Case Report

Craniospinal Radiotherapy for Medulloblastoma in aMan with Severe Kyphoscoliosis

B. K. Yap, B. Magee and S. E. VollansChristie Hospital, Manchester, UK

Abstract. Medulloblastoma is an uncommon tumour in the adult population. Maximum surgical resection followed by

craniospinal irradiation with a posterior fossa boost is the standard treatment. We report the case history of an adult with

medulloblastoma and severe kyphoscoliosis. The unusual anatomy of the patient posed a technical challenge to the oncologist

and the physicist in planning the craniospinal radiotherapy. A shaped spinal field matched to a parallel opposed pair of shaped

head fields was used. The technique used in treating this patient was made possible with the use of a multileaf collimation and

verification with an electronic portal imaging device. The patient remains well with no sign of relapse 4 years after treatment.

Keywords: Adult; Craniospinal radiotherapy; Kyphoscoliosis; Medulloblastoma; Multileaf collimation; Portal imaging

Clinical Oncology Clinical Oncology (2001)13:117–119# The Royal College of Radiologists

Introduction

Medulloblastoma (also referred to as infratentorial primi-

tive neuroectodermal tumour) is the commonest in patients

between 4 and 10 years of age. However, it accounts for

less than 1% of adult central nervous system tumours [1].

The treatment approach in adults is similar to that in

children, with maximum resection of the primary tumour

followed by radiotherapy. Owing to the tumour’s tendency

to seed the cerebrospinal fluid, the treatment usually

involves craniospinal axis radiotherapy as well as irradia-

tion of the posterior fossa. The complexity of the treatment

volume for craniospinal irradiation has led to a variety of

treatment techniques. The standard approach at this

institute is to use a posterior oblique pair of wedged

fields to treat the spinal axis, matched to a lateral parallel

opposed pair of cranial fields [2]. We describe an adult

patient with medulloblastoma who has severe kyphosco-

liosis, in whom this standard approach was not appropriate

and in whom field shaping using multileaf collimation

(MLC) and electronic portal imaging for verification were

useful for treatment delivery.

Case Report

A 50-year-old Caucasian man presented in December 1995

to another hospital with difficulty with speech and balance.

He was found to have inco-ordination of the upper and

lower limbs, dysarthria, nystagmus, dysdiadochokinesia

Correspondence and offprint requests to: Dr B. K. Yap,Department of Clinical Oncology, Christie Hospital, WilmslowRoad, Manchester M20 4BX, UK. Tel: 0161 4463000.

and poor balance with a tendency to veer to the left. He was

noted to have a short stature and gross kyphoscoliosis; he

used a hearing aid in the left ear. An initial computed

tomographic scan showed ventricular dilatation and a space

occupying lesion. A magnetic resonance (MR) scan of the

neuraxis showed a 2 6 1 cm non-enhancing solid mass on

the right superior cerebellar vermis. Apart from severe

thoracolumbar kyphoscoliosis, no focal mass lesion was

identified within the spine. The patient underwent posterior

fossa craniotomy in July 1996, with insertion of a

ventricular shunt and macroscopic excision of the tumour.

Histological examination showed a malignant small cell

tumour. The malignant cells formed sheets and were

trabecular with a hint of rosette formation. Immunostaining

for cytokeratin (MNF 116 and CAM5.2) and epithelial

membrane antigen were negative. In addition, synaptophy-

sin showed generalized positivity and glial fibrillary acidic

protein was focally positive. These histological features

were consistent with a diagnosis of medulloblastoma,

An initial assessment of the patient in the clinic and on

the treatment simulator revealed several problems for

treatment planning. The severe spinal curvature could not

be covered in a conventional rectangular field without

undue irradiation of critical organs. The kyphoscoliosis

caused difficulty with positioning on the treatment couch

and raised concerns about reproducibility for daily

treatment. It was decided to treat the patient in a supine

position with head immobilization using a lightweight cast

(Posicast). This approach appeared most appropriate for the

patient’s comfort and reasonably acceptable treatment

reproducibility was anticipated.

The treatment consisted of a lateral parallel opposed pair

of head fields and a single posterior spine field. MLC was

used to generate the head field shape (Fig. 1), which

Fig. 1. The head field shape.

Fig. 2. Shaped single posterior field generated by MLC. Fig. 3. Target volume drawn on the X-ray film.

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shielded the face and orbit. The head was treated

isocentrically by using a head shell with the patient lying

supine; the isocentre was 15 cm above the couch. The spine

was treated with a shaped single posterior field generated

by MLC (Fig. 2). A 108 diaphragm twist of the head field

was used in order to match the lower edge of the head field

to the divergent edge of the spine field. An additional 2 cm

gap at the craniospinal junction was used to avoid any risk

of overlap. This was a clinical decision and may have been

overly cautious, but there were reservations regarding

immobilizations and reproducibility in treating this patient.

