Abstract
BackgroundTo investigate the feasibility and dosimetric improvements of a novel technique to temporarily displace critical structures in the pelvis and abdomen from tumor during high-dose radiotherapy.MethodsBetween 2010 and 2012, 11 patients received high-dose image-guided intensity-modulated radiotherapy with temporary organ displacement (TOD) at our institution. In all cases, imaging revealed tumor abutting critical structures. An all-purpose drainage catheter was introduced between the gross tumor volume (GTV) and critical organs at risk (OAR) and infused with normal saline (NS) containing 5-10% iohexol. Radiation planning was performed with the displaced OARs and positional reproducibility was confirmed with cone-beam CT (CBCT). Patients were treated within 36 hours of catheter placement. Radiation plans were re-optimized using pre-TOD OARs to the same prescription and dosimetrically compared with post-TOD plans. A two-tailed permutation test was performed on each dosimetric measure.ResultsThe bowel/rectum was displaced in six patients and kidney in four patients. One patient was excluded due to poor visualization of the OAR; thus 10 patients were analyzed. A mean of 229 ml (range, 80–1000) of NS 5-10% iohexol infusion resulted in OAR mean displacement of 17.5 mm (range, 7–32). The median dose prescribed was 2400 cGy in one fraction (range, 2100–3000 in 3 fractions). The mean GTV Dmin and PTV Dmin pre- and post-bowel TOD IG-IMRT dosimetry significantly increased from 1473 cGy to 2086 cGy (p=0.015) and 714 cGy to 1214 cGy (p=0.021), respectively. TOD increased mean PTV D95 by 27.14% of prescription (p=0.014) while the PTV D05 decreased by 9.2% (p=0.011). TOD of the bowel resulted in a 39% decrease in mean bowel Dmax (p=0.008) confirmed by CBCT. TOD of the kidney significantly decreased mean kidney dose and Dmax by 25% (0.022).ConclusionsTOD was well tolerated, reproducible, and facilitated dose escalation to previously radioresistant tumors abutting critical structures while minimizing dose to OARs.
Highlights
Radiation treatment planning and delivery methods have become increasingly conformal over the past 50 years
We present a cohort of patients treated with tumor-ablative radiosurgery and temporary organ displacement (TOD) for radioresistant tumors that abutted critical normal tissues
The first patient was excluded from this analysis secondary to lack of contrast in injected saline during computed tomography (CT) simulation, resulting in poor visualization of the organs at risk (OAR), leaving 10 patients
Summary
Radiation treatment planning and delivery methods have become increasingly conformal over the past 50 years. Multiple techniques aimed at shifting critical structures apart from the PTV have been employed in conventionally fractionated conformal radiation. Simple maneuvers such as moderate-deep inspiration breath hold during radiation have achieved substantial internal organ displacement in the treatment of left-sided breast cancer, resulting in decreased cardiac dose [3]. Due to lengthy treatment times of conventional fractionation of up to 9 weeks, optimal spacers have yet to be routinely incorporated into clinical practice Another technique to decrease dose to normal tissues through tighter margins via target immobilization was the endorectal balloon (ERB) which reduced maximal tumor displacement from 4 mm to ≤ 1 mm [7]. To investigate the feasibility and dosimetric improvements of a novel technique to temporarily displace critical structures in the pelvis and abdomen from tumor during high-dose radiotherapy
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