensity-modulated proton therapy (IMPT) plans were created in Raystation using Monte Carlo dose calculation algorithm. VMAT, CK, GK and MRL plans were generated in RayStation, Accuray Precision, Leksell Gamma Plan, and Monaco treatment planning systems, separately. Planning goals were to achieve the best target coverage of prescribed dose without compromising the critical organs at risk dose volume constraints of the clinical treatment plans. Plans were compared based on percent CTV coverage, Paddick conformity index (PCI), gradient index (GI, V50/V100), dose homogeneity index (HI, (D2-D98)/D50), low dose bath volume (LDBV, ratio of total volume irradiated between 20% and 50% prescription dose and the target volume), beam-on-time (BOT), and mean/maximum doses to brainstems.

RESULTS

The median target volume was 15.5 cm3 (range 1.0 - 36.23 cm3). The prescription was 45 Gy in 5 fractions for VMAT patients, and 21 - 27 Gy in 3 fractions for GK patients. The comparison of the treatment plans of these 5 delivery modalities was shown in table. All techniques achieved comparable CTV coverage. GI was superior for GK plans and outstanding in CK and IMPT plans. IMPT plans were also outstanding in regard to BOT and PCI. Significantly improved HI, LDBV and brainstem mean doses were achieved in IMPT plans. For adjacent brainstem and other OARs, maximum doses were comparable among all techniques.

CONCLUSION

In these five advanced radiation therapy modalities, proton therapy SBRT showed dosimetric advantage over other modalities to spare nearby OARs without sacrifice of target coverage. Further studies are needed to utilize this clinical benefit and investigate plan robustness.

Effects of caffeinated coffee consumption on intraocular pressure, ocular perfusion pressure, and ocular pulse amplitude: a randomized controlled trial

PURPOSE

To examine the effects of caffeinated coffee consumption on intraocular pressure (IOP), ocular perfusion pressure (OPP), and ocular pulse amplitude (OPA) in those with or at risk for primary open-angle glaucoma (POAG).

METHODS

We conducted a prospective, double-masked, crossover, randomized controlled trial with 106 subjects: 22 with high tension POAG, 18 with normal tension POAG, 20 with ocular hypertension, 21 POAG suspects, and 25 healthy participants. Subjects ingested either 237 ml of caffeinated (182 mg caffeine) or decaffeinated (4 mg caffeine) coffee for the first visit and the alternate beverage for the second visit. Blood pressure (BP) and pascal dynamic contour tonometer measurements of IOP, OPA, and heart rate were measured before and at 60 and 90 min after coffee ingestion per visit. OPP was calculated from BP and IOP measurements. Results were analysed using paired t-tests. Multivariable models assessed determinants of IOP, OPP, and OPA changes.

RESULTS

There were no significant differences in baseline IOP, OPP, and OPA between the caffeinated and decaffeinated visits. After caffeinated as compared with decaffeinated coffee ingestion, mean mm Hg changes (± SD) in IOP, OPP, and OPA were as follows: 0.99 (± 1.52, P<0.0001), 1.57 (± 6.40, P=0.0129), and 0.23 (± 0.52, P<0.0001) at 60 min, respectively; and 1.06 (± 1.67, P<0.0001), 1.26 (± 6.23, P=0.0398), and 0.18 (± 0.52, P=0.0006) at 90 min, respectively. Regression analyses revealed sporadic and inconsistent associations with IOP, OPP, and OPA changes.

CONCLUSION

Consuming one cup of caffeinated coffee (182 mg caffeine) statistically increases, but likely does not clinically impact, IOP and OPP in those with or at risk for POAG.

Frequency and prognosis of delayed facial palsy after microvascular decompression for hemifacial spasm

BACKGROUND

Microvascular decompression (MVD) for hemifacial spasm (HFS) provides a long-term cure rate. Delayed facial palsy (DFP) is not an unusual complication, but it has only been sporadically described in the literature. The purpose of this report is to evaluate the incidence of delayed facial palsy after MVD and its clinical course and final results.

METHODS

From January, 1998 to April, 2004, 410 patients underwent microvascular decompression for hemifacial spasm at our Institute. During this time, 21 patients (5.4%) developed delayed facial weakness; eighteen of them were given steroid medication and they were followed up in the out-patient clinic.

FINDINGS

Twenty-one patients developed DFP after microvascular decompression an incidence of 5.4%. There were seventeen women (81.0%) among the 21 patients with DFP who were included in this study. In twenty of them, the symptoms of HFS improved completely after the operation, but the spasm remained with one of them. The onset of palsy occurred between postoperative day 7 and 23 (average: 12.1 days). The palsy was at least Grade II or worse on the House-Brackmann (HB) scale. The time to recovery averaged 5.7 weeks (range: 25 days-17 weeks); 20 patients improved to complete recovery and 1 patient remained with minimal weakness, as Grade II on the HB scale, at the follow-up examination.

