The current status of image-guided external beam radiotherapy for prostate cancer:

ACR Appropriateness Criteria for external beam radiation therapy treatment planning for clinically localized prostate cancer, part II of II

PURPOSE

To present the most updated American College of Radiology (ACR) Appropriateness Criteria formed by an expert panel on the appropriate delivery of external beam radiation to manage stage T1 and T2 prostate cancer (in the definitive setting and post-prostatectomy) and to provide clinical variants with expert recommendations based on accompanying Appropriateness Criteria for target volumes and treatment planning.

METHODS AND MATERIALS

The ACR Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a panel of multidisciplinary experts. The guideline development and revision process includes an extensive analysis of current medical literature from peer-reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In instances in which evidence is lacking or equivocal, expert opinion may supplement available evidence to recommend imaging or treatment.

RESULTS

The panel summarizes the most recent and relevant literature on the topic, including organ motion and localization methods, image guidance, and delivery techniques (eg, 3-dimensional conformal intensity modulation). The panel presents 7 clinical variants, including (1) a standard case and cases with (2) a distended rectum, (3) a large-volume prostate, (4) bilateral hip implants, (5) inflammatory bowel disease, (6) prior prostatectomy, and (7) a pannus extending into the radiation field. Each case outlines the appropriate techniques for simulation, treatment planning, image guidance, dose, and fractionation. Numerical rating and commentary is given for each treatment approach in each variant.

CONCLUSIONS

External beam radiation is a key component of the curative management of T1 and T2 prostate cancer. By combining the most recent medical literature, these Appropriateness Criteria can aid clinicians in determining the appropriate treatment delivery and personalized approaches for individual patients.

Feasibility of MRI-only treatment planning for proton therapy in brain and prostate cancers: Dose calculation accuracy in substitute CT images

PURPOSE

Magnetic resonance imaging (MRI) is increasingly used for radiotherapy target delineation, image guidance, and treatment response monitoring. Recent studies have shown that an entire external x-ray radiotherapy treatment planning (RTP) workflow for brain tumor or prostate cancer patients based only on MRI reference images is feasible. This study aims to show that a MRI-only based RTP workflow is also feasible for proton beam therapy plans generated in MRI-based substitute computed tomography (sCT) images of the head and the pelvis.

METHODS

The sCTs were constructed for ten prostate cancer and ten brain tumor patients primarily by transforming the intensity values of in-phase MR images to Hounsfield units (HUs) with a dual model HU conversion technique to enable heterogeneous tissue representation. HU conversion models for the pelvis were adopted from previous studies, further extended in this study also for head MRI by generating anatomical site-specific conversion models (a new training data set of ten other brain patients). This study also evaluated two other types of simplified sCT: dual bulk density (for bone and water) and homogeneous (water only). For every clinical case, intensity modulated proton therapy (IMPT) plans robustly optimized in standard planning CTs were calculated in sCT for evaluation, and vice versa. Overall dose agreement was evaluated using dose-volume histogram parameters and 3D gamma criteria.

RESULTS

In heterogeneous sCTs, the mean absolute errors in HUs were 34 (soft tissues: 13, bones: 92) and 42 (soft tissues: 9, bones: 97) in the head and in the pelvis, respectively. The maximum absolute dose differences relative to CT in the brain tumor clinical target volume (CTV) were 1.4% for heterogeneous sCT, 1.8% for dual bulk sCT, and 8.9% for homogenous sCT. The corresponding maximum differences in the prostate CTV were 0.6%, 1.2%, and 3.6%, respectively. The percentages of dose points in the head and pelvis passing 1% and 1 mm gamma index criteria were over 91%, 85%, and 38% with heterogeneous, dual bulk, and homogeneous sCTs, respectively. There were no significant changes to gamma index pass rates for IMPT plans first optimized in CT and then calculated in heterogeneous sCT versus IMPT plans first optimized in heterogeneous sCT and then calculated on standard CT.

CONCLUSIONS

This study demonstrates that proton therapy dose calculations on heterogeneous sCTs are in good agreement with plans generated with standard planning CT. An MRI-only based RTP workflow is feasible in IMPT for brain tumors and prostate cancers.

