The accuracy of radiotherapy can be increased by correcting for geometric uncertainties and changes between radiotherapy fractions. These corrections are currently done with online adaptive treatment on a specialized linear accelerator (linac) for a small subset of patients. However, patients currently treated on a standard linac could also benefit from online adaptive radiotherapy. The objective is to determine the feasibility of online CBCT-guided adaptive radiation therapy on a standard Elekta linac.

General Inclusion Criteria:

• Patient, age ≥ 18 years, referred for a radiotherapy schedule as described in one of the cohorts.
• WHO performance score 0-3.
• Provision of signed, written and dated IC prior to any study specific procedures.

Specific inclusion criteria for prostate cohort:

• Accepted for radiotherapy of the prostate and pelvic lymph node areas.
• Pathology-proven prostate cancer.
• cT1-4
• cN1 on PSMA-PET/CT or pN1 based on node biopsy, SN-procedure or lymph node dissection.
• cM0 on PSMA-PET/CT (except for patients with M1a disease who are still considered for radiotherapy of the prostate and pelvic lymph node areas).

Specific inclusion criteria for cervical cohort:

• Accepted for radiotherapy of the cervix (with or without chemotherapy) and pelvic lymph node areas (25 fractions, followed by either a brachytherapy or external radiotherapy boost).
• Pathology-proven cervical cancer.
• FIGO IIA2, IB3 and > 6cm, IIB-IVA or N+. Or other stage and unfit for surgery.
• cM0 or cM1 and accepted for locoregional radical (chemo)radiation in 25 fractions.

Specific inclusion criteria for bladder cohort:

• Accepted for radiotherapy of the bladder, either to the entire bladder or with a boost to the tumor area (with or without chemotherapy).
• Pathology-proven bladder carcinoma.
• cT1-4
• cN0 or cN1-2 after induction treatment (with or without lymph node dissection)

Specific inclusion criteria for lung cohort:

• Accepted for radiotherapy for lung cancer with lymph node metastases (with or without chemotherapy).
• Non-small cell lung cancer (either pathology proven or enough clinical suspicion to warrant radiotherapy to primary tumor and pathologic lymph nodes.
• cT1-4 and cN1-3.
• M0 or m1 and accepted for radical radiotherapy in 24 fractions of 1 or more lymph node metastases and a primary tumor and/or pulmonary metastases.

Specific inclusion criteria for head and neck cohort:

• Accepted for radiotherapy for head and neck cancer (with or without chemotherapy).
• Pathology-proven carcinoma of the pharynx, oral cavity or larynx.
• cT1-4
• cN0-3 and indication for elective neck radiation (either 1 or 2 sides).
• cM0

General Exclusion Criteria:

• Patients who are pregnant.

Specific for prostate cohort:

• Patients with a medical condition that severely compromises CBCT image quality (mainly hip prostheses).
• Severe lower urinary tract symptoms that could make the longer treatment time problematic (according to judgement of treating physician).

Specific for cervical cohort:

- Patients with a medical condition that severely compromises CBCT image quality (mainly hip prostheses).

Specific for bladder cohort:

• Patients with a medical condition that severely compromises CBCT image quality (mainly hip prostheses).
• Severe lower urinary tract symptoms that could make the longer treatment time problematic (according to judgement of treating physician).

Specific for lung cohort:

- Severe pulmonary complaints that could make the longer treatment time problematic (according to judgement of treating physician).

Specific for head and neck cohort:

• Severe complaints that could make the longer treatment time problematic (according to judgement of treating physician).
• Pulmonary fibrosis