The average spine depth was found from a lateral film to be

8 cm, with a variation of 4–12 cm. A plain radiograph of

the whole spine was taken at a focal skin distance of 112

cm (i.e. 120 cm to the mean spine depth). The oncologist

then drew the target volume on the X-ray film (Fig. 3). This

information was digitized and transferred to the planning

computer. A tattoo was marked on the centre of the spine

field on the anterior surface of the patient (abdomen) to

facilitate treatment set-up, as discussed later. The 120 cm

source to spine distance was chosen in order to obtain an

adequate field length to cover the whole spinal axis using a

single posterior field. The longitudinal distance from the

isocentre of the head field to the centre of the spine field,

taking into account the 2 cm gap, was calculated using the

B. K. Yap et al.

geometry shown in Fig. 4. This longitudinal distance would

determine the couch movement required to change from the

isocentre of the head field to the centre of the spine field.

The alignment of the tattoo with the spine field centre after

the calculated couch movement provided a mean to verify

the day to day accuracy of set-up. Whole brain irradiation

was administered using a 6 MV photon parallel opposed

pair with a tumour dose of 30 Gy in 20 fractions and a boost

dose of 20 Gy in ten fractions, which gave a total dose of 50

Gy in 30 fractions to the posterior fossa. The whole spine

was treated in the supine position using a 6 MV photon

single posterior field irregularly shaped by an MLC to

follow the contour of the spine, with an applied dose of 35

Gy in 20 fractions. The estimated spinal dose varied from

23 Gy to 31 Gy, with a mean spine dose of 27 Gy.

The treatment set-up was verified by using an electronic

portal imaging device (SRI 100 Elekta). This was carried

out during the first two treatments and then on a weekly

basis thereafter. The portal image was checked visually as

the shape of the field had to correspond to the shape of the

spine (Fig. 2). The spine was so curved that it would have

been obvious from the image if the relative positions of the

field and the spine were wrong. A review of the portal

images showed clinically acceptable treatment reproduci-

bility.

Received for publication October 1999Accepted June 2000

Fig. 4. Calculation of the longitudinaldistance from the isocentre of the headfield to the centre of the spine field.

The patient underwent a repeat MR scan in November

1998, which showed no evidence of tumour recurrence. He

had remained well when he was reviewed in March 2000.

The only neurological deficit that he had was slight inco-

ordination of the left upper and lower limbs. However, he is

able to walk independently with a walking stick.

Discussion

The 5-year survival rate of adult patients with medullo-

blastoma is approximately 60%–70% [1,3]. Postoperative

radiotherapy would involve craniospinal irradiation to

include the entire subarachnoid space and a posterior

fossa boost. This man’s kyphoscoliosis caused initial

concern regarding obtaining a satisfactory treatment

position. However, clinical checking on the daily set-up,

and regular portal imaging using the electronic portal

imaging device, confirmed clinically acceptable treatment

reproducibility. Electronic portal imaging has been found to

be useful at this institute for verification in several different

treatment situations [4]. MLC allowed an irregularly shaped

field to be used that followed the spinal curvature and

shaping of the head fields.

A consensus exists that the dose to the posterior fossa

should be at least 50 Gy using 1.5–1.8 Gy daily fractions

[5]. The appropriate dose to the spinal axis is less clear. The

dose to the spine that is usually used to control subclinical

disease is 30–36 Gy. However, several institutes have

reported acceptable results using 25 Gy [6]. The US

Pediatric Oncology Group and the Children’s Cancer Group

trial comparing neuraxis doses of 36 Gy and 23.4 Gy in

children over the age of 3 years showed a clear advantage

for the higher dose [7]. The disadvantage in our patient of

using a single posterior megavoltage field was the

variability of spine depths; clearly, no dose uniformity

could be achieved with a wide variation of around 27 Gy.

Without MLC, treatment could have been attempted in a

prone position with lead blocking to shape the spinal field.

This was rejected in favour of the solution described and

using the technology available to us in 1995.

References

1. Giordana MT, Schiffer P, Lanotte M, et al. Epidemiology ofadult medulloblastoma. Int J Cancer 1999;80:689–92.

2. Pointon RCS, editors. The radiotherapy of malignantdisease. 2nd ed. Springer-Verlag 1991:227–9.

3. Christian C, Lasset C, Alapetite C, et al. Multivariateanalysis of prognostic factors in adult patients withmedulloblastoma. Cancer 1994;74:2352–60.

4. Kirby MC, Kane B, Williams PC. Clinical applications ofcomposite and realtime megavoltage imaging. Clin Oncol1995;7:308–16.

5. Silverman CL, Simpson JR. Cerebellar medulloblastoma:the importance of posterior fossa dose to survival andpattern of failure. Int J Radiat Oncol Biol Phys1982;8:1869–76.

6. Halberg FE, Wara WM, Fippin LF, et al. Low dosecraniospinal radiation therapy for medulloblastoma. Int JRadiat Oncol Biol Phys 1991;20:651–4.

7. Deutsch M, Thomas PR, Krischer J, et al. Results ofprospective randomised trial comparing standard doseneuraxis irradiation (36 Gy/20) with reduced neuraxisirradiation (23.4 Gy/13) in patients with low stagemedulloblastoma. A combined Children’s Cancer Group –Pediatric Oncology Group study. Pediatr Neurosurg1996;24:167–76 (discussion 176–7).

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