Three discipline collaborative radiation therapy (3DCRT) special debate: We should treat all cancer patients with hypofractionation

Abstract

Radiation Oncology is a highly multidisciplinary medical specialty, drawing significantly from three scientific disciplinesmedicine, physics, and biology. As a result, discussion of controversies or changes in practice within radiation oncology must involve input from all three disciplines. For this reason, significant effort has been expended recently to foster collaborative multidisciplinary research in radiation oncology, with substantial demonstrated benefit. 1-3 In light of these results, we endeavor here to adopt this "team-science" approach to the traditional debates featured in this journal. This article is part of a series of special debates entitled "Three Discipline Collaborative Radiation Therapy (3DCRT)" in which each debate team will include a radiation oncologist, medical physicist, and radiobiologist. We hope that this format will not only be engaging for the readership but will also foster further collaboration in the science and clinical practice of radiation oncology. 2 | INTRODUCTION Better Physics, just within this 21st century, now enables us to deliver radiation to a target volume with accuracy better than 1 mm. Given this accuracy, why fractionate at all? If we can put dose only on the cancer, and extremely little on critical normal tissue, then surely just give a high single dose to that cancer, and job done. Local tumor control is 100% with minimal toxicity. If only. Two linked issues keep Biology (radiobiology) in the clinical game. First, our ability to identify, localize, and immobilize anatomy and pathology does not yet correspond with this submillimeter accuracy of radiotherapy delivery. Second, even if that imaging resolution is reached it could still not detect occult disease. Consequently, unless the cancer is truly isolated, which it sometimes may be, for example, in organ-confined early-stage prostate cancer, it is always necessary to "degrade" the treatment plan by defining a CTV and PTV into which the radiation delivery is expanded. This inevitably imposes a risk of normaltissue radiotoxicity, therefore we must use fractionation to minimize that risk. Traditionally, that fractionation has been carried out with doses close to 2 Gy per fraction. In fractionation, the Linear-Quadratic (LQ) model describes the relationship between total dose and dose per fraction, for isoeffect. A lower α/β value indicates a steeper relationship. Generally late-reacting normal tissues exhibit lower α/β and early-reacting normal tissues exhibit higher α/β. Malignancies can have lower or higher α/β depending on the tumor type. In some malignancies, notably human prostate, clinical data indeed indicate α/ β as low as 1.5 and thus in prostate cancers, and likewise in earlystage breast cancers, hypofractionation, arbitrarily defined as a dose per fraction> 2.2 Gy, has become standard of care. In early-stage non-small cell lung cancers a higher α/β is seen, similar to early-reacting normal tissue, but these isolated malignancies can still be more effectively controlled with radical hypofractionation wh...

The future of MRI in radiation therapy: Challenges and opportunities for the MR community

“… 78 Accurate, low‐latency motion characterization will facilitate gated treatment, 79 tumor tracking during irradiation, 80 , 81 , 82 , 83 , 84 and could enable real‐time adaptive replanning. Such precise treatments, delivered to smaller PTVs, will permit safe dose escalation 85 , 86 and hypofractionation 87 to improve patient outcomes and clinical efficiency. Furthermore, management of bulk patient motion with real‐time MRI could remove the need for uncomfortable immobilization devices.…”

Optimizing Breast Reconstruction through Integration of Plastic Surgery and Radiation Oncology

“…Current ASTRO guidelines recommend hypofractionation in patients who are >50 years old, T1–T2 tumors, negative nodal disease, hormone positive cancer, and low grade disease. 16 …”

“…Current ASTRO guidelines recommend hypofractionation in patients who are >50 years old, T1-T2 tumors, negative nodal disease, hormone positive cancer, and low grade disease. 16 The radiation dose at the skin surface is lower than the dose at the target because photons require tissue interaction to build up the total radiation dose. An additional bolus may be used to increase the chest wall skin dose for patients who have an increased risk of chest wall recurrence (ie, large tumors, positive/close margins, and inflammatory breast cancer).…”