Cancers de prostate : quelles techniques de radiothérapie pour quelles tumeurs ? Enjeux éthiques et méthodologiques

Compréhension/acceptation de la radiothérapie : un dilemme éthique résolu par une éthique de la considération et de la sollicitude

PURPOSE

Ethical questions are poorly investigated specifically in radiation oncology. The objective of the study was to identify and understand the main ethical issue in radiation oncology.

MATERIALS AND METHODS

A quantitative analysis was based on the answers to a questionnaire of 200 professionals from 22 radiation oncology departments. The questionnaire mainly aimed to characterize the main ethical issue. A monocentric qualitative analysis was based on semi-structured interviews focused on the main identified ethical issue, carried out with eight technologists, and 20 patients undergoing radiotherapy.

RESULTS

The main ethical issue was the understanding and/or acceptance of the treatment by the patients (71 %), which frequently arises (more than once a month) (52 %), and corresponds to an ethical tension between the principles of respect for autonomy and beneficence (the good as viewed by the patient) as defined by Beauchamp and Childress. The technologists, wish the patient to be fully involved in his treatment, with the even possibility of refusing it. However, excluding paternalism and autonomic relentlessness, the technologists have the feeling of acting for the good of the patients by treating them with radiation, even if the patients are not always aware of it, because they are within a situation of vulnerability. If the hierarchy of principles is a compromise alternative, this problem is finally well resolved by the effective implementation of an ethic of consideration and solicitude, restoring the patient capabilities, i.e. the maximum development of his potentialities in his situation of vulnerability. Beyond the legal dimension, patient information is crucial and must consider the specific temporality of the patient.

CONCLUSION

The main ethical issue in radiation oncology is the understanding and/or acceptance of the treatment involving the development of an ethic of consideration and solicitude.

[Moderate or extreme hypofractionation and localized prostate cancer: The times are changing]

There are many treatment options for localized prostate cancers, including active surveillance, brachytherapy, external beam radiotherapy, and radical prostatectomy. Quality of life remains a primary objective in the absence of superiority of one strategy over another in terms of specific survival with similar long-term biochemical control rates. Despite a significant decrease in digestive and urinary toxicities thanks to IMRT and IGRT, external radiotherapy remains a treatment that lasts approximately 2 months or 1.5 months, when combined with a brachytherapy boost. Given the specific radiosensitivity of this tumor, several randomized studies have shown that a hypofractionated scheme is not inferior in terms of biochemical control and toxicities, allowing to divide the number of fractions by a factor 2 to 8. Given that SBRT becomes a validated therapeutic option for a selected population of patients with localized prostate cancer, extreme hypofractionation is becoming a strong challenger of conventional external radiotherapy or brachytherapy.

A treatment planning study comparing tomotherapy, volumetric modulated arc therapy, Sliding Window and proton therapy for low-risk prostate carcinoma

BACKGROUND

Comparing radiation treatment plans to ascertain the optimal intensity-modulated radiation technique for low-risk prostate cancer.

METHODS

Treatment plans for 20 randomly selected patients were generated using the same dose objectives. A dosimetric comparison was performed between various intensity-modulated techniques, including protons. All treatment plans provided conventional treatment with 79.2Gy. Dosimetric indices for the target volume and organs at risk (OAR), including homogeneity index and four conformity indices were analyzed.

RESULTS

No statistically significant differences between techniques were observed for homogeneity values. Dose distributions showed significant differences at low-to-medium doses. At doses above 50Gy all techniques revealed a steep dose gradient outside the planning target volume (PTV). Protons demonstrated superior rectum sparing at low-to-higher doses (V10-V70, P < .05) and bladder sparing at low-to-medium doses (V10-V30, P < .05). Helical tomotherapy (HT) provided superior rectum sparing compared to Sliding Window (SW) and Rapid Arc (RA) (V10-V70, P < .05). SW displayed superior bladder sparing compared to HT and RA (V10-V50, P < .05). Protons generated significantly higher femoral heads exposure and HT had superior sparing of those.

