Withington, Manchester M20 4BX, UK. Abstract. Intracavitary radiotherapy is conceptually an attractive method of boosting dose to nasopharynx cancer whilst ...
T he British Journal of Radiology, 70 (1997), 412–414
© 1997 The British Institute of Radiology
Short communication
Intracavitary radiotherapy boosting for nasopharynx cancer 1N J SLEVIN, 2J M WILKINSON, 2H M FILBY and 1N K GUPTA Departments of 1Clinical Oncology and 2Medical Physics, Christie Hospital NHS Trust, Wilmslow Road, Withington, Manchester M20 4BX, UK Abstract. Intracavitary radiotherapy is conceptually an attractive method of boosting dose to nasopharynx cancer whilst sparing sensitive normal tissues. A high dose rate (HDR) microselectron can be used to deliver a brachytherapy boost conveniently, safely, comfortably and effectively. Following external radiotherapy a single outpatient treatment has been given to patients using the remote afterloading system of sources placed in modified paediatric endotracheal tubes. This has been associated with good primary control and no evidence of serious morbidity in eight patients. The main limitation of this method is restriction of its utilization to small volume primary disease.
Introduction There is renewed interest in using brachytherapy techniques in the treatment of nasopharynx cancer. The earliest intracavitary methods utilized preloaded radium for low dose rate therapy, with source access to the nasopharynx often via the oral cavity [1, 2]. Intranasal devices have also been used [3, 4] and treatment can now be conveniently and safely delivered using remote afterloading high dose rate systems [5]. Control of primary nasopharyngeal disease by external beam radiotherapy is dependent on the primary volume and radiation dose [6]. The tolerance of normal tissue structures anatomically close to the nasopharynx limits the external radiotherapy dose which can safely be applied. The potential advantage of using intracavitary irradiation is the relative sparing of these structures which include the brain stem, spinal cord, temporal lobes, visual apparatus, audio-vestibular system, pituitary and pterygoid muscles (Figure 1). Since 1990, the Christie Hospital has utilized an HDR microselectron (Nucletron) for delivering an intracavitary boost for small primary volume nasopharynx cancer and we report our preliminary experience of this technique.
posterolateral spread, those given adjuvant chemotherapy (potential for augmenting radiotherapy effect on late responding normal tissues) were not boosted. The minimum follow-up was 3 years.
Technique The dose of external beam radiotherapy to the primary was 45–50 Gy over 3 weeks using a fixed field technique for patients with limited neck node disease and 60 Gy over 6 weeks for patients with massive lymphadenopathy. Access to the nasopharynx was formerly provided by two cuffed small bore endotracheal tubes (5.6 mm outside diameter)
Patients Since 1990 selected patients with stage T1, T2 and limited T3 nasopharynx cancer have received a single intracavitary boost following external beam radiotherapy. Patients with base of skull/T4 disease, extensive anterior, inferior or Received 11 September 1996 and in revised form 5 December 1996, accepted 8 January 1997. 412
Figure 1. Sagittal MR T weighted image showing bal1 loons filled with 4 ml of diluted gadolinium contrast abutting on to primary disease site (posterior nasopharynx) demonstrating potential of local treatment for sparing critical structures such as brain stem, optic nerves, temporal lobes. T he British Journal of Radiology, April 1997
Short communication: Intracavitary radiotherapy boosting for nasopharynx cancer
with fixation in the treatment position secured by inflating each balloon (of 3 cm length) side-to-side within the nasopharyngeal cavity. It is now possible to use even narrower catheters (4 mm outside diameter) to minimize patient discomfort (Figure 2). Local anaesthesia is achieved by lignocaine spray for the oropharynx and cocaine/adrenaline gauze for the nasal passages. The balloons are inflated with radio-opaque contrast (one part Urografin 150 to one part water) and their position
in the nasopharynx checked by fluoroscopic screening. Anteroposterior (AP) and lateral films are taken with the patient in a supine position and a graduated wire inserted into the closed end of each tube. Initially the dose was expressed on a balloon surface relevant to tumour position so as to deliver 5–7.5 Gy to all the balloon surface reference points. Based on this experience a quicker standardized approach is now used in which the total reference air kerma per unit prescribed dose is tabulated as a function of length of line source (usually 3.5 cm) with separation of lines (1–2 cm) and height from line to superior balloon surface (0.75–1.5 cm). The product of this value (in mGy Gy−1) and the prescribed dose (Gy) divided by the reference air kerma rate for the iridium source (mGy s−1) gives the total irradiation time (in seconds). The whole procedure takes approximately 1 h from local anaesthetic to completion of treatment.
