Intensity-Modulated Radiotherapy as Primary Therapy for Prostate Cancer: Report on Acute Toxicity After Dose Escalation With Simultaneous Integrated Boost to Intraprostatic Lesion

The aim of this study was assess the patient setup errors for various tumor sites based on clinical data from a sufficient number of treatments with volumetric‐modulated arc therapy (VMAT) using daily pretreatment CBCT imaging guidance. In addition, we calculated and compared the planning target volume (PTV) margins for all disease sites based on an analysis of specific systematic and random errors in our institution. All patients underwent pretreatment kV‐CBCT imaging. The various tumor sites were divided into four categories; 21 brain (438 fractions), 35 head‐and‐neck tumors (H&N, 933 fractions), 19 thorax and abdomen tumors (T&A, 313 fractions), and 17 prostate cancer tumors (546 fractions). Overall distributions of setup corrections in all directions, frequencies of 3D vector lengths, institution‐specific setup error, and PTV margins were analyzed. The longitudinal distribution for the T&A site represented an asymmetric offset in the negative direction. Rotational distributions were comparable for all treatment sites, and the prostate site had the narrowest distribution of ≤±2∘. The cumulative frequencies of 3D vector length of ≥ 7 mm were rare for brain lesions and H&N, but more common for T&A and prostate lesions at 25.6% and 12.1%, respectively. The overall mean error for all treatment sites were within ±1 mm and ±0.1∘, with the exception of the T&A site, which had overall mean error of 2 mm in the negative longitudinal direction. The largest magnitude of systematic error and random error for the brain lesions and H&N was 1.4 mm in the translational directions, and 3.3 mm for T&A and prostate lesions. The PTV margins required in this analysis are ≤ 4 mm for the brain lesions and H&N in all translational directions, but ranged from 4 to 10 mm for T&A and prostate lesions. Analysis of each institution's specific setup errors using daily CBCT is essential for determining PTV margins and reducing setup uncertainties, because setup errors vary according to each immobilization system and patient.PACS number: 87.55.km

Section: Introductionmentioning

confidence: 99%

Assessment of setup uncertainties for various tumor sites when using daily CBCT for more than 2200 VMAT treatments

Baek

Kim

et al. 2014

“…In order for an axial slice to be reconstructed, the helical dataset needs to be interpolated to create a full set of projection data within the plane of reconstruction. The use of projection data from outside the reconstructed volume leads to a reduction in axial resolution 1 , 2 , 3 , 4 , 5 The slice sensitivity profile (SSP) allows the measurement of the axial resolution of helical CT systems.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of techniques for slice sensitivity profile measurement and analysis

Greene

Rong

2014

The purpose of this study was to compare the resulting full width at half maximum of slice sensitivity profiles (SSP) generated by several commercially available point response phantoms, and determine an appropriate imaging technique and analysis method. Four CT phantoms containing point response objects designed to produce a delta impulse signal used in this study: a Fluke CT‐SSP phantom, a Gammex 464, a CatPhan 600, and a Kagaku Micro Disc phantom. Each phantom was imaged using 120 kVp, 325 mAs, head scan field of view, 32×0.625 mm helical scan with a 20 mm beam width and a pitch of 0.969. The acquired images were then reconstructed into all available slice thicknesses false(0.625 mm−5.0 mmfalse). A computer program was developed to analyze the images of each dataset for generating a SSP from which the full width at half maximum (FWHM) was determined. Two methods for generating SSPs were evaluated and compared by choosing the mean vs. maximum value in the ROI, along with two methods for evaluating the FWHM of the SSP, linear interpolation and Gaussian curve fitting. FWHMs were compared with the manufacturer's specifications using percent error and z‐test with a significance value of p<0.05. The FWHMs from each phantom were not significantly different false(p≥0.089false) with an average error of 3.5%. The FWHMs from SSPs generated from the mean value were statistically different false(p≤3.99×1013false). The FWHMs from the different FWHM methods were not statistically different false(p≤0.499false). Evaluation of the SSP is dependent on the ROI value used. The maximum value from the ROI should be used to generate the SSP whenever possible. SSP measurement is independent of the phantoms used in this study.PACS number: 87.

“…Singh et al (11) used a 3 mm margin due to limitations in image guidance. Fonteyne et al (2) used an 8 mm margin to account for planning uncertainties. Ippoliot et al (4) and Riches et al (10) do not provide an explanation of their choices of 5 mm and 2 mm margins, respectively.…”

Section: Discussionmentioning

confidence: 99%

“…One disease site in radiation oncology that has seen an increase in MRI is the prostate, where the high‐risk intraprostatic lesion (IPL) can be identified 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 . Since dose escalation can improve cure rates, delivering an escalated dose to the IPL while treating the remainder of the prostate to the normal prescription dose can reduce toxicity while increasing tumor control 12 , 13 , 14 .…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Quantification of the margin required for treating intraprostatic lesions

Studenski

Valenciaga

Abramowitz

et al. 2016

Advances in magnetic resonance imaging (MRI) sequences allow physicians to define the dominant intraprostatic lesion (IPL) in prostate radiation therapy treatments allowing for dose escalation and potentially increased tumor control. This work quantifies the margin required around the MRI‐defined IPL accounting for both prostate motion and deformation. Ten patients treated with a simultaneous integrated intraprostatic boost (SIIB) were retrospectively selected and replanned with incremental 1 mm margins from 0‐5 mm around the IPL to determine if there were any significant differences in dosimetric parameters. Sensitivity analysis was then performed accounting for random and systematic uncertainties in both prostate motion and deformation to ensure adequate dose was delivered to the IPL. Prostate deformation was assessed using daily CBCT imaging and implanted fiducial markers. The average IPL volume without margin was 2.3% of the PTV volume and increased to 11.8% with a 5 mm margin. Despite these changes in volume, the only statistically significant dosimetric difference was found for the PTV maximum dose, which increased with increasing margin. The sensitivity analysis demonstrated that a 3.0 mm margin ensures >95% IPL coverage accounting for both motion and deformation. We found that a margin of 3.0 mm around the MRI defined IPL is sufficient to account for random and systematic errors in IPL position for the majority of cases.PACS number(s): 87.55.de