Image-Guided Radiotherapy for Prostate Cancer using 3 Different Techniques: Localization Data of 186 Patients

ESTRO ACROP consensus guideline on the use of image guided radiation therapy for localized prostate cancer

Use of image-guided radiation therapy (IGRT) helps to account for daily prostate position changes during radiation therapy for prostate cancer. However, guidelines for the use of IGRT are scarce. An ESTRO panel consisting of leading radiation oncologists and medical physicists was assembled to review the literature and formulate a consensus guideline of methods and procedure for IGRT in prostate cases. Advanced methods and procedures are also described which the committee judged relevant to further improve clinical practice. Moreover, ranges for margins for the three most popular IGRT scenarios have been suggested as examples.

Impact of image guidance on toxicity and tumour outcome in moderately hypofractionated external-beam radiotherapy for prostate cancer

To report toxicity and efficacy outcome of moderately hypofractionated image-guided external-beam radiotherapy in a large series of patients treated for prostate cancer (PCa). Between 10/2006 and 12/2015, 572 T1-T3N0M0 PCa patients received 70.2 Gy in 26 fractions at 2.7 Gy/fraction: 344 patients (60%) with three-dimensional conformal radiotherapy (3D-CRT) and 228 (40%) with intensity-modulated radiotherapy (IMRT). Radiation Therapy Oncology Group/European Organization for Research and Treatment of Cancer criteria and Houston definition (nadir + 2) were used for toxicity and biochemical failure evaluation, respectively. Median age was 74 years (interquartile range 69-77). Compared with 3D-CRT, in IMRT group more high-risk patients (29% vs 18%; P = 0.002) and more high-volume target (75% vs 60%; P < 0.001) were included. Acute gastro-intestinal (GI) toxicity G > 1 were registered in 8% and in 11% IMRT and 3D-CRT patients, respectively, whereas late GI G > 1 were observed in 2% and 16% IMRT and 3D-CRT patients, respectively. Acute genito-urinary (GU) toxicity G > 1 were registered in 26% and 40% IMRT and 3D-CRT patients, respectively, whereas late GU G > 1 occurred in 5% IMRT and 15% 3D-CRT patients. Multivariate proportional hazard Cox models confirmed significantly greater risk of late toxicity with 3D-CRT compared to IMRT for GU > 1 (P = 0.004) and for GI > 1 (P < 0.001). With a median 4-year follow-up, overall survival (OS), clinical progression-free survival (cPFS) and biochemical PFS (bPFS) for the whole series were 91%, 92% and 91%, respectively. cPFS and bPFS were significantly different by risk groups. Multivariate Cox models for bPFS and cPFS showed no difference between irradiation techniques and a significant impact of risk group and initial PSA. Moderately hypofractionated radiotherapy is a viable treatment option for localized PCa with excellent tumour control and satisfactory toxicity profile. IMRT seems associated with a reduction in toxicity, whereas tumour control was equal between IMRT and 3D-CRT patients and depended mainly on the risk category.

Cone-beam CT-based inter-fraction localization errors for tumors in the pelvic region

PURPOSE

To evaluate inter-fraction tumor localization errors (TE) in the RapidArc® treatment of pelvic cancers based on CBCT. Appropriate CTV-to PTV margins in a non-IGRT scenario have been proposed.

METHODS

Data of 928 patients with prostate, gynecological, and rectum/anal canal cancers were retrospectively analyzed to determine systematic and random localization errors. Two protocols were used: daily online IGRT (d-IGRT) and weekly IGRT. The latter consisted in acquiring a CBCT for the first 3 fractions and subsequently once a week. TE for patients who underwent d-IGRT protocol were calculated using either all CBCTs or the first 3.

RESULTS

The systematic (and random) TE in the AP, LL, and SI direction were: for prostate bed 2.7(3.2), 2.3(2.8) and 1.9(2.2) mm; for prostate 4.2(3.1), 2.9(2.8) and 2.3(2.2) mm; for gynecological 3.0(3.6), 2.4(2.7) and 2.3(2.5) mm; for rectum 2.8(2.8), 2.4(2.8) and 2.3(2.5) mm; for anal canal 3.1(3.3), 2.1(2.5) and 2.2(2.7) mm. CTV-to-PTV margins determined from all CBCTs were 14 mm in the AP, 10 mm in the LL and 9-9.5 mm in the SI directions for the prostate and the gynecological groups and 9.5-10.5 mm in AP, 9 mm in LL and 8-10 mm in the SI direction for the prostate bed and the rectum/anal canal groups. If assessed on the basis of the first 3 CBCTs, the calculated CTV-to-PTV margins were slightly larger.

