Emmanuel Egger

Intensity modulated proton therapy: A clinical example

In this paper, we report on the clinical application of fully automated three-dimensional intensity modulated proton therapy, as applied to a 34-year-old patient presenting with a thoracic chordoma. Due to the anatomically challenging position of the lesion, a three-field technique was adopted in which fields incident through the lungs and heart, as well as beams directed directly at the spinal cord, could be avoided. A homogeneous target dose and sparing of the spinal cord was achieved through field patching and computer optimization of the 3D fluence of each field. Sensitivity of the resultant plan to delivery and calculational errors was determined through both the assessment of the potential effects of range and patient setup errors, and by the application of Monte Carlo dose calculation methods. Ionization chamber profile measurements and 2D dosimetry using a scintillator/CCD camera arrangement were performed to verify the calculated fields in water. Modeling of a 10% overshoot of proton range showed that the maximum dose to the spinal cord remained unchanged, but setup error analysis showed that dose homogeneity in the target volume could be sensitive to offsets in the AP direction. No significant difference between the MC and analytic dose calculations was found and the measured dosimetry for all fields was accurate to 3% for all measured points. Over the course of the treatment, a setup accuracy of +/-4 mm (2 s.d.) could be achieved, with a mean offset in the AP direction of 0.1 mm. Inhalation/exhalation CT scans indicated that organ motion in the region of the target volume was negligible. We conclude that 3D IMPT plans can be applied clinically and safely without modification to our existing delivery system. However, analysis of the calculated intensity matrices should be performed to assess the practicality, or otherwise, of the plan.

Cobalt-60 Treatment of Choroidal Hemangiomas

PURPOSE We investigated the therapeutic possibilities of gamma brachytherapy to improve the final functional results of eyes with choroidal hemangiomas, which are benign vascular tumors that can induce progressive impairment of visual acuity. METHODS We treated 41 patients with choroidal hemangioma with cobalt-60 applicators. The lesions consisted of 39 circumscribed hemangiomas and two diffuse hemangiomas in patients with Sturge-Weber syndrome. Before treatment, visual acuity in the affected eye was 20/200 in ten patients, 20/200 to 20/50 in 17 patients, 20/40 to 20/25 in 11 patients, and 20/20 in three patients. All patients were symptomatic. The macula was infiltrated by the tumor in 12 eyes (29.3%). There was retinal detachment in 40 eyes (97.6%), cystoid edema in ten eyes (24.4%), subretinal fibrosis in eight eyes (19.5%), and areolar atrophy in two eyes (4.9%). RESULTS After treatment, the retina was reattached in all eyes, and the tumor progressively transformed into a flat scar. The postirradiation macular lesions that we identified were pigment migrations in the macular region, subretinal fibrosis, and an areolar atrophic scar. We correlated the functional results at two, five, and ten years after treatment with the initial visual acuity, and with pre-existing and posttreatment macular lesions. CONCLUSIONS Our results suggest that radiotherapy is a valuable therapeutic modality for choroidal hemangiomas, particularly in hemangiomas that involve the macula, and for tumors associated with bullous retinal detachment.

Proton beam irradiation of choroidal hemangiomas

PURPOSE To present a large series of choroidal hemangiomas treated with proton beam irradiation and to describe the treatment outcomes. METHODS We treated 54 eyes of 53 patients with choroidal hemangioma. The lesions consisted of 48 circumscribed hemangiomas and six diffuse hemangiomas in patients with Sturge-Weber syndrome. The total applied dose was 27.3 Gy in four eyes, 22.7 Gy in three eyes, and 16.4 Gy to 18.2 Gy in 47 eyes. RESULTS The retina reattached within six months after treatment in all 54 eyes and no recurrence of the secondary retinal detachment occurred within the follow-up period of 6 months to 9 years. Tumors treated with the higher doses regressed faster than tumors treated with the lower doses, but radiation-induced complications of the optic nerve appeared in all four eyes treated with a total dose of 27.3 Gy. Of 31 eyes treated with 16.4 to 18.2 Gy and followed for more than 1 year, 22 had an improvement in their visual acuity, and nine retained the same visual acuity. At the last follow-up examination, the best-corrected visual acuity was 20/20 or better in nine eyes, 20/40 to 20/25 in 13 eyes, 20/100 to 20/50 in six eyes, and 20/200 or less in three eyes. CONCLUSIONS Proton beam irradiation of choroidal hemangiomas appears to be a valid therapeutic alternative. A total proton dose ranging from 16.4 to 18.2 Gy applied in four daily fractions seems adequate to ensure local control of both tumor and secondary retinal detachment.