CONCLUSION

Our findings demonstrated that the incidence of DFP was not so low as has been reported the literature, and it did not have any striking predisposing factors. Even though the degree of facial palsy was variable, almost all patients exhibited a complete recovery without any further special treatment. The etiology of DFP and its association with herpes infection should be further clarified.

Intraocular pressure alterations following intravitreal triamcinolone acetonide

AIMS

To determine the prevalence of intraocular pressure (IOP) alterations following intravitreal injection of triamcinolone acetonide (IVTA) and to assess possible risk factors of IOP elevation in eyes receiving single and/or repeat injections.

METHODS

Retrospective, consecutive case series. 570 consecutive eyes of 536 patients who received a single IVTA injection (4 mg/0.1 ml) and a second set of 43 eyes of 40 patients who received a second injection. Retrospective review of all IVTA cases performed by three vitreoretinal surgeons over a 42 month period beginning in 2000. The main outcome measure was change in IOP defined as absolute value of IOP elevation (5 mm Hg or higher, 10 mm Hg or higher), and percentage of baseline (30% or higher increase from baseline IOP).

RESULTS

Of the 528 eyes receiving single injections, 281 (53.2%) had an IOP elevation; 267 eyes (50.6%) experienced an elevation of IOP of at least 30%, and 245 (45.8%) and 75 (14.2%) eyes had an increase of 5 mm Hg or 10 mm Hg or more, respectively. Baseline IOP greater than 16 mm Hg is a risk factor for post-injection IOP elevation. Of the 43 eyes which received a second injection, 28 (65.1%) experienced an increase in IOP of at least 30% of baseline. Filtering surgery was required in five (0.094%) of the single and one (2.3%) of repeat injection eyes.

CONCLUSIONS

Elevated IOP after IVTA is common and patients should be monitored beyond 6 months post-injection. Patients with a baseline IOP more than 16 mm Hg or receiving a second injection should be carefully monitored for an elevated IOP.

Selective laser trabeculoplasty: predictive value of early intraocular pressure measurements for success at 3 months

AIM

To determine the predictive value of the 2 week post-selective laser trabeculoplasty (SLT) intraocular pressure (IOP) by comparing it to the 4 week and 3 month values.

METHODS

A retrospective chart review of eyes that underwent SLT between 2001 and 2004 was performed. The primary outcome measure was IOP. Demographic and medical data were collected for correlational analysis.

RESULTS

132 eyes of 95 patients were identified, none was excluded. Of the eyes that exhibited a decrease in IOP of >1 mm Hg at 2 weeks postoperatively, 99.24% continued to show a lowered IOP at the 4 week and 3 month visits. For these patients, the Pearson's r value between 2 weeks and 4 weeks was 0.708 (p value = 0.01) while the r value between 2 weeks and 3 months was 0.513 (p value = 0.01).

CONCLUSIONS

The 2 week visit post-SLT predicted the 4 week and 3 month visits if the 2 week visit demonstrated a decrease in IOP. These findings suggest that those patients who had a decreased IOP at 2 weeks and are at their goal IOP may not need to be screened until 3 months postoperatively.

Complementary and alternative medicine for glaucoma

Given the recent interest in complementary and alternative medicine (CAM), some patients may seek such treatments to supplement their traditional glaucoma management. The prevalence of CAM use for glaucoma is approximately 5%. We reviewed the literature to determine the potential benefit of various alternative treatments. Aside from a temporary osmotic effect from high dose intravenous ascorbic acid, there is no evidence that megavitamin supplementation has a beneficial effect on glaucoma. During exercise, autoregulation in healthy eyes seems to maintain a consistent blood flow rate to the optic nerve despite fluctuations in intraocular pressure (IOP). In a glaucomatous eye, the very modest IOP-lowering that follows exercise may be offset by the initial elevation in IOP that occurs when one first initiates exercise. At this time, there is no evidence to encourage or discourage the use of special diets, acupuncture, relaxation techniques, or therapeutic touch specifically for the treatment of glaucoma. Very little research has been done on the majority of herbal remedies with regard to their treatment of glaucoma. Marijuana can cause a profound lowering of IOP, but the high nonresponse rate, short half life, and significant toxicity are strong indicators that it is not an appropriate therapeutic agent. Ginkgo biloba and some other Chinese herbal remedies do not affect IOP, but may improve blood flow to the optic nerve and, as such, may have a beneficial effect on glaucoma. These agents have recognized toxicities. Although there are some well-designed studies of alternative treatments, many of the recommendations for using alternative treatments are currently unsupported by the data provided.