Results The outcome of patients treated is shown in Table 1. There was no serious morbidity either in terms of mucosal ulceration or severe late effects. The only patient who developed primary recurrence had presented with adenoid cystic carcinoma which endoscopically and radiologically appeared limited to the nasopharynx. Recurrence in the orbit has been retreated with external beam radiotherapy 3D years following her initial treatment.
Discussion W hy was intracavitary boosting so infrequently used?
Figure 2. Modified cuffed paediatric endotracheal tube (outside diameter 4 mm) with 3 cm balloon, two of which are inflated side-to-side within nasopharyngeal cavity.
The brachytherapy depth dose characteristics (Table 2) are such as to exclude patients who have significant primary extension beyond the postnasal space. If the primary site is in the relatively inaccessible fossa of Rosenmuller then primary
Table 1. Outcome of patients treated Histology stage
Patient outcome (8)
Post-radiotherapy follow-up (years)
Mucosal melanoma ‘‘T3’’ N0 Squamous carcinoma T3 N0 Squamous carcinoma T2 N2 Adenoid Cystic ca T2 N0 Squamous ca T2 N2 Squamous ca T2 N2 Squamous ca T3 N0 Squamous ca T1 N3
Alive and well Alive and well Alive and well Alive, primary recurrence (orbit) (adenoid cystic) Alive, node recurrence, primary well Alive, node recurrence, primary well Died Ca bronchus (endobronchial ), primary well Died bone mets, primary well
5N!Y 3N!Y 3 5 3 3 3 2
Total number of patients with nasopharynx cancer from mid-1990 to mid-1993: 43. HDR microselectron boost (three T3; four T2; one T1): 8. T4; large volume T3; adjuvant chemotherapy (not boosted): 35.
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N J Slevin, J M W ilkinson, H M Filby and N K Gupta Table 2. Fall-off in dose above balloon surface
Example: height of balloon surface from line, 10 mm; active length of line, 35 mm; line separation, 20 mm.
limitations of this approach are rapid fall-off in dose from the line sources thus excluding patients with primary disease extending from the nasopharyngeal cavity. The use of a single intracavitary boost following external radiotherapy affords good control, albeit with small numbers and limited follow-up in this series. The selection criteria for boosting in this report may have been too restrictively applied.
extension or large retropharyngeal nodes undermine the concept of intracavitary boost.
Acknowledgments
Height (mm)
Dose (%)
10 +2.5 +5 +10
100 83 68 48
Could excellent primary control be achieved with external radiotherapy alone? Using conventional fractionation (2 Gy per daily fraction) excellent local control for T1–T3 disease can be achieved with doses above 60 Gy. However, at these dose levels there is some risk of serious normal tissue morbidity. It has been calculated that for doses of 58–65 Gy there is a 3% risk of brain necrosis [7].
W hen should the boost be delivered ? The approach in this study was to deliver the boost as soon as possible ( less than 1 week) following external beam radiotherapy to avoid the potential for accelerated repopulation of possible residual tumour clonogens during the gap [8]. An alternative approach is to have a gap of some months to allow resolution of tumour and acute toxicity thus permitting selection of patients for boosting based on histological confirmation of residual disease [9]. A single boost rather than fractionationed treatments has been associated with no serious complications in this and other series [5].
Conclusion The rationale for intracavitary boosting is an expected dose–response relationship for tumour control and sparing of late responding critical normal tissues close to the nasopharynx. The
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We are grateful to Mrs Odette Spiteri-Bell for setting out the manuscript, and to the Departments of Diagnostic Radiology and Medical Illustration for Figures 1 and 2.
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