Editing Radiation therapy (section)

==Medical uses==
[[File:Palliative Care Options for a Young Adult Patient with a Diffuse Intrinsic Pontine Glioma - Fig. 3.png|thumb|Radiation therapy for a patient with a [[diffuse intrinsic pontine glioma]], with radiation dose color-coded]]
It is estimated that half of the US' 1.2M invasive cancer cases diagnosed in 2022 received radiation therapy in their treatment program.<ref name="PMID 29261879">{{cite journal |journal=StatPearls|last1=Cooper |first1=Jeffrey S. |last2=Hanley |first2=Mary E. |last3=Hendriksen |first3=Stephen |last4=Robins |first4=Marc |title=Hyperbaric Treatment of Delayed Radiation Injury |url=https://www.ncbi.nlm.nih.gov/books/NBK470447/ |publisher=StatPearls Publishing|via=National Center for Biotechnology Information |access-date=23 July 2023 |date=August 30, 2022|pmid=29261879 }}</ref>  Different cancers respond to radiation therapy in different ways.<ref>CK Bomford, IH Kunkler, J Walter. Walter and Miller's Textbook of Radiation therapy (6th Ed), p311</ref><ref>{{cite web | title = Radiosensitivity | work = GP Notebook | url = http://www.gpnotebook.co.uk/simplepage.cfm?ID=2060451853 }}</ref><ref>{{cite web | vauthors = Tidy C | veditors = Bonsall A| date = 23 December 2015 | title = Radiation therapy- what GPs need to know | work = patient.co.uk | url = http://patient.info/doctor/radiotherapy }}</ref><!-- Note: these refs support the whole list here -->

The response of a cancer to radiation is described by its radiosensitivity.
Highly radiosensitive cancer cells are rapidly killed by modest doses of radiation. These include [[leukemias]], most [[lymphomas]], and [[germ cell tumors]].
The majority of [[epithelial cancers]] are only moderately radiosensitive, and require a significantly higher dose of radiation (60–70&nbsp;Gy) to achieve a radical cure.
Some types of cancer are notably radioresistant, that is, much higher doses are required to produce a radical cure than may be safe in clinical practice. [[Renal cell cancer]] and [[melanoma]] are generally considered to be radioresistant but radiation therapy is still a palliative option for many patients with [[metastatic]] melanoma. Combining radiation therapy with [[immunotherapy]] is an active area of investigation and has shown some promise for melanoma and other cancers.<ref>{{cite journal | vauthors = Maverakis E, Cornelius LA, Bowen GM, Phan T, Patel FB, Fitzmaurice S, He Y, Burrall B, Duong C, Kloxin AM, Sultani H, Wilken R, Martinez SR, Patel F | display-authors = 6 | title = Metastatic melanoma - a review of current and future treatment options | journal = Acta Dermato-Venereologica | volume = 95 | issue = 5 | pages = 516–524 | date = May 2015 | pmid = 25520039 | doi = 10.2340/00015555-2035 | doi-access = free }}</ref>

It is important to distinguish the radiosensitivity of a particular tumor, which to some extent is a laboratory measure, from the radiation "curability" of a cancer in actual clinical practice. For example, leukemias are not generally curable with radiation therapy, because they are disseminated through the body. Lymphoma may be radically curable if it is localized to one area of the body. Similarly, many of the common, moderately radioresponsive tumors are routinely treated with curative doses of radiation therapy if they are at an early stage. For example, [[Skin neoplasm|non-melanoma skin cancer]], [[head and neck cancer]], [[breast cancer]], [[non-small cell lung cancer]], [[cervical cancer]], [[anal cancer]], and [[prostate cancer]]. With the exception of oligometastatic disease, [[metastatic]] cancers are incurable with radiation therapy because it is not possible to treat the whole body.{{cn|date=February 2024}}

Modern radiation therapy relies on a CT scan to identify the tumor and surrounding normal structures and to perform dose calculations for the creation of a complex radiation treatment plan. The patient receives small skin marks to guide the placement of treatment fields.<ref name=camphausen>{{cite book | vauthors = Camphausen KA, Lawrence RC | chapter-url = http://www.cancernetwork.com/cancer-management-11/chapter02/article/10165/1399960 | chapter = Principles of Radiation Therapy | archive-url = https://web.archive.org/web/20090515031929/http://www.cancernetwork.com/cancer-management-11/chapter02/article/10165/1399960 | archive-date = 15 May 2009 | veditors = Pazdur R, Wagman LD, Camphausen KA, Hoskins WJ | title = Cancer Management: A Multidisciplinary Approach | edition = 11th | date = 2008 | publisher =  UBM Medica LLC }}</ref> Patient positioning is crucial at this stage as the patient will have to be placed in an identical position during each treatment.  Many patient positioning devices have been developed for this purpose, including masks and cushions which can be molded to the patient. [[Image-guided radiation therapy]] is a method that uses imaging to correct for positional errors of each treatment session.{{cn|date=February 2024}}