Correlation between patients' anatomical characteristics and interfractional internal prostate motion during intensity modulated radiation therapy for prostate cancer

Intensity modulated radiation therapy (IMRT) is one of a standard treatment for localized prostate cancer. Although lower complication is expected for smaller target margin, determination of optimal margin is important. For bony-structure based registration, internal prostate motion is the main factor determining the margin from clinical target volume to planning target volume. The purpose of this study was to measure interfractional internal motion of the prostate and to identity the factors which enlarge or reduce the margin, with special focus on patients’ anatomical characteristics. The 586 image sets of 16 patients acquired with megavoltage cone beam computed tomography were analyzed. For each patient, prostate shift in three directions was recorded for each fraction to calculate the required margin. Correlations between these values and patients’ anatomical characteristics were evaluated. The posteriorly required margin correlated positively with rectal volume and rectal mean area (p = 0.015 and p = 0.008), while random error in lateral, craniocaudal and anteroposterior direction correlated negatively (p = 0.014, 0.04 and 0.0026, respectively) with body mass index (BMI). In addition to the previously identified factor of distended rectum, BMI was newly identified as another significant factor influencing interfractional internal prostate motion.

Future directions from past experience: a century of prostate radiotherapy

Prostate cancer is the most commonly diagnosed noncutaneous malignancy in men, yet 100 years ago it was considered a rare disease. Over the past century, radiation therapy has evolved from a radium source placed in the urethra to today's advanced proton therapy delivered by only a few specialized centers. As techniques in radiation have evolved, the treatment of localized prostate cancer has become one of the most debated topics in oncology. Today, patients with prostate cancer must often make a difficult decision between multiple treatment modalities, each with the risk of permanent sequelae, without robust randomized data to compare every treatment option. Meanwhile, opinions of urologists and radiation oncologists about the risks and benefits involved with each modality vary widely. Further complicating the issue is rapidly advancing technology which often outpaces clinical data. This article represents a complete description of the evolution of prostate cancer radiation therapy with the goal of illuminating the historical basis for current challenges facing oncologists and their patients.

Present and future innovations in radiation oncology

The purpose of this article is to provide a review of innovations in radiation oncology that have been recently adopted as well as those that are likely to be adopted in the near future. Physics and engineering innovations, including image-guidance technologies and charged particle therapy, are discussed. Biologic innovations, including novel radiation sensitizers, functional imaging for use in treatment planning, and altered fractionation, are also discussed.

Conformal radiotherapy plus high dose rate brachytherapy prostate boost in patients with intermediate and high risk prostate cancer: our experience in Asian males

Purpose: Recent studies have shown increased prostate cancer control rates with radiation dose escalation. Herein the experience of dose escalation by high dose rate brachytherapy (HDR-BT) adjunct to the three-dimensional conformal radiation therapy (3D-CRT) for prostate cancer is presented.

Patients and methods: During the period between August 2005 and July 2007, patients with intermediate and high risk prostate cancer were treated with 3D-CRT of dose 46Gy ÷ 23 fractions to whole pelvis followed by: Arm A (102 patients): prostate boost with HDR-BT 14 Gy × 2 sessions and Arm B (103 patients): prostate boost via 3D-CRT of dose 26 Gy ÷ 13 fractions. Primary objectives were overall survival (OS), distant metastases free survival (DMFS) and PSA progression free survival (PPFS) rates. Secondary objectives were the toxicity profile and post-radiation histopathological response.

Results: At median follow up of 3.5 years, PPFS, DMFS and OS rates were; 97.8% versus 89.0% (p = 0.009), 98.1% versus 93.6% (p = 0.13) and 98.8% versus 91.6% (p = 0.24) in Arm A and Arm B. respectively. Grade 3 or 4 delayed genitourinary toxicities occurred in 2% and 4.8% of patients in Arm A and Arm B, respectively. Delayed grade 3 and 4 gastrointestinal toxicities were seen in 2% and 3.9% of patients in Arm A and Arm B, respectively. The post-radiation prostate biopsies were negative in 14/17(82.3%) and 9/15 (60%) in Arm A and Arm B, respectively.

Conclusion: 3D-CRT combined with HDR-BT resulted in better PPFS and lower morbidity than 3DCRT alone for intermediate and high risk prostate cancer.