A plan comparison study between rapid arc and conventional intensity-modulated radiation treatment plans in nasopharyngeal carcinoma patients

Introduction

Head and neck cancers are one of the common malignancies in Indian population. It's entity, nasopharyngeal carcinoma is among the aggressive malignancies with its location and spread near very critical structures. Thus requires a highly conformal radiotherapy delivery techniques.

Purpose

The aim of the study is to dosimetrically evaluate and to compare Intensity modulated radiation therapy (IMRT) plans and RAPID ARC plans for irradiation of nasopharyngeal carcinoma.

Material and Method

A retrospective study is done on 10 nasopharyngeal carcinoma patients, who were treated with Radiotherapy at ATRCTRI Bikaner. Radiotherapy was delivered by IMRT technique (Total of 70 Gy in 33 fractions). Same patients are now planned on Rapid arc technique. Dosimetric comparison is done in terms of PTV coverage, OAR dose, conformity index, homogeneity index.

Result

PTV coverage is similar with both the plans. Homogeneity index is higher for IMRT plans 0.119+/- 0.020 compared to 0.104 +/- 0.018 for Rapid arc plans (statistically significant).The Rapid arc plans achieved slightly better conformity 1.018+/-0.09, whereas 1.105+/-0.12 for IMRT plans. Rapid arc achieved better results for OAR, statistically significant for Brainstem (54.4 +/-10.4 Gy for IMRT and 49.7+/-4.2 Gy for Rapid Arc, Lens (Left lens and Right lens received 10.55+/-5.8 Gy and 9.44+/-9.08 by IMRT and 6.12+/-6.1 Gy and 5.45+/-6.05 Gy for Rapid Arc), optic nerves (Right and Left optic nerve received 34.36 and 35.01 Gy for IMRT plans and 30.06 and 30.05 Gy for Rapid Arc plans. However the gains are statistically insignificant for spinal cord and vestibulocochlear nerve. No major difference found for Right and left parotid between both the arms.

Conclusions

Rapid Arc is better technique compared to IMRT for Nasopharyngeal carcinoma treatment, that provides better dose conformity, more homogeneous coverage and OAR sparing. However study is retrospective and has lesser patients, thus requires prospective study with more number of patients along with comparison of clinical outcome.

Estimation of radiation-induced second cancer risk associated with the institutional field matching craniospinal irradiation technique: A comparative treatment planning study

Aim

To estimate and compare the lifetime attributable risk (LAR) of radiation-induced second cancer (SC) in pediatric medulloblastoma patients planned with institutional 3D conformal field matching method, gap junction method and Intensity Modulated Radiotherapy (IMRT).

Background

The epidemiological studies on childhood cancer survivors reported that long-term cancer survivors who received radiotherapy are at a significantly increased risk for the development of SC. Hence, the increased concern to predict the SC risk for long-term survivors.

Materials and methods

In addition to institutional field matching planning method, IMRT and gap junction methods were created for ten pediatric medulloblastoma patients. The risk estimates were made based on the site-specific cancer risk coefficient provided by the BEIR VII committee according to the organ equivalent dose for various critical organs. Also, plans were compared for target volume dose distribution and dose received by critical organs.

Results

When compared to the gap junction method, the IMRT and institutional field matching method were superior in normal tissue sparing and dose conformity. However, highly significant volume of low dose associated with IMRT was the main concern for the SC risk. The accumulated LAR for all the critical organs with 3D conformal gap junction and IMRT method was 23-25% while for the 3D conformal field matching method it was 21%.

Conclusion

The LAR associated with the institutional field matching technique was substantially lower. As this method is highly robust and easy to set up, it can be a better choice of a craniospinal irradiation technique where 3DCRT is the only choice of treatment.

Necessity of CT-MRI based treatment planning for cervical tumors with retroverted uterus: A case report with review of literature

Treatment of carcinoma cervix is a complex issue influenced by numerous factors, including the patient's age, clinical stage of the disease, position of the uterus, comorbidities, etc. The major drawback of the conventional four-field box technique is the lack of complete information about the flexion of the uterus and topography of the tumor. These are further influenced by bladder and rectal filling, which may lead to geographical miss of the clinical target volume (CTV). This problem was noticed mainly in the anterior and posterior borders of the lateral fields and in the superior and lateral borders of the anteroposterior fields. We demonstrate the need for computed tomographic-magnetic resonance imaging (MRI)-based 3D planning of each patient and necessity of sagittal MRI for designing lateral portal in case of conventional four-field technique through an example of a patient's sagittal MRI of pelvis showing retroverted uterus.

A simple planning technique of craniospinal irradiation in the eclipse treatment planning system

A new planning method for Craniospinal Irradiation by Eclipse treatment planning system using Field alignment, Field-in-Field technique was developed. Advantage of this planning method was also studied retrospectively for previously treated five patients of medulloblastoma with variable spine length. Plan consists of half beam blocked parallel opposed cranium, and a single posterior cervicospine field was created by sharing the same isocenter, which obviates divergence matching. Further, a single symmetrical field was created to treat remaining Lumbosacral spine. Matching between a inferior diverging edge of cervicospine field and superior diverging edge of a Lumbosacral field was done using the field alignment option. 'Field alignment' is specific option in the Eclipse Treatment Planning System, which automatically matches the field edge divergence as per field alignment rule. Multiple segments were applied in both the spine field to manage with hot and cold spots created by varying depth of spinal cord. Plan becomes fully computerized using this field alignment option and multiple segments. Plan evaluation and calculated mean modified Homogeneity Index (1.04 and 0.1) ensured that dose to target volume is homogeneous and critical organ doses were within tolerance. Dose variation at the spinal field junction was verified using ionization chamber array (I'MatriXX) for matched, overlapped and gap junction spine fields; the delivered dose distribution confirmed the ideal clinical match, over exposure and under exposure at the junction, respectively. This method is simple to plan, executable in Record and Verify mode and can be adopted for various length of spinal cord with only two isocenter in shorter treatment time.