Motility disturbance due to true Tenon cyst in a child with a Baerveldt glaucoma drainage implant

Epithelial ingrowth of the bleb cavity, a true Tenon cyst, is a rare complication of a glaucoma drainage implant. Previous cases have been associated with persistent bleb leak, and most have occurred in eyes with prior extraocular surgery. We describe a case of a true Tenon cyst causing strabismus and an elevated intraocular pressure that was successfully treated by surgical revision.

Retrograde infusion of fluorescein to confirm location and patency of a glaucoma drainage device

BACKGROUND

During surgical revision of a glaucoma drainage device, the status of the implant tube can be in question. We report two cases in which retrograde infusion of fluorescein-stained balanced salt solution was used to confirm the patency and location of the tube.

METHODS

Fluorescein-stained balanced salt solution was made by dipping a sterile fluorescein strip into a 3-mL syringe of balanced salt solution until the fluid was visibly yellow. A 30-gauge canula was inserted into the tube at the reservoir end, and fluorescein-stained balanced salt solution was infused into the eye.

RESULTS

Retrograde infusion of fluorescein-stained balanced salt solution confirmed the location and patency of the glaucoma drainage device implant tube, obviating the need for more extensive surgical intervention in these two cases. Neither patient experienced an adverse event.

CONCLUSION

Retrograde infusion of fluorescein-stained balanced salt solution is a useful adjunctive technique for surgical revision of glaucoma drainage devices.

Intraocular pressure trends after supranormal pressurization to aid closure of sutureless cataract wounds

PURPOSE

To measure intraocular pressure (IOP) immediately and 25 minutes after small sutureless cataract surgery to estimate the duration of any elevation and to evaluate the relationship between supranormal pressurization and an elevated IOP 24 hours postoperatively.

SETTING

Routine outpatient cataract surgery at a tertiary referral center.

METHODS

Thirty-six consecutive eyes that had uneventful phacoemulsification cataract extraction were studied in a prospective fashion. Supranormal pressurization was attempted in all cases. Surgery was performed through a 3.5 mm scleral wound.

RESULTS

Mean IOP dropped from 38.8 mm Hg +/- 11.4 (SD) to 19.8 +/- 5.3 mm Hg 25 minutes after the surgery (P < .0001). A subgroup of patients (n = 6) whose IOP was greater than 24 mm Hg 24 hours postoperatively had a pressure drop from 36.8 +/- 12.3 mm Hg to 23.2 +/- 6.2 mm Hg 25 minutes postoperatively (P = .051). In this subgroup, the mean 24 hour IOP then rose to 30.8 +/- 5.2 mm Hg (P = .043). Another subgroup of patients (n = 7) whose IOP was greater than 24 mm Hg at 25 minutes had a pressure drop from 46.3 +/- 8.5 mm Hg to 27.9 +/- 2.4 mm Hg (P = .0014), falling to 21.7 +/- 6.6 mm Hg at 24 hours (P = .018).

CONCLUSION

These findings demonstrate the rapid decline of IOP after supranormal pressurization at the conclusion of cataract surgery. In addition, supranormal pressurization did not seem to contribute to IOP elevation at 24 hours.

Sulfhydryl compounds and antioxidants inhibit cytotoxicity to outer hair cells of a gentamicin metabolite in vitro

Aminoglycoside antibiotics such as gentamicin have long been known to destroy cochlear and vestibular hair cells in vivo. In the cochlea outer hair cells are preferentially affected. In contrast, gentamicin will not damage outer hair cells in vitro unless it has been enzymatically converted to a cytotoxic metabolite. Several potential inhibitors of this enzymatic reaction were tested in an in vitro assay against outer hair cells isolated from the guinea pig cochlea. Viability of hair cells (viable cells as per cent of total number of cells observed) averaged about 70% under control conditions. Addition of metabolized gentamicin significantly reduced viability to less than 50% in one hour. Sulfhydryl compounds (glutathione, dithioerythritol) and antioxidants (vitamin C, phenylene diamine, trolox) prevented the cytotoxic actions of the gentamicin metabolite. Inhibitors of amine oxidases and compounds reportedly protective against renal and acute lethal toxicity of aminoglycosides (poly-L-aspartate and pyridoxal phosphate, respectively) were ineffective as protectants. The results reinforce the hypothesis that gentamicin is enzymatically converted to a cytotoxin and imply the participation of sulfhydryl-sensitive groups or free radicals in this reaction. Alternatively or additionally, sulfhydryl compounds or antioxidants may participate in detoxification reactions.