The normal tissue sparing potential of an adaptive plan selection strategy for re-irradiation of recurrent rectal cancer

Abstract

Background and purpose: Radiotherapy (RT) of rectal cancer is challenged by potentially large interfractional anatomy changes. The risk of radiation-induced morbidity is a particular concern in patients receiving re-irradiation for recurrent disease. We propose an adaptive RT plan selection strategy for these patients and report on its clinical feasibility and normal tissue sparing potential. Material and methods: Eight patients with pelvic recurrence were re-irradiated according to a hyperfractionation protocol (ReRAD-I; 40.8 Gy) using margins around the clinical target volume (CTV) of 15 mm trimmed to anatomical barriers (Plan L). Two new library plans (S and M) were created for each patient, with the target volumes covering the CTV with isotropic margins of 5 and 10 mm. Pre-treatment cone beam CTs were assessed to determine which plan would cover the CTV following soft-tissue match. The selected plans were compared to the clinically delivered plan in terms of normal tissue volume receiving 95% of the dose (V95%) and the volume of bone receiving 30 Gy (V30 Gy). Results: Plan selections could be performed on all CBCTs for all patients. Plan S was chosen in 213 fractions (79%), plan M in 53 (20%) and plan L in 2 fractions. Normal tissue V95% was reduced by 67% (median; range 30-79%) while bone V30 Gy was reduced by 66% (median; range 40-100%). Conclusion: The CTV and/or surrogate structures were visible on all CBCTs. Margins smaller than those used clinically would have accounted for 99% of the observed target deformations, translating into a considerable normal tissue sparing potential.

Dosimetric benefit of an adaptive treatment by means of plan selection for rectal cancer patients in both short and long course radiation therapy

“…Passoni et al and Raso et al [31,32] also reported on an adaptive procedure, but applied to the boost of the residual tumor during the last 6 fractions of LCRT. Byskov et al [33] describe an adaptive approach to re-irradiation of rectal recurrence. As neither strategy is applied to the mesorectum, they cannot easily be compared.…”

Patterns of practice for adaptive and real-time radiation therapy (POP-ART RT) part II: Offline and online plan adaption for interfractional changes

“…Online adaption using a plan library is well suited for tumours with predictable, potentially large and frequent interfractional anatomical variations while intrafraction changes remain comparatively small. Examples are bladder [11] , [12] , cervix [13] , [14] or rectum [15] , [16] , [17] where different bladder or rectal fillings can be anticipated and a library of plans covering several scenarios are made available for treatment. Online daily replanning can address any type of anatomical changes but is the most resource-demanding approach and as such, its clinical implementation has only been demonstrated in few treatment sites and institutions so far [18] , [19] , [20] , [21] , [22] .…”

Re-irradiation for recurrent rectal cancer – a single-center experience

“…Currently, IMRT or VMAT is the standard technique for reRT in our institution. A recent planning study demonstrated that with IMRT, the margins can be reduced, yielding considerable normal tissue sparing [33]. Also, preliminary data on proton therapy in this field are promising [34].…”