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A simple technique for craniospinal radiotherapy in the supine position
Radiotherapy and Oncology 80 (2006) 394–395 www.thegreenjournal.com
Letters to the Editor A simple technique for craniospinal radiotherapy in the supine position To the Editor We read with interest the report by Parker and Freeman on their technique for craniospinal radiation [1]. We have employed a similar CT simulator based technique for those patients who cannot tolerate a prone position or in whom supine positioning is required for airway access (such as children requiring general anaesthetic). Like Parker et al., we utilize a half beam blocked cranial field but match this to a half beam blocked thoracic spine field, analogous to a single isocentric head and neck technique. A thermoplast shell is used for immobilization for the head and shoulders. The use of the two half-beam blocked fields allows the use of junction shifts with asymmetric collimation without a need to account for the changes in overlap introduced with a fixed collimator rotation on the cranial field. The half beam match also facilitates the use of unconventional spinal irradiation techniques as outlined in the case described. In order to ensure an adequate cranial field size for adults with half beam blocking, extended distance on the lateral cranial fields may be required and this can easily be set using fixed lateral couch translations with corresponding setup marks laterally on the thermoplast shell. Like Parker et al we use an asymmetrically collimated inferior spine field matched to the superior spine fields, with fixed longitudinal couch shifts based on the brain isocentre to locate the spine isocentres. We typically introduce junction shifts at 9 Gy intervals with shifts superior and inferior to the junction at the brain spine interface. Compensators are used on the brain and spine fields as required. We applied this technique for the treatment of a 25-yearold man with a disseminated primitive neuroectodermal tumor. This individual required a thoracic laminectomy and biopsy of an intradural mass in the upper T-spine for diagnosis. Subsequent wound dehiscence led to the need for packing and healing by secondary intent. In order to commence radiotherapy promptly while minimizing further wound healing
complications, the patient was treated with the supine technique (due to inability to lie prone) and a half beam blocked wedged pair for the thoracic field. The matching of the physical wedged pair thoracic field was facilitated by the use of the half beam brain fields without collimator rotation. The wedge pair avoided direct irradiation of the wound and the higher superficial soft tissue doses experienced with the traditional use of a single posterior field. (Fig. 1) In addition to the wedge, simple field-in-field MLC for the thoracic fields was used to compensate for superior–inferior dose variations without the use of the accessory mount, thus avoiding potential couch collisions. Treatment proceeded without incident during a regular (15 min) treatment slot with excellent matching noted on port films with each junction shift. The combined half beam blocking at the cranial and upper spine junction was essential to the successful delivery of this variation of craniospinal treatment.
Reference [1] Parker WA, Freeman CR. A simple technique for craniospinal radiotherapy in the supine position. Radiother Oncol 2006;78:217–22.
Glenn Bauman* Eugene Wong Kristina Trenka Danielle Scott Department of Radiation Oncology, London Regional Cancer Program, London Health Sciences Centre, 790 Commissioners Rd E, London, Ont., Canada N6A 4L6 E-mail address: [email protected]
*
Corresponding author. Received 28 April 2006; received in revised form 29 June 2006; accepted 11 July 2006; Available online 17 August 2006
Fig. 1. Sparing of the healing laminectomy wound (arrow) by a wedged pair providing 95% isodose coverage to spinal canal while reducing dose to superficial soft tissues to 50% or less.
0167-8140/$ - see front matter c 2006 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.radonc.2006.07.011
Letters to the Editor A simple technique for craniospinal radiotherapy in the supine position To the Editor We read with interest the report by Parker and Freeman on their technique for craniospinal radiation [1]. We have employed a similar CT simulator based technique for those patients who cannot tolerate a prone position or in whom supine positioning is required for airway access (such as children requiring general anaesthetic). Like Parker et al., we utilize a half beam blocked cranial field but match this to a half beam blocked thoracic spine field, analogous to a single isocentric head and neck technique. A thermoplast shell is used for immobilization for the head and shoulders. The use of the two half-beam blocked fields allows the use of junction shifts with asymmetric collimation without a need to account for the changes in overlap introduced with a fixed collimator rotation on the cranial field. The half beam match also facilitates the use of unconventional spinal irradiation techniques as outlined in the case described. In order to ensure an adequate cranial field size for adults with half beam blocking, extended distance on the lateral cranial fields may be required and this can easily be set using fixed lateral couch translations with corresponding setup marks laterally on the thermoplast shell. Like Parker et al we use an asymmetrically collimated inferior spine field matched to the superior spine fields, with fixed longitudinal couch shifts based on the brain isocentre to locate the spine isocentres. We typically introduce junction shifts at 9 Gy intervals with shifts superior and inferior to the junction at the brain spine interface. Compensators are used on the brain and spine fields as required. We applied this technique for the treatment of a 25-yearold man with a disseminated primitive neuroectodermal tumor. This individual required a thoracic laminectomy and biopsy of an intradural mass in the upper T-spine for diagnosis. Subsequent wound dehiscence led to the need for packing and healing by secondary intent. In order to commence radiotherapy promptly while minimizing further wound healing
complications, the patient was treated with the supine technique (due to inability to lie prone) and a half beam blocked wedged pair for the thoracic field. The matching of the physical wedged pair thoracic field was facilitated by the use of the half beam brain fields without collimator rotation. The wedge pair avoided direct irradiation of the wound and the higher superficial soft tissue doses experienced with the traditional use of a single posterior field. (Fig. 1) In addition to the wedge, simple field-in-field MLC for the thoracic fields was used to compensate for superior–inferior dose variations without the use of the accessory mount, thus avoiding potential couch collisions. Treatment proceeded without incident during a regular (15 min) treatment slot with excellent matching noted on port films with each junction shift. The combined half beam blocking at the cranial and upper spine junction was essential to the successful delivery of this variation of craniospinal treatment.
Reference [1] Parker WA, Freeman CR. A simple technique for craniospinal radiotherapy in the supine position. Radiother Oncol 2006;78:217–22.
Glenn Bauman* Eugene Wong Kristina Trenka Danielle Scott Department of Radiation Oncology, London Regional Cancer Program, London Health Sciences Centre, 790 Commissioners Rd E, London, Ont., Canada N6A 4L6 E-mail address: [email protected]
*
Corresponding author. Received 28 April 2006; received in revised form 29 June 2006; accepted 11 July 2006; Available online 17 August 2006
Fig. 1. Sparing of the healing laminectomy wound (arrow) by a wedged pair providing 95% isodose coverage to spinal canal while reducing dose to superficial soft tissues to 50% or less.
0167-8140/$ - see front matter c 2006 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.radonc.2006.07.011