Quality Assurance of Simultaneous Treatment of Multiple Targets Planned with Mono Isocenter using three Dimensional Conformal Radiotherapy (3DCRT) Technique

Research Article

Austin J Radiat Oncol & Cancer. 2015; 1(3): 1013.

Quality Assurance of Simultaneous Treatment of Multiple Targets Planned with Mono Isocenter using three Dimensional Conformal Radiotherapy (3DCRT) Technique

Suman Kumar Putha1, Saxena PU1, Banerjee S1, Challapalli Srinivas1*, Vadhiraja BM2, Arun Kumar ES1, Sridhar Chinthamani3 and Dinesh Pai K1

1Department of Radiotherapy & Oncology, Kasturba Medical College Hospital, Mangalore, India

2Department of Radiation Oncology, Manipal Hospital, Bangalore, India

3Department of Radiation Oncology, Father Muller Oncology Center, Mangalore, India

*Corresponding author: Challapalli Srinivas, Professor in Medical Radiation Physics, Department of Radiotherapy and Oncology, Kasturba Medical College Hospital, India

Received: November 02, 2015; Accepted: December 01, 2015; Published: December 02, 2015


Objective: The purpose of this study was to conduct quality assurance (QA) of plans of four patients having multiple metastatic lesions (targets) simultaneously treated with mono isocentric three dimensional conformal radiotherapy.

Material and Methods: Patient geometry was simulated with two/three water equivalent phantom shaving ionization chamber (IC) sleeves (IC-1, IC-2 & IC-3 as if targets are in different locations of patient).QA plans were generated using mono isocenter technique with a dose prescription of 3.0 Gy to the targets for point dose verification. Plan evaluations was done using dose volume histogram (DVH) in terms of maximum, mean doses to target, conformity index (CI) and homogeneity index (HI). A two dimensional ion chamber array detector was used for fluence verification.

Results: Calculated maximum dose (Gy), mean dose (Gy), CI and HI values with standard deviation around the targets in all QA plans were 3.09±0.02, 3.03±0.02, 0.96±0.03 and 0.04±0.03 respectively. Measured point doses to all lesions were within ±2.0% of the computed dose in all QA plans. A pass percentage of 97% was obtained with the set criteria of 3mm distance to agreement and 3% dose difference for fluence verification around the targets in QA plans.

Conclusion: Treatment execution of multiple targets simultaneously with mono isocenter can reduce positional errors and delivery time.

Keywords: Quality assurance; Multiple targets; Mono isocenter; Conformal radiotherapy


Solid tumours in pelvic / vertebral region may present with multiple metastases (targets) necessitating their simultaneous radio therapeutic treatment. Such treatments are usually executed using modern radiotherapy techniques such as Intensity Modulated Radiotherapy (IMRT), Stereotactic Body Radiation Therapy (SBRT), Stereotactic Radio Surgery (SRS), rapid arc, Volumetric Arc Radiotherapy (VMAT), cyberknife® and tomotherapy. In convention, multiple targets can be treated individually with a set of beams having their own isocenter. Treatment planning and execution of multiple targets results in prolongation of treatment time (starting from pretreatment Quality Assurance (QA), patient positioning, and setup corrections for every target treatment and treatment delivery) [1]. Another method is to have a common isocenter, around which the gantry rotates and delivers the radiation to multiple target sites, one at a time. This method can be an alternative in 3DCRT treatments for multiple lesions using mono isocenter instead of multiple isocentric technique. Many investigators have verified the dosimetric quality of a common isocentric plan to treat multiple tumours especially in brain metastatic lesions [2,3]. In another study, the quality of target coverage and dose conformity with mono isocentric VMAT-SRS plans to Dynamic Conformal Arc Therapy (DCAT) was compared [4]. Several authors have studied the validity of mono isocentric plans and concluded that it could be a better option of treatment delivery with less systematic errors [5-7]. Marks et al have confirmed through their investigation that three dimensional conformal radiotherapy (3DCRT) technique can be a possible alternative to radio surgery with fixed shaped coplanar or non-coplanar techniques with wedged radiation fields having beams conformed to irregular shaped intracranial lesions, as the goal of both the techniques is to achieve better dose conformity [8]. Similar logic can be used to treat multiple lesions simultaneously with different/single beam sets conformed to different lesion sites elsewhere extra cranially which can be less error prone compared to multiple isocentric treatment plans since the treatment plans with multiple isocenter are time consuming and may attribute many uncertainties in setup and positioning resulting in large systematic errors in the treatment delivery. Planning of these techniques with 3DCRT using Treatment Planning System (TPS), requires a logical approach (different beam sets conformed to multiple lesions sharing a common isocenter, having different weight points, the feasibility/flexibility to use different wedge angles using motorized wedge option, to obtain better conformal dose coverage [9-11]. The objective of this study is to validate a mono isocentric plan generated by 3DCRT technique in terms of dose conformity and coverage for the treatment of multiple metastatic lesions using composite point dose method and Two Dimensional (2D) ion chamber array detector.

Methods and Materials

Four patients having multiple metastatic lesions (targets) which are covered in the region of Multi Leaf Collimator (MLC) were selected for this study. Clinical descriptions of individual cases as shown in (Figure 1) are a) Carcinoma of lung with bilateral hip bone and femoral metastases where both targets lie along the transverse plane, b) Carcinoma right lung with vertebral metastases where both targets lie along longitudinal plane, c) Renal cell carcinoma with pubic and ace tabular metastases where both targets lies in different planes and d) Carcinoma of penis post partial penectomy with bilateral inguinal & one vertebral metastatic lesions where the inguinal targets are in different plane with respect to the vertebral target. A dose of 30 Gy in 10 fractions was prescribed to the 100% isodose line that is covering the targets. All patients were planned for palliative radiotherapy using mono isocenter 3DCRT technique. CMS XiO® (Elekta Ltd, Crawly, UK) version 4.80.02 Treatment Planning System (TPS) utilizes Clarkson, convolution, superposition and fast superposition algorithms. However, superposition algorithm was used for dose calculations. Treatments were executed with medical linear accelerator (M/s Elekta Compact), using 6 MV (Mega voltage) photon beam at a dose rate of 350 MU/min with 40 pair multi leaf collimator (MLC) leaves (projected leaf width 1.0 cm at isocenter) arranged in two banks and also having motorized wedge facility.