CONCLUSIONS

without IGRT, large CTV-to-PTV margins up to 15 mm are required to account for inter-fraction tumor localization errors. Daily IGRT should be used for all hypo-fractionated treatments to reduce margins and avoid increased toxicity to critical organs.

Recent advances in radiation oncology

Radiotherapy (RT) is very much a technology-driven treatment modality in the management of cancer. RT techniques have changed significantly over the past few decades, thanks to improvements in engineering and computing. We aim to highlight the recent developments in radiation oncology, focusing on the technological and biological advances. We will present state-of-the-art treatment techniques, employing photon beams, such as intensity-modulated RT, volumetric-modulated arc therapy, stereotactic body RT and adaptive RT, which make possible a highly tailored dose distribution with maximum normal tissue sparing. We will analyse all the steps involved in the treatment: imaging, delineation of the tumour and organs at risk, treatment planning and finally image-guidance for accurate tumour localisation before and during treatment delivery. Particular attention will be given to the crucial role that imaging plays throughout the entire process. In the case of adaptive RT, the precise identification of target volumes as well as the monitoring of tumour response/modification during the course of treatment is mainly based on multimodality imaging that integrates morphological, functional and metabolic information. Moreover, real-time imaging of the tumour is essential in breathing adaptive techniques to compensate for tumour motion due to respiration. Brief reference will be made to the recent spread of particle beam therapy, in particular to the use of protons, but also to the yet limited experience of using heavy particles such as carbon ions. Finally, we will analyse the latest biological advances in tumour targeting. Indeed, the effectiveness of RT has been improved not only by technological developments but also through the integration of radiobiological knowledge to produce more efficient and personalised treatment strategies.

Volumetric-modulated arc therapy and intensity-modulated radiation therapy treatment planning for prostate cancer with flattened beam and flattening filter free linear accelerators

This study on patients with localized prostate cancer was set up to investigate valuable differences using flattened beam (FB) and flattening filter free (FFF) mode in the application of intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT). For ten patients, four different plans were calculated with Oncentra planning system of Elekta, using Synergy machines: IMRT and VMAT, with and without flattening filter. Homogeneity and conformity indexes, dose to the organs at risk, and measurements of peripheral dose and dosimetric plan verification including record of the delivery times were analyzed and statistically evaluated. The indexes for homogeneity and conformity (CTV and PTV) are either advantageous or not significantly different for FFF compared to FB with one minor exception. Regarding the doses to the organs at risk and the measured peripheral dose, equivalent or lower doses were delivered for FFF than with FB. Furthermore, the delivery times were significantly shorter for FFF. VMAT compared to IMRT reveals benefits or at least equivalent values. VMAT-FFF combines the most advantageous plan quality parameters with the shortest delivery times and reduced peripheral dose and is therefore recommended for the given equipment and cancer localization.

Three-dimensional surface and ultrasound imaging for daily IGRT of prostate cancer

Background

Image guided radiotherapy (IGRT) is an essential pre-requisite for delivering high precision radiotherapy. We compared daily variation detected by two non-ionizing imaging modalities (surface imaging and trans-abdominal ultrasound, US) to verify prostate patient setup and internal organ variations.

Methods

Forty patients with organ confined prostate cancer and candidates to curative radiotherapy were enrolled in this prospective study. At each treatment session, after laser alignment, all patients received imaging by a 3D-surface and a 3D-US system. The shifts along the three directions (anterior-posterior AP, cranial-caudal CC, and later-lateral LL) were measured in terms of systematic and random errors. Then, we performed statistical analysis on the differences and the possible correlations between the two modalities.

Results

For both IGRT modalities, surface imaging and US, 1318 acquisitions were collected. According with Shapiro Wilk test, the positioning error distributions were not Gaussian for both modalities.

The differences between the systematic errors detected by the two modalities were statistically significant only in LL direction (p < 0.05), while the differences between the random errors were not statistically significant in any directions.

The 95% confidence interval of the residual errors obtained by subtracting the random errors detected with surface images to those detected with US was included in the range from −7 mm to 7 mm corresponding to the minimum PTV margin adopted in AP direction in our clinical routine.

Conclusions

From our data, it emerges that setup misalignments measured by surface imaging can be predictive of US displacements after the adjustment for systematic errors. Moreover, surface imaging can detect setup errors predictive of registration errors measured by US. This data suggest that the two IGRT modalities could be considered as complementary to each other and could represent a daily “low-cost” and non-invasive IGRT modality in prostate cancer patients.