Building on the principles of [[Image-guided radiation therapy]], Daily MR-guided ART (MRgART) offers many dosimetric advantages over the traditional single-plan RT workflow, including the ability to conform the high-dose region to the tumor as the anatomy changes throughout the course of RT.<ref>{{Cite journal |last1=Winkel |first1=Dennis |last2=Bol |first2=Gijsbert H. |last3=Kroon |first3=Petra S. |last4=van Asselen |first4=Bram |last5=Hackett |first5=Sara S. |last6=Werensteijn-Honingh |first6=Anita M. |last7=Intven |first7=Martijn P.W. |last8=Eppinga |first8=Wietse S.C. |last9=Tijssen |first9=Rob H.N. |last10=Kerkmeijer |first10=Linda G.W. |last11=de Boer |first11=Hans C.J. |last12=Mook |first12=Stella |last13=Meijer |first13=Gert J. |last14=Hes |first14=Jochem |last15=Willemsen-Bosman |first15=Mirjam |date=September 2019 |title=Adaptive radiotherapy: The Elekta Unity MR-linac concept |journal=Clinical and Translational Radiation Oncology |language=en |volume=18 |pages=54–59 |doi=10.1016/j.ctro.2019.04.001 |pmc=6630157 |pmid=31341976}}</ref><ref>{{Cite journal |last1=Hall |first1=William A. |last2=Paulson |first2=Eric S. |last3=van der Heide |first3=Uulke A. |last4=Fuller |first4=Clifton D. |last5=Raaymakers |first5=B.W. |last6=Lagendijk |first6=Jan J.W. |last7=Li |first7=X. Allen |last8=Jaffray |first8=David A. |last9=Dawson |first9=Laura A. |last10=Erickson |first10=Beth |last11=Verheij |first11=Marcel |last12=Harrington |first12=Kevin J. |last13=Sahgal |first13=Arjun |last14=Lee |first14=Percy |last15=Parikh |first15=Parag J. |date=November 2019 |title=The transformation of radiation oncology using real-time magnetic resonance guidance: A review |journal=European Journal of Cancer |language=en |volume=122 |pages=42–52 |doi=10.1016/j.ejca.2019.07.021 |pmc=8447225 |pmid=31614288}}</ref><ref>{{Cite journal |last1=McDonald |first1=Brigid A. |last2=Zachiu |first2=Cornel |last3=Christodouleas |first3=John |last4=Naser |first4=Mohamed A. |last5=Ruschin |first5=Mark |last6=Sonke |first6=Jan-Jakob |last7=Thorwarth |first7=Daniela |last8=Létourneau |first8=Daniel |last9=Tyagi |first9=Neelam |last10=Tadic |first10=Tony |last11=Yang |first11=Jinzhong |last12=Li |first12=X. Allen |last13=Bernchou |first13=Uffe |last14=Hyer |first14=Daniel E. |last15=Snyder |first15=Jeffrey E. |date=2023-01-26 |title=Dose accumulation for MR-guided adaptive radiotherapy: From practical considerations to state-of-the-art clinical implementation |journal=Frontiers in Oncology |language=English |volume=12 |doi=10.3389/fonc.2022.1086258 |doi-access=free |issn=2234-943X |pmc=9909539 |pmid=36776378}}</ref>

The response of a tumor to radiation therapy is also related to its size. Due to complex [[radiobiology]], very large tumors are affected less by radiation compared to smaller tumors or microscopic disease. Various strategies are used to overcome this effect. The most common technique is surgical resection prior to radiation therapy. This is most commonly seen in the treatment of breast cancer with [[wide local excision]] or [[mastectomy]] followed by [[adjuvant radiation therapy]]. Another method is to shrink the tumor with [[neoadjuvant]] chemotherapy prior to radical radiation therapy. A third technique is to enhance the radiosensitivity of the cancer by giving certain drugs during a course of radiation therapy. Examples of radiosensitizing drugs include [[cisplatin]], [[nimorazole]], and [[cetuximab]].<ref>{{cite journal | vauthors = Falls KC, Sharma RA, Lawrence YR, Amos RA, Advani SJ, Ahmed MM, Vikram B, Coleman CN, Prasanna PG | display-authors = 6 | title = Radiation-Drug Combinations to Improve Clinical Outcomes and Reduce Normal Tissue Toxicities: Current Challenges and New Approaches: Report of the Symposium Held at the 63rd Annual Meeting of the Radiation Research Society, 15-18 October 2017; Cancun, Mexico | journal = Radiation Research | volume = 190 | issue = 4 | pages = 350–360 | date = October 2018 | pmid = 30280985 | pmc = 6322391 | doi = 10.1667/rr15121.1 | publisher = Europe PMC | bibcode = 2018RadR..190..350F }}</ref>

The impact of radiotherapy varies between different types of cancer and different groups.<ref>{{cite book | vauthors = Seidlitz A, Combs SE, Debus J, Baumann M | veditors = Kerr DJ, Haller DG, van de Velde CJ, Baumann M |title=Oxford Textbook of Oncology |date=2016 |publisher=Oxford University Press |isbn=9780191065101 |page=173 |chapter-url=https://books.google.com/books?id=mrcoCwAAQBAJ&pg=PA173 |language=en |chapter=Practice points for radiation oncology}}</ref> For example, for breast cancer after [[breast-conserving surgery]], radiotherapy has been found to halve the rate at which the disease recurs.<ref>{{cite journal | vauthors = Darby S, McGale P, Correa C, Taylor C, Arriagada R, Clarke M, Cutter D, Davies C, Ewertz M, Godwin J, Gray R, Pierce L, Whelan T, Wang Y, Peto R | display-authors = 6 | title = Effect of radiotherapy after breast-conserving surgery on 10-year recurrence and 15-year breast cancer death: meta-analysis of individual patient data for 10,801 women in 17 randomised trials | journal = Lancet | volume = 378 | issue = 9804 | pages = 1707–1716 | date = November 2011 | pmid = 22019144 | pmc = 3254252 | doi = 10.1016/S0140-6736(11)61629-2 | doi-access = free }}</ref> In pancreatic cancer, radiotherapy has increased survival times for inoperable tumors.<ref>{{cite journal | vauthors = Reyngold M, Parikh P, Crane CH | title = Ablative radiation therapy for locally advanced pancreatic cancer: techniques and results | journal = Radiation Oncology | volume = 14 | issue = 1 | pages = 95 | date = June 2019 | pmid = 31171025 | pmc = 6555709 | doi = 10.1186/s13014-019-1309-x | doi-access = free }}</ref>