Initial experience of using an active beam delivery technique at PSI

SummaryAt PSI a new proton therapy facility has been assembled and commissioned. The major features of the facility are the spot scanning technique and the very compact gantry. The operation of the facility was started in 1997 and the feasibility of the spot scanning technique has been demonstrated in practice with patient treatments. In this report we discuss the usual initial difficulties encountered in the commissioning of a new technology, the very positive preliminary experience with the system and the optimistic expectations for the future. The long range goal of this project is to parallel the recent developments regarding inverse planning for photons with a similar advanced technology optimized for a proton beam.

Experimental study on the fractionation schedule for proton irradiation of uveal melanoma

Greene melanoma in the anterior chamber of rabbits was irradiated by protons to find the isoeffect curve for proton irradiation fractionated into one, two, three or four doses. The isoeffect curve for tumor tissue remained constant between one- and three-dose fractionations and rose with four-dose fractionation. The isoeffect curve for normal tissue approximately followed the Ellis equation. Therefore, the optimal irradiation schedule should be in the range of three fractions because this best spares normal tissue while delivering a tumoricidal dose to the lesion. The relative reduction of the total dose from four- to one-dose fractions of intraoperative irradiation should be 20%.

Subclinical experimental optic neuropathy after accelerated proton beam irradiation.

Background: Accelerated proton beam irradiation has been used for several years to treat intraocular tumors. The pathophysiology of proton-beam-induced retinopathy and neuropathy has not been characterized to date. The present study investigates the early effects of irradiation with an accelerated proton beam on the optic nerve of the rabbit. Materials and Methods: The optic nerve head of Albino New Zealand rabbits (n = 14) was irradiated with a narrow beam of accelerated protons using the total dose of 60 and 43 Gy, respectively. This dose was split up into 4 equal sessions taking place on 4 consecutive days. Ophthalmoscopic examination was performed regularly, and the rabbits were sacrificed at 1, 3 and 8 months after irradiation. The eyes were enucleated and processed for light and electron microscopy. Results: Despite the absence of ophthalmoscopically detectable optic neuropathy in all 14 rabbits irrespective of the dose of irradiation, light and electron microscopy of the optic nerve showed a glial and fibrotic perivascular scar made up predominantly of altered astrocytes. This scar formation was seen as early as 1 month after irradiation and was at times accompanied by infiltration with inflammatory cells perivascularly both outside and within the optic nerve. In contrast to the astrocytes, oligodendrocytes did not show degenerative cellular alterations. During the 8-month follow-up, no signs of vascular occlusion were found. Conclusions: The observed lesions in the glial tissues with consecutive fibrosis appear to stem from a direct effect of irradiation. This may represent the initial mechanism of early subclinical irradiation-induced damage to the optic nerve before vascular occlusions may occur at a later stage, which may lead to more severe damage.

Proton Beam Irradiation of Choroidal Melanoma: Technique and Results

Since March, 1984, proton beam radiotherapy (PBRT) has been used at the Paul Scherrer Institute (PSI) in a project being conducted jointly with the University Ophthalmological Hospital in Lausanne (Hopital Ophtalmique Jules Gonin) for the treatment of patients with ocular tumors. Up to now we have treated over 3,000 patients. Among 2,705 cases treated by the end of 1998, there were 2,435 cases of uveal melanoma, 11 of melanoma of the iris, 50 of recurrence of melanoma (some of which had previously been exposed to brachytherapy with Ru-106 or Co-60 plaques), 77 of choroidal hemangioma, 50 of melanoma of the conjunctiva, 32 of intraocular metastases, 34 of age-related macular degeneration, 8 of vascular tumor of the retina, 2 of tumor of the eyelids, and 6 of miscellaneous ocular tumors.

Intensity modulated proton therapy: A first clinical example

By the end of 1999, over 40 patients will have been treated at the Paul Scherrer Institute with protons using the spot scanning technique [1]. For each of these treatments, an optimisation process has been used to calculate the weights of the many thousands of individually applied proton pencil beams which typically make up a single treatment port [2,3]. For the majority of these treatments however, the optimisation procedure has been applied on a field-by-field basis only, and in such a way as to ensure that a homogenous dose is applied across the target volume from each individual field.