What is SSD and sad technique in radiotherapy?
Modern photon beam radiotherapy is carried out with a variety of beam energies and field sizes under one of two set-up conventions: a constant source to surface distance (SSD) for all beams or an isocentric set-up with a constant source to axis distance (SAD).
Why does PDD increase with SSD?
The percentage depth dose (PDD) increases with SSD due to the effects of inverse square law. NO dependance on the SAD or SSD. and hν constant TMR decreases with increasing z. constant TMR increases with increasing hν.
Why are wedges used in radiotherapy?
In radiation oncology, wedge filters are commonly used to improve the dose uniformity in the target volume. They can be used as missing tissue compensators or wedge pairs to alter the shape of isodose curves so that two beams can be angled with a small hinge angle at a target volume without creating a hotspot.
What is Dmean in radiotherapy?
The association between mean dose (Dmean), maximum dose (Dmax), VX (% SCM volume that received more than X Gy), DX (dose to X% of the SCM volume) at X values of 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80 and SCM atrophy at 3 years after IMRT were analyzed.
What is four field box technique in radiotherapy?
Background: The advantage of 4-field radiation to the pelvis is that the use of lateral portals spares a portion of the small bowel anteriorly and rectum posteriorly. The standard lateral portals defined in textbooks are not always adequate especially in advanced cancer cervix.
What is Isocentric mounting?
An isocentric technique is where all beams used in a radiation treatment have a common focus point, a.k.a. the isocenter. Isocentric techniques require less patient repositioning as multiple field arrangements can be delivered with gantry and collimator movements, reducing treatment times.
How is PDD measured?
PDDs were measured at 100 cm source-to-surface distance (SSD), for fields of size: 5 cm × 5 cm, 10 cm × 10 cm, 20 cm × 20 cm, 30 cm × 30 cm, and 40 cm × 40 cm. PDDs were measured at all available dose rates for 6 FFF and 10 FFF as PDD curves smoothing vary with dose rate.
What is the relationship between PDD and field size?
It was found that the values of PDD0 increase as field size increases.
What is penumbra in radiation therapy?
In external beam therapy, radiation penumbra is one of the factors which hinder the confinement of the dose to tumour volume and cause unnecessary irradiation of the surrounding normal tissues in the penumbral region.
What is compensator in radiotherapy?
Compensators have been used in radiotherapy for decades to produce simple forms of intensity modulation. As the sophistication level of radiotherapy treatment planning and delivery techniques improved over the years, so did compensator techniques and their application.
What is the isocenter in radiation therapy?
The radiation isocenter (in contrast to the mechanical isocenter) is the point in space where radiation beams intersect when the Gantry is rotated during beam-on.
What is non isocentric technique?
The authors developed a nonisocentric treatment strategy for breast cancer radiation therapy. By strategically placing multiple nonconverging beams each with its isocenter within the patient, the proposed nonisocentric technique substantially improves sparing of the ipsilateral lung.