Local relapse rates remain around 50% even with macroscopic complete resection, hence the interest in adjuvant therapies such as radiotherapy to improve local control. As with limb sarcomas, radiotherapy can be delivered either pre-operatively or post-operatively. There are potential advantages to the pre-operative approach:
(a) the primary tumourin siturepresents a well-defined target volume;
(b) the tumour itself acts a spacer, displacing the small bowel from high dose treatment volume, thus reducing acute and late toxicity;
(c) radiotherapy may be more effective in the pre-operative setting because of better oxygenation;
(d) pre-operative radiotherapy may thicken the pseudo-capsule of the tumour, thus aiding surgical resection and reducing intra-peritoneal spillage; and
(d) it may render an unresectable tumour resectable.
Two prospective trials16of pre-operative radiotherapy have shown favourable local control rates of 60% following macroscopically complete resection. The dose for pre-operative radiotherapy is 50 Gy. The use of advanced radiotherapy delivery techniques such as intensity modulated radiation therapy (IMRT) or tomotherapy allows selective dose escalation beyond 55 Gy to the margin at risk and may be considered.17A randomised trial to compare surgery alone versus pre-operative radiotherapy and surgery was attempted in North America, but closed due to poor accrual. A similar trial in Europe has been ongoing since 2012, but results are not expected until some years later.18
Intra-operative radiotherapy has been shown in retrospective series to improve local control rates and should be considered where available, usually in combination with pre- or post-operative external beam radiotherapy.19
A non-randomised retrospective series20have has documented improved local control without overall survival benefit with post-operative radiotherapy. However, the presence of radiation dose-limiting structures in the post-operative target volume presents a significant challenge and often limits the dose to 50-55 Gy to well defined areas at risk.21If it is to be considered, the use of omentum or other tissue spacers to displace bowel from the tumour bed is recommended to reduce the risk of radiation induced bowel toxicity.5
In summary, while a number of retrospective studies showing favourable local control with both pre- and post-operative radiotherapy exist, there is a distinct lack of level 1 randomised trial evidence for radiotherapy in retroperitoneal sarcomas. Therefore, while the general indications for radiating any soft tissue sarcomas are still valid (large, intermediate-high grade, incompletely resected) ,5, the unique difficulties posed by the proximity of radiosensitive organs at risk mandate multi-disciplinary discussion to determine feasibility and sequencing of radiation therapy.