CONCLUSION

All techniques are able to provide a homogeneous and highly conformal dose distribution. Protons demonstrated superior sparing of the rectum and bladder at a wide dose spectrum. The radiation technique itself as well as treatment planning algorithms result in different OAR sparing between HT, SW and RA, with superior rectum sparing by HT and superior bladder sparing by SW. Radiation plans can be further optimized by individual modification of dose objectives dependent on treatment plan strategy.

[Clinical to planning target volume margins in prostate cancer radiotherapy]

The knowledge of inter- and intrafraction motion and deformations of the intrapelvic target volumes (prostate, seminal vesicles, prostatectomy bed and lymph nodes) as well as the main organs at risk (bladder and rectum) allow to define rational clinical to planning target volume margins, depending on the different radiotherapy techniques and their uncertainties. In case of image-guided radiotherapy, prostate margins and seminal vesicles margins can be between 5 and 10mm. The margins around the prostatectomy bed vary from 10 to 15mm and those around the lymph node clinical target volume between 7 and 10mm. Stereotactic body radiotherapy allows lower margins, which are 3 to 5mm around the prostate. Image-guided and stereotactic body radiotherapy with adequate margins allow finally moderate or extreme hypofractionation.

[Image-guided radiotherapy]

The IGRT is described in its various equipment and implementation. IGRT can be based either on ionizing radiation generating 2D imaging (MV or kV) or 3D imaging (CBCT or MV-CT) or on non-ionizing radiation (ultrasound, optical imaging, MRI or radiofrequency). Adaptive radiation therapy is then presented in its principles of implementation. The function of the technicians for IGRT is then presented and the possible dose delivered by the on-board imaging is discussed. The quality control of IGRT devices is finally described.

[Interobserver variability study for daily cone beam computed tomography registration of prostate volumetric modulated arc therapy]

PURPOSE

This work evaluated the interobserver variability in cone beam computed tomography (CBCT) registration for prostate cancers treated with intensity-modulated radiotherapy.

MATERIAL AND METHODS

Twelve technologists realized 286 CBCT/CT registrations (bone registration followed by prostate to prostate registration). The registration results were compared to those obtained by two radiation oncologists (reference). Each technologist reported the shifts calculated by the software in all three axes. A statistical analysis allowed us to calculate the minimum threshold under which 95% of the observers found similar values. A variance analysis followed by the post hoc test were used to find differences in interobserver registration variability and determine whether any individual users performed registrations which differed significantly from those of the other users.

RESULTS

The registration differences compared to the reference in the three directions in terms of 95th percentile are: 2.1mm left-right, 3.5mm target-gun, 7.3mm anterior-posterior. In the posterior direction, 4% of the observers have found differences superior to 8mm, margin used in routine without the use of a daily CBCT. The variance test revealed a P-value <0.05 only for target-gun and for all observers there was no significant difference compared to the reference.

CONCLUSION

This study confirmed the interest of a 3D tissue registration for prostate treatments. The registration study showed a good interobserver reproducibility. This showed the importance of a daily CBCT/CT registration in prostate treatment with the possibility of a planning target volume margin reduction in the three directions. An evaluation of a partial delegation of registration to technologists should be done by the radiation oncologists.

[Strategy for technical evaluation in radiation oncology: methodological and ethical aspects, the French society for radiation oncology's opinion]

Evidence-based medicine is a paradigm founded on a hierarchy of research design, accepted as a dogma. Applied to radiation oncology, and specifically to radiotherapy technical comparisons, evidence-based medicine implies methodological and ethical problems. The concept of "incremental" evolution and the dosimetric evidence are proposed as an acceptable alternative to comparative clinical trials if total dose, time, fractionation, and target volumes are not modified. For other situations, either randomized comparative trials or observational studies are needed. When randomized comparative trials are not possible, observational studies, whose validity can be enhanced by appropriate methodology, must be considered as a valid method.