289 Background: This clinical study assessed the potential of helical tomotherapy-based, image-guided radiotherapy (IGRT) to increase the accuracy of bladder irradiation using a plan of the day adaptive radiotherapy (ART) technique. Methods: Ten patients with stage T2b-T4- N0 M0, histologically proven bladder transitional cell carcinoma, who underwent bladder preservation with trimodality therapy in an ongoing trial, are reported. All patients received a dose of 64Gy/32# to the whole bladder. Seven of these also received a simultaneous integrated boost of 68Gy/32 fractions to tumor bed. The ART technique entailed the generation of six planning PTVs and thus six separate IMRT plans for each patient. All patients underwent daily pre and post treatment MVCT imaging to correct for positioning errors, choose the plan of the day, depending on deformation of the bladder, and verify intrafraction filling at the end of treatment. Margins needed to encompass the bladder wall in each direction during radiotherapy was determined in the following three scenarios: (a) centers with availability of daily IGRT and performing ART, (b) centers with IGRT not doing ART, and (c) centers without IGRT using electronic portal imaging for setup. Results: At a median follow-up of 12.2 months, all patients had a complete response in the bladder and one patient had a pelvic nodal recurrence. No patient developed treatment related grade 3 toxicity. Post treatment MVCT scans (n=315) were used to generate margins for centers with varying resources. Overall, the margin needed to encompass the anterior and superior walls 85 to 95% of the time was more than the other walls (Table, margins for six walls in cm). Maximum geographical miss in spite of IGRT was noted for the superior (13.8%) and anterior walls (10.3%). Conclusions: Plan of the day ART is a feasible and promising technique for optimal treatment and dose escalation in bladder cancer. [Table: see text] No significant financial relationships to disclose.
Daily dosimetric variation between image-guided volumetric modulated arc radiotherapy and MR-guided daily adaptive radiotherapy for prostate cancer stereotactic body radiotherapy
